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4L60E tranny fluid blow-by issue

Discussion in 'GM Powertrain' started by SurrealOne, Aug 17, 2012.

  1. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    I noticed a new drip under the truck, today, and took a dive into it. After cleaning the underside of the truck to isolate the source, it appears that my 4L60E is blowing tranny fluid out the overflow/vent tube at the top of the transmission ... which is then all sorts of fun to find because it hits the spinning shaft and is, thus, spun/slung radially along the underside of the truck.

    I've read that a common cause of this is transmission overheating -- due to hauling/towing heavy loads and/or the impact of mountainous terrain. I've not been hauling or towing anything except myself and a small backpack these last few weeks ... and I've been on mostly flat terrain, so I don't suspect I've got an overheating problem. (As I don't yet have a working trany gauge in my 04 Sierra 1500, I'm stuck with looking at driving patterns.)

    I also read, today, that a common cause is overfilling the tranny fluid. So, I warmed up the truck and checked the tranny fluid level while the engine was running and found that the fluid level was just fine.

    The last thing I read on the issue is that the transmission oil pump could be the culprit -- either its seals are leaking or the chamfer in the pump body rotor pocket is too large. Those mentioning this have replaced their tranny oil pumps with rebuilt pumps (and presumably new seals) .... which resolved their blow-by issues.

    I'm mechanically inclined ... but I'm largely engine and tranny-stupid. I don't mind learning but I'd prefer to learn in small chunks. I'm curious how bad it is to replace a tranny oil pump. I know the tranny pan and filter must be removed. It looks like an adapter on the valve assembly (which is held in by a retaining clip) must come off and then the torque converter solenoid must be removed. At this point I think the oil pump assembly can be gently pried out and removed/replaced (in addition to replacing its gaskets/seals).

    My big question is whether or not the tranny must be removed from the truck to do all of this ... or if the work can be done with the tranny in place. Please advise, as I'd like some guidance from more informed/learned transmission folk, and thanks in advance for reading.
    Last edited: Aug 17, 2012
  2. Sawfish

    Sawfish Member

    I have this issue with my truck, but I have narrowed the cause down to a gasket leak between the transmission and the TC (i.e. fluid leaks from the transmission into the TC and blows out the overflow). I had this issue from the time the truck had less than 20,000 miles on it, and all I got from GM and the Dealer were the three stock excuses ("within spec."; "never heard of that before"; and "unable to duplicate condition which caused customer complaint"). Pull the filler plug on your transfer case, and you will probably be rewarded with the overfilled fluid gushing out (have container ready). I have to "bleed" mine every 6 months or so to avoid the mass overflow which literally coated the underside of the vehicle, and sprayed all over the Jeep I was towing. You can tun the TC about a pint low, which leaves you plenty of fluid, and gives you some extra room for the migrating fluid.
  3. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    Surreal, what spinning shaft are you talking about.

    Without the spinning shaft info (above) I'll venture a guess. The dipstick should have a 90 deg thumb operated latch to hold the stick into the tube. Operating the latch should compress the gasket at the top of the stick. This gasket, and the compression latch, are there to keep the fluid from blowing out the tube. Maybe the gasket is leaking.

    Saw, are you talking about the transmission fill tube, or the transfer case vent?
  4. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    The drive shaft. The fluid seems to be coming from the tranny overflow tube, nearby. It's -not- coming out of the fill/dipstick tube; all is good, there.

    Thanks. That's superbly useful information for someone who is transmission-challenged like I am. I'm still figuring out how to handle this, long-term. Since it's just messy with no increase in drip and no tranny problems I'm taking my time on it. I see a rebuild in my future in the next 6 months... as I'd prefer to control the conditions in which I have to give up my truck for some time. Plus I'm pretty sure the tranny was poorly treated (a la lift and big tires ... with no re-gear) long before I got the truck...
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Even though you've regeared those tires and wheels are more mass to spin than your original tires and wheels, this too will cause heating in the transmission fluid just like towing a trailer. As the trans gets older you may be seeing this problem due to a combination of the different items you mentioned.
  6. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    I have the Tru-Cool 40k GVWR installed, so I hope heat isn't the problem! (Sadly, still no operable tranny temp gauge... I'll get there. I deferred work on that when the leak began.) I truly believe it was mis-treated for 7 years of its life ... but I knew that was a risk when I bought it. The fact that it was trouble free for the better part of a year after buying it used has me pretty happy.

    Besides, I always look at broken stuff as an excuse for upgrades! :great:
  7. PantheraUncia

    PantheraUncia Active Member 2 Years 1000 Posts

    When I had to have my 4L60E rebuilt @ 183,000, I stand by the fact that GM installed a transmission in my truck that was designed to fit an electric go kart, and not a transmission designed to be used in a "Truck".

    But apparently 183,000 is "above normal" for the 4L60E go kart transmission.
  8. Sawfish

    Sawfish Member

    Transfer case vent, and also the wet seal where the driveshaft yoke fits into the TC. Occasional bleeding and running it a bit low has controlled the problem, but this is something that GM ducked addressing long ago. (And they wonder why my last truck was a Dodge.)
  9. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    Yesterday on my road trip I saw a tricked out, fantastic looking Dodge. 6" lift, 20" moto metal wheels running some aggresive MT's, aftermarket shocks, dual exhaust straight out the back, custom decals, deep tint. Man it looked great on that flatbed that was taking it somewhere with the amber lights going...
    :lol:
  10. Sawfish

    Sawfish Member

    Don't get the wrong idea, I love my Suburban. That is why we have been together since 1993. It is just very annoying to find problems that should have never left the Janesville Plant, and/or are due to some "questionable" engineering. Unfortunately, "Old Blue" has had his turn(s) riding on the flat bed, but not the Ram.(LOL)

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