Topic: dual mass flywheel
in Forum: C4 Driveline Components
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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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I seem to remember that only the '92 to '96, LT-1 and LT-4's had dual mass flywheels.
They all came equiped with ZF trannys. (Except girl vettes with slush boxes)
I've heard that if you switch to a SMF it will have a wicked vibration at idle.
But, I'm old. I forget things.
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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Duncanville, TX - USA
Joined: 3/18/2009
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Vette(s): 1985 Coupe-L98/Auto,Bright Red/Carmine.
1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.
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".
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".
Joel Adams 
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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.
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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San Pedro, CA - USA
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Vette(s): 1992 Polo Green Coupe
1987 Bright Red Coupe
Ok... this is a topic that never dies...
|UPDATED|9/11/2013 7:24:38 PM (AZT)|/UPDATED|
1. The DMFW as mentioned, was designed to mitigate gear rattle in the ZF6. Not so much gear rattle as shift rail rattle... regardless, I have had any number of "experts" tell me I had thrown a rod or my transmission is ready to explode.
2. The clutch assembly is very sensitive to position, from a geometric stand point. If the flywheel has been cut down too much (more than say a quick hit from a pneumatic die grinder with a steel brush). it will change the lever and potentially overload the hydraulics. This is why cutting the DMFW is a bad idea. Again, a quick resurfacing isn't bad... also, what makes it a dual mass, the coil springs and ball bearings inside the part are prone to failure after about 120k miles, give or take depending on driving style.
3. If you have a good DMFW, then simply replace it with a SMFW from an F-body. To do this, get an LT1 Camaro or Firebird part, then cut it down .090 to match geometry, then have it match balanced to the DMFW. The clutch itself is neutral balanced. A match balancer is a strange machine where you install the two items 180* out from each other and then spin... add weight to the target part and in time, they will match. Please note that the DMFW came from the factory with holes to fine tune the balance. Leave those weights in there when doing the match balance. Well mallory or tungsten to the SMFW to bring it up to weight.
4. The DMFW is one heavy SOB... a nominal 40lbs. Aluminum is about 14 lbs... but it's kinda pricy (well, still half the price of the unobtainium DMFW) at about $450. I don't like the aluminum ones for the street, tho... too light. The OEM Camaro FWs are about 20 lbs each. A nice middle ground.
5. Rockauto shows the Camaro flywheel for under $110.00. From there, you will need the Corvette pressure plate and the Camaro friction disc. The disc is about $120, for a Sachs part, and the pressure plate is not available on it's own... but the LuK kit is about $280.00. This is where hitting up Summit or one of the performance Corvette providers might help.
Incase you are feeling sorry for yourself, Ferrari 348 use a DMFW... it's about $3400 for a new flywheel.
If it make anyone feel better, I think I got the last DMFW in the country... It took my parts guy about 3 days to find one in a warehouse in Nebraska...
|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.
in Forum: C4 Driveline Components
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