I recently installed a solid mass flywheel conversion in my ZF-6 equipped Duramax, The problem I am having now after 4000mi is that while pulling a mild load in 6th gear when i depress the clutch to down shift it feels like nothing is there, and i am unable to remove from gear. This is untill I pump the clutch, having to depress and then lift the pedal with my toe. WTF is going on. Plenty of fluid in resivior, no leaks, or air in the lines.

HELP PLEASE, I am at my wits end with this.

I honestly don't know but if memory serves me correctly, in the past people that had these issues some would say the clutch is on it's way out.

Who's kit did you use? Did you replace the clutch at the same time?

Usually Its the flywheel going south, but if you have a solid flywheel and not a dual mass now im stumped!

Clutch fingers or throw out bearing....either way its gotta come out to check/fix...

South Bend every thing was new installed at the same time, some one at work suggested the clutch master cyl, not the slave.

any luck finding out.... did you try to bench bleed the master??

Sounds like typical single disk sixth gear slip. Drop a gear and keep the revs up, and it should be fine. Or turn down the power.

Last I talked to Peter he was working on developing a new PP for the single disk guys. Might give him a call and see what's what. The stock Luk just doesn't have the clamping force to hold extra power in high gear, especially if you let it drop revs...

No slip, that can be felt at all. But on saturday I went to a tractor auction and bought 2 70hp tractors, and while hauling them home on stock level it happend again. It does not matter what gear I am in. It only does it while pulling a load, and after maybe 45-60 miles. I'm starting to think it may be the slave cyl getting hot and bleeding off, but no loss of fluid that I can see. Maybe its bypassing?

have you ever replaced the lines from the master to the slave. I know gm has control check balls in the cars to keep the fluid from slamming thru. could be that these are getting stuck?? did you change the fluid when you changed the clutch??

I had the same problem a while back, and I was told to put DOT4 fluid in because of the boiling point. The DOT3 has a lower boiling point, and can get past the master cylinder plunger, because of the extra heat from pulling a load.
Here is a boiling point chart.
Dry Boiling PointWet Boiling PointDOT 3401ºF284º F
DOT 4446º F311º FDOT 5500º F356º FDOT 5.1518º F375º F

That chart didn't come out right.
DOT3 will boil at 401deg.f
DOT4 at 446deg.f
DOT5 at 500deg.f
DOT5.1 at 518deg.f

These are dry boiling points.
Wet boiling points;284, 311, 356, and 375.

Hydraulic Clutch System (6–Speed Trans.)
Hydraulic Clutch Fluid. Use only
GM Part No. U.S. 88958860, in
Canada 88901244, Super DOT-4
brake fluid. <-- I think it says dot-4 on the little bottle where you fill it up too.

For what it's worth, my clutch pedal goes a little limp on long cruises and won't feel normal until I pump it a few times. Does it empty or under load. Some guys install a fluid cooler and pump to help with the situation. Have you asked for help from South Bend? Maybe they can point you in the right direction since they're the clutch experts.

For what it's worth, my clutch pedal goes a little limp on long cruises and won't feel normal until I pump it a few times. Does it empty or under load. Some guys install a fluid cooler and pump to help with the situation. .

that is what mine does.

Mine will stick if I have the tuner on a higher setting and push it really hard but I slip my foot under the pedal and pull it back and its fine as long as I don't keep the go pedal to the floor.

Mine will stick if I have the tuner on a higher setting and push it really hard but I slip my foot under the pedal and pull it back and its fine as long as I don't keep the go pedal to the floor.


Be careful pulling the peddal back, there is a plastic bushing/keeper in the pedal assembly, that holds the master cylinder shaft. If it breaks, you can't just buy the bushing, you have to buy a clutch pedal assembly. The clutch will still work, but it will pop every time you depress the peddal, and will come up a little higher than normal. I think some of the master cylinders come with the bushing also.

Be careful pulling the peddal back, there is a plastic bushing/keeper in the pedal assembly, that holds the master cylinder shaft. If it breaks, you can't just buy the bushing, you have to buy a clutch pedal assembly. The clutch will still work, but it will pop every time you depress the peddal, and will come up a little higher than normal. I think some of the master cylinders come with the bushing also.

Thanks for the warning! I usually just pull it back to where its normal resting place is and I never have had to force it back.

Just thought I would throw that in there. That is what happened to me, and that popping noise will drive you crazy, and I'm not talking about the popping noise that is heard at about 10:00 A.M., on Monday mornings.