Lex_GTX

I'm trying to diagnose the source of a strange vibration that happens often but not all the time.

When above 4.5-5k RPM and especially if under boost, I press the clutch pedal to shift up and I feel a fairly strong vibration in the pedal that is at the same speed as the engine. The higher the engine speed, the more it vibrates.

On some shifts it does this more than on others.

I am suspecting the pilot bearing but could it be something else?

I tried to listen for the worn torque tube bearings. When the car is cold and I decelerate, there is no noise. When the car is warm and has been driven harder there is some rattling/coffee grinder noises in the lower gears from what sounds to be the rear of the car.

Finally, when the car is properly hot and idling in neutral there is a rattle in the rear of the transmission. I have read this as the 5th gear rattle and not something to worry about.

The clutch is currently not slipping and I haven't changed it since taking ownership of the car.

Just looking into some insight on what the clutch vibration when pushing the pedal in under high load/rpm is and what I should look for and expect to replace.

Thank you!

Lex_GTX

No one has experienced clutch vibrations when pressing in the pedal at higher loads and RPM?

Chris White

A bad pilot bearing or a failing torque tube bearing may create vibrations - but you would feel them in the drive train, not in the clutch pedal.

I would guess that your throw out bearing is not centered in the pressure plate. The throw out bearing 'floats' around a little in the pressure plate so it can be uncentered. typically it gets centered by the clutch fork....so you may have a worn or possible slightly bent fork that is not centering the throw out bearing.

Its also possible that the clutch disk has become unbalanced - that would cause vibrations when its released - but it would vibrate other stuff as well as the clutch pedal.

If it still has the original factory clutch or a factory replacement you may have broken one of the small springs. the springs fall out and get caught up some where else in the system and that can cause a out of balance feel or even jamb the pressure plate open when you least expect it!

Lex_GTX

Thanks for the great response Chris! Initially I was thinking the throwout bearing but a lot of torque tube discussions in my searches had me looking there.

There is definitely a gear lash noise/coffee grinder noise when coasting in 1st and 2nd especially around 2500-3000 RPM but it's not really audible in other gears. It is coming from the rear of the car. Not very loud and only when the car is warm. Is this the transmission gear lash or torque tube? How could I tell them apart? When free revving in neutral with the clutch released (torque tube engaged) I don't hear any noises from the tube.

The clutch vibration happens sometimes (70-80%) of the time and the fact that it's intermittent definitely lines up with something being centred sometimes and not others such as the throwout bearing. I expect to do the clutch in the next year (about 25-30% remaining in the inspection window) and didn't want to pull it apart if it wasn't going to cause damage to anything else until then.

When doing the clutch I assume the torque tube bearings should be done as well? Might as well since I'm "in there."

Chris White

The 951 transaxle can be very noisy. if you have a solid or semi solid trans mount it makes it twice as loud.

The answer is somewhere between no and hell no!
Torque tube bearings are really a massive pain in the *** to change - I would not change them unless they have failed.

Lex_GTX

How can you verify for sure that they have failed?

Also how would I diagnose a failed or failing transmission mount? My motor mounts have already been replaced.

Thanks again for your input.

Chris White

The torque tube will get pretty noisy and once you have the transaxle out and the torque tube pulled back you can rotate the shaft by hand and feel the bad bearings (does not turn smoothly)
Not much in the stock trans mount to go bad. if you can get the transaxle to move side to side a lot then the rubber in the stock mount may be tired.

Lex_GTX

So it sounds like the vibrations I am feeling are not related to the transmission mount or torque tube. Sounds like the real issue is the clutch, throwout, fork and possible pilot bearing.

When doing this job I should be able to "feel" the torque tube bearings fairly easily regardless which means I will put further checking off until I do the clutch and have everything apart.

mahoney944

I noticed a similiar effect when my slave cylinder started leaking (but still working) the diaphram was slightly torn and caused pressure issues inside the slave. This caused a chain effect where the slave didn't operate properly, causing the clutch to be choppy and the pedal to get some vibration, usually during a downshift or high boosting.

Lex_GTX

Very interesting. I replaced the master ... don't remember when and if the slave was done.

mahoney944

From my understanding, you should always change them both together. Ive read many reports of people replacing one and soon after the other fails. I suppose that when replacing one only, it over powers the old one, causing it to fail or fail sooner. Luckily the slave is not bad to change or that expensive.