Troubleshoot my clutch hydraulic issue (nv3500)

Discussion in 'Transmissions' started by 4wheelsteering, Aug 8, 2018 at 11:01 PM.

  1. 4wheelsteering

    4wheelsteering Newbie

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    '97 GMC K1500, have only owned since May. It has 180,000 km on it so I didn't expect issues like this.

    I started having a problem where the clutch pedal would go soft and I'd lose the clutch intermittently. It would work after pumping the pedal a lot - sometimes over 100 times to get started, and I was pumping constantly at every red light and stop sign. At one point, I was even pumping between gears because 3rd gear synchro isn't good enough to powershift into 3rd.

    I took it in. Mechanic said it's either the master or slave cylinder, and being an internal slave let's do the master first. Ok, makes sense to me. He replaced the master and the truck drove perfectly for two weeks, but now it's back to the same problems. Not quite as bad yet, I only have to pump ~30 times before I start driving and a few times per stoplight.

    Can a new master cylinder fail that quickly, and if so is there something else causing it?

    If it's the slave, why did replacing the master fix the symptoms for two weeks?

    Thanks...
     
  2. gstubbz

    gstubbz Hi I'm Gavin and I have an OBSession

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    I would place bets on the slave cylinder. 9 times out of 10 when I have a problem with a clutch it ends up being the slave cylinder.

    As far as the problem being temporarily "solved", it's a matter of pressure from the pedal to the slave pushing out the slave cylinder and there very well could have been something wrong with the master as well; I've had my share of problems with them where seals would break and air would get into the system giving me all kinds of trouble.

    Little side note, I had a truck with sub 200k on the odo and constantly had problems from the pedal to the throwout bearing. I literally replaced everything but the slave cylinder last - and it bit me in the ass. On a friend of mine's truck we had a problem where pushing in the clutch pedal effectively did nothing, to the point where it could be not running, throw it into first gear, push in the clutch to start the truck, and the truck would start moving - his problem? Slave cylinder.

    Only crappy part is yours is internal and not external like the pre-95 trucks. The internal slaves do also have a problem where if you get them really really hot, you may get a hard clutch pedal and seem like the throwout bearing isn't doing anything. Not really much you can do with a NV3500, but the NV4500 guys would swap the bell housing to gain an external slave cylinder to avoid this issue.
     
  3. gstubbz

    gstubbz Hi I'm Gavin and I have an OBSession

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    If you're curious, here is what your slave cylinder looks like. I took this photo of a 98 that had a nv3500:

    [​IMG]
     
  4. 4wheelsteering

    4wheelsteering Newbie

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    Welp... that's not good news but at least it's consistent. Thanks!
     
  5. Sparkysikes

    Sparkysikes OBS Enthusiast

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    I always try and replace in pairs I had so many issues finally decided. On auto swap, well that was my final. Excuse! How ever mine was slave and master 3x in 60k miles. It would get fairly firm than blow out. I was told after I swapped it was probably the pivot on my pedal! Luckily mine was external. And I could swap the pair with bleeding in an hour! Good luck with a internal slave. Also mine was NV4500
     

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