notchy, almost impossible shifting

[mini64]

Newly rebuilt 3-rail tranny has, over two race weekends, become almost impossible to shift at speed. Seems to be all gears, upshifting and downshifting. About the only anomally I notice is at slower engine speeds it is a bit easier, but far more notchy then it used to be. I can reproduce the problem in the garage with the rear up on jack stands. Going say from 3rd to 4th at high rpm you have to wait for the engine speed to drop before it will go in gear and then its still very hard. Downshifting, with a good throttle blip, doesnt help, you almost have to wait till all is down to about 2000rpm before it goes. The clutch is fully disengaging - i can put it in gear and have my co-driver press the clutch and the wheels spin freely, no clutch drag.

Any ideas?

I have always put a good quality gear lube in and never had a problem before. But after some reading I just drained it and put redline manual tranny fluid in, shifted in the garage about a 100 times and it is no better.

[rgh0]

My first area to look would be to confirm the clutch is disengaging correctly.

cheers
Rohan

[reb53]

"The clutch is fully disengaging - i can put it in gear and have my co-driver press the clutch and the wheels spin freely, no clutch drag."

That's under a no load condition.

I'd be real suspicious about the clutch.
I have occassional problems with mine when it seems not to dis-engage fully, resulting in a crunchy gear change, and sometimes when backing out of the garage the car would keep moving even though the clutch was fully depressed.

My best guess was that the plate was sticking on the splines and not moving back a little when the clutch was depressed.
To confirm it I managed to get a long thin tube up thru the clutch gaiter hole and squirted a bit of lubricant in what I figured was the general direction of the centre of the clutch plate.
The transformation was immediate and miraculous. I now had the best, most linear clutch action I'd had for years. It lasted for about 1000 miles before the old problems came back.

The thought of pulling the box, replacing shafts that are probably unavailable anyway, ( if I could afford them), filled me with a horror that has ensured that I have learned to live with the problem when it occassionally rears it's head.

Cheers
Ralph.

[mini64]

yes, my clutch dis-engagement test is under no load so maybe not valid. this plus the fact that i tried shifting without the clutch and it is pretty much the same. maybe I should squirt some lube up there?

another theory- my pilot bearing is too big. I use the small one but I dont remember telling my engine builder which one to use when it was freshened before all these problems started (timeline - engine rebuilt, gearbox started having trouble shifting into 3rd-4th, the shift we do most, rebuilt gearbox, back to being bad again). maybe at speed the gearbox input shaft is vibrating around due to the too large pilot bearing and binding?

[david.g.chapman]

I have used "3 in 1" Spray Lubricant with PTFE in the past to good effect. I had a release bearing that was getting noisy due to me inadventently washing out its lubricant. I made up an extension tube to reach the release bearing in situ, and give it a squirt every year. Maybe its the PTFE, but it lasts and lasts.

You could try the same stuff with your clutch mechanism.

Dave Chapman.

[mini64]

i sprayed wd40 and no help. then sprayed a teflon containing dry lube but no help. But in peering up in there I can see all my pressure plate fingers are not even when the clutch is engaged (pedal off). then as the pedal is pushed they arent all hitting at the same time. something is up. I last replaced the p-plate in '04 so maybe it is having problems that only show up when the engine is running.

[rgh0]

Yes if wrong pilot bearing flywheel will not be square with clutch plate and will drag causing the change problems

regards
Rohan

[reb53]

"peering up in there I can see all my pressure plate fingers are not even ".

Yep, that'll do it.
Reading this rang some bells 'cos the same thing happened to me about
25 years ago (!), so you can forgive me for not remembering straight away.....

When I got the pressure plate out the fingers were all tilted over.
To have gotten them to, firstly, all even up and then, secondly, actually
push in enough to actually operate the clutch would have required too much distance for the slave cylinder to handle.
The result was the clutch never fully disengaging.

Hard to find stuff like that then, and in my part of the world, so had a company rebuild it.
Worked fine for years.

Cheers
Ralph.

[mini64]

conclusion:

found about 1/4 of the clutch friction material on one side of the clutch disc loose and flapping around on one rivet. it had obviously been flying out from centrifugal force and rubbing the clutch pressure plate by the way it is worn. this was then locking the clutch and giving us the "shifting as though the clutch wasnt disengaging" effect. The material hanging out was what caused the pressure plate to sit uneven and allow me to see the fingers not all at the same angle.

hadn't changed the disc since '05. plus may have been damaged from previous flywheel unbalanced problems.