Has anyone been able to reduce the gearbox buzz/rattle ( in neutral) ? I have a 96 CE that had the tranny replaced, used tranny has total of 50,000 miles on it. Clutch assembly was replaced about 5,000 miles ago (throw-out bearing, clutch, pressure plate.). I know these things rattle but sheesh, there has to be a better solution than turning the radio volume up. Thanks guys.. I am in Tampa Fl , in case anyone knows someone they could refer me to

 

These cars used a dual-mass flywheel from the factory to quiet the gearboxes. Given what you're hearing, it's likely that your car has had the DM replaced with a single-mass wheel. The amount of gear rattle this induces varies a lot from car to car. The mass of the SM wheel will be a factor, as will the helical angle of the gears (two different cuts were used in these ZF boxes).

Be advised that it won't be an easy or inexpensive fix. The gearbox will almost surely have to be removed from the car.

Contact Bill Boudreau (the ZF Doc) at ZR51 Performance about this. He will give you great advice about your options to quiet things down. You can reach him here:

Bill Boudreau

ZR51 Performance

5612 East Almeda Court

Cave Creek, AZ 85331-6405

602-319-6575

Live well,

SJW

 

Yea I read the fix that he has on his site.
Not sure if its worth the fix in the long run
Appreciate your help though.
Thanks

 

Your DMF can also be worn out (they don't last forever) and they will stop absorbing the chatter. I replaced one on my 89 about 12 years ago and it was great for a while. I then replaced that with an Aluminum SMF (don't let anybody tell you it's not that much different, it is). It sounds like a dump truck idling with the clutch out. It's embarrassing enough that I consciously make sure my clutch is in when idling because I don't want to explain "straight cut gears" to gawkers... My worn out DMF was still much quieter than the Al SMF.

If it's bothering you, the only thing you can do is replace the DMF with a new one.

The Al SMF is cool for the occasional "Woomah" and is easier for spirited shifting. It is noticeably more difficult to get the car off the line though.

 

I would agree with above; even with a Zf Doc optimized blue tag trans that was new when installed I still get a ton of noise with a light weight single mass flywheel. Just something that I have gotten use to.

 

Are you guys saying the steel single flywheel is a better chioce than aluminum ?

i'm replacing clutch and flywheel this year and trying to decide the best choices !!

 

It depends on what you define as "better". If you're looking for accleration performance, than the lightest flywheel is better, but it will have more gear rattle. If better means quieter and easier to drive on the street, than a dual mass is your optimum, or the heaviest steel single mass you can find.

The gear rattle is caused by the gear cut in the transmission. The dual mass has a large spring in between the two masses that absorbed much of the back and forth motion of the input shaft and helped to keep the gear noise down. However, it adds a lot of weight to the rotating assembly, which will slow down acceleration response. However, this extra weight does add momentum to the rotating assembly, making it easier for stop and go driving. The lighter wheel tend to need more engine rpm to get going from a stop, since that momentum is not there.

 

The noise doesnt come from the flywheel.

The flywheel dampens the noise.

I got rid of the noise and have the benefits of an aluminu. Flywheel.

You have to remove the trans to instaall zfdocs countershaft shim to trim the transmission.

This made all noises go away, even with my 12 lb flywheel.

 

The greater the mass of the flywheel and clutch assembly, the less crankshaft pulses will be coupled into the input shaft of the gearbox.

I installed the extra-weight billet steel SMF from Spec in my '94, and have almost no added noise from the ZF, as compared to when I still had the OEM DMF in the car. The only time I hear anything is when I'm rolling at very low RPM in the upper gears, with the ragtop and windows up and the stereo off, and even then, it's so slight that I didn't notice it until I'd driven the car for months. Nobody who has ridden in the car has ever commented on it. I'm sure I'm the only person who's ever noticed it. It is very, very faint.

I went with the heavy flywheel because I really did not want a lot of clatter out of the gearbox, and I'm very glad I made that choice. I would make the same decision again without hesitation.

Live well,

SJW

 

I'm confused , if a lighter flywheel is better for performance and acceleration. How come a heavier one is easy to stop and go !


is this heavier than oem ? do you have part number ? and does it fit carloina clutch kit ?

 

First question. The flywheel is always turning. The weight of the heavier flywheel carries more rotating momentum due to the added mass. So when you a starting from a stop, it takes less engine rpm to get the driveline moving. This helps to make starts in traffic a little easier.

With the lighter flywheel, it takes more rpm to overcome the still intertia of the driveline, and makes it a little more difficult to make a smooth slow start in traffic.

The lightweight wheel is better in terms of performance for the same reason. It takes away less engergy to get the driveline spinning faster, as in the rear wheels. For example, doing a 40 roll, you will accelerate to 100 much faster. From a standing start, it will a bit more of challenge to prevent wheel spin, but once you do, you'll get up to speed much quicker.

Now it depends on your choice of set up. I have a Spec 22lb flywheel and a Carolina Clutch Stage II disc. So, ahile I need a little more rpm to get the momentum needed, the clutch, while solid, isn't so grabby that I can't slide it enough for a smooth start. I have heard of some going with a higher grip clutch that makes this more difficult. There is also the noise factor. I have an audible gear rattle, for some it would be a real issue. I know what it is, so it doesn't really bother me that much.

Second question. The dual mass weighs in at about 40lbs. Many of the single mass stell wheels are 36-38lbs. When used with a sprung hub clutch, the added mass will help to absorb some of that gear rattle in neutral, and take off. They are not quite as effective as the large spring in the dual mass, but better than the lightweight wheels.

 

Thanks a lot , that was informative.

I need to make up my mind on which flywheel to get. alu or steel.

What do you suggest ?

My car has boltons and hot cam. 334rwhp/334rwtq.

I think it has a single mass flywheel because I hear little rattle when idling.

it's a weekend car , very few 1/4 runs during the year.

 

The car I speak of has a brand new (OEM blue tag) that was fully optimized by Bill at ZFDoc (while I watched). During that process he shimmed everything to the optimum spec.... Again, with an ultralight flywheel and clutch package there is no getting around the noise...if there was the company that engineered the thing would have come up with this solution in the beginning.

To the OP; if you think you may sell the car someday, I would think about a DM. If you plan on keeping the car for some time and are more into performance than anything else you probably won't have an issue with the SM. Just my .02, hope this helps.

 

I guess im an odd man out. I dont mind the noise as a matter of fact i kind of like it. Mechanical noises like that remind you your driving a performance car not a prius.

 

Right, I agree. As I stated earlier, if I know what the sound is, and why, and that it is a part of normal operation, I really don't mind it.

However, if there is a fix for it, and it can be greatly diminished for not alot of money or added work, why not? Now, it wasn't until I had finished my flwheel/clutch swap that I learned about the shim. I don't really want to go back in just for that, but when I do the u-joints here shortly, and I'm a mere 5 bolts from having the trans out, I'll probably do it then.

Now, alos understand that part of this issue is that the DMF is no longer available, at least new by a vendor. Many people would like to keeps that factory spec as much as possible. But when the old DMF goes bad, there's just not alot of options for keeping a quiet transmission.

 

The noise - the rattle - is not caused by the nature of the gears, it's caused by the nature of the transmission.

All the various rods and shafts simply make a lot of noise in there.

the gearbox was altered to lower the gear whine in first and second, not to stop rattles.

The dual mass does nothing to stop gear whine.

 

Just wanna report back again. Had the car out today and low gear rattles / vibration are gone After shim mod.

Now, the light rapping at neutral/ clutch disengaged (ie. Pedal not depressed) is still there, maybe not as bad.

This shim made a huge difference and again, this is nothing unique to the corvette zf6. Its called trimming the transmission. A buddy had a picture of him, on facebook, doing the same thing on his 03 mustang cobra

as a reminder: blue tag, remanufacured for gm trans with a fidanza 12 lb alum flywheel and spec stage 3+ clutch.