C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Six speed upgrade

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Old 06-26-2024, 12:00 PM
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CaptainJ
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Default Six speed upgrade

Hi fellow vet owners, my name is Jack and I just required a 85 C4 from my boss. He upgraded the motor with a 425hp crate motor then a six speed transmission. After going for a short ride I was having a hard time getting it into gear so I nursed it home and ordered a slave and master cylinder for the clutch and a new line. I have put the parts on bled the system and I’m still not getting very good pedal. I am suspicious of the pressure plate and throw out bearing since I can watch the slave and arm move. So I would like to order the parts before I take it apart but I have been noticing that the clutch and pressure plates are a little larger not sure if these upgrades were done at time of swap. The swap was done around 15yrs ago and the cat has not been driven for 5 yrs any suggestions?
Old 06-26-2024, 12:49 PM
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Gixxerman
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Welcome to the Forum, going to move you out of Introductions to this section for further discussion... Good Luck
Old 06-26-2024, 01:11 PM
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ajp01
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Can you post some pictures of the clutch / gearbox / slave assembly so that we can see what parts you're working with?
Old 06-26-2024, 08:23 PM
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kkupec02
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Old 06-26-2024, 08:35 PM
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AZSP33D
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The hydraulics degrade causing shift issues like you’ve described, especially in reverse (that’s usually where it’s noticed first). If left this way, the transmission will be damaged. Replacing the Master and Slave typically solves the issue, but there can be a few things to look for. First of all, components need to be primed when installed, and then the system is best bled using a pressure pot at the slave, rather than vacuum. Second, the original ZF slaves are no longer available, and some of the offshore replacements are a poor quality. ZF Doc can source the parts to rebuild the original properly if it’s not scored up. Just need some small circlip pliers, such as tru-arc.

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