younkin1

(NOTE- I realize my question pertains to a Express van, but Silverado and Express van share the same drivetrain components. Any help would be appreciated).

OK guy's, here is my problem- I just bought a 2007 Express 3500 cargo with the 6.0 and the 4l80E transmission. It has about 230000 miles on it and I just had the transmission rebuilt because the fluid was badly burnt and it was slipping in 3rd and 4th gears. We installed the rebuilt tranny and now I have a shifting problem. I'll do my best to describe it. When starting from a stop the transmission seems to feel like it drops out of gear for a couple of milliseconds and then goes back into gear. It seems like the trans is trying to go into 2nd gear but then snaps back into 1st kind of harshly. Maybe the words stutter or stumble would best describe it. The transmission shift great after that. It only happen when starting from a stop. It never sets a code. It seems to be worse after the transmission warms up. It won't do it in direct 1 or direct 2, but does it in 3 or 4. Fluid condition is great no smells or discoloration. We check the operating pressure and everything in within specs. We've had the valve body down 3 times, replaced the shift solenoids, checked voltages, double and triple check everything including the wiring hardness (internal & external) and found nothing. We just removed the tranny and torn it down and inspected everything and found nothing. Has anyone else had a similar problem? One more thing and this may not have any correlation, but I believe it may. When servicing the engine I tried to reset the oil service light using the KOEO, throttle pedal to the floor within 5 second sequence as designed. But the ECM will not respond to it, so I'm unable to reset the oil light... Most mechanics know about the problems a faulty TPS (the old 3-lead) can have on a transmissions shift points. This van has a drive by wire throttle set up that I'm not familliar with. Does anyone think maybe it could be the TPS or the floor pedal potentiometer? Do you think there could be a correlation? I need help in a bad way- Thanks Guy's

Allan In NE

The ECM cannot "see" mechanical problems and is why you're not getting any codes.

Since the problem does not occur in manual low or second, this means you have a low overrun issue going on in direct. The truck does launch, therefore the clutch is installed properly; just slipping.

Further, I'd bet my wife's pet cat that somewhere along the line someone has used some snake oil in this guy. GM transmissions cannot stand transmission additives, as that stuff simply ruins these over-run clutches.

Replace the roller and you'll be good to go.

Allan

younkin1

@Allen, Thanks for your input. This was a known fleet vehicle (local company) and no additives were ever used as far as I know. Straight ATF in cuurently. We're going to reinstall it and use a break-out box to check operations that way. If you think of anything else, let me know. Thanks