Odd Sierra NV3500 Trans leak. 5 speed

Discussion in 'GM Powertrain' started by defektes, Jan 30, 2010.

  1. defektes

    defektes New Member


    Long time lurker here, I have used this site before to find useful information for my 5.3 and 5.7 GM engines.

    However, I have a odd transmission leak that is puzzling me. My workhorse truck 2002 GMC Sierra 1500 with the 4.3 5 speed transmission (NV3500) is leaking from the output shaft seal. I have replaced the seal correctly and the leak persists. It is not leaking from the front and only leaks when parked on a incline or after warming it up. The yoke that goes into the transmission was smooth and shiny, had very little lines or virtually no damage at all.

    The leak is very small, and really only leaks after a long drive. When I re-installed the seal I used a large socket and drove the seal in square into the housing. I also lubed it up with Synchromesh Gear oil, and some grease on the inside. I also used emery cloth and fine steel wool to fine-polish the yoke. I also lubed that with grease too (my chilton book suggested it.)

    The drive shaft has absolutely no play at all. nor does the yoke.

    The truck has 128k miles and I take the best care I can of it, having a leak I cannot solve is really frustrating.

    Thank you in advance,

    Last edited: Jan 31, 2010
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Your yoke may be leaking at the very end where there is a cap which is permanently sealed at the factory. Jack up the front end of the truck and place on jack stands. Clean off the back of the yoke with Brake Cleaner and let it sit until it leaks. Some yokes have a small air bleed in the center of the yoke. If your yoke has this hole and it's leaking fluid then an o ring needs to be replaced on the inside tail shaft. I don't know for sure but I think only automatics have this air bleed hole. If the yoke is leaking at the rear you will need to remove the driveshaft and seal it with a silicone sealer and a cardboard slug the size of a silver dollar. This is the cheap way to fix it but it works.
  3. defektes

    defektes New Member

    Thank you for the reply,

    I did what you suggested this morning when I woke up. I degreased the entire transmission and left it spotless. I jacked it up and placed jack stands on the front. I am familiar with the breather you speak off but I do not think mine is equipped with one. My Astro van did however and it sure did leak. You are speaking of a small round hole on the back of the yoke in the center correct? If so, my truck is not equipped with one.

    Hopefully I can pinpoint the exact location it is leaking. The oil seal is dry if I put my finger across it, but the area under it is soaked (or was soaked.) Left 3 stains on my driveway in three different places. One stain directly under the seal, another to the right of the seal near the driver door. And the final dripping off the filler plug. The front of the transmission is dry, just the back was soaked in gear oil.

    Thanks again,
  4. defektes

    defektes New Member


    It is leaking from the top where it connects to the square rubber bushing type deal that covers the shifter.


    Please tell me I do not have to remove the trans for this. I verified it was coming from there, I degreased the entire thing and i see this gold fluid leaking from there.
  5. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    It shouldn't be leaking there unless the transmission is overfull. Did you check the fluid level?
  6. defektes

    defektes New Member

    I verified it was coming from there. I drained all the fluid and replaced it. Lets see what happens.
  7. defektes

    defektes New Member

    Even after draining all the fluid and replacing with the correct ammount the transmission is still leaking from the top.
  8. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Time to take the top boot off and see why it's leaking. May have a loose bolt or something is loose there.
  9. defektes

    defektes New Member

    I removed top boot and discovered 2 completely loose shifter housing bolts. I re-torqued all of them and hope that fixes the leak.

    Thank you for your help!:great:
  10. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Glad you found the problem.:sign0173:

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