Clutch pedal won't move.

[blacksheep4x4]

Well I took my Megacab down to Riverside CA two weeks ago. All was good until the clutch pedal started acting up. It seems to only happen when I accellerate hard or get up to 80mph. Pedal won't push in and can not get truck out of gear. I had to pullover turn truck of pull transmission out of gear and force pedal down and pump several times before it would free up. Doesn't give me any problems if if I accelerate slowly and keep it under 75mph.

Any thoughts? I am thinking it may be a bad throw out bearing ,but it does not make any noise. Could the clutch already be shot? Only 20,000 miles on the truck. Thanks, in advance.

mike

 

[jelag]

There's not enough information to make an informed decision as to the problem... .



1 - is the pedal hard??..... 2 - If you let up on the accelator will the transmission slide out of gear?? if not... . does it feel like it's stuck??



Throw out bearings usually fail and nothing happens except the pedal will move up and down and nothing happens..... the bearing has fallen apart from lack of grease, usually caused by heat... . excessive heat melts the grease out of the bearing and it fails...



A hard pedal or no pedal movement usually means something is bound up in the clutch assembly and the cover won't release... there is a plastic sleeve on the release bearing that floats on the input shaft colar... . if this has melted from heat... . than cooled it could cause it to stick...



On the other hand with what you've done to the engine... . You could have easily slipped the clutch, caused it to overheat... . and this would cause the grease in the pilot bearing and release bearing to run out... causing both bearings to fail... all kinds of things... .



Since you are your own warranty station after all the modifications... . just take it apart and tell us what you've found.....

 

[RobertP]

mine does it all the time your clutch is slipping so bad that it welds it self to the flywheel and you have to force it back in a few times then its back to normal. i had to turn my box off tho keep this from happening.



it did go back to normal once you pumped it a few times right?



then as long as you dont romp on it hard in 5th or 6th gear it wont do it again.

 

[GCroyle]

Does the clutch slip under power?

 

[ENafziger]

I agree with RobertP. Your clutch is slipping and glueing itself to the flywheel. My truck does the same thing. Try driving around with the chips off, and I bet you won't have any problem. With these G56 transmissions and dual mass flywheel/clutch, it isn't as obvious when the clutch is slipping... at least until you try to change gears! If you pump the clutch pedal about 4 times, the clutch disc should pull free from the flywheel.

 

[RobertP]

you can hear and feel the clutch slipping after about 40 plus times of over heating it. i can feel mine slipping now but at first it would just glue itself to the flywheel and i would have to stomp on the clutch pedal to get it to release.

 

[South Bend Clutch]

blacksheep4x4,



This is a common problem in trucks equipped with dual mass flywheels (DMF) designed by Luk. The Chevy Duramax has the same issues. Both trucks, yours and the Duramax have the same design just different sizes. Here is what is going own to the best of our knowledge.



The way that they put these flywheels together is with tin plates and springs holding the primary (part that bolts to the crank) to the secondary (part that the pressure plate bolts to). Under hard acceleration especially when HP has been added to the trucks, the flywheel over rotates and starts to separate. When this happens, the secondary part of the flywheel where the pressure plate is bolted moves towards the transmission. This action causes the throwout bearing to begin to move towards the transmission as well. The hydraulic fluid starts to travel back to the resivour. In the hydraulic line there is a silver cylinder that we refer to as a check valve. When fluid is being forced through it in an untimely manner (prior to clutch depression) the valve shuts down stopping any fluid travel setting up the fluids on either side of the valve improperly. The hard pedal is the caused from the valve being closed and the pumping of the pedal resets the fluid in the line. We have found that once we replace the DMF with a solid flywheel in the trucks equipped with this setup, the problem goes away.



This is only our opinion and we may be incorrect.



Peter

 

[RobertP]

thanks peter. you explained that much better than i could ever. but that is 100% correct in what is happening or at least the feeling that i am feeling. as soon as i can save some money i will get the con fe setup from you.

 

[blacksheep4x4]

mine does it all the time your clutch is slipping so bad that it welds it self to the flywheel and you have to force it back in a few times then its back to normal. i had to turn my box off tho keep this from happening.



it did go back to normal once you pumped it a few times right?



then as long as you dont romp on it hard in 5th or 6th gear it wont do it again.

Thats is exactly what is happening. I guess it's time to call Southbend!

 

[blacksheep4x4]

blacksheep4x4,



This is a common problem in trucks equipped with dual mass flywheels (DMF) designed by Luk. The Chevy Duramax has the same issues. Both trucks, yours and the Duramax have the same design just different sizes. Here is what is going own to the best of our knowledge.



The way that they put these flywheels together is with tin plates and springs holding the primary (part that bolts to the crank) to the secondary (part that the pressure plate bolts to). Under hard acceleration especially when HP has been added to the trucks, the flywheel over rotates and starts to separate. When this happens, the secondary part of the flywheel where the pressure plate is bolted moves towards the transmission. This action causes the throwout bearing to begin to move towards the transmission as well. The hydraulic fluid starts to travel back to the resivour. In the hydraulic line there is a silver cylinder that we refer to as a check valve. When fluid is being forced through it in an untimely manner (prior to clutch depression) the valve shuts down stopping any fluid travel setting up the fluids on either side of the valve improperly. The hard pedal is the caused from the valve being closed and the pumping of the pedal resets the fluid in the line. We have found that once we replace the DMF with a solid flywheel in the trucks equipped with this setup, the problem goes away.



This is only our opinion and we may be incorrect.



Peter

Your explanation does sound very good, and I have contacted you before about the price for a new single mass flywheel and clutch kit. I guess I will be contacting you to puchase that kit.

thanks, Mike

 

[blacksheep4x4]

Since you are your own warranty station after all the modifications... . just take it apart and tell us what you've found.....

Even though my truck has mods my dealership still upholds the warranty.

This is the very reason I have bought three trucks from them in a one year period.

 

[RobertP]

i had my first clutch replaced under warranty. but it helps im my own service manager. :-laf

 

[blacksheep4x4]

Well the south bend is going in to the truck. It should be done tomorrow. No more dual mass flywheel for me! I can't wait to feel the power now that my clutch won't be slipping.

 

[ENafziger]

Did you go with a single or double disc?

 

[JGheen]

Keep us updated on this Blacksheep, as I am interested to find out your results from going to a solid flywheel design. Any install issues or short cuts that you found let us know as well.



Thanks, Joe

 

[blacksheep4x4]

I went with the dual disk. The install took about 9 hrs. All the new clutch parts were very nice. I was very impressed with SBs product. Things I don't like about it. Clutch pedal is very stiff, I hope it will get easier with time. When truck is in neutral I get a very noticible rattle from the transmission. Clutch is touchy when letting it out to take of in second gear. truck doesn't seem ready to go like the stock set up. With the stock clutch you could let the clutch pedal out and with no go pedal the truck would take off fairly smoothly (probably due to the dual mass flywheel). Not so now, the clutch slips ( not really slipping but thats the only way I can descibe what I am feeling) a bit and truck almost dies if you don't step on the go pedal. This clutch will also let you know when you're in the wrong gear at certain RPMs. If you don't have enough RPMs for the gear you're in it will chatter something fierce. With the stock clutch I could let the truck idle down to about 1000 RPMs before it started to complain. The SBC likes 1400 RPMs. What I do like about it. Dump the clutch and hit the pedal hard and the truck takes off like a rocket. It'll even lay a 5' patch of rubber when shifting in to 3rd. Stock clutch was slipping to bad to do this. You can deffinitely tell this clutch will not slip when you put the power to it. I think that once I get use to it and relearn how to drive my truck I won't have any complaints. Next year I plan on thrashing this clutch at the Yellowstone drag strip, so I will have more of an idea as to what this clutch will be capabile of. In the mean time I will be pulling quite a few trailers with it.

 

[JGheen]

Clutch pedal is very stiff, I hope it will get easier with time. When truck is in neutral I get a very noticible rattle from the transmission. .

Typical characteristics of a double disk clutch. It will make all sorts of noises with the clutch pedal to the floor, with it in neutral, maybe driving down the road and shifting. Pedal pressure is definately normal as well, I guess a common phrase to use would be "you'll get a feel for it. " :-laf



Joe

 

[ENafziger]

Did you install the hydraulic upgrade as well?

 

[blacksheep4x4]

Did you install the hydraulic upgrade as well?

Yes, we upgraded the Hydraulic slave cylinder. Which is why I was so surprised at how stiff the pedal is. The new slave cylinder is huge!!!

 

[JGheen]

Doh! My bad, thought you didn't get that upgrade, which does make it interesting that the pedal is stiff with the stronger hyrdolics.



Joe