kostas86

1990 with a 6 speed. Just hit 54k miles.
When I shut off the car, I am able to move shifter into each gear (without using clutch). Start up the car, clutch in and even with full force can't get the shifter into gear (there's been handful of times where I managed to but involved shredding my shirt from all the bicep muscle required lol). In addition, when trying to force the shifter into gear, the car tries to creep forward (in gears 1-6) or backward (reverse gear). Currently fluid levels are normal.
Am I safe to assume that the clutch master cylinder is dead?

Tom400CFI

No.

You're surely safe to assume that the clutch isn't releasing...and continued abuse like "forcing" it into gear will ruin the synchro's in the trans.

What you need to do now is diagnose the reason. The most common reasons, in order of greatest to least are:
*Air in the system/soft pedal
*Leaking/failed master OR slave cylinder -most commonly diagnosed by leaking fluid from the problem cylinder
*Worn clutch fork/pivot.

Time to "get out and get under" as the old song goes, and see where the issue is.


.

kostas86

Thank you, hoping I find a leak somewhere

jsmn4vu

Just remember that a failing master cylinder usually does not leak externally. When the piston/bore get worn, the fluid just leaks past it (internally).

Tom400CFI

It leaks into the car -the inside of the firewall, frequently.

mcguirjf

+1 on the master leaking internally onto firewall. Also the slave suffers from the same fate. Check my thread and you can see the replacement I did on my 1989. Go to page 10 of thread.

Goldcylon

If there is fluid what is its color? If it's black it's contaminated with both clutch dust and/or moisture. Clean out the bowl and add fresh fluid and pump the clutch. Repeat this procedure until the clutch fluid is clean. It's likely your clutch master is toast but dirty fluid will cause shifting problems as well

Kevova

I would just plan on replacing both clutch master and slave cylinders. Too many times when one fails the other follows. If you chose to try to replace only one, there is a tool that will pump fluid thru the slave cylinder towards the master. I recommend using it.

Tom400CFI

I'm still trying to figure out how one gets clutch dust into a system where the slave is outside the bell housing. (?)

Later model designs, where the slave/TOB assy is IN the bell housing where all the dust is, that I "get". Outside? Not so much.

Klondike

YIKES! If you're moving the car with the shifter, your synchros are trying to stop the dragging clutch from turning. That's not good for the synchros.
The tiny amount of fluid in the clutch system doesn't take much to contaminate it. But on the good side, it doesn't take much to flush it all out with fresh fluid either.
The hard part is trying to pump a darn air bubble down hill!
Good luck.

Goldcylon

It's not just clutch dust, dirt, grit , moisture contaminants etc. Also if the clutch master seal is already compromised.. More crap gets and looks exactly like the fluid in this video

Yukon Corleone

Clutch master and or slave cylinder would be my guess too. Are you doing the work or taking it to a shop? If a shop which one? I have a 1990 also and live south of you. I am sure mine will need to be replaced again.

trilkb

Lot of answers I can't make much sense of.

Easy answer, your clutch master or slave went out or you have a leak.

Buy all new master, slave, and braided clutch hose...be trouble free for atleast 10 years.

Tom400CFI

Yes, I'm very familiar w/the "Ranger" clutch dust videos. The cars featured in those vids have the slave inside the bell housing. The C4 does not.

I totally agree w/you that the fluid gets old, water logged and contaminated. Never under stood the "Clutch dust " claim though. You certainly aren't the only one who makes that statement. I think people "displace" the concept from when they read about it happening on cars w/the slave in the bell housing...into the C4.

SJW

Agreed. If a C4 is generating enough clutch debris outside of the bellhousing that it's getting drawn into the clutch fluid via the slave cylinder, it's gonna need far more than just replacement of the hydraulic components.

Live well,

SJW

Goldcylon

Yep I was not making that argument its just one possibility of crap that can get into the system. Yep the C4 ZF-6 features an external clutch master and salve cylinder

Yep while I can see how the dust gathers in an internal system I have seen the ZF-6 fluid equally as dirty as what was being syringed out in the video. What I like about that video its shows a great maintenance procedure that all Manual C4s should be using routinely. Also dirty fluid will cause shifting problems

kostas86

Thank you everyone for the feedback. Been a chaotic week/weekend and haven't got to the Vette again. I'll double check, the fluid (I can't recall the color). And just to clarify, when I was forcing the car into gear I wasn't driving, just on my driveway.
Is there a preferred clutch master and slave cylinder that everyone has been purchasing? I have read about tossing in the '91+ slave as the bleed screw is at the bottom (vs older on top) so much easier to bleed. If that's the case and no other modifications are needed, I am assuming better to go this route and reduce the amount of swears and headaches lol.

Yukon Corleone: Unfortunately I do not know any shops or have a preferred one yet for the Vette. When I replaced the waterpump and belt, I took it to the dealer as they only wanted slightly more than everyone else and included loaner.
I was debating on tackling this repair as the master cylinder appears to be fairly straightforward and the slave not too bad also.

jsmn4vu

Further on my earlier -- if there is no leakage apparent and the fluid is not low, the problem is either the master cylinder or air in the system. If you replace it, I'd go ahead and replace the slave, too.

Daniel_Mc

kostas86,

Regardless of the mileage the car is still 26 years old. My gut is that the master or slave is gone however I do not agree that you need to replace the parts. The "new" stuff is junk. Have your OEM master and slave rebuilt by Jim at Power Torque Systems it will save you in the long run.
http://www.powertorquesystems.com/
The aftermarket slaves have a thicker flange and about 1/2 of an inch longer length this will cause you to remove the 1-4 skip module from the trans to remove or install. The OEM unit will fit no problem. Plus MUCH better quality material. I am servicing a buddies ZR-1 now and the Chinese junk slave rod snapped causing his failure. Also this is not a difficult repair to do yourself. The toughest part is getting under the dash to remove the clip on the end of the rod for the master.

-Daniel

maddogwyatt

I've had this where it's not yet bad enough to stop you engaging gear, but within a few seconds the clutch starts to engage and drive the car away even though you still have the pedal to the floor. it's quite exciting!!