What is the recommended clearance for the triple gear bushings?
I've had 2 sets of bushings wear out after only a year of driving. Both done by a professional engine rebuilder.
Dave Loving: There has been gallons of spilled ink over what clearance to give triple gear bushings. One big part of the argument has been what does RUNNING CLEARANCE mean. Glen Chaffin (who I think is one of the most knowledgeable persons on this forum) says it means clearance on both sides of the bushing. Others will argue that it is on one side only.
I build a lot of Transmission for people and I never measure clearance. I give them a good spin and if they continue spinning for a couple of seconds I consider it good. If it does not continue spinning I will ream it some more. This may upset some people who spend a lot of time measuring them but I never have any problems and I think I drive as much as almost anyone on this forum
This will be a long thread.. For some reason bushings reamed to Ford's tolerances has a tendency to fail catastrophically in modern times, so something differs today compared to back then. Might be the bushing material that differs?
Most restorers gets great service from their triple gear bushings with a just a little larger tolerances than Ford specified.
What was the problem when you had to redo your trans bushings twice? What were the symptoms of the bushing wearing out? Mostly worn transmissions seems to work rather OK..
My recently rebuilt engine was put together with used original Ford bushings in the transmission - works fine almost without noise. (I pressed out the triple gear bushings, put thin washers to get the bushing flange higher than the gear face, then pressed the bushings back)
I've seen people posting about trouble with triple gear bushings when driving without any magnets or paddles on the flywheel. The trans needs a lot of oil mist flying around inside to get properly lubed.
Running clearance of .002. That means that you would have a total of .004 difference between the pin and bushing when measured. The Transmission repair book is kinda vague on this as it simply states .002 to .005 (upper limit for wear) clearance on the transmission bushings. That would give you .004 to .010 when measured difference. If they are only giving you a total clearance of .002 that would be only .001 running and would be way too tight as the parts heat up and expand could give you no clearance.
How are you figuring they are worn?
How are the pins? What clearance is being used for the gear to flywheel clearance?
Some people do start out with a bit more running clearance maybe .0025 (total of .005).
My experience has been that rarely do the Ford triple gear bushings need replacement. The pins however almost always seem to need replacement. So I probably fall more into Dave Huson's "camp" on this subject.
Further on the subject of transmission bushings; the only ones that I always seem to have to replace are the three that run on the main shaft. The low and reverse I usually just ignore.
I always dynamically balance the flywheel
I agree to a point, Les but what I have found is that the bushing thrust face is gone letting the triple gear run against the flywheel.
A easy fix is to go to a good industrial supply and buy three 3/4" "machinery washers". These are a close tolerance washer intended to be used as a shim and are available in various thicknesses. Another option would be to go to a bearing supplier and buy three Torrington TR(B)-1220 thrust washers. These are case hardened and intended for use with needle roller thrust bearings. The "B" ones are 1/16" thick. They are available from .030-.154" thick. Probably they will cost you $2-$3 each and won't wear out in your lifetime!!
I have never found that pin and bushing didn't need replaced, unless your cobbling.
A N.O.S. Ford pin, and a N.O.S. K.R. Wilson triple gear bushing reamer gives a total clearance of .003 thousandths.
Always worked for me.
The repro. pins are normaly to big and have to be polished down.
Here's the way it looks to me. You are working with 3 gears in mesh with one gear. So you need enough clearance that all 3 gears will turn without binding. As the pins or bushings wear, you will get more noise, however it is not likely it will lock up. If too tight it will tend to lock up and spin the bushings within the gears. The pins will wear on the side facing the center of the flywheel because that's where the pressure is exerted. The trick is to have things tight enough not to be noisy, but not tight enough to bind while being loose enough where all gears will turn freely.
Dan McEachern convinced me the basic triple gear bushing/pin design is marginal at best.
I am using this solution in a engine I am currently having built.
I like this solution for the following reasons in Dan's own words previously posted on this Forum:
A few facts regarding triple gears and the loads that the bushings (or bearings)are expected to support need to be understood so that factual and accurate information is available to those interested in the subject of triple gear bushing failure. I'll try to keep this brief and to the point. If one calculates the reaction forces for a triple gear set transmitting 20 HP @ 2000 engine rpm, the load on a triple gear bushing/shaft is about 650 lbs. At 2000 rpm in low gear, a triple gear is spinning on the shaft at about 1300 rpm., (higher in reverse). The load on the bronze bushing under these conditions is about DOUBLE what most bronze bearing manufacturers recommend under the most favorable conditions for a sleeve bearing of this type. The majority of this load is a function of the square of engine speed, so if you are a T owner who just putts around in your car, you may never have problems. Granted, this is a worst case condition, but many T's are capable of putting out well over 20 HP, and are regularly wound up pretty tight on long steep grades or when trying to keep up with modern traffic when getting up to speed. Simply stated, at worst case conditions, the oil film in a simple journal bearing this size cannot support this large a load without metal to metal contact due to failure of the oil film.
Prior to developing the needle bearing conversion, I experimented with various bushing materials, oiling methods etc. without much success. Several of us experienced bushing problems in cars that had previously been run hard thousands of miles with no problems. This was about 12-13 years ago, and I attribute these failures to a change in oil formulations at that time. This is just my own theory as far as the oil.
Don't attribute these failures with oilite bronze bushings or insufficient oil clearances. These were out-of-the-blue failures in long running reliable automobiles that I had built the engines and transmissions in. Enough history.
In high gear the needle bearings do nothing for you- heck- the triple gears themselves do nothing for you in high gear! The needle bearings have been in cars for over 9 years now without a single failure. Why in the world would you allow the oil in a Model T to get so much trash in it to even be a concern? What about the camshaft, timing gears, main bearings etc?
Some have expressed concern that the needle bearings are not capable of carrying the load that the bronze bearing can due to surface area. I covered the bushing load issue previously. The dynamic load rating of the needle bearings I use in the conversion is actually about 3½ times greater than the worst case load discussed above, so there is very little chance of bearing failure.
The shafts themselves are properly designed, heat treated and ground-they are not converted or modified stock shafts. Correctly engineered shafts are critical to this application.
The triple gears we make are made from aircraft quality vacuum remelt 4340.
I'm not saying that it is not possible to obtain ok results with the stock bushings, but even though the T transmission is a wonderful design for its time, it does have weaknesses, and the analysis of the loads on these bushings explains one of those weaknesses.
I think the needle roller is great idea but Dan doesn't return emails so I guess I need to make a few sets myself
Thank you Dave for the kind words. I am glad that someone agrees with me. It's amazing how some people just won't listen to the facts and want to argue with success. The triple gear bushings need clearance, especially how fast we drive the cars today, and 0.002 In is just not enough. Ford gave clearance for most every bushing in the Model T. But for the Tripple Gear bushing he said Running Clearance which means 0.004 in. 0.002 on each side. That's running clearance.
With any Model T transmission bushing a touch too loose is always better than a touch too tight.
I never read where anybody is concerned about the roofing tar some use for motor oil.
Ford said to use a light oil, I don't think they meant SAE 40 or 20-50.
Thanks for the info, Les.
I must have several dozen original O.K. bushings with worn thrust beyond serviceable limits.
What I have done on occasion when the bushings are a good fit on the pins but the thrust face is worn is to push the bushing out just a bit and put a shim between the thrust face and the triple gear, then press the bushing back into place. Of course, this requires cutting a circle of shim material to put in there. Les' method sounds a lot easier.
The Torrington washer is probably the best item
I used whatever clearance yellow Timesaver gives. No problems after 5-6 years. 'Course, I'm just cobbling.
With the gears being where they are and with centrifugal force throwing oil away from the gears it's a miracle they get any oil at oil until the engine shuts down and some oil slobbers down the flywheel.
At least bronze is "sort of" self lubricating whereas needle bearings are not.
As mentioned above......sometimes more is better.
In response to triple gear bushing clearance I finally have to admit that I do pretty much the same thing in obtaining the clearance that Dave Huson does.
After I install the bushing in the triple gear I ream it till I can get the gear to spin without binding. When it spins for a few turns I consider it done.
This is another 'damed ol cobbler' doin it the country boy way. Funny thing is it really works! Howse bout that!
I guess I was just cobbling when I shimmed those thrust faces on the triple gear bushings, and Les was just cobbling when he added some washers. Seems like there's a lot of "cobblers" here in the Model T Family.
Yup, I guess so.
I know I sure couldn't choose who would have the first Bragging Rights.
Cobbling is a Model T heritage. That is why most of us like these cars! The vast majority of us cobble many, many years up to a life time without any real trouble. I, for one will enjoy cobbling with most of you rather than falling pray to a self appointed nasty, snarky A hole that thinks they are the final answer.
Who EVER could you mean?
Guys. Please ignore those postings. Postings of that type contribute nothing and only drag us all down. Thx
Well Mikeska, you for got some of the other names I answer to, but thanks.
Davis, try brushing your teeth with time saver sometime. Yellow would maybe match your teeth.
Some day, somebody is going to get hurt or killed with the crap the cobblers think is main stream repair.
The big laugh here is "well, I run it for 5 or 6 years with no trouble" The Fact is unless you tear it down and look, you have no idea what it is doing. Model T's will run wore out, until they don't.
When the thrust is gone on a triple gear bushing, the bushing is junk, along with the pin. The flange starts wearing, because the gear bushing is tipping, because the pin is wore, which in turn wears the bushing inside at the top, to let it and the gear tip to wear the gears and digs in to the flywheel.
By putting washers under the pin, you still have the same problem, but now the gear is just Independent from the thrust, everything else is still wore that caused the flange to wear in the first place.
Moving a set bushing for any reason, and reusing it that way, is not a good Practice.
I started machine work when I was 12 years old. This is the only thing that I have ever heard in terms used in clearance.
1. PRESS FIT, normally used in brass = Plus .002.
2. Interference Fit, varies with job = plus .000-50 to around Minus .000-50.
3. SLIP FIT, This is about Plus .000-50 to Plus .001.
4. RUNNING FIT, Running fit means just that. Running fit is a fit that will be used in motion.
We already know that .002 total clearance is to small, with the parts we have now. Another thing that spc. in the book of .002, by the pictures was before 1916 before Wilson started making tools for Ford, because none of the pictures shows his tools.
Fact, I know the Wilson reamers cut a Running clearance of .003., using N.O.S. Ford pins.
A running clearance of .004 thousandths, makes no sense to me at all because I know that it is not needed.
Now the book says to replace if over .005, so .004 now even makes less sense to me now, as they are only allowing .001 thousandths for wear.
Herman, The Wilson reamers may cut to 0.003 clearance and that may work where 0.002 will not. But Ford recommended 0.002 running fit and that is what I give them. the problem is many want to argue what running fit means and it doesn't mean clearance. If it meant clearance that is what he would have said just like he did everywhere else.
Ah, I see you resorted to the old "Call 'em by their last name" insult. Somehow I knew that was coming. Ooooh, and a yellow teeth joke. Looks like your mental maturity level peaked about the same time you started machining.
Oh, No, mental maturity level, right to the bone, that's going to leave a mark.
I agree with Herman. Oh no, did I say that.
Running fit is NOT a change to the way fit is measured. It simply means that it has a higher standard of precision. The clearance is still .002" per Ford.
Quit making up your own definitions Glen. We all know that with the current crap that is sold for triple gear bushings that the clearance needs to be greater. It's because of the expansion rate of the cheap bearing material that the vendors are passing off as replacements. SAE 660 should not be used unless the clearance is increased. You end up with a pre-worn transmission, that's all.
So I took a set of the new replacement triple gear pins that are "hardened and ground" and did some testing on them.
Yes they are hard, best guess is about 60-62 Rc. Here comes the BUT part. The hardness is very thin, best guess is .002-.003".
The hardness would be fine for needle bearings, but the thinness concerns me for needle bearings.
In regards to Ken's posting, I found the pins to be very consistent dimensionally, Dimensionally the quality was excellent and they are definitely HARD.
As I posted above I almost never run the new bushings, so I can not comment about the currently available ones.
In regards to a comment made about getting "5-6 years of use". My '13 has now got 12 years of running time and the first set of Firestone tires are now reaching the end of their tread wear. I figure about 8-10,000 miles. I regularly receive compliments about how quiet and smooth it runs and it will run away from most T's on tour.
I did my own babbit, line bore, rods, and transmission and all assembly. And yes it has new pins on used bushings!!
Ken, I am not making up any definitions, Ford did. But I am not going to engage in an argument with you. You can believe what you want but I know what works. The old bushings made by Bob were 660 bronze. They were not crap as you assert but they were not Z bronze. Snyder's bushings available today are made with C92300 bronze. This is the same number given to Z bronze back in Fords day and they are almost identical. There is an ever so slight difference. There is nothing else available today that comes closer to Z bronze. So these bushings are not crap but they still need adequate clearance and 0.002 in just doesn't work. I am really tired of the bickering that goes on here. When someone has experience and offers help that help should be appreciated and not just criticized because you think this needs to be a spit and argue club. If that's what you want I'm out of here.
Where does it say they use C92300 Bronze?
Ken, I have researched this subject thoroughly. I have talked with Bob's , I have talked with Snyders, I have talked with Steve Coniff, I have had independent tests run on original Ford triple gear bushings and repos. I have copies of the original Ford specs. If you don't believe me call Snyder's, look up the specs yourself. Snyders bushings are ever bit as good as the originals and I have found orginal Ford bushings frozen on the shafts and turning in the gears so don't tell me I don't know what I am talking about.
All this talk of bushing has gotten me thinking, I know scary stuff!!
I wonder if anyone has tried babbit lining these bronze bushings.
One of the problems with bronze bushings as opposed to babbitt bearings is the "embedability" factor of the babbitt. A thin coating (about .001") of babbitt has a very high load rating. I have made babbitt lined bronze shells for some other old engines. I made split shells with about .002-.003 of babbitt. A option might be to bore them for about .001" clearance and then "time saver" them to just turn freely after pressing into the gear.
Sigh another project to try!! So many things to do, so little time!!
I'm with Dave Huson on this one. I've owned 5 Model T's, and have always done them like Dave says, and have NEVER had one seize up yet! After all, we don't run around in low gear or reverse all day long! I'll also go along with Herm.
In that the clearance is .003 or that we are all a bunch of cobblers?
Does the replacement triple gear bushing you are using have the internal oil grove extending out each end? The new transmission bushing that a friend received did not have the oil groves extending out each end. He took a small file and modified each bushing end so the oil grove now extend all the way thru just like the original bushings that Ford provided.
If the oil does not have a direct channel to easily get inside the bushing.....may be an answer for replacement bushings not holding up like the originals.
I have been using original bushings and pins in our 13 touring for 15 years and have never had a problem.
I spent some time talking to a knowledgeable person that works (Hands On) in the Greenfield Village repair shop. They set the triple gear bushing so they are easily spun on the new pins with oil. I was told, they are using the original style triple gear bushing and did not have good luck using the pinion bearing style.
Was told that a 1914 reproduction touring I was looking at (One Of Several) had over 100,000 miles one it. The shop does a lot of work keeping the cars at Greenfield Village on the road. Greenfield Village is a real test "Track" for Model T's.
I consider myself as a very luck person....being in the right spot, talking to the people in the know while visiting Greenfield Village.
Wished I lived much closer and could enjoy spending time at the village with other Model T owners.
I was at Greenfield Village recently, and they do have those T's running all day long. It would be interesting to know how many miles per day they drive. Another point, we all know what the Ford Service book says on the triple gear bushing clearance. What I find confusing is there are a number of people on this discussion saying we need .004" clearance, so why would the Ford book say they need to be replaced with only .001" wear? That makes no sense. I have seen old stock bushings with straight grooves, and curved grooves, with most all having curved grooves.
Lets be precise. The Ford service manual says to ream bushings to 0.002 running fit. The question is what is running fit. It doesn't say clearance. But then Ford says If there is more than 0.005 clearance between bushings and shaft new bushings should be installed and reamed. Notice, he said more than 0.005 clearance, he didn't say running fit. Notice more than 0.005 clearance. There has to be a difference between running fit and clearance Those are Fords words not mine. In my opinion running fit means clearance on all sides. You are entitled to your opinion but lets keep it civil. As I said before, this is a forum, not a spit and argue club. Opinions are ok but when facts are presented we should listen, You might learn something. We should be here to share our knowledge and experience and not to just try and belittle someone else. That is not helpful and has no place here.
Larry, did you ask what kind of band linings they use?
Over 50 thousand miles on a cobble job and still going, I agree completely with Glen. That's my story and I'm sticking to it! Oh yeah forgot to say that everything was slavered over with time saver including rods and mains, don't think I ever got it all washed out, oh well. KGB
Keith, that's the point with timesaver, it's not harmful even if some of it isn't washed out - the grinding power gets lost with use. I'm a firm believer, it's great to be able to crank start a fresh (cobbled up) engine ;)
They are not using cotton or wood, think he said Kelvar. Also not using original Ford clutch disks on re-builds. Was told they found parts of the original style steel disks in pans. Switched over to the 400 style disks which are holding up well. They added safety hubs and RM brakes for safety reasons. Seems like the Depot Hack broke a couple of axles probably from over loading. Have not had any broken axles with the other T's. Run 4 to 1 rear end gears for ease of driving in park. Use 15-40 wt. oil. Also use double thrust bearings on drive shafts for pinion support. No water pumps but do use alt. to keep the batt. charged. The engines are sent out for re-building. Had several fresh engine on shelf in case a car goes down.
Larry Smith......this is a BIG one for you....they are still using original style coils. According to what you keep tossing at me...."It not a model T if you are not running coils".....even though they have made numerous improvements to keep the cars running.....they are still T's in your mind.
Also they set the timing/valves by piston/valve location.
One might think the shop would have all the correct Model T reamers, pullers and special tools that we all dream of having. Nope! They have a machine shop available in another building to provide support when needed.
Also, the 1914 T's have had problems with the rivets loosing in the two pice steering column tops. When that happens, they change the column to the one pice later style.
I may have missed a few things.....a lot was talked about in the hour we spent together. It was very informative and a great exchange of information. A once in a life time experience.
They have a big job keeping all the model T's & A's running. A job many can only dream of having. The drivers may even have a better job driving the cars around and talking Model T with those interested.
Loose rivets in two piece steering gear box;
I wonder if they soldered them together along with the rivets as they were originally. I've never seen one come loose if soldered AND riveted
Sorry for the thread drift!!
Les....The one I looked at did not look like it was ever soldered. The rivet heads looked larger than those on our 13 which is soldered. If it were me, I would have tried silver solder before replacing the column.
As the 14's age....they look more original. I did not ask at the time....wished I did....wonder how they obtain old used parts.
Also, Wife & I are thinking about going on the Cochrane, Alberta tour, 2015. Hope it works out for us to go. Friends near where we live are also interested. Sounds like alot of fun and would enjoy visiting with you.
The other Les in learning.
Invaluable information Les V. Thanks!
The last time I rode in a Model T in Greenfield Village was in the late 70's. I remember seeing a note on the dashboard reminding the driver's to check the radiator water often. Unfortunately, my driver didn't seem too thrilled with driving a Model T, something I couldn't understand as it would have been my dream job! The car appeared to be a little "frayed around the edges" and less well kept than I had remembered from my first ride there a few years earlier.
Are the cars pristine these days or do they look like an everyday car displaced into the 21st century?
I must admit that technically I agree with Glen, but in practice I follow the advice of my mechanical mentor, Lee Pierce, who does it the same as Dave Huson.
By the way, all this discussion is somewhat academic as the gears below ran quite well but a little noisy....
@ Glen - Apparently, we don't have any machinists here except for myself that will corroborate the meaning of running fit. As I said before, it means that the clearance must fall within a range of tolerance and does NOT mean that you double the clearance. I don't care who you "talked" to but if you could read, you would stop propagating false information. We go through this discussion every time the subject comes up. Your stubborn affinity for bad information must stop so here is the proof...Again!
The image below is from the 15th edition of Machinery's Handbook, page 1072. It shows the standards of fits for holes and shafts. A "running fit" means that the clearance has a higher precision or Closer Fit than a loose fit. Just so you won't have to invent another definition, the H8 column is for holes, f8 is for shafts.
The table above calls for an even tighter tolerance between the pin and bushing than we are arguing about which would make the likelihood of the bushing seizing on the pin even more likely under load. You must also factor in that we are talking about three separate pins spaced apart 120 degrees. Now remember, trapped between these three fixed points (pins and triple gears) is the driven gear which is attached to the clutch / brake drum. Now, keeping this in mind, lets also consider the following.
When you rebuild a typical transmission, the used main gear shaft (Part #3331) is often re-installed and new bushing installed and reamed in the brake drum (Part #3311)to the point it can clear the unworn portion of the shaft that the small internal clutch drum (Part #3332) is pressed onto and locked in place by a key and lock bolt. As a result, the clearance between the shaft and the bushings can and often will be a little sloppy. Now stay with me a bit further.
Once the transmission drums are installed on the main gear shaft all turns well an free while on the work bench. The transmission drums as a unit move around the main gear shaft and all appears well.
Now, lets install the transmission to the engine and install the transmission cover and bands. While in low gear, the transmission band contracts around the low speed drum. In doing so, pressure is applied on the low speed drum from right to left as the band contracts. Because there is often wear on the gear shaft where the brake drum bushing ride, the brake drum is allowed to moved several thousandths of an inch to the left as pressure is applied to the low speed drum while depressing the clutch pedal. Once that occurs, the clearance between the low speed gear and the triple gears is greatly reduced. Possibly creating a no clearance at all scenario.
Because of this likelihood, it is imperative a near new gear shaft be used and special attention is given to fitting the bushings to the gear shaft. To avoid this scenario from happening, fitting the triple gear bushing on the loose side will definitely not hurt.
How many times have you heard people negatively comment about the growling noise their transmission makes after a rebuild while in low gear? I suspect this is because the transmission drums are moving slightly off center on the shaft to the left when the low pedal is applied, causing zero clearance between the low speed gear and the triple gears. Although this movement may be only a few thousandths, it can make all the difference in the world. Makes sense to me. Especially, when we are arguing about the difference of one or two thousandths of an inch.
Lastly, this may also explain why some find triple gear bushing which have seized on the pins and are loose in the gears when tearing an excessively used transmission down for a rebuild. Opinions can and will vary.
All valid points but not pertinent to the original disagreement. The facts remain that "running fit" does NOT mean that the machinist should double the clearance as Glen keeps regurgitating. It's simply a tolerance level to be maintained between surfaces.
And if you actually READ the chart you'll see that the tolerance is greater for running fits than for standard fits. Ford wanted a looser fit for the bearings and says so by specifying a "running fit".
There is NO disagreement that the clearance should be more than .002" as I've always concurred. I'm just saying that the definition used by Glen to justify it is incorrect when he keeps saying running fit means to double the clearance. The ones that keep saying it have a clear ignorance of machining standards.
Forgot to mention:
Mark - Your first statement is incorrect. The tolerance allows a range of .0032 to .004" clearance on the upper end. This just goes to show you what happens when non-machinists get evolved in definitions.
Ken, with respect, I cannot see the term "running clearance" in your table.
Where did you version of the definition come from?
Just looking to learn....
Ken is that chart for steel on steel or does it cover steel shafts in bronze/brass bushings? Even I as a non-machinist, knows that steel on steel VS steel on bronze/brass will have a different expansion rates for fit allowance. What has been describe to me as cold flow between the brass and steel could also come into play if the clearance is too tight.
You would be right, I am not a machinist nor have I studied metallurgy, just a cobbler trying to keep some cars on the road that will never get driven more than a 500 miles a year and over 35 MPH.
OK Ken, so your the expert. So tell us what 0.002 thousands running clearance means. Why did Ford use those terms and what do they mean? Your chart makes no sense. For running fit it shows For a shaft size of 0.677, +0.001 for the bushing and -0.0016 for the shaft. This makes no sense.
You provide a tolerance range of .0032 to .0040 "on the upper end". Not sure where you are going with that. I thought we were arguing over one or two thousandths clearance.
Since you like charts. take a quick look at the chart in this link that specifically speaks about pins and bushings as it relates to "running clearance".
Refer to Class III and Class IV specs which state the following for a pin diameter of .688 which is close to the triple gear pin diameter of .677.
Class III "Medium Running Fit Tolerances"
Pin Diameter .6869
Hole (Bushing) Diameter should be .6875
Running fit is .0006
Pin Diameter .6860
Hole (Bushing) Diameter should be .6884
Running fit is .0024
Class IV "Transitional Fit (Snug)"
Pin Diameter .6873
Hole (Bushing) Diameter should be .6875
Running fit is .0002
Pin Diameter .6867
Hole (Bushing) Diameter should be .6884
Running fit is .0017
Again, according to the information contained in the chart, .0002 would be the extreme minimum clearance for a Class IV application whereas .0006 would be the extreme minimum for a Class III application. Draw your own conclusion, but .0002 is just way to tight of a tolerance when it comes to triple gear bushings and pins.
Lastly, noticed I shared all this information without making any rude comments about you.
Mark, I see that you know nothing about gear sets. The three gears are 120 degree,s apart. But the sun gear is self centering. You cannot apply more pressure on one side. the drums will be on center. They may have more clearance from using worn shafts but will be on center when a load is on them. Glen, KR Wilson made a reamer that had .003 clearance. Even with your 40 years of tinkering Iam sure the KR Wilson reamer has machined more bushings than you have ever seen. Scott
Now with this information in mind look at Class II which refers to "Free fit" or Class I which is "Loose" running fit. Since the Model T engine does not exceed 600 RPM while in low gear, Class I and Class II would be most appropriate. Class II loose fit maximum is .0034 and class I is .0047. Much closer to .0040. Again, open for interpretation. Again, +/- .0010 is academic.
Ken is right on this, there just isn't anything left for chance.
The best way to dummy this out for those that don't deal with this kind of stuff, is get your own copy of Machinery's Handbook.
If you don't want to spend the money, Libraries should have them to check out.
I have a 13 edition, and in my book, pages of interest are 1058 to 1072, you just can't dispute.
.004 thousandths will never seize on a .676-50 to a .677 Ford pin, but it will stress gears, and thrust day one.
The last thing, you have got to have Mic's that will give a true Measurement to a 1/10 of a thousandths every time, or you don't know what you have.
Call it one size, when it is really another.
That goes for any I.D., or O.D. on anything.
The drive gear is not perfectly centered on the shaft if there is clearance between the shaft and the bushing. We all know you must ream the brake drum bushings to clear the unworn portion of the shaft where the clutch drum is pressed on. This results in the bushing then riding on the worn portion of the shaft. Worn out bushing are evident in a used transmission by grabbing all three drums and compressing them towards one another to see the rock.
Also, a KR Wilson reamer .003 oversize does not ream a brass bushing .003 oversize. In most cases, a little more material is often removed in the reaming process.
Over two hundred rebuilds and not one triple gear bushing / pin failure. I'll go with any day. Suit yourself. I'm out.
Thanks Herm! From someone that also knows by doing, I respect your opinions as well. Enjoy your day.
Even if you agree with Ken. When it comes to triple gear pins, I'll go a thousandth or two over as added insurance. Again, academic.
Also, a KR Wilson reamer .003 oversize does not ream a brass bushing .003 oversize. In most cases, a little more material is often removed in the reaming process. "END QUOTE"
Boy, Mark, are you wrong about that!
We all know you must ream the brake drum bushings to clear the unworn portion of the shaft where the clutch drum is pressed on. "END QUOTE"
We don't have that problem, as we don't use those kind of parts.
Over two hundred rebuilds and not one triple gear bushing / pin failure. I'll go with any day. Suit yourself. I'm out.
You wouldn't Mark with those kind of clearance's.
When the transmission band is engaged it pushes all of the respective bushings against their respective shafts. nothing is on center. If the low drum bushing has .003-.004 clearance it's gear will be pushed against the triple gear forcing it to the side and against it's shaft. So everything needs clearance. Thanks Mark for posting these charts. I am glad you finally found something that says running clearance. I agree, the most applicable charts are the class one and class two which support what I am saying. Kens chart is English which explains why it is so difficult to understand
You are correct, I drifted off the size line but these are NOT clearances. They are Tolerances to the clearance! That's what the +/- are for. I shouldn't have expected you guys to understand but I tried. The chart simply gives the tolerance of the fit. There are numerous "fit" types/classifications. Just as there are classifications for threads such as H1, H2, H3, etc. You won't find a machine screw or nut that is exactly #10-32. They have classifications for fit that allow a tolerance in the size.
And you are correct that Ford only used this classification of fit for the triple gear bushings. The others are to be assumed as standard fit for the application and as such should hold a closer "tolerance".
The chart is for tolerance of a fit designed by the engineer for a given application and material. The class of fit has nothing to do, per say, with the material. It simply states the +/- allowance when the type of fit is specified.
There are other charts that give general recommended clearance based on size and material but the "fit" determines the +/- tolerance. These are two entirely different specifications.
When a clearance is specified, it should always include a +/- tolerance in some form. And that's what "fit" does. You even see this in Ford's specs for window glass. It's implied as +/- 1/32". This is the acceptable "tolerance" for a given measurement.
Take for example the triple gear pin. The size is specified as .6770 over .6775". This not only gives the minimum/maximum size but also the implied tolerance. The "dead-on" size would be .67725" and the tolerance would be +/- .00025".
No one can hit a dead-on measurement or clearance, especially with reamers. Tools wear, bearings in machines heat up and expand, even room temperatures change and there's a tolerance for the tool measurement itself.
Would it be correct to say that the pin/bushing fit would fall somewhere in the range of RC6 to RC7 by the description and chart in above?
Glen, the chart may say British Standard (c.1916) but it was the ONLY standard in existence when Ford built cars and he followed it. The BS standard (originated in the late 1800s) was later adopted as the ABC Standard (American, British, Canadian) in 1954. The standard remains the same today.
The whole point is that "running fit" does NOT mean you double the clearance.
Mark C., Your chart is from the ASME standard of 2009. Neither SAE nor ASME specs existed when Ford prepared the manual. All Ford specs would be based on the BS standard.
Mark G., Who cares? It doesn't matter what the chart says. See above.
Ken, We could argue this point until we are both dead. But what difference does it make. 0.002 doesn't work. There are very few people who set their triple gear clearance to 0.002 who haven't had a bushing seizure problem. Those who haven't don't drive their cars. Ford should have been more specific about what he recommended but he wasn't. This is not a new problem. I have seen several original engines with seized bushings so they did it wrong in the old days also. These bushings need more clearance, especially the way we drive the cars today. I say they need a minimum of 0.003 and 0.004 is better and falls within the specs posted in the charts posted by Mark. We all know that 0.002 doesn't work so why argue about it just use what you think is right and hopefully it will work. Personally I know what works.
I'm not arguing the point of the clearance number, Glen. When are you going to get THAT through your head? You said that "running fit" means the clearance is on "both sides" of the shaft effectively doubling it and it is not. It doesn't mean that at all.
There is only one way to specify clearance and that is the space between the two parts. It is not clearance times two.
I might add, I have no problem with the increase in clearance. Ford's spec at the time would have put the clearance of .003" within the limits of the then engineered parts and materials. Todays materials and owner misuse have forced this limit wider.
If I read Glen's last post correctly he does not say say anything about doubling the number, he simply states a clearance of .003 to .004.
RE;Mark G., Who cares?
I am sorry if I offended you by posted a link to the 24th edition of the Machinery's Handbook put out by the ANSI because it may not be YOUR book of choice but there are others that may be using it. So the point would still be "Would it be correct to say that the pin/bushing fit would fall somewhere in the range of RC6 to RC7 by the description and chart in above?"
Interesting stuff Ken. So they are saying a total clearance of .002-.0028
I think your theory has a lot of merit
At least we agree that 0.003 should be the minimum. But that is your opinion and mine not Fords. That is not what he said. So Fords spec did not set the clearance at .003 as you suggest. What he said was 0.002 running fit and there is no definition for running fit or running clearance on the internet. So your guess is as good as mine on what he meant. I choose to believe that running fit means clearance on all sides and not just clearance. 0.004 is clearly supported by the charts posted by Mark which puts the maximum clearance at 0.0047 for the Ford shaft size. You can believe what you want but I choose to believe what works and we have never had a transmission failure or seized bushings. He have fixed a lot of transmissions for people who have had failures and never had a complaint. Humble Howard had his transmission fail twice. It was a combination of bearings being too tight and lack of proper lubrication. After we opened up his clearance to 0.004 and added scoops to his magnetless flywheel he had no more problems and he drives the hell out of his racer.
There is a definition for running fit. It's in the standards. Just as there is a definition for clearance. Mark's chart didn't exist when Ford wrote the specs.
You can't explain nuclear physics to a janitor if he doesn't understand the terminology. This thread is the same.
My best advice for you, Glen, is to stay away from machining.
ding...ding...ding...ding (that's the time out bell ringing)!
You are all saying the same thing...a good attention to detail rebuild at somewhere around 0.0035" works, for those that have honed their mindset and ways over building 100's! That's fine for the guys that always debate this topic...but...
The newbie/first timer doesn't have this SME (subject matter expert) hands on experience...and will usually need an additional 1/2 thou to full thou' to overcome his own innocent sins of omission or co-mission as a newbie!
Don't be afraid of that 0.005" clearance warning from Ford. On the one hand, if done correct and with a cleanliness is next to Godliness attitude and a break in period once done and not winding out to 2000RPM in low all the time thereafter and don't get to fancy with oil grooves or lack thereof...it will take a long, long time to ever grow to 0.005"
The reason for this long time is the bushes self-lap to create the micro-finish needed by the system and then stop wearing while still in the 4th decimal place and... with a proper oil film...and internal 'oil pump' from bush technology in rotation making 'lift'... and with clean oil...further wear is next to nothing for thousands of miles!
Not that I advocate it, but I have also seen and inspected bushings that get to 3 times more clearance than suggested max from Ford. Almost a moot point, because as stated earlier...done right and driven right it will take a long, long, long time before whatever clearance you start with grows to 0.005" These too were from a Interstate 5 high speed driver, but I don't blame the last rebuild...driving on Interstate 5 at those crazy speeds with just take a small issue and magnify it through the tranny...the rebuild on that one went with the DMC conversion because at the time the feeling was the T would continue jaunting up and down Interstate 5 at unrestrained speeds.
OK, back to Week 1 football TV for us on the east coast Play nice...
But first, if your T-level (yes also a metaphor ) is high and if you guys want to debate stuff further...answer some imponderable curiosity's...caution - new thread may be required?
1- Why did Ford specify an oil groove wrap of 128 degrees/45 minutes on the drawing?
2- Why did Ford specify the oil groove by actual dimension apparently looking for it to be 'shaped' to size by a draw bar and not look like it was done by eye with a Dremel?
3- Why are there presently TWO vendors of differing pins that are definitely not the same? Yet no one but me and 1 or 2 others have ever noticed? The pins without grinding centers are in fact made to different tolerances and finishes than the ones with grinding centers!
4- Have any of you who enjoy the debate ever looked at the actual drawings involved? Want to throw logic on the table?...Can't argue with drawings and it doesn't take a rocket scientist to add and subtract to determine the 'desired' original clearance! I have, and it only confuses since we know that today we can't get there. Someday I hope the actual process cards for each piece part turn up at the Benson Ford, it will show the 'how' rather than the 'I think'.
Ok Ken you finally got my goat. You just like to argue and make no sense no matter how good a machinest you think you are. You said that there is a definition for running fit. THEN WHY DON'T YOU PUBLISH IT so we can all see it and understand it? Isn't that what we have been talking about? But no, you just want to argue. So thanks very much, just argue with yourself. This is suppose to be a place were we help each other. But you are helping no one. I'm out of here. This is just a waste of time.
Not a definition of running fit but printed at the end of the Model T production. So it maybe in the wheel house so to speak.
The Machinist's Practical Guide 1929 the following was printed.
Running fit for a .500” to 1.00” shaft with speeds under 600 RPM ordinary working conditions = 0.00075” to 0.0015”
Running fit for a .500” to1.00” shaft with speeds above 600 RPM heavy pressure, severe working conditions = 0.001 to 0.002”
Also stated "For special cases, it maybe necessary to increase or decrease the allowances given."
It appears that the question that keeps coming up is the definition for running fit.
I don't have anything that is in print as to that definition.
I do agree that .002" clearance is to tight IMO
I really think that the term 'running clearance' or 'running fit' as used in whatever original Ford instruction we are referring to was 'coined' by a guy who didn't know what it meant either
Point is, when used the first time by someone at FORD, the term 'running whatever' was never defined to begin with and I'll bet a buffalo head nickel that he never ran his term past the boys in the design room!
Ford came up with the term and then failed to define it. I think my definition is as good as anyone elses in spite of what Ken thinks. Running fit means that the parts are moving. If the shaft is moving it is implied that it is centered in the bushing. If it is centered in the bushing it has a clearance to each side. Ford specified 0.002 running fit. What do you think that means?
Getting back to cobbling, I thought a cobbler did shoe repair. With the advent of all sorts of modern rubber soled shoes, the demand for shoe repair has fallen off dramatically. Apparently many of them have taken up the repair of Model T Fords as a means to keep groceries on the table. This of course has given other Model T mechanics running fits. Those that have survived have loosened up a bit and can sit back an chuckle a bit at all this carrying on.
"Thinking is the hardest work there is, which is probably the reason why so few engage in it."
I think a very important point is that the bushing is reamed or honed square without the correct jig it is probable to ream or hone off a thou or two. I reamed a set of bushings to a very good fit they spin free for a couple of seconds but I question my own method as they may be off or may be on. Checking with a local machine shop the honing of such parts is placed in a machine to assure vertical. The "clearance" is all things to all people but "vertical" is equally important.
This discussion will never end! I remember several years ago while on this subject, it was agreed that we should get the transmission bushings made out of Ford Z bronze. So, Bob Bergstadt got the formula from somewhere, and Bob spent thousands of dollars having this stuff made. That is what we now have, except it's my understanding that there was one operation that was left out of the process, and I think it had to do with heat treating? Today, I believe there are a number of T owners that don't understand how to drive a T properly, and they assume they can drive like a modern car. If you do that, most likely those triple gear bushings are going to seize up on you. I do my bushings like Dave Huson does, which is probably close to .003, I don't know, I've never checked. I just ream them until they spin freely on the shaft and that is it. I've never had one seize up ever, and I drive at least a thousand miles per year. If I encounter a hill that Ruckstell won't pull, I engage low pedal and proceed at a moderate speed.
Dad had driven Model T's from the time he was 9, until he was 22 which he had a New 1925 touring.
They lived about 12 miles from Masnon, Iowa, and every Sat. morning, when he was 9 on up, with the roads they had drove in low gear there and back.
Also the Cop would crank the car when they left town.
Looking at the picture again, the bushing may not be oil-lite, as there were also a cheaper bronze, or Brass for a while, and had no oil grooves, but that was all I could get, so I waited.
Wow, I put my last post on the wrong Post.
I am going to take a Nap.
I agree with you Herman, a nap sounds like a good idea, but I don't want Ken talking about us napping together!!!! Have a good nap. Glen
Gee wiz Herm, You put the whole thread to sleep. Good job.
Ken, Would you please publish the definition for running fit you found We would all like to see it.
I did a search for running fit standards and all I got was tennis shoes. If my definition is wrong I want to know what is correct. I think I have a little experience with tolerances as we manufacture over 200 new parts for the Model T Ford. They all are made to the original Ford specs and work perfectly. Have never had a complaint unless the part was not machined correctly and anyone making parts has had that problem.
Glen, I had to shut it down, when I Nap, I need piece, and Quiet!
The scanner doesn't pick up well near the binding but I think you can still read it. The image below is from page 1056 of Machinery's Handbook, 15th Edition, published 1956. (Other editions are available from 1914 to current.)
Well, we now have the definition but it still does not provide the answer as to how the clearance is measured. How about showing the clearance table mentioned as RC 3, RC 4, RC 5 and RC 6. I suspect these will be similar to those previously posted.