GMC Truck Transmission question

The 4L80E is near bulletproof. Perform the recommended "severe duty" maintenance on it and it will last 200K miles easy. BTW, the overheating problem mentioned by others resulting in ATF puking out the dipstick tube burning several trucks to the ground was caused by people who refused to read their manuals (and visor label warning)... "DO NOT TOW IN OD". There was insufficient oil flow through the cooler in OD to cool the tranny. In '95 or '96 that problem was fixed.

Mitch

Dump the guy who is giving you advice about the pump "bypassing". This guy must not know that the 4L80E uses a variable vane pump and is supposed to continually "bypass".

If the truck were mine, I would go out right now and hook up the trailer. Take 'er out on the road and see if it still pukes. Perhaps your original cooler line problem was your only problem.

Those units are pretty darned tough,

Allan

GM used a 4T80 for just a few years in the early and mid eighties in their Eldorados, Riveras and the Toronados. This was along about the time when the diesels were the rage. These trannys were all cable controlled working against a governor.

But as for the trucks, I'm pretty sure GM went straight from the 3L80 directly to the electronic overdriven 400, the 4L80E. Just don't think that this transmission was ever a manually controlled tranny.

Somebody will straighten me out if I'm wrong?

Allan

I could never figure that one out and I screamed til I was blue in the face. Total time was 3.9 to R&R, gut it and replace that silly gear.

But, that was GM. They raped their people. In 1999, I went to Ford and worked as a Service Manager. They did the same thing to their people too. :>(

I rebuilt my first automatic transmission in 1959, a cast iron powerglide, and thru the years got to the point where I knew every transmission on the road, down to the last oil circuit and it's mechanical power flow.

Like you, I could tell what was wrong with 'em before I ever lifted the things off the ground. :>)

Built my last 4L60E in 2000 and I don't miss the rascals one little bit. :>)

Thanks for the hollar,

Allan

You got it right about he 4L80E having a variable displacement vane pump, but fumbled when you ageed with him that the pump is "bypassing all the time".

The pump simply pumps the amount of oil required to maintain the computer-directed line pressure, so NO BYPASSING IS NEEDED. The older trannies with fixed displacment pumps were always pumping more oil than needed, and the pressure regulator was continuously bypassing the excess flow.

Right you are; I used the wrong choice of words. Should've said "variable displacement". :>)

See what happens? A little horse sh!t here, and a little there. This thing is gettin' totally outta control! :>)

Allan

But, it was either '90 or '91 there were two TSBs: One to replace the dip stick with a locking barrel type and also another to install an 8" piece of rubber hose on the vent and then to route it in such a way as to make it dump away from the exhaust in case of an overheat.

The hose modification paid .3 of an hour and I swore that I had "hosed" every truck in the country. :>(

When the transmission got hot, the fluid would come up over the top, spill on the exhaust and then the real fun began.

Allan

The real kicker was when GM, in all it's infinite wisdom, decided that the rear internal gear could crack on the 4L80E and should be replaced per a TSB.

What this meant was that the complete tranny had to be removed from the vehicle, mounted in the tranny fixture and totally gutted since this particular gear lives clear at the back of the case.

GM paid a whopping 3.9 hours for this update. It was at this time that it finally dawned on me that I was in the wrong occupation. :>(

Allan