grantar2

Replaced the blown out dual mass flywheel with a steel flywheel from Carolina. Happy with the performance, but not the sound under load, sounds like a fork in the blender under certain loads / acceleration.

I vaguely remember someone claimed that putting the fork from the ZR1 would fix it, but not sure what else was required.

Would be interesting in knowing what others have done, and if anyone knows of a source for dual mass flywheels for a 1990 with ZF6 speed.

grantar2

Sorry, not familiar with RAM? Do you have a link?

I have a steel flywheel but it is lightened because I was balancing for Autocross when the flywheel was replaced.

MatthewMiller

I can't imagine how changing the clutch fork would make a difference in the sound of the transmission under load. The issue is loose tolerances at the countershaft shim in the ZF. It's normal, and that's why GM used the DM flywheel in the first place. ZF Doc talks about carefully selecting a shims thickness to take up as much slack as possible, which can help make it quieter.

GREGGPENN

I hadn't heard the fork thing either. I also thought it was a shim issue (that could help).

I'm 99.99999% sure no source for NOS DMF's still exists. I bought the second-to-last one left (in the USA's main distribution chain) back in 2010. They've been out-of-production that long. There was some talk of retooling a run around 2011-2012 but it fell through. Despite the high production count of C4's, the ZF percentage must be small enough to negate interest of aftermarket or post-production runs?

If you want to return to the DMF setup, you need to find a used donor...or possibly someone still sitting on a NOS unit. Won't be cheap if THAT ever happens!

QCVette

Something sounds wrong.

Like MatthewMiller said the common ZF transmission noise is rattle when not under load. Under load they have some gear whine, but nothing like a "fork in a blender".

The only thing I can think of that would sound that bad is if the flywheel/clutch are not in the same location as stock so they are hitting the clutch fork. That is not a problem of the clutch fork, it may be a problem with the right parts for the flywheel/clutch.

Perhaps the pivot stud is not all the way in, but that would be a rare off the wall guess.

Perhaps the bell housing was installed without the shims and is physically forward of where it should be, so closer to the engine which allows the fork to hit the back side of the pressure plate. (If you have the magnesium bell housing that uses shims between it and the block. If you have the aluminum bell housing, they do not use the shims.)

I wouldn't have expected the crank to move forward and back enough to make a difference though, but if very close, a slight movement under load might make it contact.

In short I don't know what is the problem, but under load is not the normal ZF noise to sound like yours.

Good luck.

WVZR-1

Any number of things are possible. The OP needs to mention all parts used by part # for a good evaluation by anyone. A conversation with Carolina is in order. A broken/cracked/split fork at the pivot ball I don't recall creating the noises, just created function issues.

The LT5 fork ain't different! The stud is

OP never mentioned the clutch!! Most all SMF installs require a different clutch. I'd think the issue is likely 'self-inflicted'!

MatthewMiller

To be clear, though, they can make a little noise when really lugged down in gear. For instance, if you're pulling 1000rpm in 4th gear and get on the gas you might get a little gear rattle with a single-mass flywheel. But it usually isn't as loud as when the car is idling with the tans in neutral and clutch out (engaged).

Oh damn, I forgot to mention this! Yeah, the stock DM flywheel requires a solid hub on the disk - no springs. That is what shows up if you look up a replacement clutch disk for a ZF-equipped C4. But if you switch to a single-mass flywheel, then you need to use a sprung hub, or else it would be very noisy.

Tom400CFI

There is one for sale right HERE, on these very forums. A smokin' deal at $55.00.

grantar2

Bummer sold before I got there.

grantar2

To be clear, though, they can make a little noise when really lugged down in gear. For instance, if you're pulling 1000rpm in 4th gear and get on the gas you might get a little gear rattle with a single-mass flywheel. But it usually isn't as loud as when the car is idling with the tans in neutral and clutch out (engaged).


Oh damn, I forgot to mention this! Yeah, the stock DM flywheel requires a solid hub on the disk - no springs. That is what shows up if you look up a replacement clutch disk for a ZF-equipped C4. But if you switch to a single-mass flywheel, then you need to use a sprung hub, or else it would be very noisy.[/QUOTE]

Clutch and flywheel were sold as a kit from Carolina.

My rattle comes under well running, not at idle. At idle all is quite.

MatthewMiller

That is unusual. It does make me wonder if your fork pivot stud has backed partially out. I'm not sure what else would make it do that.

Kubs

Thats what I was thinking also, or wrong size throw out bearing?

856SPEED

Clutch and flywheel were sold as a kit from Carolina.

My rattle comes under well running, not at idle. At idle all is quite.[/QUOTE]

This is not common^


At idle w/o the clutch engaged and lugging the engine in a higher gear at low RPM are common parameters to hear "gear rattle" in the ZF with a single mass FW; I have aluminum FW so I know.

What I have done to mitigate that is raise my idle speed to 1,000 RPM; very quiet (well, more quiet) at that speed vs. 750 RPM or lower. I run an aftermarket cam (so that idle speed doesn't seem that high) and aftermarket ECM (which allows changing idle speed much easier) however.

The other mitigant like mentioned above is ZF Doc's shims for the countershaft; I heard he is the guru on these things.

Other than that short of the DM FW; it is what it is.

WVZR-1

OP has never mentioned his location or the part#'s of parts used. Was this a DIY or a 'for hire' replacement?

I'd think his next move should be - have someone who understands these SMF installs in early L98 ZF-builds drive the car.

He needs to mention part#s not just 'kit', what else was replaced at the same time and post the information/build of the ZF from the label on the right side of the ZF. Number would start with 1052.

Everything to this point is a WAG - that could go on till He!! freezes over.

He needs to supply info!!!

GREGGPENN

Carolina Clutch is (or at least used to be) very knowledgeable about C4s and a GREAT source for C4 clutches. I would THINK they'd send correct pairs of FW and hub-sprung clutches. It IS their biz.

Though we don't know anything about the installer.

I'd wonder if it wouldn't help to put the car on a rack (or jack it) and stethoscope the noise?

cv67

x3 on the countershaft shim. Call Bill at ZF doc for the fix.

WVZR-1

I actually doubt the 'shim' if it's an original German built ZF - it's amazing what's passed on to be fact here on the WWW ......

If the ZF is on the bench and being built it's certainly something that's always confirmed but I do believe it's a stretch as far as being a valid as a 'just do'

grantar2

I will have to get the car up on the lift.

Car is in California so has to be kept California Compliant, limits messing with the programing, besides it was run in SCCA B-Stock Production which further limited messing with it. Clutch and Flywheel were purchased as a package, allegedly with all parts required. It was installed by my regular mechanic during an engine over haul.

Gearbox itself is stock ZF with a Hurst Short Throw Shifter. The car before I got it was run out of the Dick Gulstrand group which is where the car had been built to stock. 3 championships for the original owner, 1 for me. Plus a second, third and fourth in five seasons.

Clutch has about 2,500 miles on it.

I appreciate all the help. Will have to look up ZF Doc to see if I can get this worked out. Currently in the shop for rewiring, had a fire in the A/C / Heater Blower segment. Appears a relay shorted and caught fire. Got my fire bottle on it pretty fast, the coolant tank also contributed it's contents, so the car is officially being totaled, but will run again, but will have to pass, brake, light and smog inspections again.

856SPEED

Talk to Tom at Carolina; he will set you up (if need be).