Clutch Not Workin!

Discussion in 'GM Powertrain' started by Luckow, Mar 6, 2011.

  1. Luckow

    Luckow New Member

    I got a 99 chevy 2500 with a 7.4 big block and NV 4200 manual tranny. I love this truck but i've had alot of problems. I was driving it kinda hard and all of sudden lost my clutch, no funny noise or grinding but it just seems like the slave cylinder just isnt pushing far enough, yet if you get under and look seems to be moving the pressure plate springs far enough to where I would think it should be ingaging. It has a new tranny as of 5000 miles ago, whole new clutch pack about 30,000 miles ago and slave cylinder about 20,000 miles ago. Its bad to where to get it home I had to start it in gear. I tried to bleed the slave cylinder think maybe I got air in the line but still no success. The slave master cylinder has never been replaced but when I bleed the slave it seemed to have pressure from that end. Kinda stumped and dont wanna pull the tranny more then once. Any advise or something im over looking please let me know what you think!! Thanks Luckow
  2. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Sounds like the clutch master cyl what it will do is push a enough and then let all the fluid go right by.. I would change it and go from there.. Pretty easy job and only takes about 30 minutes.
  3. stephan

    stephan Rockstar 4 Years 5000 Posts

    Welcome to the GM truck club Lucklow. I'm not convinced that hard driving could cause hydrolic problems in your clutch, but how much travel are you getting? Have a helper get in & push down on the clutch while you measure it. Also watch it closely while they hold the pedal down & see if it is releasing back.. If it is then the pressure is bleeding off & isn't holding it dis-engaged. If the pressure is bleeding backwards, then I would try re-bleeding the system because you could have a small piece of dirt or crud stuck under one of the seals & by bleeding it you might be able to clean it out of there.

    This is what I think your problem most likely is --> Since this happend after some hard driving, you may have bulged your clutch disc to where it is so thick that the pressure plate can not disengage it now regardless of how much travel your slave cylinder is giving it. I had two of these after some burnouts, & high RPM shifting :)
  4. Luckow

    Luckow New Member

    Wow quick responce guys! I'm gettin about 3/4 in of travel at the slave and don't seam to have any bleed by in a few min. hold. Nothing is leaking and master was full when this all happened. I would think with any failure of the pressure plate or clutch plates there would be some noise or something yet this all seams to work great besides the fact it dont work. And how much does a guy bleed threw the system before ya say F it And does anybody know what the correct travel should be cause the pressure plate doesn't look like it could take much more? Thanks for the Help.
  5. stephan

    stephan Rockstar 4 Years 5000 Posts

    ok, if the slave isn't giving up after 3 minutes of holding then the hydrolic system is fine. Actually it only needs to hold the pressure plate in long enough to make the shift & it is certainly doing that.

    When a clutch disc bulges you don't necessairly hear any noise like you would if a pressure plate exploded & pieces & parts were flying around. The friction material on the disc has just expanded (blown up) too much & won't allow the proper clearance between the pressure plate & the flywheel to disengage the transmissions mainshaft so it is staying locked to the engine no matter how much travel you are getting on the throw out bearing. After I popped mine I looked in there & all I could see were a few little shreads of friction material, & every thing looked normal, but it was obvious that the disc had bulged because the pressure plate wouldn't disengage it.
  6. Luckow

    Luckow New Member

    Yep now I got ya, I think what I'm guna do is bein the master and slave seem good I'll just go for the clutch, now being theres not many miles on the clutch does a guy replace the pressure plate also being I'm already there??? The reason I ask is cause GM offers them solo not in a pack like the after market set i bought last time, and in sayin that is there a possible chance that I could have a problem running a GM clutch with a After Market pressure plate??? I don't think I'm gunna take the chance but just seein what U guys think.To be honest with ya I can't believe the clutch did this in about 1 mile of beattin it, I baby this truck for the most part so it pissed me off, I mean isn't that what a Big Block truck with a Hook is for from time to time hahaha. Thanks for the info guys! Luckow
  7. stephan

    stephan Rockstar 4 Years 5000 Posts

    What you should choose depends on how you're going to drive it. I blew up a matched Bork & Beck clutch with my small block & I was only launching 2500 lbs. on a dead level dragstrip. I would definitely replace the pressure plate at the same time. It is little money compared to the labor involved in doing it over again. You should also consider the t o & definitely replace the pilot bearing in the back of the crank unless this is all low mileage stuff. If you replace the clutch & pressure plate with equivelent stuff to what you have now, then you aren't going to be able to rod the snot out of it like you were. My personal prefrence these days would be a Centerforce C & PP. Their PP design puts more pressure inward on the clutch disc at higher RPMs & keeps the clutch disc from bulging so you can run the snot outta your truck occasionally without too much worry.

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