mnorton

I have a vibration problem with a new clutch installation.

The engine is a stock 1987 LB9 5-Speed. The Flywheel was Replaced with a brand new GM part, and a stock Clutch kit was used. The car now has a bad vibration that you can feel up through the seat of your pants. The vibration gets worse at 2400 & then again 2800 RPM with the transmission in neutral. I feels even worse while driving and decelerating to a stop.

The work is being done at a GM Dealership. Mr. Goodwrench has now removed the flywheel and pressure plate and checked them both for balance on an external jig. They check out as neutral balance, everything looks normal so we are all stumped….

Could it be the wrong Flywheel was used? Is there more to balancing a new flywheel on this engine? Also when I test drove the car, the clutch pedal pressure was really soft as compared to before the repair. It feels soft like a Toyota clutch… Is that normal?

mnorton

Ideas anyone? no?

Other work that was done was to replace the Oil Pan Gasket and Rear Main Seal (maybe the Front Seal too...) Do you have to remove the Crankshaft Rear Main Bearing Cap in order to replace a One Piece Rear Main Seal? If so maybe the Cap is loose...

Could one of the Engine Motor Mounts have broken?

Could it be that the Harmonic Balancer on the front of the crankshaft has failed somehow?

I'm just thinking out loud, hoping that someone here can shed some light...

Saculia

iTrader: (1)

Could be in the drive shaft. Does it vibrate when you press the clutch in with the car moving?

skinny z

" Flywheel Assembly/Torque Convertor Clutch Vibration Test Procedure ".
This is in the GM manual. It explains that despite the flywheel, pressure plate, etc having a "neutral balance" sometimes the tolerances stack up and a vibration results.
The test procedure outlines decoupling the flywheel from the pressure plate, rotating the unit 120 degrees (until the bolts and holes line up again), reassembing the unit and testing.
It solved my vibration and I had been at it for years.

mnorton

It vibrates when in gear and when in neutral so I don't see how it could be the driveshaft. Maybe the tolerances can stack up and cause this.... I wonder what GM Manual has the Flywheel Test Proceedure... I'll mention that proceedure to the Repairman and see if he can find it.

Saculia

iTrader: (1)

If the vibration comes when the car is moving at a certain speed and the vibration disappears when you press on the clutch, the issue would be flywheel/clutch related. If however the vibration still remains at that speed, then the drive shaft being out of balance or the output shaft in the transmission could be the problems.
It sounds like that's not what's going on in your case, since if I understand you correctly, you experience the vibration while the car is standing still and running.

mnorton

Yes it vibrates standing still and running.

I just spoke with the mechanic and the plan is to get another harmonic balancer to compare with and perhaps install. It may have slipped. They also sent the driveshaft out to be checked for balance, they did install one new U-Joint so I suppose that could be an issue. I suggested that they install a different flywheel and clutch kit as well.

skinny z

When speaking to your mechanic be sure to refer to it as the " Flywheel Assembly/Torque Convertor/Clutch Vibration Test".
It covers both manual and automatic transmissions.
In my case I have a GM service manual (doesn't matter which model) from 1990. Page 7A-6.
Good luck

Dizturbed One

They would have dropped the crank to do both seals. And I bet they trashed your harmonic balancer while prying on your oilpan (they get REALLY stuck on there sometimes) or they knocked a main bearing loose/out of alignment on one of the caps. It could even be a really crappy torque sequence on your main caps causing all of this. If they do decent work (which is NOT the vibe I'm getting from the approach so far) it is probably the flywheel and pressure plate combo, but it can be all or any of these.

In any case, if it is not either part that is causing the out of balance situation, then it is 90% likely THEY caused the vibration while doing your main seals as I said before. If I were you I would be very active in this and make sure they aren't charging for parts or labor on any of thier own mistakes (which they sound like they already have and will most likely still try to do to you). They should have known %100 after one test drive and a run on the lift that it is not a U-joint or driveshaft, and should be able to at least point to the area of origin. I am not confident in thier work so far, you shouldn't be either.

mnorton

I have the 1987 Shop Manual and did find a procedure, it's called " Flexplate/Torque Converter Vibration Test Procedure" page 7A2-2 in my book. Says to bolt on the Flexplate (the Flywheel on a Manual Transmission is the same as the Flexplate on an Automatic) run the engine and check for vibrations, then to rotate it 1/3 turn (120 degs.) and check for vibrations again. When I spoke to the mechanic today he told me that the Flywheel on my car is not only bolted, but pinned, and thus not "rotate-able", but that the Pressure plate is "rotate-able". I will show this procedure to the shop guys tomorrow and discuss again. Thanks for the advice.

I think that with a one piece Main Seal that they don't drop the Crankshaft at all. Even if I'm right about that it doesn't mean that he didn't pry against the Harmonic Balancer when removing the Oil Pan. I think that the mechanic is "trying" to do a good job. It's obvious to him that my car is special to me. (I have hand wiped clean the entire under carriage several times, and painted all of the suspension components etc.) I told them to go ahead and replace the Harmonic Balancer. I will ask them to perform the Flexplate Vibration Test as well.

The mechanic didn't take the car for a test drive, at least not out of the parking lot. That may not be his fault, mangement may him over booked with jobs or something else... I'm dissappointed about all this, but not pssed off. As long as it's right when I get it back, I'll be OK with it.

Thanks for sharing your ideas guys.

Dizturbed One

You're right about the seal, I was thinking backwards on that. The two piece is the one that is part of the rear main bearing cap and ends up being a problem alot of the time to install cleanly and correctly. The one piece is the one on the outside that you kind of just pry off.

flotsamm

Just curious if you ever found a solution to the vibration problem. I replaced my clutch and now experience a vibration from 1100 to 1500 rpms. Thanks for any info you can provide.

mnorton

I replaced the Harmonic Balancer and it did not improve the vibration problem.

It turns out that there is a flywheel balancing procedure in the 1992 camaro shop manual and flywheel trimmer weights (called pins) available from GM. When I spoke to Mr. Goodwrench he had no idea that there was a procedure and weights for balancing. I have ordered the weights and will bring the car back to the GM shop this week to see what they have to say about this.

Oh and these engines do not have a neutral balance flywheel. They have a big balance weight on one side ~125 grams.

flotsamm

Thanks for the reply. If you could keep us posted on the results that would be great. Thanks again.

flotsamm

Small update on my problem. I replaced the new flywheel that I bought(I'll never buy a cheap flywheel again) with my oriignal that I had resurfaced at a local shop for 40 bucks. No more vibration now between 1100 and 1500 rpms.

C.W

I just bought an 86 z28 that has had a pre 1980 350 (2pc rear main) swapped it with a T5 and a new clutch. I have this same vibration issue. I originally had thought that maybe they used the flywheel from the 86 one pc rear main engine but from the research i have done on this site it appears that they wont interchange due to bolt pattern.
So my question is about the 120deg rotation of the pressure plate. Can this be done without seperating the engine and trans?
Im assuming i can just pull the starter or inspection plate and unbolt the pressure plate from the flywheel and turn it?

flotsamm

No, you will need to remove the tranny to access the PP bolts. The inspection cover only allows you to see the condition of the clutch.

C.W

Ya i wasnt thinking when i asked that.

Quzyle

iTrader: (1)

Any up date? I just replaced the clutch, rebuilt the trans and still have this dang vibration. How did the pin kit work? Thanks

Saculia

iTrader: (1)

Have you checked your drive shaft for balance? Also, what are you using for a fly wheel? Does your car vibrate only when you are moving, or does it do it when it is also standing still? A little bit more info would be helpful.

Quzyle

iTrader: (1)

Sorry, I should have explained. I bought a 1990 IROC-Z. It did not run when I bought it. I fixed the the VATS problem. When I took the car out the first time I noticed a vibration that started around 3000 RPM. So I did a little more investigating. The vibration was RPM specific. If you are not moving and rase the RPM you can fell it. If you are driving and take the car out of gear or just push the clutch in, and let the RPM drop it is gone. But if you are cruising and push the clutch in and raise the RPM is is there. So that means it can not be after the input shaft of the trans. I thought that is might be a bad pilot bearing or bad input shaft. So I pulled the trans out, when I did the pilot bushing fell out. So I thought that I was on to something. I sent the trans to be rebuilt. Resurface the flywheel and a new clutch. Put it all together yesterday, and the same thing a vibration that is RPM related. I was hoping that mnorton had been able to find a fix for his, as it seems that we are both dealing with the same problem. Ant help would be great!

Saculia

iTrader: (1)

mnorton did fix his problem according to this post. It was the cheep aftermarket flywheel that he had installed in his car. The fix was replacing the flywheel with the stock unit that had been resurfaced. Have you had the flywheel checked for balance? Do you know if it had been replaced before? Also, I have heard that sometimes the harmonic balancer may have worn out to the point where you are getting vibrations, but that is a bit unlikely. Do you seen any wobbling coming from the crank pulley? Also, what shape are your motor mounts in? A bad motor mount could also be causing the vibrations.

Quzyle

iTrader: (1)

I did not see were mnorton had posted his fix. Flotsamm did. I check the flywheel run-out and it was just under .002". The crank shaft end play was .005". Both OK. I checked the timing mark and balancer and they all look OK (with my timing light). I am having a hard time finding a shop that can balance just the flywheel. With the 125 gram weight built in no in my area can do it. The motor mounts look good, the trans mount is the poly type. Thanks for the ideas. I even took the belt off and check to make sure it was not one of the drive acc. No luck. When you are giving the car gas from under the hood, the engine seem smooth. it is when you are seated in the car that it is very noticeable. If you place something like a screwdriver on the seat it will vibrate its was to the back.