A really stupid transmission question

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2017: A really stupid transmission question
Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Saturday, November 04, 2017 - 10:51 pm:

This is a dumb one so bear with me. What exactly does the bolt that rides on the brake shaft cam adjust and when/why/how do I properly adjust it? I have some ideas but I'd like to get it right.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Saturday, November 04, 2017 - 10:57 pm:

It puts the transmission in neutral when the lever is pulled back ie; lever straight up and down the transmission is in neutral all the way back parking brakes are on too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Saturday, November 04, 2017 - 11:19 pm:

Maybe I could be clearer on that. I get the function of the cam itself, it was what the adjustment adjusted that had me scratching my head. Near as I can tell it adjusts neutral on high speed, but don't the clutch finger screws sort of do the same?

Or I can out it this way: my clutch fingers were loose so I gave them each one turn (half turn was still loose). Now I no longer have a free neutral though I still seem to have the pedal linkage set correctly. This leaves that adjustment screw that rides the cam... I think.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Saturday, November 04, 2017 - 11:33 pm:

The three finger put the clutch in neutral when you press down the low pedal. The screw adjusts the clutch lever itself to put the clutch in neutral when the lever is pulled back. Google clutch adjustment, the screw is part of the whole package in the adjustment.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Saturday, November 04, 2017 - 11:40 pm:

The 3 clutch finger screws seldom if ever need adjusting after the initial setup after a major rebuild.

If you have adjusted them and lost free neutral, I think you've answered the question.

They set the tension or transfer the force from the transmission spring to the clutch plate to clamp up high gear clutch disks. When you pull the brake handle back, you are pulling back the spring and releasing tension on the high gear disk pack. The fingers will now be "loose". If they never go loose, you always have high gear either locked up or dragging badly.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Sunday, November 05, 2017 - 01:17 am:

Yeah, I definitely did this to myself while trying to get more positive engagement of high speed. I've done some more reading and very little is ever said about the clutch finger screws which is really why I'm trying to better understand this thing. About all I can find are references to never needing to be adjusted because nothing ever wears out, unless it has fibre clutch discs then the need for an adjustment could be a sign they're toast.

As for the mechanism itself, near as I can tell the bolt that rides on the brake cam determines how far the spring gets pulled off the clutch fingers when the lever is anywhere but full forward and the fingers' screws determine how hard that spring pushes on the clutch pack. Is that close to what's going on in there?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, November 05, 2017 - 01:26 am:

Yes on the last bit.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Sunday, November 05, 2017 - 05:27 am:

No stupid questions here! I just wish I had a proper smart answer.
The model T clutch, and the way it "inter-operates" (for lack of a better term) between the low pedal and the brake handle, coupled with the convoluted idea (sort of like an oxymoron?) that the model T has NO actual neutral, makes it seem much more complicated than it really is.
First, lean back, relax, say "ohm" a few times (I worked with electronics for much of my career time, so there is an inside joke there), and clear your mind.

First of all, the idea that "no actual neutral" is strange? Is wrong. MOST automatic transmissions for the past 70 years had basically the same kind of neutral. Simply clutches not engaged. Selective sliding gear transmissions with a separate neutral from the clutch are the strange ones.

Some may want to skip the next two sections on the clutch fingers and discs, going straight down to the big "NOW" leading to the external adjustments.

The three fingers that press the clutch into engagement are a totally separate action from the clutch control shaft and yoke (its little brass horse collar down inside) , regardless of whether it is operated by the brake handle or the low pedal.
The primary purpose of the three clutch fingers is to allow proper and EVEN adjustment so that the clutch can engage or disengage smoothly without shudders or grabbing, and allow for a nice clean "neutral" without too much tendency to creep forward. There is a proper specification for that adjustment. If I recall correctly, it is 13/16 inch back between the (pressure thimble?) and the driven plate. That is with the clutch yoke not putting any influence onto the spring. Several people in the past have recommended using a common 13/16 lug nut as a go-no-go tool. Personally, I use my grandfather's antique inside caliper. It seems easier to use in my opinion.

The big spring, through the (for lack of a better word) big thimble, and adjusted through the three fingers, apply pressure to the clutch discs in order to engage high gear. High gear clutches must be disengaged for neutral, low band/gear, or reverse. However, high gear requires good pressure on the clutch discs. That 13/16 inch adjustment is the optimal position for everything to work as it should. However, IF (that big IF again) the car slips in high gear? There are several things that can cause this, including uneven adjustment of those three fingers, check that first. One of the other common causes is a weak spring. If you have eliminated other adjustment issues? A little more pressure onto the three fingers MAY help, HOWEVER, that is a band-aid repair, temporary at best. In the first place, the three fingers do not generally allow for much extra push. Secondly, failing springs usually get weaker fairly quickly, so you may be back into trouble soon. And third, moving that thimble back farther in order to put more pressure on the clutch fingers and discs, also throws the other adjustments out of optimal position, making them more difficult and troublesome.

NOW. Once the discs and fingers are at their best adjustment for the clutch to engage well, it is time to make it disengage.
There are of course two ways to do so. The "T" bar clutch shaft with its yoke (if properly installed), will tell you where the engaged clutch is. It does a fine job of sitting in that one spot.
Don't overthink this. The two ways to disengage the clutch are adjusted separately. Do one. Then do the other. Both are subject to wear over the years, they may have been bent by accident, or to compensate for something in the forgotten past. Early and late parts can be interchanged? But early and late are different because the starter got in the way. Your car may or may not be pure itself. The parts you are using may or may not have been altered to fit a different car or circumstance years ago. Check all of it for fit, for wear, and lining up properly. Some of it is easy to see, the brake cross shaft clutch cam needs to be clean and straight and line up nicely with the end of the clutch "T" shaft. Not so easy to see? How are the little clevis connectors and links connecting the other end of that "T" shaft with the low pedal. A bit of wear on all those little pieces can cause a lot of grief. The clevis pin hole on the end of the "T" shaft is usually okay. Usually, a new clevis pin is all that is needed there. Sometimes a new hole (drill) and custom oversize pin (don't want to remove much material) are needed. The combination clevis and "L" pin/rod can actually be put in either way. I have run into cars that had to have it one way, while other cars had to have it the other way. Yes, there is a right way, but I am not certain which way that is? (I usually put the "L" pin/rod on the clutch pedal end, just because most original hogsheads I have had were that way when I got them.) Usually, that "L" pin/rod does need to be replaced because they tend to wear crooked, and crooked tends to wear fast.

Another side trip. A mystery to many, but probably simply cumulative wear on all the bits and pieces and shafts and yokes and clutch discs and fingers both outside and inside the transmission, all add up to a simple problem. That combination "L" pin/rod and clevis link has become too short. Only by a little bit, mind you, but too short is still too short. There are two simple ways to fix this. Make an "L" pin/rod that is about a half inch longer. Or, because Ford used odd little clevis yokes that were lighter and shorter than what most people used both then and now? IF (that big IF again) your "L" pin/rod is in very good condition, and you really don't want to make a longer one? Just get a common modern or antique longer clevis yoke of appropriate size for both the pin and rod. A few years ago, they were still available (although not heavily stocked) at most Ace and True Value hardware stores. Although, the last time I needed a few, I had to go to two stores to find three of them.

Once all that is in proper condition, the adjustment is simple. Individually, adjust the two operational paths to the "T" shaft. For the low pedal (often also called the "clutch pedal" and marked with a "C" on the early cars), adjust the length of the combination "L" pin/rod and clevis yoke so that with the pedal pulled clear back? It puts absolutely NO pressure onto the "T" shaft. But with the pedal pushed a bit less than halfway forward, it must push the "T" shaft down enough for the brass yoke inside to pull the big thimble and spring back from the fingers and remove ALL forward pressure to the discs. It doesn't take much. I am sure there is a proper specification. I do not know what it is. I think about a 1/16 inch clearance cold should be enough. Remember, a running engine will separate the discs a bit more. So a bit more may not hurt. But when running, all the thimble has to do is barely clear the fingers.
Basically the same thing for the brake handle to clutch release. Once everything is lined up properly? The bolt needs to totally clear the cam when the handle is fully forward. The front ramp of the cam should engage the bolt by pulling the handle back only a bit, and put the bolt on the long top of the cam before the handle reaches straight up. IF that cam is in good condition? Once the adjusting bolt has reached the long top of the cam? Moving the handle back farther should not change the pressure on the clutch. So, once on the long top, simply adjust the bolt (like the with the low pedal) for the big thimble to clear the fingers. Again, it doesn't need much, about that same 1/16 inch should work fine.

While playing with the brake handle and low pedal, one may move the other slightly. But neither one actually works the other. So like I said. Keep it simple. Two separate adjustments, either used individually to just clear the pressure onto the fingers.

One other little trick. If you want your brake handle and clutch to work really nice and smoothly? What I do, is replace the bolt in the "T" shaft with a standard 3/8 fine bolt, about an inch and a half long. I grind on of the hex flats into a nice smooth ramp (about 45 degree angle). Then put the bolt in upside-down (from below so that the bolt's head rubs on the cam. That adjustment is not critical. Adjust till the clutch fingers are cleared adequately, then line up the bolt's ramp to engage against the cam's ramp, and lock in place. Note, Some cars, I have had to put the lock nut above the "T" shaft, because best adjustment didn't leave enough room for the lock nut between the "T" shaft and the bolt's head. If there is enough room, I prefer the lock nut below the "T" shaft between the shaft's arm and the bolt's head. It is a little stronger that way.

I hope some of my ramblings can help you and others to understand how the clutch works. And how simple the adjustment really is.


Top of pagePrevious messageNext messageBottom of page Link to this message  By William Hoffer on Sunday, November 05, 2017 - 06:37 am:

Wayne, have you thought about publishing a book containing your ramblings? I would buy a copy. Or gather your info into a blog. I'm pretty new at this mysterious T stuff, and have only begun digging into the forums, but your insights are terrific. Thanks for the education, Bill


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Sunday, November 05, 2017 - 08:22 am:

Thanks Wayne, it's definitely getting clearer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john pawlowski - NE Pennsylvania on Sunday, November 05, 2017 - 11:43 am:

I would definitely buy a DVD dedicated to the adjustment for neutral on a Model T. I've been following the forum and the photos but can't seem to find that sweet spot. I can start my T as long as the rear wheels are raised. With wheels on ground starter tries to turn engine and car starts moving forward.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Sunday, November 05, 2017 - 01:11 pm:

http://www.mtfca.com/discus/messages/708324/762357.html?1496974356


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, November 05, 2017 - 02:36 pm:

john p, the lugs in the brake drum might be worn out and are keeping the disks from fully releasing. If the fingers are loose when the parking brake handle is pulled back or the low pedal is pressed down then the clutch should be in neutral.
http://www.mtfca.com/discus/messages/708324/804708.html?1509851230
Once grooves get worn in the lugs, they lock the disks so they can't release.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john pawlowski - NE Pennsylvania on Sunday, November 05, 2017 - 04:03 pm:

I didn't mention that both the engine and transmission were rebuilt, so I hope nothing is worn out. They were done professionally by a rebuilder in strasburg, Pennsylvania. Schwalms is the name of the rebuilder. One other thing that I didn't mention is that when I pull the parking brake all the way back like touching the seat,it seems that the starter turned easier, but by that time the battery was dead.So I haven't been able to get the battery back in the car to see if will start and I don't feel comfortable having to hold the parking brake all the way back. Not knowing if I take my hand off brake handle the car shoots out of the shed. Not a pleasant thought.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Sunday, November 05, 2017 - 08:21 pm:

John P

you need to start a new thread for yourself. I have comments to make which will potentially hijack this thread and would be unfair to Tim


Top of pagePrevious messageNext messageBottom of page Link to this message  By john pawlowski - NE Pennsylvania on Sunday, November 05, 2017 - 09:32 pm:

Opps,sorry didn't mean to hijack .


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Sunday, November 05, 2017 - 10:19 pm:

John

it's all good...see my response to your new post :-)


Add a Message


This is a private posting area. Only registered users and moderators may post messages here.
Username:  
Password:

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration