dme

I purchased my current 951 several years ago. The previous owner had just installed a new clutch (Pressure plate, clutch disk, TB, surfaced flywheel). Within a few thousand miles I started noticing a definite vibration coming through the clutch pedal when coming to my first downshift after driving on the highway. It was fine after the shift until the next stint of spirited driving. It became progressively worse. I tore the clutch down and other then a slightly worn TB I didn't see any real issues. I replaced everything (PP,CD, and TB) while I was in there. Now a few thousand miles later the problem has returned. I fixed the symptoms, but not the cause.

I have a theory, but would like some educated thoughts from some experienced owners as to what they think could cause this.

mtnman82

Did you spin the torque tube when you had everything apart? My TT definitly needs some help ...

buxton

I would check the TT as well.

dme

no apparent issues with the TT when inspected.

xsboost90

did you replace the pilot bearing- that keeps the tt straight?

dme

The pilot bearing was replaced during the previous clutch job a few thousand miles earlier. One other note, I replaced the fork bearing, but not the fork itself.

special tool

Hmmmmm..
let's review the lubrication steps taken on the pilot bearing.
Be specific.

eyeball kid

Interested to see what you find out. My car does the exact same thing in only that senario. Less than 7k on clutch, etc.

Toolmaster

I'd wonder if there's either a slow leak in the clutch master or slave cyl's (how's the brake fluid looking?) or if the actuater rod that pushes from the clutch pedel into the master cyl might be out of adjustment, or just plan loose.

eyeball kid

Here's my thinking. If original poster is having same symptoms as I am, it seems that it is not rpm specific but speed specific. The TT has no idea if we are in 5th gear or 2nd, right? But, a high speed at boost extended run COULD (and probably does) result in some clutch slippage, right? That slippage could leave behind high spots of gummy clutch material on flywheel, PP, or clutch, whatever is revolving independent of the trans, so we feel the vibration caused by an out of balance revolving mass at the pedal. After a few engage/disengage cycles, the material burns off, everything is balanced again, no vibration.

What do you think?

buxton

Eyeball kid - I doubt that both his old clutch which was almost new and the new clutch would both be slipping. I also doubt that if there was slippage that any material or dust that got on the flywheel could cause some out of balance vibration. With 2 different clutch kits in the car and the same problem still occuring I would likely rule out the clutch and look elsewhere in the driveline.

DME - did the pilot bearing get replaced both by the PO with his clutch and by yourself with your clutch job? If so, the odds of 2 different pilot bearings doing the exact same thing seem very slim IMO.

dme

I did not replace the pilot bearing. I have the parts receipts for the original replacement with what looks like an entry for a pilot bearing. The previous owner was pretty thorough in replacing everything in there including the rear oil seal. In fact it made my job much easier as everything came apart very smoothly. The only parts I replaced were the clutch assembly, nothing else in the drive train. In fact, looking at the PET I'm trying to refresh my memory and locate the pilot bearing in the drawings. I agree that there is something else in the drive train causing the problem and the clutch issue is just the symptom. One other point from a previous post. It does not necessarily just happen at highway speeds. A lower gear high rpm shift can initiate the symptom which of course clears out after the next shift. What would engaging the clutch (or shifting gear) re-align?

eyeball kid

I'm proposing that the high torque situation of high boost is causing some intermittent slippage, thereby leaving a deposit of clutch material which causes a rotating mass to go out of balance and cause vibration.

buxton

DME - does the vibration come on at a specific rpm? Does it go away below a specific rpm? Do you get a change in sound when you are in neutral and push in the clutch?

dme

I have no indication of any issue until I press in on the clutch pedal and get a bad vibration or more like a thumping pulse coming up through the pedal. After the first shift change, it will be fine again. Eventually, if it follows the same path as before (the last clutch) it will get worse over time until shifting becomes difficult.