Gents,

My HPDE car developed a vibration at VIR last weekend. I cut my track time short, but had to drive her home. I could not find anything suspect on the engine side, so I pulled the transmission. I found the brand new Koyo pilot bearing had leaked its grease. It spun freely but felt "empty" inside and loose, if that makes any sense. The flywheel has three places where the surface is discolored, I assume from hot grease flowing down after the car gets parked, then being flung around next time she's run. The picture is the worst of those.

I have a very nice precision square. I checked the flywheel and there are no noticeable high spots. The friction plate has some discoloration. However, I did not notice any shifting problems on track or on the way home. The clutch has about 70 track days on it plus commuting, purchased in August '15.

Seems like replacing the clutch is the right thing to do. Should I replace the flywheel? It's been resurfaced once already.

Thanks,


Worst of three flywheel discolorations

 

Mine was like that and I just resurfaced and sent it!

 

That's definitely a flywheel due for resurfacing.

 

Any concerns the metal has been weakened below the surface by excessive heat?

 

No, but it isn't flat for sure.

 

What's going on with the flywheel bolt mounting area there? Why's it all scuffed up?

 

 

Curly, without grease, hasn't the bearing failed? I had hoped finding the pilot bearing had vacated its grease also meant I found the source of the vibration. You're gonna make me lose sleep.

 

Feel the movement of the bearing. If it is still smooth with no play, the bearing hasn't failed yet. Though the grease vacating means it will sooner.

 

I've had the flywheel resurfaced and sourced a Nachi bearing with the plastic seals rather than the metal shields. All I can think to do is bolt everything back up and see if the vibration is gone. At speed, the vibration felt like an out of balance tire, but I could feel it parked at idle.

Usually, she gets put into the garage after the last event of the season at the beginning of November, and I don't touch her till after the holidays. Now, I want to find out if I have a bigger problem before moving ahead with rebuilding the other motor. I've run the engine without the supercharger belt, and without the alternator belt (briefly). Then I stripped down the front of the motor so I could run her without the timing covers. I could not find anything that would point to the source of the vibration, although I did find a couple of exhaust valve clearances a little too large. Then I pulled the gearbox. I didn't find anything improperly torqued on either the engine or trans.

I plan to spin the output shaft of the transmission and see if there is any input shaft wobble, but after that I'm completely out of ideas. The motor was very strong, even with the vibration.

Any ideas would be greatly appreciated,

 

I decided to put everything back together with the resurfaced flywheel and new pilot bearing to see if that isolated the problem. The vibration is gone. Can I assume it was just the pilot bearing and not the flywheel, or flywheel too, causing the vibration?

 

 

This is a failed pilot bearing after a 4-5 money shift that hit 3rd instead. Bearing locked up and subsequently dislodged itself. Vibration was immediate noticeable. A new fly/clutch assembly cured everything. Notice the new gyration pattern from the 4 puck disc.

 

I'm the OP. Thanks for all the inputs.

Although the aforementioned vibration is now gone, it has been replaced by an annoying buzz I can feel in the shifter. Should I have replaced the clutch pack, too?

Thanks,

 

Is the vibration with engine RPM or vehicle speed? That can help you determine where in the drivetrain it is coming from

 

I feel the buzz/ vibration in the shifter, even at idle when not moving.

 

Have you changed the fluid recently? How did it look? Any over-revs? Wondering if your input bearing is going.

 

Is it just in the shifter, or is there more overall NVH (mostly vibrations) throughout the whole car....like you can just feel a but more sitting in the seat at idle and while driving? I'm saying one possiblity, coming from recent experience, is ensuring the PPF is aligned properly. It's easy to get it off when making changes/replacing parts that require loosening any part of the driveline.

It happened to me just changing out engine mounts- car had more vibrations right off the bat. Though I didn't loosen the PPF-trans bolts when changing to the mounts, it somehow became mis-aligned. The fix was loosening the PPF trans bolts, putting a jack under the trans and lifting it slightly, then tightening the bolts with the jack still holding it up a bit. I can't remember off the top of my head, but there are measurements you can take of a couple of areas to check for/to adjust correct PPF alignment.

 

I bit the bullet and replaced the clutch pack and flywheel. The buzz is gone at idle, but the weather here is **** and I didn't actually take her for a ride yet. I'm just glad I can do my own work.

 

I took her around the block yesterday. She seems back to her normal self--no vibration or buzz. Are the parts I took out scrap since I don't know which one(s) caused the problem?

Thanks,