mixalive

The ZF6 on my 92 is starting to have some issues. It seems to be grinding when shifting from 1st to 2nd and the downshift from 2nd to 1st. 1st to 3rd seems to shift ok. It sounds like a growling noise. Maybe I have synchros issues. What do you guys think? Are parts available for this transmission?

WVZR-1

Parts are available BUT expensive. Syncros are maybe only offered as a package. The ONLY distributor for our ZF is Rockland Standard Gear in NY state. It's a "manual trans as in a manual trans" but some feel there's a "single repair facility". I'd ask appropriate questions if I were inquiring about a repair, if it's a facility that does manual transmissions regularly and maybe the ZF light/medium truck repairs also I'd be comfortable.

The bearings and seals appear to be metric spec items and should be available locally.

TorchRedlt4man

I would look at the level of fluid in the clutch master cylinder.

If low, then that is where your issue is. Poorly working hydraulic system.

Even if the level is OK, might be a good idea to flush and replace the clutch fluid.

GREGGPENN

Unless you've got a TON of miles and have completely rulled out CHS problems, look to the master/slave for your answer.

theadmiral94

suggest reading info here: http://www.zfdoc.com/

WVZR-1

What transmission lubricant? How old time/miles since change? Topped off? How much to top off?

mixalive

My issues seem to be heat related. First to second shifts fine when cold. But growls when hot. I notice it when in bumper to bumper traffic.

dizwiz24

I want to state the obvious first..

Check and make sure what trans is actually in your car.

Everyone told me id have a black tag in my 93 which I bought w/ 26k miles on it. It had a remanufactured blue tag in it.

I had been for years using the wrong throwout bearing (bigged od for the black tag in it).

In fact, whoever replaced it also put the wrong to bearing in it also.

Unfortunately the to bearing for black tag will still go onto the blue tag, resulting in notchier shifts and decreased clutch life.

I just thought that was a consequence of the heavy duty zf trans.....

Hope that gave a difft direction to think.

However I agree about the master and slave. Start there (easy stuff). Jim jandik at power torque systems rebuilds these.

Don't do an autozone made in china replacement

mixalive

Thanks for that input. I am not sure which ZF I have in the 92. I had the clutch and TO bearing replaced 2 years ago and had worked mine until recently. So I have to assume they replaced it with the proper bearing. With the wrong bearing, it would have given me problems immediately, right? Corvette of Austin. I will check out the slave first.

cv67

Yes do that before rebuilding.

Any good ZF rebuilder can do that trans bazillions of them are still being made in euro cars. Some make them out to be a mystery trans that needs magic pixie dust sprinkled on it because its in a Vette.

1991Z07

Gary knows what he's doing...not likely he put the wrong throwout in your car.


Start with a complete flush of the clutch hydraulics and a change of the fluid in the transmission. I use the Castrol SRF that ZFDoc recommended...buttery smooth shifts.

If there is still a problem...cal Bill (ZFDoc) and go through the symptoms with him and what you've already done. He's rebuilt more of the ZF6 transmissions that anyone else...he'll know what the deal is.

mixalive

Yep. Gary has done some good work for me on a couple of issues. If I can't do it myself, it goes over there. I put you in my contact list. Thanks for the info..

mixalive

I wanted to give an update on this thread as I have been trying to further isolate this problem. The noise has progressed in a way that indicates a clutch engagement issue.
This is now what is happening. When the clutch pedal is fully engaged (pedal to the floor and engine running) I hear a noise that sounds like the bolts on the flywheel rubbing against part of the engagement mechanism. As the rpm increases, the speed of the noise increases. If I shift the gears with the clutch pedal a half inch from the floor, I have no noise. Please note that my clutch and throwout were replaced less than 10,000 miles ago. My first impression is pedal height needs to be adjusted. I did not think I had that type of adjustment on a 92. I will say that my clutch engages a little on the high side of the pedal movement. I am also wondering if it is possible the throwout bearing could have been installed backwards. I don't know about this setup, but seem to remember that this was possible on my last vehicle with T-10 Borg Warner. Please give me your thoughts.

bogus

something sounds amiss. I have a 92, with the ZF6... first off, it should be a black tag. IF not, it is a replacement. The blue tags were cycled in during the 1993 model year. After Jan 1, mostly.

As for hydraulics, I bought a cast slave from NAPA. Made in Taiwan, yes, but it hasn't leaked a drop of fluid in nearly 4 years.

I would be checking the hydraulics out, and perhaps, the bushing on the pedal is failing. I will have to check that for sure...

WVZR-1

Might be time to look and not wait!

There's always the clutch fork and the pivot stud. If the clutch master is full from the install 10K ago it would seem to eliminate likely the hydraulics, an internal failure of the pressure plate itself, a finger, a weight etc would seem likely also.

Here's a failed fork. How did it act prior to "catastrophic failure". I believe he mentioned fine maybe just hi-pedal release. It could also be the fork and stud were dry when installed the last time. That should only result in a high-effort which it would seem eventually to lead to a "catastrophic failure" similar to this fork.





Here's another failed fork:

TorchTarga94

^ I agree. Sounds a lot like a pivot stud and/or fork problem. Did you verify if the pivot ball stud was torqued properly when the clutch was replaced? Also could be a throw out bearing if it is making the sound only with the clutch pushed in at various heights?

mixalive

Austin Corvette replaced the clutch.

Purple92

The ZF Box is QUITE Durable, and while they tend not to like drag racing type abuse - if treated reasonably well, they are generally not the first place to look when you have problems.

My recommendation is to compare the clutch pedal feel to another manual trans (ZF) C4. The pedal isn't adjustable - but there shouldn't be more than about 3/4" of free play before you feel some resistance. If there is too much free play - or the "feel" is different from what it used to be - or from another C4 - you're starting to get the info you need to diagnose the problem.

If the pedal free play is off or if the feel is different than you remember (or what a similar C4 that works properly feels like) you can try to bleed the clutch hydraulic system. It's not the easiest thing to do and it typically requires 2 people, but it's cheap, and relatively quick (as compared to pulling the transmission). While under the car - draining the trans fluid and replacing it with a good synthetic fluid (Mobil 1, Redline, AMSOIL, etc) is never a bad thing to do - particularly if the fluid has been in there for a long time.

If the bleed seems to help, but the problem gets worse again, it's most likley the slave cylinder or the master cylinder (slave is more likley). The slave isn't that expensive or that much of a problem to change - but afterwards - you'll need to do a full bleed.

If none of that helped - you're probably going to end up pulling the trans out, and looking for damaged / worn components.


GOOD LUCK !!!

Johnny-Johnny

Instead of the ZF-doc, u could try, whiteracingproducts.com in Florida. He is strictly into Z-R1 trans's. if u have someone dig into the black-tag,the gears should mic out at over 40 thousands or more, had mine gone thru. And all micd at 48-52. The plugs that are no more than like 9 small freeze plugs, for re-assembly are 50-60$ thru him, over 250$ from ZF-doc. And White has good used gears. My check on my black-tag, was only 575$. Ive got a turbo 350/w-brake in mine, trans and all parts are up for sale if u need one, total miles on trans is between 55-60 thousand, and short throw shifter. Just dont want to c a forum member get robbed on stuff. 9 FREEZE PLUGS, AND GASKETS,60$ verses 250+, not including hard parts.....

1991Z07

Another area to look is the hose...they break down and collapse after a while.

My ZF slave went out last year...I replaced ALL of the hydraulics. If a single component is going out...the rest are likely to go soon. I had >90k miles (and 22 years) on my original master, slave & hose. I changed out fluid every other year since I autocrossed and tracked the car so much.

I've owned the car since new...so I know what has (or hasn't) been changed out.

Eliminate the known issues by replacing worn/marginal parts with new first. Chances are they've not been touched and are on the verge of failure. If it is still giving you problems...the clutch fork is the next area to look at. You'll be yanking the trans at that point anyway...check it first before sending the ZF off for expensive work it might not need.