V8Torrent

Hello everyone.

I'm facing a very weird clutch problem.

The car works fine if normally driven, but when I push a little more, the pedal feel becomes soft and clutch doesn't disengage.

The weird part is, if I put the car in 5th gear (4.10:1 diff) and pick up speed, even gradually, after a short period, the pedal becomes soft and can't shift. If I start pumping the pedal, nothing happens, but after a minute or so, I pump it a couple times and works. I keep driving normally and the pedal feels totally normal. Also If I floor it on 3rd, shift hard to 4th, keep accelerating... then I can't shift into 5th and again I have to wait a minute for it to react.

I have just replaced the master cylinder as it was leaking and I thought it was the problem, but same thing happens with the new one.

elephantrider

iTrader: (2)

you may have gotten a bad master cylinder, or you haven't gotten all
the air out of the lines. could also be a bad slave. is it leaking under
the car anywhere ?

i would start with a solid rebleed of the system, and go from there.

V8Torrent

I have tested the new master cylinder disconnected from the slave and it seems to work fine, I block the line with my thumb and can barely hold the pressure when my friend pushes the pedal. We have also made our best effort for the bleeding, put new fluid, bleed it until only new fluid comes out of the bleeder and then some. No leaks anywhere.

elephantrider

iTrader: (2)

a soft pedal can really only be two things. an issue with the master, or
an issue with the slave / tob assembly. if you've bled it and sure there is
no air in the system, that narrows it down to one of the two issues above.

if you tested the master, then it has to be a slave / tob issue.

Darth_V8r

iTrader: (4)

Are you getting full pedal height return between shifts? If not, you might not be moving enough fluid to disengage. If you didn't do the drill mod you might need to. Also can indicate weak pressure plate springs or the adjuster mechanism if the clutch is still stock.

FWIW, don't rule out the master as ok, because it's new. I went through three in less than a year. Many people end up having to upgrade to a tick unit to fix the shifting issues. That combined with a decent aftermarket clutch like a monster will do wonders for your shifting. The stock unit is barely adequate for the stock clutch, and that's debatable. That stock F body clutch was designed as much to protect the Barbie 10 bolt from the destructive force of the LS1/T56 as it was to shift gears. It's very soft on the re-engagement for that reason.

I've been running a tick master and monster S3 for well over a year and 10k miles. I love it, and when I drive someone else's stock clutch, it's always frustrating

MyFirstLS1

iTrader: (8)

Gravity bleeding is key when it comes to slave and mast replacement.

But I agree any hard shifting I did before my tick I had the same issue. the new tick set the car straight. Haven't had any issues......been 4 years since I put it in I believe with a second build shifting at 7100

V8Torrent

Well... after some changes and ideas, I was not able to test the new setting.

During first test the fast connection of the clutch line popped out as the lock was installed backwards, and after correct, re-bleed, etc, etc.. first test and the slave cylinder failed (miserably) while shifting from third to fourth gear.

Jtm2085

iTrader: (1)

Make sure your hydraulics are ran as far away from the headers as possible.

Darth_V8r

iTrader: (4)

Well looks like you may have found the issue. Good job!

V8Torrent

Well, the local market does not include parts for 2004-2006 GTO. But I found the old Silverado, S10, etc, etc. Slave Cylinder was quite similar. Just replaced the feeding line with the one from the GTO and it fitted like a glove. Sadly, local market sells chinese knock offs, but until I get to import a better one (2 or 3 weeks), a $50.- expense doesn't sounds like much...

I installed the new slave last night and went out to test the car. Some air must still be in as it started to slip in 6th gear at about 120mph (4.10 gears). The pedal was harder, but a couple pumps and it felt normal again. Will bleed it again tonight.

Thanks for all the inputs and recommendations. I have double checked the line routing for header and exhaust line clearance and will get some wraping for the exhaust "just in case".

guppymech

iTrader: (7)

Header heat is my thought. If the slave line is close to the headers the increased heat at high power levels could be boiling the fluid but just cruising around not so much heat.