Amidst the recent flurry of posts pro and con Kevlar bands, my situation is all too timely. I found some Kevlar fuzz in the inspection cover screen this afternoon followed by the unwelcome discovery of a cracked low-speed drum.
#@&%!* &#*# ^!&@%#! *%^$&@!!!
This is my third cracked low-speed drum using Kevlar bands (two in the speedster and this one in the touring). Maybe its bad luck, poor driving, poor adjustment, poor drums, but whatever the cause I'm mighty tired of the whole business.
I went with a good used drum and Guinn wood bands last time in the speedster and so far so good. This time I'm going to go with a used gear riveted to a new drum (a buddy got one of these recently and that new drum is a thing of beauty) and wood bands.
It would suit me to keep the car together until I'm ready to do the swap and would like opinions on using either of the cracked drums pictured below as my core. The left hub thrust face is galled and slightly ridged, the right drum thrust is a bit deeper ridged. I can have a local skilled machinist friend face off the thrust surface.
Which drum should I use for a core, and what problems, if any, would result from lowering the thrust surface to clean it up?
Chris, either of those gear centres looks useable from the photos. Re facing the thrust faces, you will have to put them in a lathe to face off the rivets. I would simply clean them up until the rivets are flush and leave the thrust faces. The more you machine off, the less rivet head/countersink you will have left. Having perfect thrust faces is not that important in this application.
Others may disagree.
Allan from down under
It looks like someone removed a lot of material from the drums in order to make them shiny. This weakens the drum a lot, making it crack more easily. The new drums of course will fix your problem.
For anyone using old drums that are slightly pitted or scored, for goodness sakes DON'T chuck them in a lathe and face them off. Making them shiny is not an improvement, it won't help performance, and it will improve the chances of a cracked drum.
While you're there,check the clearances on those bushings. Those drums have been run very hot. And not from the kevar.
Ouch. I feel your pain. I am a member of the multi-piece transmission drum club, too.
I have a set of wood band lining. I'll swap you for your Kevlar.
Thanks for the comments and suggestions. I expect to re-bush whichever hub I use. Both the drum faces are shiny from polishing or use, not from facing off. One of them, don't remember which, came out of my speedster a couple years ago and the other was from a spare transmission.
Keith, if those are new wood linings and you're serious, we have a deal. Bear in mind my Kevlar linings are used, meaning rivet holes but no appreciable wear. You can also have the set I took out of my Speedster this summer. PM me if you want to go ahead.
They sure don't look like any used drums I typically see. When a drum wears from use it develops irregular grooving, not mirror finish flat surfaces like yours. You may not know it, but someone faced those drums at some point in their recent past.
Regarding re - bushing the hubs, if the hub is within limits don't replace the bushing. Modern materials are not necessarily better, and the typical modern machinist tends to think that tighter clearance is better, which is not the case.
#1- Regarding facing or machining drums... It can be done properly if you have proper measuring equipment and you don't remove too much. Believe it or not, I have run into several drums that have had pits & grooves and cleaned up at .010" undersize on the diameter... I occasionally find stock, used drums that are over their blueprint diameter by as much as .035"! Finishing a drum .020" undersize of 7.500" is not going to hurt anything (providing the casting looks good - some drums are cast "off center", and you have to make a judgement call on whether to use them or not.
#2- The drums shown in that photo have been overheated. You can see the color change in the metal from dark to light going from dark at the outside to light at the center. Different colors are an indication of what temperature the metal got to. A couple possibilities what caused this are:
a- It could be operator error. For instance, if the vehicle was driven thru a slow parade with the throttle cracked open to a high idle and the driver had the pedal about half way engaged, allowing the drum to slip on the band for a long period of time (minutes at a time) instead of pushing the pedal in far enough to keep the drum from moving, creeping ahead in low gear several yards, letting the pedal up into neutral, then repeating.
b- a mechanical defect in the transmission. This sometimes is just a band that is adjusted too tight, but if you are sure that is not an issue, then the next most common problem is an improperly functioning band... There is a potential for an alignment issue to occur that can cause one ear of the band to be driven down into the drum surface when the pedal is actuated. Every time the pedal is actuated, this causes friction in one small area instead evenly over the entire length of the lining. If you have Kevlar linings, this causes extreme heat build up at that spot and is usually the cause of cracked drums in the case where the drum shows that color change. If you have the same issue with cotton or wood bands, they are far more forgiving. Generally they will rapidly wear away, burn, glaze, etc in that spot and the potential for problem is nearly eliminated. However, that issue is generally the cause for people who complain of a band that "chatters", a pedal that is hard to push, or a properly adjusted band that requires much effort to function properly. DO NOT OVERLOOK THE IMPORTANCE OF PROPERLY FUNCTIONING BAND SPRINGS. Old weak springs and poorly made reproduction springs can be a contributor to, or even a direct or indirect cause of this problem. There are, or have been some band springs with a gold plating on them that are not always suitable. They seem to be variable and some do not stay "springy enough" nor keep their original length. I've been using some springs from one vendor that are black in color and they have tested out to be quite satisfactory for over a year.
If every part of your transmission is functioning properly and aligned properly, then there really shouldn't be any reason that any material or brand of lining should not function satisfactory.
In a properly functioning and properly driven T:
-Plain cotton linings, should last at least a few thousand miles. 5,000 to 10,000 miles is probably average amongst the people who are very experienced T drivers.
-Wood linings should likely last about the same, but I have not had any conversations with people who have claimed to used them that long. I do know that the wood linings will burn, glaze, & fade just about the same as cotton in severe driving situations.
-Kevlar linings have the potential to last tens of thousands of miles if everything is "just right". If your last set of bands were cotton or wood and they only lasted a couple hundred miles, then there is only two possibilities: Something is mechanically wrong that needs to be properly diagnosed and properly repaired -OR- The T is not being driven properly. If your wood or cotton bands only lasted a few hundred miles and you switch over to Kevlar and encounter overheated and or broken drums, then the issue is going to be one of those two possibilities.
I simply do not believe that there is any unusual, unknown property in Kevlar that randomly cracks good transmission drums.
I actually used to be one of the people who had negative ideas about Kevlar linings until I actually dealt with a few of these issues on customer vehicles, figured out the actual real cause, cured it, and the vehicles went happily down the road for years afterward...
Fellows, did I miss-read Chris's post. He speaks of machining the thrust face on the gear hubs, not the band surface. I read the post as using the gears in new drums.
Adam, good advice on all counts. However, you have the cart before the horse in one sense. Rather than the casting being off-centre, it is more likely that the casting was miss chucked in the lathe and was machined off centre. Such drums are a real pain when trying to balance the drums.
Hope this helps.
Allan from down under
Most drum, or band chatter comes from the out sides of the drums NOT being true. They are some what out of round, and always have wore low spots in them. You can't expect a band to grab a surface that is irregular, and not centered with the center hub, with out chatter, especially at low take off.
Machining a center hub in a lathe, can be a tough job some times, as many people think all you have to do is center the out side of the hub surface, and that has to be, but you have to make sure that both ends are in Alignment to bore the bushing, you can't just center the middle, or either end, to get the inside perfect with the out side of the hub. If you don't, the center of the bushing will make the band hub way out to where it is not useable, with out putting in a new bushing.
A K.R.Wilson Jig, centers the hub with the out side drum, NOT the reamer, and bores the bushing to the hub. A reamer with out the jig will make the hole the size of the bearing surface it runs on, but with the Jig used with it, it bores the bushing to the length of the straightness of the length of the hub.
Before any machining is done on the hubs, "Bushings", the Hubs should be checked with an expanding Mandrel, between centers, with out a New bushing, to see if there are any issues with the drums.
Like Adem, we turn ALL drums, and with the amounts that he used. As far as any rivet grooves, we leave if they are to deep to cut out, and not deep enough to hurt any thing, if O K-ed with the customer!
45 years, and NO Tranny problems!
An Expanding Mandrel is used to cut the out sides of the drums, with true center of the Hubs.
Herm... I just switched over to expanding mandrels for "tuning up" trans drums. Much easier & faster, but also very expensive... The only way I could justify buying the mandrels is because I just turned 40, and will probably be doing this for 30 more years. Before I got the mandrels, I was setting them up in a four jaw, indicating off the hub with no bushing to get the drum concentric and get the wiggle out, then cutting the outside of the drum. I would then remove the drum from the lathe, install the busing, put the drum back in the 4 jaw, this time indicating off the finished outside diameter, and then go in with a boring bar and skin a little off the reverse bushing to ensure it was concentric with the outside of the drum. It has been a "must" to do this with reverse bushings as the oil grooves are manufactured a bit too deep and the bushing "puckers" up a little irregularly and can not go directly to honing without a very light cut on the lathe to dress down the high spots. The low bushings available for the last nine months or so have grooves so deep they are unusable. They distort so much on installation that I don't think they will even stay solidly put in the drum over the long term. I'm having some Low drum bushings made to the Ford prints for my own use on transmissions I am rebuilding here in the shop, but they are cost-prohibitive for the average hobbyist (around $40 ea). I have never seen a real KRW drum busing reaming fixture in person, only photos in books... I can't help but be suspicious about their accuracy because the natural nature of any reamer is to "follow the hole"... They just don't like to cut off center. You are right about drums not being concentric with their hubs. I have found many T trans drums that are up to .015" out of being concentric. I can't imagine just clamping a drum in a fixture that runs a reamer thru the bushing and fixing that big of a machining error. There isn't enough material in the bushing to remove, and the reamer will move off center unless the fixture has absolutely zero slop. I have always had the idea that the KRW fixture was meant more to make the reamer enter the bushing absolutely parallel to the band surface than it was to correct "runout" at the bushing... Of course, never having seen one in person, I have to admit that I could be missing some critical detail in my assessment.
Allen: You may be absolutely correct. In the case of drums where the casting appears off center, It may very well be that they were set up sloppy and machined off center. It also may be that they were cast from a match plate mold where the cope mold was mostly the inside diameter and the drag mold was the outside diameter (or vice-versa). If this was the case, you would also see a mis-matched parting line somewhere on the casting, but every parting line on this casting would be machined off in the manufacturing process, so I guess there is no way to tell... Either way: mis-cast or mis-machined = exact same issue. (also makes them way out of balance).
Adam, I have a KR Wilson drum reamer, I bought it for a wall hanger, I did try it out and it does ream the drums with in .004 if the drum has not been turned down or have some wear to it. I use the lathe to bore the hole cause there is not that many true drums out there.
Good point Joe about there not being many true drums out there. I do find drums that are pretty concentric between the hub and the outer diameter, but I have also found plenty that are not concentric by as much as .015"!
I don't think you would notice a drum being .015" out of round, at least not by driving the car.
Yo, Adem, yes the mandrels work real well. I have them from .430 to the size in the picture above, and use them all the time. Mine are K.O.Lee's.
All bushings distort when thy were put in a pressed position, even if the inside of the bushing was trued before being installed.
The depth of the oil groves should not matter in any case.
Just putting a reamer in a hole to ream is fine, as all you have to do is fit a shaft to a hole, with out any other considerations! such as wrist pin hole, and the pin bearing of a rod, they only have to be the correct clearance. Yes they will be out of alignment, but that is what Rod aligners are for.
Before I for get, yes .015 out on the drum, in side the band can cause chatter, and much unneeded wear. Can you imagine a wobble wheel inside your band pushing it around in a circle with each revolution!
Adem, honing a bushing to round, on a sunnen, is great, but it still is just honing, not align honing.
There are better ways! As you say, a normal reamer will just follow a given hole, and so will a Wilson, if that would be the way you use it, but it is not!
Lets use the reverse drum as an example. The reamers will do you no good, with out the Jig to go with them. First as I said before, you should make sure that the drums are not sprung, by checking on a expanding Mandrel, and lathe centers, and NO BUSHINGS.
You put the reamer in the drum, and push it out of the way. Then place the drum, and slide the reamer into the start of the bushing hole. I might say here, the Wilson Reamers have a front taper on them, and it acts like a centering cone!. Then you tighten the drum down, and remove the reamer to make sure nothing was binding. You do not want to jam the reamer in the bushing, just a light pressure.
Adem, this is the part now that you are not aware of. The reamer shaft in held in the Jig in its bearing, and Align Reams the hole, it does not follow the hole by the cutting end, it follows the path the Jig tells it to, then re check on the expanding mandrel again, and then you are ready, to true the out side.
Herm, Very good info on how those original KRW Trans drum bushing reaming fixtures work. Thanks.
I am quite satisfied with the bushing alignment I am getting using the lathe and Sunnen hone. Most important step is VERIFICATION and QUALITY CONTROL... Checking your work leaves no doubts!
Some bushings distort more than others when pressed in. I generally find enough distortion in low and reverse bushings that after pressing them in, I have to set the drum up in the lathe and skin a couple thousandths from the bushing to give the hone a proper starting point. On the rest of the bushings, I can usually skip the lathe and go right to the hone. I don't take any chances though; If they need additional work, they get it.
The repro low and reverse bushing grooves are so deep that the bushing buckles inward at the bottom of the grooove. They change size when installed instead of retaining their shape which equals a substandard press fit...