Technical Clutch fade when hot. I'm sort of out of ideas.

This is happening on my A coupe. It has a mechanical linkage that's set up pull style on hiem joints. It has a steel fly wheel and a nice hays clutch disk and pressure plate. Adjusted nicely as usual and has a return spring. I have had the t-10 out 3 times in the last 2 weeks tryin to figure this out and I'm stumped.
When the car is cold it works perfect. Stop, start, shifts at 7 grand no sweat. But when you get some time on it say 20 mins or so, you start to lose disengagement. I mean it gets to the point where it's "shut it off to get it back in to gear at a stop light to get rolling". I have even tried to jack " too much" preload into the linkage just to see if it would change it, same deal. I have tried different stroke ratios on the linkage you name it.
I can't be the only guy who experiences this. I know it to be common on a hydraulic set up but not full mechanical. I can post pics or whatever you guys think.

Hack

 

What it sounds like, to me, is that your throw out bearing is not moving far enough away from the pressure plate. As you use the clutch and it warms up it swells a bit. When it does and you push the throw out bearing into the pressure plate it is not moving the surface of the pressure plate far enough away from the disk. My guess is that there is some obstruction on the bearing retainer of the transmission. You could adjust the linkage so that you have much more clearance than you do now and see if that helps. Is it possible you have a bad motor mount that gets loose when the motor warms it up??

 

Sounds like the pilot bearing tightening up on the front shaft. Had it happen to me many years ago.
Only happened when I got in traffic.

 

^^^^^^^^^^^^

 

Are you able to shift through the rest of the gears ok when it's hot ?

 

I just took out a diaphragm clutch that had that issue. I found that the edge of the diaphragm was just barely contacting the radius part of the pressure plate. I think when it got hot it was "off the edge" and loosing throw somehow. Anyway, I took apart two other old ones to see what it should look like and combined parts to make one good one where the diaphragm could roll over the radius on the pressure plate and still have a small margin of safety where the wear marks are. A slightly larger outside diameter spring.

Also the thickness of the diaphragm spring changes the force of clamping and the pedal force too. I found springs from .118 to .140 in thickness.

 

Is the pilot bearing a bush?? If so, I agree with "Hoop".. Struck it once, years ago on a bush type pilot/spigot bearing..

 

So you guys are thinking that the front shaft of the trans. isn't stopping because the shaft is ''swollen'' inside the pilot bearing ?

 

^^^^ Yes ^^^^

 

I had a problem because the clutch disc hub was just touching the crank and causing drag. It was the correct clutch set but the tolerances stacked up wrong...

 

Yes... Something could be binding between the pilot bushing and the end of the clutch gear. Slight misalignment of the transmission mounting or bellhousing could make matters worse. Or something could be hanging up where the T.O. bearing slides on the bearing retainer. Was the O.D. on the retainer smooth and rust free? Also check for any funny wear patterns on the contact surfaces of the clutch fingers, and where they contact the face of the T.O. bearing. Both surfaces should both be smooth with no ridges or burrs.

 

or the pilot /bushing bearing is not in the crank far enough and when it grows it makes a solid drive or the clearances on it are too tight or a burr on the input shaft . had that happen from someone who was afraid to hammer the bearing/bushing in hard enough and didn't seat it .the edge of it was machined /burnished from the input shaft snout were it made contact

 

The pilot is an oil light bushing. I checked all the clearances and everything looks great. Everything looks beautiful when I take it apart. You can slam through the gears like crazy. But say you come to a stop, you can't get it into first gear because the main shaft is still slightly spinning like the clutch is engaged slightly. None of this happens when it's cold. I am off today and I'm going to try a few adjustment changes. As far as loose motor mounts, I go through that car weekly and I can assure you that that's not the problem and everything is tight. I think fuzzy may be onto something there. It's got to be something stupid like that. I will start there and report back. Thanks for all of the replies.

BH

 

so what motor /trans do you have? When the problem happens does the "free play" or toe play in the clutch pedel change any compaired to when it is cold?

 

Please post what fix's it. Wow !!

 

I know you said its an oilite bush , but did you put a little grease in there anyway....I would , also a LITTLE lube on the input splines wouldn't hurt
dave

 

Yes I put grease on the input. The pedal seems slightly softer but not very much. I tried to go with the extra slack and it would not disengage enough to get it into gear. So I ran it up pretty tight on the throw out and it works. The thing that baffles me is it seems that it would be the other way around and the clutch would slip. Anyway it shifts fine for a while then does the same shit again. It hooks up like crazy though. As far as clamping force it works great. I took it to a show today and had to start it in gear to get out of the show. Upon my departure I did a nice 7500rpm clutch drop. Tire smoke for a block. So I feel better about it today hahah. I'm going to pull it apart this week and I will post pics of what I discover. Thanks guys.

 

Sorry the engine is a solid roller 11.5 to 1 small block. Basically an all out 500 hp drag engine. Really good internals that we could go into if you would like. The trans is a 62 t10 that I rebuilt. Hand lapped the syncro's and blueprinted everything. When the clutch is working well the trans acts as it should and receives flogging weekly. The flywheel is a steel neutral balance piece that is brand new. The pressure plate is a diaphragm stock car piece from Speedway and the disk is a solid hub stock car piece as well.

 

Could the disc be in backwards? Seen it before.

 

I think it's the linkage-- Not enough throw

 

pressure plate fingers bent slightly or softened.. gets worse when they heat up

caused by abuse

 

You're saying that you've checked clearances so I'm assuming you've checked the ID of the bronze ? pilot bushing and the OD of the input shaft. But you're checking them cold, as you should, and I'm wondering if the bronze pilot bearing is getting hot and grabbing the input shaft and keeping the main shaft spinning.

 

I'm subscribing because I've had this problem off and on for awhile now and then.

 

As one more thing to check you need to know what you have for disc clearance with pedal depressed...at least .045 an not more than .060...You need to put a hole in the bell housing in line with flywheel face to check..1" dia would be enough..I am leaning towards clutch disc warping when hot; I question the choice of stock car clutch parts..

 

My thoughts as well...

 

Is the pressure plate a high-cone or low-cone diaphragm? And is the rest of the clutch linkage and the T.O. bearing compatible with whichever pressure plate you have?

You wouldn't have a weak or cracked clutch release fork that's got a bit of flex in it, would you?

 

Also look at the z-bar for cracked welds, etc.

 

Show us a pic of the diaphragm cover and throw out bearing some throw out bearing surfaces are round ..some ground flat. You need to make sure you have the right throwout bearing riding on your clutch diaphragm. There are also different height throw out bearings..... Hope you find it...

 

Don't want to knock Speedway. I use their stuff too. But I do know a bunch of it is made off-shore. Is it possible the pressure plate fingers are getting soft when hot? Can you see the clutch disc/pressure plate thru the bottom of the belhousing? If so, maybe you could see if you can get a feeler gauge in between the two when hot. I think we used to use a .025?

 

Hmmm... 'Pressure plate fingers getting soft when hot?'
More like trapped heat in the bell housing swelling clutch lining when it heats up.
Was the pilot bushing ever 'honed' to size after all the confab about bushing/bearing choice?
And...as mentioned previously: Could that disc have been installed backwards?
Just a concern with so many factors, the hassle involved in removing components, etc.
I like the idea of the wire gauge (.025") inserted thru a hole in line with the disc...
May tell the story when 'hot'...