Vibration Following Clutch Install - Please Help
 

I recently had an ACT Heavy Duty pressure plate and street disc installed in my '94. At the time the new clutch was installed, the mechanic had NAPA resurface the stock flywheel. Ever since the new clutch went in, I've noticed significantly increased vibration coming out of my engine at idle and throughout the rev range.

I don't think the problem is in the drive shaft as some local people have suggested, becuase the vibration exists even when I run the car up in neutral.

I spoke to one knowledgeable RX7 owner and he said that he had seen a similar problem in a TII, and that replacing the flywheel solved the problem.

A reputable rotay shop suggested that the problem is in the transmission mount, and that "disturbing" the tranny mount during the install caused the problem -- but that doesn't make any sense to me.

Incidentally, the vibration is most noticeable at RPMs that are integer multiples of 850 (where my stock idle is set and I can feel the vibration at every stoop light).

The car never behaved this way prior to the new clutch installation.

Please let me know if you have any idea what might be causing the vibration, and what I can do to reconclie the problem.

Thanks.

-Dave

Well you can rule ot the tranny mount because we don't have one. If the vibration increase with the RPM increasing, I would check the flywheel to see if it got done evenly. It might be out of balance.

That same thing happened to me, actually the same "most noticeable at RPMs" and idle pattern. It resuts it was the exhaust mid pipe in contact with the protection gray bar conected between> In fact, the problem ocurred while "disturbing" one of the exhausts mounts during the installation ...

Move the car to a ramp. Then load it while braking (with the emerg. brake) in first gear while watching under it, if the problem is a loosen part you might hear/see it...

It would be rare, but I have heard of defective pressure plates that have been out of balance.

The only other thing I can think of off-hand is if one of the dowl pins on the FW fell out and went unnoticed...?

Thanks for the ideas. I'll check under the car to see if the midpipe is in contact with one of the tranny tunnel braces.

I called ACT and they assured me that their pressure plates are neutral balanced at the factory. The interesting thing is that I was talking to a local mechanic (whom I trust) who does a lot of work on DSMs and he informed me that he has seen many pressure plates ship unbalanced, and that ACT is one of the worst offenders.

Regarding the dowel pins, I watched the mechanic reassemble the car, and I'm certain that the dowel pins were in place. Good idea though.

At this point, I think the car needs to be taken apart again. The problem is that I'm just not absolutely certain what to do once it's apart. If it turns out that a balance issue appears to be the most likely culprit (i.e., I rulle out the MP contact issue), I wonder if there is anyone around who can balance my FW and pressure plate together. And frankly, I don't even know if this is a good idea since I know that our flywheels are counterweighted.

Or, perhaps I could buy a new flywheel and have somone check the pressure plate for proper balance. Is there anyone who does this kind of work?

-Dave

How much material did he take off your flywheel? The weight of the stock flywheel is not evenly distributed, so any weight you take off is going to affect the balance. If he turned it down its trashed. If you look at the back of the flywheel, there is a chunk of weight up against one side. That's why when you buy an aftermarket flywheel you have to use the automatic tranny counter balance. In general I think you can get away with a very light honing, However I've been told that if it needs resurfacing, it should be replaced. Also if it is out of balance your bearings are going to get worn prematurely. I wouldn't drive it whole lot until you figure it out. My car is heavly modded and it purs at idle and I have a stock flywheel and a very old act clutch that has been on and off three motors.

Off subject, but I ran 12flat @ 116 saturday on 2 year old BFG KD street tires...0-60ft 1.75, with my ACT clutch that has over 25k miles on it(stock fly wheel), unfortunatly is was slipping in 3rd so I had to back off a little. With a little help from racelogic TC :-) Unfortanutely my buddy's 500hp to the wheels 2004 cobra broke and had to ride home on my trailer while he drove my 10 year old car home :-) He ran 11.9, 120mph 0-60ft 1.95 on MT's earlier.

Good luck

Thanks for the input. This is exactly consistent with what Jeff Hoskinson told me -- that following the resurfacing of a FW on a TII, there was a balance issue, and that replacing the FW solved the problem. Perhaps it's time for a new FW.

BTW, a 1.75 0-60' on true street tires is amazing! How do you manage to get such good launches -- by slipping the clutch somewhat? Also, have you done anythign to mitigate wheel hop?

-Dave