The old 94 has been on jack stands since the middle of April... Been busy with other things. Life sometimes takes you in new directions and sometimes it is all fun stuff. Now all the other adventures are in the rear view and I am back from a fantastic hunting trip in Colorado. So back to the garage I go.

This project started with two rear hubs going belly up and grew into a rear suspension rebuild and then universal joints etc... before I knew it, I had dropped everything from the engine back. The car is now sitting up with the tranny and the Dana 44 off the car. Time to start re-assembling things so that I can do a little fall driving!

Here is my main question, the flywheel has about 117K on it. I am third or fourth owner so I am only guessing. It shows no signs of leakage and appears sound. I was referred to a shop that can machine the flywheel but I am skeptical about machining the DM flywheel.

What do I look for to determine if the flywheel needs replacing? (I will try to post a few picture of the actual DM later tonight.) Don't want to place this back in the car only to have to pull it again soon...

 

DM flywheels cannot be resurfaced, unfortunately...Just clean it up with a maroon scotch brite pad you get at an auto parts store.

Was it making any noise when you parked it? If not, it should be fine.

 

It's probably a gonner to be honest. Even without leaking, the springs are most likely shot at this point.

You can leave it and not harm anything, but I would bet that it has exceeded it's service life.

If you can twist it more than a couple inches with your hands, the springs are worn beyond spec.

 

Were there any issues before disassembly?
Did you test it per the factory service manual and did it pass?

If the answer is "yes" then it's fine.

 

Multiple reason for dropping the tranny and taking a good look at the clutch and the flywheel...

1. I was getting the somewhat common "Whirring" noise when the clutch pedal was released / let out.

2. I wanted to check the flywheel for "obvious" wear issues.

3. Clutch slave was beginning to malfunction.

4. Gasket at tail of the ZF was leaking a little fluild.

5. Add ZF Doc Beam plates.

6. replace universal joints in Driveshaft.

Plus I was in a dissembly mode...

The machine shop that resurfaces the flywheels claims to have a "system" down pat on the DM flywheels. I was told by another forum member that many of the Ford Diesel F250s and large trucks have DM flywheels with the manual trannys. This machine shop is supposed to have mastered a resurfacing technique for the Ford Truck guys. The Ford DM Flywheels are even more expensive than the Corvette's.

I will check the factory service manual and then make my decision.

 

At least with the Ford stuff, a new flywheel is available. With your car, depending on how long you drag this out, a new flywheel might not be available. That would make me hesitant about trying to machine it.

I think it can probably be done, I have an idea in my head how to attempt it, but I don't know that it would work. I would be nervous about them trying something on the ZF6 dual mass since there is possibly NO replacement available.

I'm curious what their process is. Mind sharing?

Also, if the springs are worn out, machining is pretty pointless. With the mileage on your car, I would bet a steak dinner that the slop in the springs is well beyond spec.

 

Wouldn't that depend on the amount of rattle weak springs would induce. Bill (ZFDoc) says you can run a DMF with weak springs -- no problem. It's when the seal gives out that things get ugly.

Obviously, weak springs wouldn't dampen as well. But, IYO, do you think it would tear something up?

(Note: I'm asking only to make a generalization. I have a 58k DMF and I also bought a new one right before the drought hit.)

 

jakers,

Presume there's no question about replacing the clutch disc, pressure plate and release-bearing (i.e. do it).

If you've got an extra $700-$1000, put in a new DM and pilot-bearing along with a new rear-main oil seal (one piece unit, easy to install with a short lenth of schedule-40 PVC, which fits it perfectly). Check supporting vendors or ebay (thepartsladi).

NEVER machine a Corvette DM flywheel, anyone who has have had nothing but problems (including noise/leakage and clearance issues with it being thinner).

If $'s are an issue, do the DM test in the FSM, and if it passes just re-install (but do the rear-main oil seal as if it isn't leaking it will very soon).

BTW, also check the clutch-fork for contact rubbing, which might clarify the pivot ball was backing out and that the locking 'nut' was loose -- don't forget to reinstall both with blue lock-tite.

 

I don't know his technique. I am not that knowledgable about the machine shop business. I spoke to them on the phone about it. They did say that it takes them 45 minutes to set up the jigs. Seemed to be experienced guys and had done quite a few DM flywheels fopr vettes. I agree no use machining if alot of slop exists. (See Measurements below.)

I have a LT4 Hotcam in the car. It has always had a rattle... Maybe it would not with a fresher (New) DM Flywheel.

Good advice. The engine was rebuilt just a few thousand miles ago. New seals were installed, fortunately I am good to go there. Also had a new clutch installed when the engine was put in. Overall a pretty good install, however, I did learn that the wrong pilot bearing was installed and installed too deeply. Learned this after speaking with Bill at ZF Doc in a few of the conversations with him on while trying to track down the "Whirring sound" when the clutch was released with the car in neutral.

I did the DM test as indicated in FSM Section 7C-12 "Flywheel Lash Measurement" My flywheel measured 1.25 pushed hard (against spring). If I let it settle by taking my hand off of it, mark to mark is 1.125. Sounds like it passes..? I am curious how much lash a new DM Flywheel has?

This has been helpful, keep that info coming...

 

My flywheel is making a lot of noise. If the flywheel were to break while driving what would that do to the transmission?

 

Why would you want to go through this again. Replace it now.

 

That is something I am seriously considering. Just have to cough up some more cash! No DM flywheels out there now. Would have to go with a solid steel because the Aluminum is too loud.

 

Spoke to Bill Boudreau today at ZF Doc. One of the good guys on the C4 scene! Gave him the specs on the flywheel and he gave me some other pointers on diagnosing the health of this flywheel*. We are estimating 117 k on this flywheel. He gave it passing marks based on my description. I will be proceeding with my reinstall starting tomorrow! Wish me luck!

*Lash test within acceptable range. ---Passed

*On the front of the flywheel (The surface facing the front of the car) look for fluid leaks / fluid weeping from the flywheel and being spun out in a centrifugal manner from the perimeter of the flywheel --- Passed

*Look for significant cracks --- Passed but I am going to triple check tonight!

*Scour with a Red Scotch Brite Pad

Moving forward.

BTW, Bill noted that the later Flywheels 91-96 are more durable that the 89-90 flywheels. With mine being a 94 it could go 200k.

Thank you Bill!

 

Great post, I feel a whole lot better about mine now..Thanks

 

I had been worried about mine. The conversation with Bill was most positive. I had always been told that the life of the DM flywheel was about 100K. Bill has seen many go 150K to 200K in the later version (91-96) of the DM Flywheel. Some of the first generation of the DM flywheel did not reach 60K according to Bill. I am always on the look out for extra C4 parts and pieces so I will keep an eye open for a backup flywheel, but for now this flywheel will be serviceable. The car is a weekend car and I only put 1500 to 2000 miles a year on the car right now.