We just got done doing a clutch on a buddies car.

2000 FRC, with <40kmi. Put in a Spec 3+ with billet steel flywheel.

Did the whole project following the GM service manual. Came apart and went back together just fine.

First test drive, he drove it and everything was perfect. Then I drove it to feel the clutch and everything felt great. He drove it a third time no problems. The next day he eventually got it up over 4000 rpm (still being easy on the clutch and now has driveline vibrations. I haven't seen it yet, but here are the symptoms.

Symptons:
1. vibrates at idle
2. doesn't vibrate between 1200-2500 rpm
3. vibrates above 2500 rpm
4. feel it in the shifter and butt, but not the wheel

Anybody with experience or suggestions as to what is going on? Thanks!

 

Clutch pressure plate and flywheel is not balanced. BEEN THERE DONE THAT. Do the same test with the clutch IN and see if it is the same. If so, they only thing that is turning is the engine and the only thing you changed on the engine was the clutch and flywheel. THAT IS YOUR PROBLEM

 

HMMM,

Came as a balanced set from Spec. The alignment pins on the flywheel only allowed us to put the pressure plate on one way....

What do you thin, once it got spun up to a certain RPM something move, shifted, and started the vibration? Why didn't it vibrate from the beginning?

 

Sounds like a balance issue causing resonances at the RPM's you have identified. Do you know if the pressure plate and flywheel were zero balanced? Do you have the old parts in case you need to get the original assembly balance? Some guys have found that from the factory their clutches were not zero balanced and therefore had to resort to match balancing the new assembly to the original. Are there any balance weights installed in the original flywheel?

 

All I know is that it was "balanced" by Spec. We do have the old parts. Followed the GM manual that says existing engine, new flywheel = don't add balancing weights. I don't recall what kind of balancing there was on the old flywheel.

 

I agree its a balance issue. At least with the old parts you can re-establish the baseline if you need to. Sounds like it needs to come out again unfortunately. If the balance is bad, maybe Spec will help.

 

What you believe and what really is are two different things. I always have balance checked and on the two specs I've used they were off and needed it.

 

I recently had a similar problem but it was due to the pilot bearing in the crank snout gave out. It basically disintegrated....

Derrick

 

I agree 100%..

It is physically impossible for a clutch to progressively go out of balance. Its either off, or its not.

Being that this ran fine in the beginning, its not a balance issue. I'd be willing to bet you've got a pilot bearing that took a **** on you.

When you install the clutch, the inside of the pilot bearing has a slight edge on it where it wraps around the needle bearings. If you install the shaft and hit that edge, it can bend it. That will cause the needle bearings to start to come apart..

Been there, done that..

Heres a test. Drive down a long (Straight) street. Get up to speed, and push in the clutch. Shut the car off (leave the key in the on position so you still have steering). With clutch depressed, and the motor off, the output shaft and clutch discs are turning, but the motor, flywheel, and PP are not. If the vibration goes away, then you know its the clutch/flywheel balance. If it does not, then it is drivetrain related.

With the clutch pedal IN, change gears. This will increase and decrease the output shaft speed. If you notice the vibration gets slower the higher the gear, then you know its between the driveshaft and pilot bearing, and NOT the clutch itself..

Again, my bet is its the pilot bearing..

EVERY SPEC clutch I have purchased for inventory or install, I've had balance checked. Every one of them has been less than a gram off.

 

Thanks for all the input guys!

We did put a brand new pilot bearing in with the clutch.

We'll start to tackle it on Tuesday - because I'm going to VIR tomorrow!!!

 

Be carefull. Cause if its the pilot bearing you'll trash your output shaft.

If its out of balance, you'll destroy a whole lot of stuff if you beat on it long enough.

 

One more thought, did you use loctite on both the flywheel bolts and pressure plate bolts?
There is a small possibility they could have come loose.
The reason I ask is because you said it was fine on initial drive, and both of you guys drove it.
Then once he took it out the next day, it began to vibrate over 4000rpm.
Since then it now vibrates at idle, and throughout the rev range, except at certain rpm points.
Just a thought.

 

Loctite on the flywheel bolts, not on the pressure plate bolts.

GM service manual did not say to loctite either.

 

A little blue loctite there wouldn't hurt either.
I'm not saying that's the problem, just that it's a big job, hate to have that problem after bolting it all back together.

 

DO NOT EVER USE PILOT NEDDLE ROLLER BEARINGS they are garbage they usually distort when installed they also eat away at the shaft etc, go with good old pilot bushing and save yourself many headaches from roller bearings.

 

It is a clutch imbalance issue (Ask me how I know). It is not the Pilot bearing as you can only damage it during initial install. It cannot be damaged during the instillation of the input shaft, unless it already installed incorrectly.

I had the same exact thing when I did my clutch install. Drove it a few times, and right around the third time I felt a vibration through my shift ****. It was always there I just didn't know to look for it.

Do you still have the OEM Clutch FF/PP combo?

 

Maybe you didn't realize how old this thread was/is?

 

Thanks, I just wanted to add info to this thread incase someone else stumbled across it like I did. Most people will use this forum (and any for that matter) for info, but never contribute. Without contributing members a forum will come to a stand still.