Hydraulic clutch problem 1996 C4 corvette
 

I'm a new member of Corvette Forum, but not with Corvettes. I presently own a 1958 Corvette which I've had for over 40 years and a 1977 Corvette which I've had for 21 years. Both of these Corvettes have manual 4 speed transmissions and over the years have replaced clutch and pressure plate several times in both. I have an extensive automotive background and I’m a engineer. I'm in need of a second opinion concerning my recent purchase of a 1996 Corvette with LT 4 engine and ZF six speed manual transmission, mileage is 79,750. The problem is with the hydraulic master/slave cylinder system. When I depress the clutch pedal to start the engine I hear a noise coming from the bell housing. The noise sounds like the clutch arm is hitting the back of a pressure plate and not a throw out bearing growling noise. When I release the clutch pedal about half an inch the noise goes away and everything is fine. I can shift the transmission with no noise or problem. I've inspected both the clutch master cylinder and slave cylinder for leaks, neither are leaking. When I checked the clutch master cylinder reservoir I noticed the clutch fluid was black and metallic looking, indicating extensive wear. I flushed and replaced the DOT 3 fluid in both master cylinder and slave cylinder which did not correct the problem. Since the hydraulic clutch system does not have any adjustments. I think I need to replace both the clutch master cylinder and slave cylinder because of wear and metallic looking fluid. Before I remove the transmission and bell housing to inspect the clutch arm, pressure plate and clutch components, let me know what you think the clutch problem is ?????

1996 LT4 clutch
 

I had the same noise in our '96 LT4. It turned out to be the pivot ball in the bell housing that the clutch release fork pivots on. The ball works it's way toward the flywheel, and the clutch fork actually hits on the pressure plate when the pedal is pushed to disengage the clutch. I replaced the clutch, throw out bearing, flywheel, pivot ball, pilot bearing while I was in there. Now it's nice and quiet! I don't know if you could just take out the bolts in the trans and swivel it to gain access to the pivot ball, and take an allen wrench and turn it back to it's original position? I had 69,000 miles on our LT4 when it happened, so I thought while I had to tear it down that far I might as well replace everything since I wanted to repair this just once! When I replaced the pivot ball, I put some Lock-tite red on the threads so it won't back out ever again. Fix this now--it will only get worse!

Same Here.That's exactly what has happened.GM forgot the Locking set screw for the ball on my 95'.Might put a new clutch disc in while your there.

Same with mine, except my noise started after some hole in the wall mechanic shop replaced my slave cylinder with a stock GM one. I believe the push rod in the slave cylinder is too long thus causing the fork arm to hit the pressure plate as its spinning. I finally figured it out when another mechanic replaced my clutch thinking it was that and saw the scoring on the inside of the bell housing from where the fork was hitting.