Shifting into OD problem

[lvxa1]

I am having shifting problems on my 1994, 6.5 Chev 3/4 ton.
The tranny is a THM 4L80-E. Up shift into OD is a problem, after I drive 2 to 8 miles it begins to work better, then when I stop and start again it won't shift up into OD until I drive a few more miles.
Does anyone have any helpful information to help me solve this problem?

[rustyk]

There are several possibilities:

1. Low fluid
2. Dirty filter
3. Throttle Position sender
4. Bad connections on tranny controller
5. Need for rebuild (dropping O/D is limp mode)

Check 1., but 2. seems most likely based on your symptoms

[Robyn]

Could be that a fluid change may help, but I am inclined to look at the 3-4 shift solenoid.

These are electric valves that plug into the Valve body.

There are a couple other little "O" ring issues that can occur with these trannies that can cause this same issue.

A tranny shop can plug the scanner into the rig and check that the ECM is actually calling for a shift. If the shift is called for and not happening then the issue is likely a shift valve.

Been through this issue myself a while back.

If the fluid is clean (RED) then a trip to the shop for a quick electronics check is the next step.

Good luck

Missy

[Beedee]

The first thing that any of the local shops recommend it to change the trans oil.

I had an issue with mine not going into OD and a bit of a shudder on down shift went away after I changed out the oil. The oil didn't look that bad when it came out, but once I sat down an worked out how long it had been in I was surprised.

It is a quick and easy fix, if it doesn't work then you can dig deeper into the problem.

Rule out the easy ones first.

Good luck

Brian

[JohnC]

First get the codes. All you need is a paper clip and some knowledge.

Are you sure the problem is with OD and not with the torque converter lockup? They are often confused with one another.