hi guys I'm glad I find this forum before buying the truck the truck is a 1989 gaz gmc 1500 4x4 converted to a 6.2l 1986 diesel.my fear is about the transmission... it's still the original v8 automatic (over-drive)I planed to make it as snow plow truck. My question is: are the gaz an diesel transmission the same ? and if not, did the original one can do the job?I searched all over google and cant find an awnser.Hope you guys can help me.thanks

Diesel and gas trannies are the same, but the torque converter is different. Not completely sure on the 89 model, probably a 700R4, so with correct converter it will work. Now for using it, probably not the 1st choice to use for plowing but if its what you have use it til it blows up and get a 400 if you want auto or find a 4 speed manual.

govenor is also different. 89 700r should have all the upgrades and be a solid tranny

does a th400 fits on 4x4? and is really tougher? should i put a used on instead of rebuild my 700r?

switch to th400, you lose lower 1st gear and overdrive= milage. th400 is a bit tougher if your really going to be hauling and working it lots

Lots of full size RVs that have the Chevy engine has the T400 behind it so if it can haul a 35' RV it can do what you want. Any of the 3 trannies, T350, T400 and 700R4 are available in 2 or 4 wheel drive.

The '89 GM transmission, if it is original, is called a 4L60. The original 700R4 was extensively improved and strengthened in 1987-88 and GM changed its name. This is an excellent transmission and it can really be toughened up with after market components if needed. You can check to see if the transmission is the original one. The year and model code is stamped on the right rear side of the transmission just above the pan.

The governor weights and the torque converter should have been changed when the previous owner did the conversion, otherwise, it will wait until the engine is really turning up before it shifts.

Is the truck running now and shifting OK?

Yeah, the above posters hit the nail on the head with the converter and the governor.

Truth is, a plain old gas transmission will work though. Not going to feel quite right, but it will work just fine.

as said above a diesel has its own torque convertor which has a different stall rpm and there is a different govenor also which gives your your lower shift points. but you will be just fine leaving it as is.