Dual mass flywheel questions
 

What is the lifespan of a dual mass flywheel and how can you tell if it's worn out? I'm not talking about the mating surface for the clutch disc, I'm talking about the dampener in it. How do you test it to see if its still good? Also, can the dual mass flywheel from an L-98 be used on an LT-1? I have three dual mass flywheels, two are from LT-1 cars and one is from an L-98 car. They look identical including the balance weight on the back of it so I'm assuming they are interchangable? The only difference I can see on the L-98 flywheel is the part number stamped on it, it's a different number than what's on the LT-1 flywheels. Any help is appreciated.

All non-ZR1 DMFs are interchangeable. If the seal is bad, the clutch will slip. With the trans removed, you will see the bad seal (leakage). Somewhere around 91 (I think), the seals were improved -- making the newer ones somewhat less prone to seal failure. If the internal springs are bad, it will "knock" when sitting in neutral. This is subjective because it will knock worse the weaker the springs get. Otherwise, they don't necessarily go "bad" unless/until excess surface material has been removed. They can be driven with the idle "knock". It's just annoying. Non-stock clutch installations will exacerbate this issue as well.

Regardless of the car (when interchanging DMFs), you should inspect to see if any "peg" weights are installed on the perimeter. Seems like there was a piston "skirt" issue that caused a few engines (can't remember if late L98 or early LT1) to require a field balance -- which was accomplished via those DMF perimeter weights. If you don't know WHICH DMF came off a car AND it happened to have perimeter weights that weren't copied, you can end up with vibration. (There's a field balance procedure issued by GM that states how to eliminate most vibration -- if it occurs. This is probably more than you need to know...unless you also consider the RARE possibility a DMF has been converted to neutral weight. Because they were installed on 1pc RMS engines, they have an external counterweight bolted onto the surface. You can easily see it.

I would also direct you to ZFDOC for additional reading.

The L98/LT1/LT4 dual mass are interchangeable. I currently have an L98 on my LT4 without any issues or vibration.
The ZR1 is different. It even has a different number of bolts to attach it to the crank. It will not work on the L98/LT1/LT4.

There is a test for the springs on a dual mass. You basically rotate the two parts in relation to each other and then release them. You measure the distance at the edge of the flywheel to see how far it rotated. The picture below shows a 96, but it is the same for all dual mass flywheels.

The peg weights were used on many dual mass flywheels for final balancing of the part. I have heard that some LT4's went through an additional balance and may have changed these peg weights (add/remover/relocate). On mine I did not change the peg weights from my '90 flywheel and it works fine with no vibration on my LT4.

If there is a vibration, they did a study on the most common locations to add these peg weights and a procedure to change them. The procedure is meant to be done with the engine still in the car. Not the easiest, but it can work. If you need that procedure, I can find it to email or find a link to it again. Let me know if you need it.

Good luck.

https://cimg5.ibsrv.net/gimg/www.cor...9a79218107.jpg

Thanks for the replies, the info was very helpful. When I get home from work today I'll check the play in the flywheels and use the best one on the car. It's a '96 LT-4 that someone replaced the original dual mass flywheel and clutch with a Fidanza flywheel and Carolina clutch and because of that the transmission makes a god awful buzzing noise. I have the shim kit from ZFdoc which is supposed to vastly reduce if not eliminate the noise and I'm going to install it when the transmission comes out for the flywheel change. Going back to a dual mass flywheel and putting the shim kit in the trans should completely eliminate the noise.

Does your clutch disc have springs in it? If so you have the wrong disc, dual mass flywheels are supposed to be used with solid (unsprung) discs. Either way your trans shouldn't be making any noise with s dual mass flywheel. I just replaced the aftermarket flywheel in mine with a dual mass flywheel and added the shim kit from ZFdoc to the trans and all the noise my trans was making is gone.