I don't know if my L98 ZF 6 speed still has the DMF.  The PO spoke about having the clutch replaced during his ownership... but how was the repair done?  Are there any clear signs that it has been replaced to a SMF?  Since I've owned this vette the clutch engages very late in the pedal release and from my experience of driving other vehicle make stick shifts the clutch usually engages mid pedal release.  I don't know if that's normal, a sign of a worn clutch, something not properly bled, or is that just the result of having a different non-oe clutch setup?  I just don't have a friend that I could drive their vette for comparison.  Also when the engine is running with the transmission in neutral and the clutch pedal fully released it makes a sound.  Input shaft just free spinning I guess?  I've read somewhere that that isn't good... but I'm unsure why.  I see on ebay there are DMF for sale, but they state they can't be used with L98 only ZR-1 models... is that true?  Lastly if I need and then can obtain a DMF can you still purchase a clutch kit to mate with it? 

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Have I stumped y'all?

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I seem to remember that only the '92 to '96, LT-1 and LT-4's had dual mass flywheels.

hmm...  Well I just see from http://www.amazon.com/dp/B001MVGIM0/ref=as_li_ss_tl?ie=UTF8&tag=justprofit-20 which is the "LUK DMF008" with description of "Luk Dual Mass Flywheel 89-96 Chevy Corvette L98 Lt1 Lt4."  From Amazon and everywhere else it's sadly discontinued...

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Swapping to a non-dual mass will NOT create a vibration...unless the flywheel is not balanced to begin with, that is.
The dual mass set-up is to help quieten some of the gear rattle on the ZF trans. Going to a non dual mass will make the gear rattle louder, but it will NOT damage anything. Gear rattle on the ZFs has always been an annoyance, but has never been a durability issue.
Check with your local Pep Boys...they carry LUK clutches, and may be able to get you the correct set, either as a dual mass, or "regular".

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Joel Adams  
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Consult with Jim JANDIK at Powertorque Systems (powertorque@msn.com) (website: www.powertorquesystems.com) for all things relating to dual-mass flywheels, clutches, pressure plates and clutch hydraulics.  He re-surfaced the OEM dmf for my '93 and provided a replacement Valeo pressure plate and new Valeo clutch disc, as well as re-built hydraulics.  (Correctly operating master and slave cylinders are critical to satisfactory C-4 clutch operation.)  I had been running an aftermarket single mass flywheel, pressure plate, disk, and hydraulics that were both noisy and generally unsatisfactory in operation.  After installing the restored OEM flywheel/clutch package (and spec'ed ZF 6-speed from ZF Doc), the car drives better than new.  Jim is generous with his advice and counsel and his prices represent excellent value.

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Wow thank you for that info!  He sounds like the go to guy for any and all know all for ZF DMF and transmissions!  I'm almost nervous to email him!

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Go for it! Jim is a great guy to talk and work with. Also, remember that OEM flywheels for externally balanced engines hold the only balance information available anywhere for the particular engines to which they are mated. Even if the original flywheel is completely unusable, don't ever get rid of it, as it can provide the information necessary to balance a new flywheel of any type. P.S. I just finished a couple of laps at Watkins Glen, and the drivetrain was flawless.

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Ok... this is a topic that never dies...

|UPDATED|9/11/2013 7:24:38 PM (AZT)|/UPDATED|

I would agree that a deep cut on a DMF is probably not a good idea, but there is a fair amount of tolerance built into the flywheel/friction disk/pressure plate relationship to account for manufacturing differences and friction disk wear. A light clean-up cut on a properly jigged DMF should not cause the assembly to exceed the acceptable limits. As to installing a lighter SMF, I find that is more of a question of the car's ultimate use and the driver's tolerance for noise and down graded driveability. I found that having the gearbox sound like the engine was ready to throw a rod unacceptable for a daily driver and my base LT1 engine (3.45 final drive) was not happy around town with a lighter SMF. If a moderately lighter combination DMF/ pressure plate is desired, Valeo did make a ten pound lighter pressure plate that is difficult to find, but out there. For a well mannered daily driver, I think you can't beat a properly set up DMF.

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hello

My 91 L98 ate its clutch and flywheel at 130K. My mechanic suggested stick with it to avoid unwanted vibration.
He was able to obtain a DMF and new clutch and , while it was god awful expensive, its been fine ever since.

The info at the time was:

The DMF cannot be machined.
After market SF might vibrate and damage every thing.

If at idle, in amongst the rattles you hear an intermittent clunk, that noise is the flywheel starting to fail.

Having said all that I do note that none of the big parts suppliers seem to have the DMF, most will supply a Fidanza
aluminum SPF. I doubt the big boys would supply something that would break transmissions, but they do indicate additional noise.

I'd say, find a DMF if you can, if not there may be no other choice. If you get the work done, have it completed at a shop by a mechanic you can trust, maybe a corvette specialist. IF its done right it should be problem free, that is of course until you blow the master and /or slave cylinders. These should probably be replaced at the same time.

So if you like your corvette, get yer wallet out. There really is no cheap , good fix. Good luck. Post when you get it done and let us all know how you make out.


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I had trouble with the duel mass from the factory,it was so bad that it affected my knock sensor.i talked to gorden kilabrew from gm  and he told me that that flywheel was nothing but problems,very heavy and a big drag on the engine and if I wanted more horsepower and less drag on my engine to get a aluminum flywheel and a good after market clutch.i did that, a fidenza flywheel and a centerforce clutch.the difference in performance is stunning.yes there is a little vibration,but you a driving a corvette not a cadilac or worse a c5.the cost is much less then the dmf and factory clutch but way better performer and you will immediately feel the difference.enjoy your ride.

summit raceing has everything and adamsapple is correct 

Did a quick search @ Summit Racing and this swap setup looks pretty good -  http://www.summitracing.com/parts/ram-900800/overview/year/1990/make/chevrolet/model/corvette

 "These RAM single disc push-type conversion C4 Corvette clutch kits are designed to replace the pull-style clutch and dual mass flywheel in your factory 1989-96 C4 Chevrolet Corvette. They consist of an aluminum flywheel, a high-clamp Borg and Beck-style pressure plate with a 2,800 lb. clamp load, and a RAM 300 Series organic clutch disc. The RAM single disc push-type conversion C4 Corvette clutch kits use an internal hydraulic throwout bearing, replacing the factory release mechanism, to complete the install. Best of all, these clutch kits are capable of handling up to a 700 hp holding capacity."

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As I noted earlier, it's all a matter of what you expect from the car in the way of noise and tractability.  The set up you describe - including the aluminum Fidanza flywheel and RAM hydraulic throwout bearing - is what I had installed when the clutch on my '93 packed it in, and I replaced it after about 2,000 miles with my original DMF flywheel that was resurfaced, Valeo pressure plate and disk, and OEM master and slave cylinders.  Although the throttle response with the lighter SMF was improved over the DMF, the added noise from the gearbox (which was louder than the Borla exhaust I have on the car) and the dramatic reduction in tractability, especially at low RPMs, made the car much less pleasant to drive.  The aftermarket stuff is in my basement waiting to be made into a planter or something useful.

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The new C7 manual 7-speed transmission comes with a Dual Mass flywheel (also a twin clutch). The introduction of the DMF on the '89 Vette was the first use of its kind in a passenger car.

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Ferrari 348 used a DMF... 

Please define HOW you would go about "properly balancing" a replacement non-zero balanced flywheel to the existing engine's rotating assembly, Mr. "Guru".

I've driven 3 LT1 engines with replacement flywheels, and every single one of them had engine RPM ranges where the harmonic vibrations were immediately noticeable and objectionable, and probably harmful to the engine if operated at these RPM's for extended durations.

IMO this is an often overlooked or ignored problem with flywheel replacement on externally balanced engines. What's your solution? I know what mine is, and it isn't cheap OR "easy" at all. Another reason to favor automatics when considering a used car purchase that has an externally balanced engine. Especially high mileage where the flywheel is nearing replacement, or has already been replaced, and now the engine has harmonic vibrations.








|UPDATED|9/27/2013 10:56:09 AM (AZT)|/UPDATED|

hello all,