The Stovebolt Site Forums The Shop Area Engine Shop Transmission swap??

I've just purchased a 70 chevy 3/4 ton 4x4 with a bad automatic transmission in it, and was wondering if the 2-wheel drives used the same transmission (less transfer case)? I've got an opportunity to purchase a 1976 chevy 1/2 ton 2-wheel drive with a good transmission in it, but am not sure if it is compatible.I am told the 1/2 ton has a TH350 in it, but am not sure how to tell what I have in the 3/4 ton?

yes thy are just remove tail section and change end shaft from yours to the new one

shape of pan. if it is perfectly square its a th350

Thanks for the feedback. I've swapped out several 4/5-speed manual tranny's, but the automatics are new for me.

The 3/4 ton probably has a TH400 in it. The pan on it is shaped like Texas. The 350 is square like Bill said & has a bevel on it.

Can you replace the TH400 with a TH350, and will the transfer case interchange? Which transmission is better?

The 400 is better. I doubt the replacement would be easy because the two transmissions are somewhat different in length.

Well maybe better said is the 400 is built stronger. If you are not going to work the truck hard a 350 weighs less and uses less power so it would be more economical to operate.

For a 3/4-ton four wheel drive I'd choose the 400 but its really a little more complicated than that...

Before you start pulling the tranny,did you try flushing it out and giving it a new filter and fluid? I've had a couple of 'em that responded to just a service and lasted quite a while with no problems. This might not do any good,but if it does,look at all the money and work you saved yourself.
Speed

munjorroad,
Have a friend who owned 3 early '70's 3/4 4x4
pickups. 2 Chevy's and one GMC,all of them had
TH350's in them. Also another friend of mine had a '73 with a TH350. I don't know if the TH350 was
the base automatic and the 400 an option or not.
As far as the way the pickup is used the TH350 held up well in 2 of the early pickups,but they were not used very hard. The third one was a work truck and I overhauled that one twice in 5
years.
I agree with speed that the first thing you should do is service the trans.
The info on the shape of the pans is correct.
In order to change the output shaft on the TH350
you will have to completely tear the trans down.
It's one of the first components installed in the
case when disassemled.
I might add that the TH350 is prone to developing cross leakage in the case,especially
in 4x4 applications. I would guess it's from the twisting thats encountered when off road.

Arnie

The TH400s first came out behind the big blocks in about 1970. One way you could tell them from 350s was that the transmission hump was taller. So perhaps they were larger in all diminsions.

I've correctly identified it as the TH350. The truck has'nt been started for about 5 years, and was parked because the front seal went out on the transmission. Thanks for all the input, I think I might try your sugestions and replace the seal and service the existing transmission before I try finding a replacement.

i changed from a 350 to a 400 in a 73 jimmy years ago. the 400 was out of a 2 wheel drive like your talking about. i pulled the tail section, took tranny to a tranny shop to have the shaft changed. its not an end shaft, the front pump has to come off, the shaft runs full length of tranny. they only charged me $20, it took him about 15 minutes. i should ad i already had the shorter shaft.