Trans swap?

5

Asked by Apr 08, 2009 at 09:52 PM about the 1990 GMC Sierra 1500

Question type: Car Customization

My truck has the 700r4 trans and I cant get one but I did find both the 350 and 400 at my local juckyard at a price that I can afford. Now will either of these work in my truck? I know after searching online that with the 400 I would have to get either the 9" tail piece or a longer driveshaft but what about the electrical connections? Will the truck still run right with these other trans in it?

2 Answers

155

The 700r4 is a fully hydraulic transmission, no wires or transmission control modules to worry about. Depending on the engine you have, a turbo 350 should run in your truck no problem. The 400 isn't as much of a bolt in as the 350 though. Also, keep in mind the 700r4 is a 4 speed transmission, and the 350 is a 3 speed, so your fuel mileage will suffer. But, the 350 is a lot more bulletproof than the 700r4. It all depends on what your willing to sacrifice.

45

i would try my best to get a 700r4 because you will of course get better mpg but you top end will be great now if your pulling something the 700r4 is still good but the th400 if u get an older one will near about be indestructable its greatest power is in the low ranges though but i personally like 700r4 i have a shift kit put into mine and it is an automatic and a stall converter it have never given me any problem and i have a greater top speed compared to a th400 or th350

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