Six speed upgrade
Thread Starter
1st Gear
Joined: Jun 2024
Posts: 1
Likes: 0
From: Michigan
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?
Moderator
Joined: May 2010
Posts: 15,232
Likes: 4,195
From: Northern Illinois
2023 Corvette of the Year Winner - Modified
2022 C7 of the Year Winner - Modified
St. Jude Donor '18 thru '25
Welcome to the Forum, going to move you out of Introductions to this section for further discussion... Good Luck
Drifting
Joined: Jun 2020
Posts: 1,695
Likes: 728
From: Stay dangerous my friends
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.
