Dangerous C4 Clutch Problem
Thread Starter
Navigator
Joined: Mar 2008
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Dangerous C4 Clutch Problem
I started 1990 in neutral, depressed clutch, but couldn't get car in gear. I kept pumping clutch, but car still would not go into gear. I was attempting to put the car on my lift to check out the problem. Suddenly the car shot forward! I had my feet on the brake and the clutch peddle to the floor, but the car kept going! It went onto the lift, forward over the front diamond plate braces, under my work bench and stopped at the wall because it finally stalled!!! Thank goodness nobody was standing in front of me!
So now I investigate. From reading the shop manual I figure it could be the clutch actuator or slave cylinder. So I go through the process of draining, replacing, refilling, and bleeding the slave cylinder. The clutch feels good and tight. I start the car in neutral, but it won't go in gear. Since I'm scared to death to repeat the previous incident, I don't want to start it in gear.
Any ideas? Thanks.
So now I investigate. From reading the shop manual I figure it could be the clutch actuator or slave cylinder. So I go through the process of draining, replacing, refilling, and bleeding the slave cylinder. The clutch feels good and tight. I start the car in neutral, but it won't go in gear. Since I'm scared to death to repeat the previous incident, I don't want to start it in gear.
Any ideas? Thanks.
Le Mans Master
Joined: Oct 2007
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From: Akron Ohio
2025 Corvette of the Year Finalist - Modified
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St. Jude Donor '09-'10-'11
Did you say you actually replaced the slave or just looked at the procedure? I just replaced the master and slave on mine and had a similar issue after bleeding it. I went to start the car in neutral in my driveway and could not get it in gear with the engine running. I had a goo pedal feel, and before a let the car down off the jacks I was able to move a tire with the car in gear and someone pushing the clutch, so i knew it was disengaging. I went ahead and started it in gear. It moved a little bit, very slowly and then stopped. I was able to drive up and down my driveway working it back and forth from reverse to first with no issues.
If you only replaced the slave and still have a soft pedal, look inside the car by the pedal for fluid. If the master cylinder is bad it will leak into the car, not on the outside. Make sure before you start the car or let in down that you are able to rotate a tire when the car is in gear and the clutch is pressed. If not then you have more bleeding to do.
If you only replaced the slave and still have a soft pedal, look inside the car by the pedal for fluid. If the master cylinder is bad it will leak into the car, not on the outside. Make sure before you start the car or let in down that you are able to rotate a tire when the car is in gear and the clutch is pressed. If not then you have more bleeding to do.
Le Mans Master
Joined: Oct 2007
Posts: 9,659
Likes: 3,358
From: Akron Ohio
2025 Corvette of the Year Finalist - Modified
2024 C5 of the Year Winner - Modified
2023 C5 of the Year Finalist - Modified
2022 C5 of the Year Finalist - Modified
St. Jude Donor '09-'10-'11
Try pushing it to someplace where if you start it in gear it wont hit anything. Keep in mind it might move. Start it in gear and drive one way or another and try changing directions then.
Did you try spinning a tire while it was in the air?
Did you try spinning a tire while it was in the air?
Team Owner
Joined: Mar 2001
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From: Boston, Dallas, Detroit, SoCal, back to Boston MA
You've seen this right?
http://www.zfdoc.com/CHS_Actuator_Seal_Fault.htm
http://www.zfdoc.com/CHS_Actuator_Seal_Fault.htm
We found the cause of the problem of which many C4 ZF Clutch Hydraulic Systems were having operational problems during the last several years. As of June 2008, GM discontinued selling both the master and actuator cylinder. The actuator (slave) cylinder seals have been installed backwards during manufacturing assembly. We disassembled three brand new slaves and all had the seal installed backwards.
Le Mans Master
Joined: Oct 2007
Posts: 9,659
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From: Akron Ohio
2025 Corvette of the Year Finalist - Modified
2024 C5 of the Year Winner - Modified
2023 C5 of the Year Finalist - Modified
2022 C5 of the Year Finalist - Modified
St. Jude Donor '09-'10-'11
The one I got was recommended by Bill to get from Rock Auto. It was the Dorman unit. Part number CS360017. It is a cast unit not DOM and comes with a lifetime warranty.
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From: moraga ca
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Team Owner
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You can't get the car in gear because your master/slave is not disengaging the clutch, but when you pumped it up, it disengaged the clutch, went into gear and then suddenly let the clutch out and off you went. You need a new clutch master and slave cylinder.
Thread Starter
Navigator
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The 1990 clutch problem is now resolved! After replacing both the slave cylinder and the master cylinder, bled the lines, started the car with the back end jacked up, all seems to be working well. We took it out for a test drive, and it shifts better now than it ever did! It took quite awhile to get the parts, and three weeks later, we are very satisfied. Thanks to all for the excellent suggestions.
