What Transmission is in my truck?

Redmax · December 9, 2003

I just blew my transmission plowing, it is a 1988 GMC 2500 4x4 6.2 Diesel and was wondering what transmission is in there. Is it a 4l80e? Thanks, Tim

Engineer · December 9, 2003

The 4L80E was not available until 1993 I belive? What you probably have is the non-overdrive TH400, and it may or may not be electronically shifted.

Is your truck OD or non-OD? If it is an over drive, then it is likely to be the TH700R4, in which case it would be bad news at your house right now!!

Redmax · December 9, 2003

OD it is

but I dont think it is a 700

C/K Man · December 9, 2003

In 1988, 3/4 ton 6.2's had the Turbo 700R4 if they were the 'regular' 3/4 ton (6 lug nuts). The 3/4 ton 'heavy duty' (8 lug nuts) 6.2's had the good old Turbo 400, which is a non-overdrive 3 speed.

Colorado Kid · December 10, 2003

Sorry, but TH-700R4 was the only 4 speed automatic GM had (not counting FWD transaxels) in 1988, so that's what it is, unless it was swapped later. (Not likely considering different tranny lengths between TH-700R4 and 4L80-E, which would mean new drive shafts, the requirement for a stand-alone controller for the 4L80-E, etc.)