delta881972

does the 3sp auto trans that came stock with the 350 rocket in 1972 bolt up to a 455? or is the 4sp auto needed?

joe_padavano

There was never a 4 spd AT behind a 455. The TH350 in the 72 will bolt directly to any Olds motor. How long it will live behind a 455 is a function of the trans condition, the strength of the 455, and the weight of your right foot.

Olds64

Doesn't the 200 4R (4 speed) transmission with the BOP bell housing bolt to the 455 as well? This transmission is available in 80s vehicles such as the Custom Cruiser station wagon and Cutlass Supreme. It will definitely need work to hold up to a 455 though.

delta881972

if im not mistaken the '72 88-98 cars came with two engne options....... a 350 big block, and a 455 big block. the 350 cars came with a turbo hydra matic 375(3 speed) and the 455 cars came with the turbo hydra-matic 400(4 speed)
above info taken directly from my 1972 owners manual.


my car currently has the stock 350(down to the 2 bbl and orig air cleaner) with the 375 three speed. to the best of my knowledge anyway

further thoughts on compatibility and options?

2blu442

Hello Delta
I'm afraid you have that wrong, the TH400 is a 3 speed automatic. In 1972 the only automatics were all three speeds. I'm not familiar with the TH375 but the two that I've encountered the most are the TH350 and TH400. The TH400 is several inches longer than the TH350 and has a larger tail shaft where the driveline yolk goes in. You could adapt a newer 4 speed automatic to the car but everything I've heard is that you would need to beef it up to use it behind a 455 engine. If you do a search on this site I believe you'll find some threads discussing transmission swaps. John

Olds64

I thought the TH 375 was a beefier version of the TH 350 available in trucks and vans in the late 70s. I don't think it was available in the BOP bellhousing.

Allan R

Ok, I accept the 455 BBO because that's a fact. A 350 BBO??? I think you've got this wrong. 350 is a small block. Always was. The Olds Line of 88/98 is referred to as B Body.

Anyway, the rocket 350 (L33) is the standard engine for Delta 88 and Delta 88 Royale. The optional L35, also a 350, was basically an higher performance engine that had valve rotators on the intake and exhaust valves to let the engine eat and breath better. You could also order a Delta with 455 power (L74)

The 98 and Custom Cruiser models came standard with 455 power (L74). 455's came from the factory mated with a TH400. I also had never heard of the TH375. While doing some reading I saw a reference that Olds had a special version of the TH400 that was designed "expressly" for the 350 engine. Didn't see any other clues, but maybe that's what was being referred to as a TH375???

About the 4 speed. Yes Oldsmobile had a 4 speed tranny. BUT, it was a manual transmission, not auto. Another BUT, it was only offered on the A body cars. I agree with the others about being cautious bolting a TH350 to a 455. It just won't last. If you've already got a matched 350/TH350 why don't you beef up both of them and keep them working together?

Olds64

Here is some good info on the TH 400 variations taken from Ron Sessions' "How to Work with and Modify the Turbo hydra-matic 400 Transmission."

"The Turbo 375 used only in '72-76 models, is identifiable by the 1/4 in high 6 in long bold script cast onto the bottom of the extension housing. It reads THM 375."

There is alot of good info on the TH 400, 375, and 475 in this book. I got it for my eventual build of the TH 400 after I finish my engine. Whenever that happens.

joe_padavano

Just so we're all clear, there are two different transmissions called the TH375. The first is a light duty TH400, as used behind small blocks in heavy cars. The second is the TH375B which is a beefed TH350.

csstrux

In the interest of education, how would one Identify one of these th 375s? are there any external differences, or is it strictly internal? also if differences are internal, are casings common to their "standard" counterparts? I E if I had a th375, th400 derivative, could that unit be built to th400 specs, and conversely, could a th350 trans be rebuild to th375 specs? May be this is just my add getting to me again, but thought this might be of interest. I don't know if this question has any practical validity.

Olds64

In my book on TH 400s it shows a picture of a TH 375. It is easily identifiable by the TH 375 stamped into the bottom of the tailshaft. The book says they were weaker versions of the TH 400 with fewer fiber and steel clutches. I had no idea there was a TH 375B.

BTW, it mentions the TH 475 was a beefy TH 400 available in motorhomes with an upgraded sun and planetary gear set.

csstrux

I take it castings are the same then, and all differences are internal?

68conv455

TH350 / TH400 debate:
Some other notes that you can think about while you decide:
The TH350 is lighter and uses less HP than the TH400 and often preferred by racers for this reason. It is "relatively" inexpensive to get one beefed up to handle the 455. Your gas mileage would be marginally better for this reason as well.
The TH400 is very strong in stock condition, and therefore, would be your least expensive to install. You can beat them senseless and they will still work.

J-(Chicago)

I had a 72 delta 88 convertible. It had the 455 and a th400 transmission.
The one thing I would like to point out is that the 72 deltas had a 9'' tailshaft so keep that in mind if you plan a swap.

Olds64

Isn't that the because the B bodies had a the long shaft TH 400 and the A bodies had the short shaft? Or is it the other way around? I remember hearing something about that.

joe_padavano

There are actually three different TH400 tailhousing lengths, not counting the 4x4 adapter for trucks. The 4" housing was used on A-body cars (and, I assume, F-body and X-body cars), the 9" was used on B-body and C-body cars. I'm assuming the 13" tailhousing was used on 2WD trucks.