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Well its been a couple months since I had the flywheel changed out and the clutch pedal got stiff on me yesterday again. Had cruise control on set at 65mph and on the highway about fifteen miles, approached the exit ramp and went to push the clutch in and it was really stiff. I am calling the dealer today and will keep you all posted. If anybody has additional info please let me know what you all think. Thanks
 

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My new one has been in for 2 months. Last weekend I pulled my 5K trailer. The clutch was a bit stiff but not like before. Nothing you can really do with a stock flywheel.
 

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Have you guys had a problem with the clutch slipping when this happens? A friend of mine has had this happen when he was pulling up a grade and the EGT's went to 1000 or 1100. The dealer said it was hydrolocking and put a transmission cooler on it and it hasn't helped it.
 

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Have you guys had a problem with the clutch slipping when this happens?quote]

It will do it when it slips in extreme conditions. The hard pedal is a sign of the clutch getting ready to slip due to too much power. My pedal would get hard when I would put almost too much power to it and would stick to the floor if I did slip it. Thats what I have seen and seen a lot of with my truck before my SMF. Now its all behind me as well as the dodge and fords!!:ro) :lol:
 

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Do you think this is all due to the DMF? This is at stock power levels.
 

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It will do it when it slips in extreme conditions. The hard pedal is a sign of the clutch getting ready to slip due to too much power. My pedal would get hard when I would put almost too much power to it and would stick to the floor if I did slip it. Thats what I have seen and seen a lot of with my truck before my SMF. Now its all behind me as well as the dodge and fords!!:ro) :lol:
:exactly:
Do you think this is all due to the DMF? This is at stock power levels.
Yes....the DMF is the total problem....it is a POS.
 

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I think Peter said it is more the PP that ratchets back when it has power (even stock power) put to it and pushes the SC back and makes the first push of the pedal a hard one. Some use to think it was just build up of heat and the SC was hyrolocking so many people tried tranny coolers and it still didn't help much if any. I could start my truck up and go 50 feet and stand on it and get a hard pedal so to say heat is the main and only factor in my mind is BS because there is no way in 50 feet and just a short quick jab of the throttle could not generate enough heat to hyrolock DOT 4 brake fluid which I think has an over 4000* F boiling point.

As far as the DMF making the clutch slip I don't know for sure I have my own thoughts on it but am not sure. I would rather someone who has more details about it to say something rather than putting my foot in my mouth. My .02

Hope it helps
Nathan
 

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Duramax Farmer, that is the most logical reason I've heard yet. Thanks!
 

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just is dissapointing that gm corp. doesn't do a thing about it. build the bell housing a little larger so you could use a off the shelve hd clutch,bigger diameter flywheel and put the slave cylinder on the out side of it again and give you some ajustmen. every one wants a pickup to be as comfortable as a car and when the 1% go out and really use them and it doesn't work gm gives you the "you should of bought an allison" I guess I live in OZ.
 

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Here is what we have come to learn about the hard/sticky clutch pedal.

The DMF is a two piece flywheel and the primary is bolted to the crank. The secondary is held by tin plates and springs to the primary. The pressure plate is bolted to the secondary. When under hard load or acceleration, the secondary part of the flywheel separates from the primary. When this happens it moves the secondary portion of the flywheel with the pressure plate towards the transmission. The hydraulic throw out bearing rides on the fingers of the pressure plate at all times. When the pressure plate starts to move towards the transmission, it forces the throwout bearing backwards moving the fluid in the hydraulics to the reservoir. The silver cylinders in the hydraulic lines act as check valves and try to stop the fluid from returning to the reservoir at the wrong time thus creating the hard pedal.

I hope this helps.

Peter
SBC
 

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thanks for the explaination, takes alot of the mystery out of it. we have not had the hard pedal problem but, if the person was experiencing the hard pedal and completely released the pedal wouldn't the fluid travel back up to the resevoir? and the hard pedal would go away? at least for that episode . one other question. on the stock clutch cover with the built in auto ajustment does it only adjust tighter ? can you reset the adjustment if you replaced just the disc? thanks
 

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thanks for the explaination, takes alot of the mystery out of it. we have not had the hard pedal problem but, if the person was experiencing the hard pedal and completely released the pedal wouldn't the fluid travel back up to the resevoir? and the hard pedal would go away? at least for that episode . one other question. on the stock clutch cover with the built in auto ajustment does it only adjust tighter ? can you reset the adjustment if you replaced just the disc? thanks

When the pressure plate adjusts itself, the ratchet system turns counter clockwise moving the casting towards the flywheel/disc to accommodate the ware in the material on the disc. What you ask can be done. However, it can be a little tricky. The fingers of the pressure plate have to be pushed in like the clutch would be released and at the same time, rotate the spring loaded plastic tabs in the top of the cover clockwise all the way. Then, while holding the position, release the fingers on the pressure plate. Bolt/install the clutch as normal and once you operate the clutch hydraulics (pump the clutch pedal) after complete install the pressure plate will set itself to the proper position.

Peter
 

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thanks for the info!!!!!!!!!!!
 

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FYI, I have an 8.1L/ZF truck which has a single mass flywheel. My clutch will do the same thing, pedal gets stiff after long freeway travels. I'm on my third GM clutch assembly and slave/master with 58,000 miles, occasional towing of 5,000 lbs. My clutch pedal will do the typicall "stiff" stuff until it gets to the point where it seems the slave is bleeding pressure off, failure, then it flip flops and the pedal gets soft after long freeway trips.

My only assumption now is that this is a heat related issue and the heat eventually kills the seals in the slave cylinder causing it to bleed off.

So where is the heat coming from?
transmission case?
slipping clutch?

GM replaced my first clutch due to a heat checked and cracked pressure plate. Clutch #2 was replaced by GM when it failed to disengage the clutch but everything looked OK when it came out. Clutch #3 now needs a new slave & master due to a soft pedal.

My next clutch will not be a GM unit, I'll go to South Bend.
 

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Here is what we have come to learn about the hard/sticky clutch pedal.

The DMF is a two piece flywheel and the primary is bolted to the crank. The secondary is held by tin plates and springs to the primary. The pressure plate is bolted to the secondary. When under hard load or acceleration, the secondary part of the flywheel separates from the primary. When this happens it moves the secondary portion of the flywheel with the pressure plate towards the transmission. The hydraulic throw out bearing rides on the fingers of the pressure plate at all times. When the pressure plate starts to move towards the transmission, it forces the throwout bearing backwards moving the fluid in the hydraulics to the reservoir. The silver cylinders in the hydraulic lines act as check valves and try to stop the fluid from returning to the reservoir at the wrong time thus creating the hard pedal.

I hope this helps.

Peter
SBC


:exactly: :exactly: :exactly:
That should clear things up for alot of folks!!!!!
 

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I must correct my earlier post upon quizing my 80 year old dad he finally said that while pulling his house trailer, only on this trip, the pedal got hard . but it was at least a hundred miles after he pulled the only grade. he said he was slowing down to pull off into a rest area. pedal was hard an half way to the floor before it did anything. I still think it is a heat issue in my case. I think his clutch was started slipping on the grade, found out he was in OD pulling the hill just so he could tell his buddies he pulled cabbage hill with trailer on in OD. told him bragging rights cost him around $1800. (for new flywheel and clutch at gm) I have been reading all the threads I can absorb on this issue and I hear what is being said about the seperation of the DMF under pull making the pedal hard and I can see. if this is the only explaination for the hard pedal then it should not be happening under coasting or deceleration should it? and what about the SMF in the gasser rig having the same issue. Did anyone (GM,FORD,DODGE) use these one way check valves in the hydrolic clutch system before? I don't remember seeing them on our 87 6.2. our 87 would always loose the pedal after a long hard pull with a load it did not get hard to push and would come back if you gave it a break to cool.only replaced the clutch once in 145k. sorry for running on, and on and on.
 
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