Trans Swap From 700r4 To Th350

kawtoy_77 · December 21, 2009

My buddy has a 1992 GMC W/T 4.3 with what I am assuming is a 700R4 OD transmission, a TH350 of the same length would be a better Trans for him.... I am pretty sure this is a direct bolt up swap other than your gear selector being slightly off. Am I correct in thinking this?

Mike G · December 21, 2009

What is wrong with the 700R that you are trying to get him into the TH350? Personally, I like the 700R, it gives you an extra gear to use when on the highway. The 700 also has computer controls that I believe the 350 does not have. If you are doing the swap, you will need to look into that too. Also check into the output splines, I do not know if they are the same.

--Mike

kawtoy_77 · December 21, 2009

Reverse is out in the 700, and my buddy is tired of it kicking in and out of OD depending on hills, wind, and how you hold your tongue, lol! I told him a TH350 wouldn't have that problem.

gmtech4 · December 22, 2009

your in for a big head ache ,and bad fuel milage,I would not do it

59ih340 · December 22, 2009

is it a 700r4 or a 4l60?either way it's easier to just throw another one in. it was a common swap in the earlier models for plowing etc. but by the '90's they're not that bad in a light truck like that.

kawtoy_77 · December 22, 2009

your in for a big head ache ,and bad fuel milage,I would not do it

He drives mostly always in town, and the 4.3 doesn't develop enough power to keep the truck in OD now, so I don't see where he would be losing the MPG. City + V6 + 1992 Fullsize SCLB = crappy mileage anyhow. My other friends 4.8L V8 he says it kicks out of OD driving into the wind on bad days, and going up hills too. My 5.3L has never kicked out of OD yet... up hills, down hills, windy day... doesn't matter.

ON another note I am not 100% on what it is that he has. He said a 700R4 sounds right, but I am not sure what year they changed over to a 4l60 either. For City Traffic and reliability I would think the 350 would be better than the 700 if thats what he has. The truck only has like 70,000 miles on it give or take!? He isn't rough on vehicles at all. I am just guessing that it is a 700R4 by the symptom (reverse went out) a common failure in that transmission.

Mike G · December 23, 2009

Should be a 700r, but they are pretty much the same trans. I would have it rebuilt and drive it. We put 195k on mine before it went out, but my son decided to try hauling a double axle trailer behind it. If your buddy doesn't put it into OD, it won't shift to it..

--Mike

mjlimo82 · December 28, 2009

The 700R4, 4L60, and 4L60-E are all the exact same transmission internally, the only difference is the 4L60-E is electronically controlled where the other two are vacuum. 4L60-E also has a different bellhousing bolt pattern on Vortec engines. A 350 will go in, but you'll have to find one with a longer tailshaft (or change it to one) and the driveshaft may not be the correct length so it may have to be altered. The crossmember will have to be moved also for it to bolt up correctly.

The name change from 700 to 4L60 came in '90, and the -E was implemented in trucks starting in'93.

I have a friend who's '83 GMC Sierra he has has had both transmissions. Came with a 350, changed it to a 700, then back to a 350. It can be done, and it's not that hard to do. His dad was a GM transmission tech for over 20 years. He's taught me a LOT.

herkdriver007 · January 15, 2010

Get another 700R4 and tell your buddy if he puts it in "3" or "D" (depending on your display) then it will be just like the TH350... Plus if one day they decide to drive on the highway they'll still have the OD to save a few $$ in gas.

Just my 2 cents....