mark kibort

when the TT makes noise, how long before it becomes a problem. mine is making noise in neutral, clutch not pressed in. noise is coming from the torque tube.

dprantl

Mine never made any noise. What started making noises was the clutch (because of the loose guide tube bolts machining themselves and the guide tube bouncing around) and the clutch pedal would vibrate at over 3k RPM. The vibration was bad enough that it would make the slave cylinder leak and the clutch would not come back up all the way after a long run at high RPM.

Dan
'91 928GT S/C 475hp/460lb.ft

Opelotus

Are you saying the superbearings are more expensive than a rebuilt TT or more expensive than standard bearings for replacement?

dprantl

You should check with Constantine about latest prices. I believe the SuperBearings were only slightly more expensive than a rebuilt tube with original bearings, but Constantine was offering a free TT rebuild service if you bought a set.

Dan
'91 928GT S/C 475hp/460lb.ft

Opelotus

Just pulled the master cylinder, good call Mrmerlin, I do indeed have the shorter stroke piston.
I will take some careful measurements/calculate how much to cut off the pin/spring, using 4-5mm as a reference. Are the dimensions of the slot in the end critical? And how do I get the lip seals of the piston back into the bore without tearing them?

Opelotus

Phase one complete: Piston has been shortened 4mm. If my measurements/calculations are correct, 4mm is the max reduction allowing a bit of room for error. Reground a slot in the end, spring didn't need to be cut. Now to bleed the system; I removed all the fluid from the reservoir to level of the blue hose, would it work if I connected a tube to slave cylinder and dip it into a brake fluid bottle and then apply vacuum pump on the blue hose directly?

Landseer

You got any pictures of this. That would sure help us.

dprantl

I can see the different piston stroke causing your dragging/disengaging problem, but how could this cause your vibration issue? I assume you have the vibrations at higher RPM when the clutch is not being pressed, but not all the time, right?

Dan
'91 928GT S/C 475hp/460lb.ft

Opelotus

Here are pics. Maybe the piston's slot should be wider...we will see.
dprantl, I don't expect this to fix the clutch shudder/roughness/vibration, but it should fix the dragging issue. I have been meaning to sort out the dragging for some time, my transmission can't take any more abuse
Majority of the vibration occurs @ ~2000-2500 RPM. Next phase is to drop the lower bell housing and check the front TT bearing, guide tube, etc.

Please note that the spring is backwards in the photo, the little end goes against the piston.

Opelotus

Phase two complete, after bleeding the system and taking it for a short test drive, all feels good so far. Clutch pedal definitely feels better so far, although the extra travel is going to take some getting used to.
Also, the scraping/roughness was not present, but that is not surprising because it comes and goes. I need to put a couple of miles on it to see what's what.

Opelotus

So the dragging clutch issue is solved, but the rough pedal/odd engagement is still present!!! It has been driving me nuts lately. Definitely seems temperature related; clutch is smooth as butter in the morning when engine is cold - shifts beautifully and clutch catches low where it should. As engine warms up, pedal begins to feel rough, gear changes aren't as smooth, engagement is somewhat unpredictable. After engine is up to temp, if I stop somewhere for about 10 minutes, then fire it back up the pedal feels like absolute crap. Heat soak issue of some sort? Also worth mentioning that this "roughness" is only present whenever the engine is running. PLEASE HELP!!!

Bill Ball

You didn't mention your evaluation of the TT issues to which Dan was directing you.

Opelotus

I measured about 10" from the front TT bearing to the opening in the bell housing (probably closer to 9" if most people measure to the end of the TT itself), or 12" from the bearing to the forwardmost bolt in the TT/stub shaft coupler.