Hard Clutch Updates Please

[DmaxCC6spd]

I have just developed the dreaded 6 speed hard clutch pedal syndrome. I did a search on the forum for this issue, but it doesn't seem that there were any definitive solutions. Does anybody have anymore information? I read about heat issues and providing a thermal barrier for the clutch fluid lines and read about dealerships that replaced just about every piece involved with the clutch and none of these seem to produce lasting results. Any more information from fellow shifters would be greatly appreciated. My warranty end is coming in March, but I only have 24,000 miles on the truck!

[CPMac632]

I assume since you just developed it that it isn't the hard pedal syndrome as some have but the kind that involves the TST box in your sig. Usually in this cold weather the only time the pedal will get hard is when the clutch slips. If not and it is just happening on a long loaded drive then you have a severe case of it. If it is the clutch slipping you don't have much chance for help from the dealer. If it's not slipping then I have no idea what it's gonna take to fix yours. Which is it?

[DmaxCC6spd]

I would doubt its the clutch slipping. I only use power level 4 (out of 9) and don't pound on the truck with burnouts and hard shifts. Its been some time since I've driven a vehicle with a slipping clutch, but I think I would know the difference. For reference, why would a slipping clutch make the pedal hard to press? I think we have seen in other posts that boiling fluid should result in a mushy pedal.

[1BADDMAX]

After long trips of 50 miles or more my pedal becomes hard to depress. I have never had any problems and figure it's the nature of the beast.

[DmaxCC6spd]

1baddmaxx, that is how mine started. But more recently, it won't let me downshift. I hope you don't have any worse issue with your truck, but not being able to downshift can be a bit unnerving.

[JMPDMax]

I fixed my hard clutch problem. I've been going to the gym since last June and I can tell you that the clutch is not as hard as it used to be. :D

Although I seriously doubt the heat issue, I did get improvements when I added fluid to the reservoir to top it off. The fluid was at the low end of normal. After adding fluid, the pedal seemed improved.

I still think something (flywheel/disc interface) is getting some type of binding action happening during a long run and that is the real cause of the problem.

Later...

[CPMac632]

DmaxCC6spd for reference I have been trying to figure out why when the clutch slips the pedal gets hard but I am still unsure. I do know that it does get hard every single time the clutch slips with a stock clutch and flywheel. If you change the disc or the PP and flywheel the pedal won't get hard when it slips no matter what. I am not positive of what the issue is but I'm working on it. I just assumed yours could be slipping but sure I could be wrong. When does it get hard, 50 mile trip, when pulling a load, every time you accelerate to pass, or what? Yesterday afternoon you posted you just developed the hard pedal syndrome and this morning you posted the hard pedal syndrome you've had for a while but more recently your truck won't downshift. Which is it?

[DmaxCC6spd]

CPMac632: For some time when making a long trips, the pedal would get hard to press. That was the only problem. Within the last week, I have had 2 episodes when getting off the interstate (20 - 30 minutes drive time)where I could not get the transmission to downshift from 6th to 5th. I pressed the stiff pedal and the shifter felt like the clutch was still engaged and would not go into 5th gear. There was no clashing or grinding of gears. I feel strongly that the transmission is fine. This has happened once while towing and once empty. For reference, I have only towed 9200 LBS once and my usual tow is about 5500 LBS. Normally the truck is loaded only with a 700 LB mower. Very little time is spent towing. For a truck that is rated to tow about 15,000 LBS, I would say the truck has had a relatively easy life. It seems that there isn't a solution from GM which leads me to believe that it is a design flaw. Does anyone offer a solid flywheel type clutch assembly for our trucks yet? It would be nice to see what effect this has on the problem rather than the GM assembly. Any word on this topic from DuraMaxAllyTech?

[DeepVee]

I think CPMac632 may be right about the factory clutches slipping. I have an 8.1L/ZF truck and recently took it in for transmission noise and the hard pedal. The tech at the dealer determined the noise was a bad bearing in the tranny. He tore out the tranny, replaced the input shaft (pitted gear), two bearings (scoring), slave cylinder/throwout bearing (pedal pressure), pressure plate and clutch disk. The clutch disk and pressure plate was replaced because the plate was heat checked and cracked on the outer diameter. Again this is an 8.1L truck and does not have a dual mass flywheel. I was surprised to see the cracked pressure plate. This truck has 30,000 miles on it and although I tow a lot I seldom tow over 5,000 lbs. Anyway, I got the truck back, the tranny seemed fixed but soon started making the noise again. The noise was now off and on unlike before when it would make the noise all the time. I noticed if I romped on the truck the noise seemed to go away for awhile. This gave me the impression that the noise may be coming from the new clutch that needed to be seated and maybe this was the root of the original problem since my original clutch appeared to have also been slipping. The tranny now makes the noise pretty regularly; anytime the drive train is loaded up. I've seen the insides of the ZF and find it hard to believe my tranny has an internal problem. I really think GM under-clutched these trucks, causing the clutch to slip and pumping heat into the slave cylinder and fluid.

[CPMac632]

DmaxCC6spd I assumed that you just developed the problem (like you stated) and with the current season being winter I made a wrong guess. I am the only one I know working on solid flywheels and have a few in working order. Like I stated before if you change the disc in the factory setup it will no longer make the pedal stiff when slipped and if you change the flywheel and pressure plate (you have to change them both because the dual mass isn't a flat flywheel) and use the factory clutch disc the pedal no longer gets hard when slipped either. When your pedal gets hard does it return to normal pressure after depressing it once?

[DmaxCC6spd]

CPMac632: The pedal pressure returns to normal after one or two cycles of the clutch. Has anyone contacted Luk or one of the other companies about a beefy replacement. CPMac632, you stated that you were working on a flat flywheel. Do you have more details?
If I am hearing you correctly, the hard pedal is due to slipping. Surely there is no slippage of the factory clutch when running unloaded on the interstate. I seem to recall some of these symptoms before I installed the TST box. Just some more thoughts. I would really like to see some "normal" clutches available for this truck.

[CPMac632]

Luk is the mfg. of the factory unit. I don't have many details on the flywheel I am working on but it should be done in 2 weeks and then will let everyone know. Slipping is one way to make the pedal hard but I know it can happen on long hauls without the clutch slipping. I don't know what exactly is causing either one. I assumed yours was slipping because it seems the cooler weather helps the problem on the long haul stuff and since you said you just developed the problem.

[Jelisfc]

When you guys think the clutch is slipping is it real obvious to you? After much thrashing my big block 4x4 would slip the clutch. Increased rpm with no gain in mph. I've thought my Dmax has slipped here and there but a split second not a definate slip.

[DeepVee]

So far I've not seen any clear signs of slippage, i.e. bump in RPM's, but something in the system is pumping heat into the clutch assembly. To me the most obvious answer is clutch slippage, especially with the chatter noises I'm hearing from my setup. Again, I don

[CPMac632]

DeepVee is the pressure plate very similar in the 496? How about the flywheel, I figured it may have a dual mass but hadn't ever looked?

[DieselsRule]

Just doing some research here but here is how I solved mine call a lawyer --- Lemon Law got everything back but about 1600 hundred dollars. I did not pay the kind of money that these things cost to put up with that especially after the clutch pedal broke on the factory rep test drive. Used the money to get the other half a Z71 Burb. I guess I'll follow the advise the dealer gave me the first time when I ordered my 02 and get the alli. My truck was back a total of 10 times with everything replaced. It seemed the more that was replaced, the worse it got. I was not putting up with a band-aid fix attempt which is what I got.
Flush fluid, wrap line, replace clutch, pressure plate, replace slave cylinder, replace master cylinder, install non OEM cooler, try Dot 4 etc etc The problem is the clutch binds releasing when it gets hot. Prove it by next time bumping it out of gear w/o the clutch after a good long hard drive and just see how easy (not) it is to get it back in gear.
Don't get me wrong,I loved my D-Max and can't wait to put another one in the garage. Next one will be an alli. I had hoped that this had been resolve already but I guess not. I prefer to drive a stick.

[ 01-25-2004, 06:40 PM: Message edited by: DieselsRule ]