Chevy Truck Tranny Question

D

DWK2

Joined
Nov 3, 2003
Messages
3,410
I've got a '93 K2500 (5.7L) with the heavy duty trailer towing package. Standard GM auto tranny for that year (4L60E or something like that). In any event, the original lasted for about 138,000 miles---which included some very hard use. I got a rebuild done by an outfit that specializes in building transmissions for serious towing applications. I have a lower gearset and all the upgrades that have been implemented since '93. I have a 2 yr/24K mile warranty on the rebuild. The mechanic has a very good reputation in our community.

The rebuilt tranny shifts beautifully and locks into gear very crisply and positively. It seems to perform perfectly in every respect except one: When you set the shifter to first gear and start a steep descent, the tranny will not hold in first gear. It upshifts to second.

The mechanic tells me that GM trannies are designed that way so that they are not overstressed trying to hold a big load back on a steep descent. He says that if they were to remain locked in first, they might "blow the pump".

This all sounds plausible except for the fact that the original tranny always held first gear for at least 137K of the first 138K miles.

So does it sound to you GM truck owners like my tranny needs adjustment or is it functioning properly?

Thanks for your thoughts!

DancesWithKnives
 
Last edited:
So, let me get this straight.

Your truck has gone 137-137.5K miles on one tranny? wow.... lucky

If your truck preformed for that long without a hiccup (upshifting) than I would say that Is what It's supposed to do. I have never heard of other Chevies shifting up under load. It's bad for everything In the drivetrain and motor.

IMO, get It adjusted or fixed, trucks are not designed to/supposed to do that, If It does that at the wrong time, you will tear something up....
 
That tranny is electronically controlled, the shifting is done with 2 solenoids inside the pan. So there probably isn't an adjustment on the tranny itself, its programmed into the controller. I have a book an this tranny, I'll dig it out and do a little reading.
 
Thanks a lot for both opinions. I certainly can't complain about the original trans and the rebuild feels even better in most respects. It just strikes me as odd that the factory tranny would hold the vehicle back in first gear on a steep descent, while the rebuilt unit won't.

Much appreciated,

DancesWithKnives
 
Just a thought, but that could be a function of one of the upgrades that were done. It is possible that experience showed locking in first gear could overpressurize the system - "blowing the pump" as the mechanic said - and a change was made to correct that problem. When he did the rebuild, installing all the upgrades that have been implemented since '93, the controls were changed to prevent possible damage.
 
A lot modern automatic transmissions do just what you said to prevent blowing them up. GM had lots of transmission issues in the timeframe you are talking about so, it is most likely included in the "updates" that were put into that transmission series after you bought your pickup.
 
You must log in or register to reply here.
Back
Top