I need to replace the tranny in my 79 chevy truck. Its a 350 engine with a TH400. Ive been told that all TH400 use essentially the same gears. Is this just a heavy duty TH350 for trucks. Can I use a TH400 out of summit for car applications? Also someone told me that the bell housing on a 350 and 400 is a different size. Is that possible if so how could they both bolt to the same engine? Thanx in advance.

The TH350 and TH400 are interchangeable as far as mounting. A 400 is not simply a beefed up 350, it is all around heavier and more durable. The transmissions are interchangeable for cars and trucks. Depending on the vehicle, you may need to change the output shaft for a 4x4 or a particular application. These are cheap, and it's not uncommon to do. As for the rest of the transmission, it is the same for car or truck. Sometimes the stall and shift points are set different, but the guts are the same.

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Shawn Peterson
1969 Z28, 406SB
http://www.geocities.com/corsican69

Thanx Shawn,
This is the first time I have dealt with anything other than a parts counter in a few years. Isnt it funny how if someone talks to you long enough how you tend to doubt your own knowledge. I dont claim to be a master mechanic, but once you understand the basics of the drivetrain its pretty much just common sense and troubleshooting. I cant believe that people will do and say anything to make a buck these days. And I just cant stand seeing that happen to fellow car enthusiasts let alone family. What is the world coming to?

The kickdowns( this is makes it go into passing gear) are different for the 350 and 400 turbos. The 350 is mechanical and 400 is electrical.

There are different length output shafts for 350's and 400's.Some 350's have long shafts, some short.Same thing for 400's.400's are longer than 350's and have a larger shaft which requires a larger yoke.The rear trans mount is also farther to the rear.This usually requires a different crossmember.Car and truck 400 transmissions are usually the same as long as the output shaft is the same length. 400's and 350's can use the same torque converters. Hope I didn't confuse you.

Big Gear Head is correct about the differences. You also mentioned bellhousing bolt patterns. In this area I think you might be thinking about the differences between the Chevy and the BOP bolt pattern rather than TH350 and TH400's. Those will not interchange except with an adapter, however they are otherwise identical.

Steve R.

I'm pretty sure the 400 is longer overall than the 350. Also the kickdown is an electric switch that must be mounted to the carb and wired to power and the trans.

The TH400 is stronger than the TH350!

The 400 is longer than a 350. As a result, you will have to modify the driveshaft if you change from one to the other.

The 400 has a kick-down switch (normally mounted at the carburator), the 350 has a kick-down cable.

BOP (buick, olds, pontiac) transmissions have a different bolt pattern where they attach to the engine. You will have to get a transmission for a Chevy (or use adapters).

The location of the trans mount is farther rearward for a 400 than a 350. If you are lucky, it's just a matter of sliding the transmission crossmember forward or rearward.



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In all of my frustration I left out a few details. The transmission has already been taken care of. The manager and old friend of mine at a local tranny shop down here told me the tranny was bad and it would cost 1000 bucks to rebuild and 1800 to replace. I damn near fell over. I figured that i could get a TCI TH 400 from summit for $700. He said "no" this truck uses a "heavy duty" TH400. I argued with him to no avail. Needless to say he didnt do the work. I talked to another guy at a nother shop and he told me that the difference was that a 400 wouldnt bolt up to a small block. Once again I couldnt believe my ears. I told him that two months ago I had just rebuilt a 400 in my friends Nova that just happens to be a small block. He said "never happened". Keep in mind this is a work truck not my car. So at this point I have two well known tranny Co. chains telling me I'm a moron. So totally unlike myself, I start to believe them. Thats when I posted this question, knowing that if I am wrong someone would tell me. Thank god, I thought I was losing my mind. It is still so frustrating to not be able to trust anyone these days. I dont take my 69 to anyone. And now thanks to this experience I never will. One last thing, I have to thank you all for being part of this. This site is the best source of information around, you have all helped me with a few problems that could have taken forever to figure out. And if you cant trust Camaro owners, Who can you trust?

[This message has been edited by SAyers69 (edited 02-20-2000).]

I agree with you SAyers69. I haven't let a mechanic touch my 69 in over five years.

After I put my ZZ3 HO 350 in my car, I was having trouble tuning the Holley carb. I couldn't solve an over rich condition. I took it to a "performance" shop and the guy assured me that they worked on hot rods all the time. Well, he solved the over-rich condition all right - he installed size 54 jets in the primaries - on a 350 hp engine!!! WHAT AN IDIOT!!!

Well, I tracked down the problem. I misread a Holley tuning guide as saying to turn the idle mixture screws out 3-4 turns. The real setting was 3/4 of one turn. Switched the primaries back out, adjusted idle mixture, and problem solved.