no overdrive

[93punow]

i have a 93 6.5td with a 4l80e trans it will not shift into overdrive all the time some time it does but not all the time any idea guys

[Hye]

Simple stuff first. Have you changed the filter and fluid in the last 10K miles? I don't know squat about transmissions, except that changing f/f has cured erratic shift problems for me, even if I've changed it three months ago.

[JohnC]

First thing to do is check for diagnostic codes. If it wants to shift and can't it'll store a code.

[cruzer]

I lost OD once after I replaced the pump. The variable speed sensor on the side of the pump was out of adjustment. Most of the things that go wrong w/a 4l80e is electronic.

[taznj63]

I had same problem with mine and no codes in computer. It turned out to be the speed sensor on engine at rear where a distributor would be if it had one. This unit is also the oil pump drive unit with a pulse xmitter on top.
Here is where I have been buying most of my parts direct from GM for the best price and free shipping over $100.00. Great service and fast ship from dealer...
John Dickinson
Team Chevrolet,Olds,GMC,Jeep,Nissan
2014 E.20th Place
Scottsbluff, NE 69361
308-632-2173/800-658-4017
fax 308-632-0974
email: teamparts@teamchev.com

Hope this helps...

[AJ650]

Same problem with mine when I bought it, needed a new tps in the tranny. Needed a whole new tranny about 12k miles later.