Hey everybody I just picked up a 96 triple black convertible with LT4 and 6 speed.
123,000 miles on it.
when I push the clutch in to the floor it makes a ticking-knocking-metal on metal contact sound. If I back off a little the sound stops.
It works ok except for the sound.
The guy I bought it from said it was changed 2 years ago with a single mass as opposed to a dual mass (no idea what this is) flywheel.
he took it back after the clutch job was done they said everything was OK the problem was the different flywheel but not to worry that it would work fine.
Well he did drive it for a couple years with no problem and it still works but no way I'm going to keep it like this, it sounds terrible.
so can anyone tell me what I'm dealing with here?
How to fix?
Dual mass flywheel?
Is there something wrong with them?
any help appreciated

 

Dual mass FW's aren't available (new) anymore. Haven't been for about 5-6 yrs. Only source is used.

Single mass doesn't "dampen" gear rattle as well. Keep in mind, this transmission was originally used, then sourced out of a German bus (to make the debut of the 89 ZR1 -- with a 6-spd. Tolerances didn't need to be stellar in a noisier bus setup. But GM/ZF employed the use of a dual-mass FW and a sprung hub clutch plate to dampen rattle.

There are videos on YouTube that will explain dual mass flywheels.

That said, there are transmission shaft shim selections that may quiet what you are hearing...There are a couple of members who have used (or been guided by) the ZFDoc (in Arizona) to improve what they hear.

More info can be found here...
http://zfdoc.com/faq.htm

And...by contacting Bill Boudreau...owner of ZFDoc.

 

I had a similar problem on my 96, problem was the ball stud retainer actually broke and started to come loose and allowed fork to actually come into contact with the flywheel. Like you I dealt with it for awhile but it actually sounded like I could not shift and I got the machine gun sound especially when going into first or reverse. The retainer that broke costs about 30 bucks and is made by Jim Jenken who knows more about this setup with a ZF than most. Although I still have my original flywheel I belief the resulting sound would be the same, single mass or dual mass. The bad part is the labor to get to and repair the 30 buck part is about the same as replacing the clutch. I can send you pic's of the new part and what the broken part looks like...Its very fragile, I believe 11 ft. lbs. of torque to install. MJP

 

thanks for the responses, I will be looking into it.
I would like to find the dual mass.
I guess junk yards.
I would like to see any pictures you can send.Thanks

 

Pics attached, what retainer looks like before and after breaking. Also, where it is located on the bell housing - installed and not installed, its the bronze colored piece.

Good luck on finding a flywheel, I have a complete flywheel clutch set-up off an LT4 crate motor, but sense I own two 96 GS cars I intend to hold on to it. Mike

 

Good info here. On my 1992 it worked itself loose. But was not broken. I was able to reuse it.

Good Luck

 

Thanks for the pictures!!!
So it's a retainer but what is it retaining?
Oh and thanks for the teaser!
I may have found one at a place called power torque systems, but not cheap by any means

 

The Clutch Fork.

 

The retainer in question retains the pivot stud for the clutch fork. They can tend to back out, and you can't torque them down very much or you'll strip the threads off of them. I recommend blue Loctite on them.

The sound the transmission makes with a lighter, single-mass flywheel is a rattle when the clutch pedal is out and the shifter is in neutral. As already stated, this is completely normal and does not indicate a malfunction. All transmissions do it a little, but it's usually not noticeable and/or is damped with a heavy and/or dual-mass flywheel. There are heavier single-mass flywheels one could use, if he really objects to the noise that much. And also as noted, there are possible options to shim one component in the trans to a closer tolerance.

To OP, I suggest you go out and pay careful attention to when you hear the noise. If you hear the noise when the trans is in neutral with the clutch pedal out, and then it goes away when you depress the clutch pedal (i.e. the input shaft stops turning), then it's probably the normal ZF6 rattle-with-single-mass-flywheel. If the noise isn't there in neutral with clutch engaged, but then appears when you press the clutch pedal in all the way (which is what you wrote), then this is not the normal ZF rattle. It is possible a loose retainer, but my bet would be that something is amiss with the throwout bearing or the fork or the pivot stud itself. This sound is not normal. Unfortunately, this will take some serious labor to pull the trans and check. If you have experienced C4 owners in your area who are accustomed to the ZF rattle after flywheel conversion, it would be helpful to ask one of them to listen to your car and help you narrow this down.

 

Power Torque Systems is the best place to start, few people know more than Jim about the clutch on our C4's...MJP

 

Interesting topic, i will share my experience of this, On my 90 L98
coupe upon buying it the clutch and DMF were changed out for a light
single mass flywheel center force brand and spring clutch. I had the gear rattle in neutral and was ok with it, but when the clutch pedal was down clutch out it made a loud knocking noise, i drove it like that
for two years untill i decided to remove the transmission and engine
for restoration. when i got clutch apart it was evident the fork was
hitting the flywheel at 3 points. the clutch pedal had a big piece of rubber around it to keep it off the floor and the slave was shimmed back with washers to try two counter for this. i was talking with Bill the Zdoc and jim from power tourque systems i put the transmission
on a pallot and shipped it to him for rebuild and short shifter mod,
when bill got the transmission apart it was trash all the gears were
wiped out clutch fork bent. this car is in a no holds barred restoration . i got another black tag ZF6 from Jason owner of
Vette to Vette with only 60K on it also have the DMF fly wheel
jason sent the flwheel to power torque systems for Jim to inspect
and surface then he sent it to me along with my overhauled hydraulic parts then i took it over to the engine shop who balanced
it onto the overhauled 355 engine. Bill modified the fork and did
the short shifter mod i put it onto my replacement. after market
clutch parts are not within specs for there application some flywheels need to be turned down as was the case with the one
in my car, I got lucky finding the low mi trans and flywheel
so without the help of Zdoc and jim and Vette to Vette i would have given up and put in a 700 auto

 

Thanks for all the input everyone.
This is what the zdoc has to say about the situation


The clutch fork is striking the rotating pressure plate aluminum cover while
rotating.
Sounds like you either have a bent clutch fork or the clutch fork pivot stud
is backing out due to a compromised or missing locking cap. The pivot stud
is turned clockwise to loosen. The clutch fork, clutch fork pivot stud and
pivot stud locking cap are all three soon to be available from Melrose
T-tops.

While the transmission is out, might as well replace the 0.075" counter
shaft bearing washer with a 0.0805" washer. Kit cost $50, install time 15
minutes (with transmission removed from vehicle). See attachment.

Install new $15 fluted pilot bushing (GM P/N 10125896) and absolutely do
not apply grease in the oil saturated pilot bushing. Doing so will cause
pilot failure within 1.5 years operation along with uneven friction surface
wear significantly shortening clutch life expectancy and performance.
Installing a pilot roller bearing is great right up until the roller bearing
fails at which time the transmission must be removed ($500) and disassembled
($400) in order to have the input shaft pilot tip either repaired ($100) or
input shaft replaced ($550) instead of installing another fluted pilot
bushing for $515.

Best regards,

Bill Boudreau
ZR51 Performance
5612 East Almeda Court
Cave Creek, AZ 85331-6405
United States
602-319-6575

 

This would make sense. You should be able to see some witness marks on the p/p and the clutch fork. Take Bill's advice on the pilot bearing! My roller bearing came out in pieces and I am very lucky to not have ruined my input shaft from that.

If you're going to do this job yourself, pull it all and inspect the fork pivot stud carefully. Try to see if it is loose before you pull it out. You need to inspect it carefully for wear where the fork pivots on it. My guess is that when the last jokers did the clutch job they either didn't reinstall the retainer at all, or didn't Loctite it and it has worked loose. If you need a new retainer, Bill may have them and I think Jim at powertorquesystems.com has them. If you need a new pivot stud before Melrose gets them in stock, then Jim may have for you.

 

That sounds right to me, Thanks for all the help.

 

Post back with any questions as you tear into it (again, assuming you are doing this yourself). I am fresh from doing a clutch job myself, and many others here are very familiar with the job. So feel free to ask for guidance!

ETA: If you're going to pull the clutch and replace the pilot bearing, you have options for how to pull the old pilot bearing. I ended up buying the three-jaw puller from Harbor Freight for about $20. It's cast with no machining (which is why it's so cheap), and so the jaws are too bulky to fit through the bearing as sold. I took my die grinder and machined away some of the size off the barbs (those are the parts that don't fit), and then ground off the face below so they'd have enough grabbing surface. After that it worked like a charm. It's really nice if you hate the thought of pounding on your thrust bearing with a hammer (bread or grease method) or a slide hammer (Autozone loaner tool method). The new one will go in with fairly light taps of a hammer.

 

The last clutch I did was my old boss 302 back in the 80's
what I recall was packing the pilot with grease and punching in a rod the same size as the pilot shaft hydrolicly pushing the bushing out. Is this what you mean by bread and grease method?

 

Yes. Some people use grease and some people use bread (literally sliced bread...go figure). I just didn't like the idea of banging on the thrust bearing of the crankshaft any more than absolutely necessary. The three-jaw puller like I used requires no hammering at all. You can't avoid using hammer action of some sort to install the new bearing, but it doesn't take huge hits to install.

ETA: Also, if your car has the original needle bearing the grease method may not work as well.

 

You don't actually strike the thrust bearing, you pound on the grease or bread which pushes the bushing out. Anyway I like the Idea of a puller
,but whatever works
Talking to Jim at power torque systems today(what an awesome Guy,he spent almost an hour on the phone with me)and he told me all LT4's
,LT5's come with the Bushing not the bearing because of higher RPM use. FYI