I might be able to get my hands on a 1991 with a bad clutch. I am very friendly with my local transmission shop and they warned me that it could be an expensive job because of the dual mass flywheels on this car. he said that the flywheels are very hard to find and they tend to chatter after clutch replacements. so, who has experience with replacing these clutches on the zf6? what flywheel should I get for a replacement? I see a lot of crap on ebay but I don't want to make a mistake on an expensive repair.

 

I have serviced and replaced numerous clutches on the ZF six speed transmissions.

If you do not use a dual mass flywheel...you WILL hear the noise inside the transmission. There is NO WAY around it. So a solid flywheel will always make some noise. I have never come across a flywheel that is a solid flywheel that does not have noise coming out of the transmission to some degree.

No one that I am aware of is reproducing the dual mass flywheels. Finding a new one...basically impossible....they have all been bought up.

I know back in the day when you could buy the flywheels from GM...some people were trying to save the money and would take the flywheel and have it re-surfaced. It can be done VERY SLOWLY and with light pressure...and those cars that had it done worked out fine....BUT...that also depended on the condition of the rubber oil impregnated bushing in the center of the flywheel....AND the amount of material it took to get the surface smooth. You can tell when this bushing is shot by turning off the engine when it is at operating temps and in neutral...and if you hear a 'knock-knock-knock'...that is the sound of the outer portion of the flywheel slapping back and forth on the toothed surface of the inner bushing area. that is why I feel how tight this bushing is and the amount of effort it takes me to rotate the outer flywheel surface to the inner surface where it is bolted to the crankshaft.

DUB

 

I had a Corvette specialist replace the clutch and flywheel on my 1992 C-4. He couldn't locate a dual-mass flywheel and installed a clutch/flywheel kit. He warned me about the noise. Man, was he understating it!

The mechanical noise started-off ok. As I drove the car it got progressively louder. By the time I arrived home it sounded like a washing machine filled with rocks! Unbearable! I drove the car for a few days and was holding the clutch in at red lights as the noise was really incredible.

I located a dual-mass flywheel on ebay - $650 - and paid to have the "kit" removed and dual mass flywheel installed. All is well in the world again. Do what you can to locate one. You won't be sorry.

If anyone wants to buy a clutch/flywheel kit with about 100 miles on it - cheap - please let me know!

 

can someone post a picture of the dual mass fly wheel and the solid one? I'm like the 7th owner of my C4. I'm curious as to which one I have. Im gonna take a peak sometime. I know I will cross this bridge someday so I too am trying to figure this out. Thanks

 

the responses here are misleading....

Yes the dual mass flywheel does a better job dampening noise.

However it is not the source of the noise and there is a way to eliminate or reduce the noise(at the source) and still use a lighter single mass flywheel.

The noise comes from a longitudinal vibration in the trans countershaft. Zfdoc sells a thicker countershaft shim to quiet it down.

This is a good cheap mod to do while the trans is out and then you will have less rAttle when using a single mass flywheel.

Use the heavy dual mass flywheel as an anchor for your boat

 

I bought a NOS dualmass flywheel, clutch, plate and throw out bearing last year for my '93 from Jim Jandik of PowerTorque. He had recently purchased a pallet of them. He can give you great advice on your options to consider. He is located in Iowa and a vendor I think here on the forum. Just don't have his phone number at the moment, but somebody may have or do a search. Many here on the forum have been helped by his help concerning clutch problems and the dual mass flywheel. Contact him.

 

Here is Jim's office, cell number. Call during business hours. Tell him Scott from Michigan referred you.

641-342-7446

 

Yes I will. Should have it posted tomorrow.


INTERESTING....Thanks for the information on a part that can aid in reducing the noise.

I am aware of where the noise is internally inside the transmission....and as I was told by people who know more about it than I...that the dual mass flywheel is needed to make it so there is no noise inside the transmission when driving or idling in neutral.

I assume you did this modification and are using a solid mass flywheel. How does it sound....and please be honest ( not saying that you wouldn't) but if it is a good choice..I can offer this modification to customers who need clutch work and I can not find a dual mass that is worthy.

DUB

 

I did the aluminum flywheel mod before the thicker shim so I know before and after.

Before, there was rattle in three driving situations.
1. WOT low gear
2. Lugging it in a too-high-of-a-geAr like climbing a hill
3. Idle with clutch out

To be honest, this car is not a Cadillac so the noise didn't bother me.

My goals for my c4 are different that most people. It's blown, modd. I like to be able to shut down newer corvettes and eventually modify it to take on liter bikes. So my goals are different than the ice cream getter / Sunday cruise types. That's probably why the rocks in a can rattle noise didn't bother me too much (ie. Was tough to hear over a 3" exhaust).

After getting use to the rattle for 10 years, I then had the trans out and remembered about zfdoc's thicker countershaft shim which I installed.

The noise went away in all 3 situations I described above. It was really weird how much smoother the trans felt.

I do have a Re manufactured blue tag zf6, which has its own quirks, so I cant guarantee everyone's experience will be the same.

 

I'm not positive, but I think I read where the countershaft shim only fit for the blue tags. I could be wrong about that.

I put the 22lb Spec flywheel in my '96. As Diz reported I had noise in those three situations. It wasn't Gawd Awful IMHO, but I also had about as close to straight pipe exhaust as you could get. If you're looking for stock quiet, and the countershaft shim is not an option, the 36lb flywheel is going to be as close as you're gonna get. I've read where they're not that bad, but have not heard one in person.

There might still be some NOS dual mass floating around out there, or at least some low mile used ones. They probably won't be real cheap though.

I recommend talking with Jim Jandik, he helped me quite a bit. I also recommend hunting down a pivot stud and fork before digging in as well.

 

There's been a couple recommendAtions to tAlk with Jim Jandik.

I found him to be helpful and then suddenly arrogant, refusing to sell any parts to me when I wanted to go with a spec stage 3+ clutch to hold up behind my 520 RWHP blown 93. He was really wanting to sell me or get me to buy a Carolina clutch stage 3 puck type clutch for some reason. As we all know puck type clutches don't have as good street manners as disk type. Anyways that spec stage 3+ has held up just great behind my combo and I recommend it.

He did do a great job rebuilding a clutch slave cylinder and I recommend him for anything related to clutch hydraulics.

 

I went with the extra-mass billet steel SMF from Spec, along with their Stage 2 clutch kit in my stock '94 LT1 car a few years ago. I hear no gear rattle at idle, and only a minuscule amount when accelerating at low RPM -- it's so faint that I doubt anybody else would ever hear it, and nobody has ever commented on it so I'm presuming I'm the only one who ever notices it. At the time I did the swap, I wasn't aware of the countershaft shim option. What's involved in adding the shim?

Live well,

SJW

 

Well, minus the removal of the transmission part of the job, it's simple to do if the trans is out Already.

Remove the plug below the input shaft, use a big set of snap ring pliers to remove the snap ring, pull out the old countershaft shim, measure it (just to make sure that the new one you are putting in is in fact slightly thicker), put the new one in, put the snap ring back, and put the plastic plug back.

It's that easy

 

Good reading and responses....Thanks to all who expressed their experiences and what they have theirs cars set up for...which makes a difference.

I use only SPEC clutches and flywheels at my shop...unless I need to re-use or install a good used dual mass flywheel....due to most of my customers want the 'Cadillac' experience. But now knowing that the 36# flywheel from SPEC has given a forum member 'SJW' good results..I can offer that as an option.

DUB

 

I replaced the dual mass flywheel in my 93. My clutch was still good, but the flywheel went. It started making banging and rattling noises when I pushed the clutch to the floor.

I went with the 35lb. billet steel flywheel from Carolina Clutch. I also put in a new clutch while I was at it. I went with the stage 2 disc type clutch (not the puck type), which had a spring damper on it.

Overall I'm quite happy with it. I have some gear growl below 3,000 rpm if you use more than half throttle. But is just a low growl, not the horrible "rocks in a can" noise that some people complain about. If you are giving it less than half throttle, or over 3,000 rpm (even at full throttle) there is no noise at all.

 

wish I knew about the shim. I even dealt with Jim and bought a new LT5 pp from Bill and no one cared to mention it Theres always next time.

 

I believe that the shim procedure is only thought to be a fix for the "crash-thru" ZF's. The '94 isn't a "crash-thru" and still a "black-tag". It's very easy I believe to assume that all ZF's are the same. I don't believe that can be assumed.

The "heavy wheel" though I believe is and for most is likely what should be considered for a replacement. The lighter flywheels I'd think only need considered for specialty builds where the person "understands" just what it is that they're doing.

I don't believe that it could be stated as fact that all "crash-thru" boxes need the shim, if the transmission was on the floor and time permitting it might be considered a "something to check".

 

Pretty much the reason I ended up with an automatic as already a member here before I bought it and read about how costly it is to fix the clutch. If I could have found a clean 89 with a stick I would have bought it and put in a Tremic if the trans acted up.

 

The Tremic would need to be modified to accommodate the c-beam and possibly the hole in the transmission tunnel may have to modified unless the Tremic has adjustable shift mounting positions.

It can be done however.

 

The SPEC extra mass 35lb flywheel does aa real good job as stock replacement on stock cars.

We've used a few and it's difficult to tell the difference between it and the DM.

If anyone is wondering how bad ZF rattle can be - Your welcome to sit in my 92.... Aluminum FW and a serious engine with a big camshaft... it'll drown out a 7.3 Powerstroke at idle.
Will