THM400 or Turbo 400, not sure what you guys talking about?

In 1964 Cadillac used two transmissions (not counting the commercial HD version), the 4 speed Hydra-Matic and the 3-speed Turbo Hydra-Matic. I have not found any reference in the 1964 Shop Manual to THM400 or any word with 400 attached to. Also checking my 1966 Shop Manual and 400 is not present there either, only Turbo Hydra-Matic. Serviceman bulletins for 1964 does also NOT state 400. Sales brochure does not use 400. Wikipedia do claim THM400 to be installed in Cadillacs from 1964, but frankly I don't trust that to be correct.

When checking my 1972 Rolls-Royce Silver Shadow Workshop Manual it is stated for left-hand drive cars GM 400 - 3 Speed. They even had different gear boxes depending on side of the steering wheel! 

So in 1964 Cadillac did not use the word THM400 or Turbo 400 or any other 400 variable for the Turbo Hydra-Matic. My guess is that 400 was invented at a later stage and was used incorrectly for our cars. Not even sure a 1964 Cadillac Turbo Hydra-Matic is fully interchangeable with a THM400.

In 1964 Buick did use a Super Turbine 400. But ours cars are not (inferior) Buicks! (I also own a Buick) ;-)

Found a very interesting site called General Motors transmissions and they use TH400 for the 3-speed 1964-'98 electric kick down, later renamed 3L80. My guess is that here they have renamed the early Turbo Hydra-Matics not knowing better.

Just to make it clear. I have briefly scanned the manuals and could have overlooked something, but think that we should use the correct words when discussing our cars. THM400 or Turbo 400 is modern and was not used in 1964 for Cadillac Turbo Hydra-Matic.

Me and my autism/ocd can now withdraw.

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Comment by Clovis on January 13, 2018 at 11:54am

Anders, our transmission's are Buick's transmissions. The buicks had them in '63 I believe and they worked so well and were much better and cheaper to produce so they put them in the Cadillacs. The super turbine 400 had a switchable torque converter that could alter the vanes inside. Very desirable piece to have today. I think later Cadillacs got that also. There is another wire connection at the transmission as evidence. Cadillac still called the alternator a generator in 64 but today we call it the latter. The same thing with the turbo 400 and turbo 350 (lighter duty) transmissions or just 400 or 350. So the turbo 400 is the turbo hydromatic. 

Comment by Clovis on January 13, 2018 at 11:58am

In 65 the adapter ring to mate the Buick transmission to the Cadillac motor was no longer needed. A new bellhousing was mad to fit the caddy motor. 

Comment by John Smith on January 15, 2018 at 9:31am

I am new to Cadillac ownership, but what I have gathered in this short time is that in 1964, all non-De Ville cars had the old Hydramatic four speed tranny while the De Villes got the TurboHydraMatic or THM400 or TH400 that have been used in most GM cars and trucks as well as in Lincolns (their Ford auto transmissions could not handle the power or weight of the big cars), Rolls Royce (and probably Bentley), Jaguar and Holden in Australia. Also, starting in 1964, all convertibles were designated as De Villes, so all '64 verts had the THM. Please feel free to correct me if I'm wrong.

Comment by Anders on January 15, 2018 at 10:47am

John, Series 62 used 4-speed Hydra-Matic. DeVille and Fleetwood series used 3-speed Turbo Hydra-Matic.

TH400, THM 400 or Turbo 400 are names of transmissions Cadillac did not state in their Shop Manual or sales publications for 1964.

Buick did have a Super Turbine in 1964 and maybe that could be used instead of the Turbo Hydra-Matic in a Cadillac. Would be interested to know if that is possible. The full size Buick in 1964 was Electra. It was fitted with a 401 Nailhead V8. And the Riviera was fitted with a 425 Nailhead V8.

Comment by Jason Edge on January 15, 2018 at 11:34am

Turbo Hydramatic 400 or simply Turbo 400 has simply become the common name of the family of transmission introduced by Buick as the Super Turbine 400 in 1964 and borrowed by Cadillac in 1964. It is just term many use to describe that type of transmission as it goes by many names. It is also confusing at this point in time to simply say Turbo Hydramatic, since the unknowing person might just as well assume you are referring the very common and mass produced Turbo 350, or other variants.

Anyway, I think the entry below from our  Engine and Transmission Facts - differences from 62 to 63 to 64 to 65 Help Page link covers the bases:

Turbo Hydra-Matic Transmissions

-The new 3 speed Turbo Hydra-matic was introduced in the Buick as the Super Turbine 400 in 1964.  In order to not let Buick get a jump on Cadillac, The 1964 deVilles, Eldorados and Fleetwood 60 Specials used the Buick transmission using an adaptor ring to mount to back of the 429 engine.  It was then introduced in Chevrolet, Pontiac and Oldsmobile in 1965.

- The Turbo Hydra-matic used in 1964 Cadillacs had a single range Drive shift pattern - PRNDL and is often called a Turbo Hydramatic 400, THM400, or Turbo 400 since other makes (e.g. Buick Super Turbine 400, Chevrolet Turbo Hydramatic 400) used 400 in the name. It has also become the common name used to refer to this family of Turbo Hydramatic transmissions.

- The 1964 "Buick Borrowed" Turbo Hydra-matic was a one year only transmission for Cadillac.   Cadillac got its own new  Turbo Hydramatic transmission in 1965.  For 1965, the bell housing casing was changed to allow the transmission to mount directly up to the 65 429, and the internal hydraulic circuitry was modified to provide a dual drive range as seen in the 1965 Cadillac Shift Quadrant below. 

Comment by Clovis on January 15, 2018 at 11:40am

Anders BPO ( Buick, Pontiac, Oldsmobile) transmissions had the same bellhousing bolt pattern. Since our transmission is actually a Buick I would venture to say that any BPO transmission would fit our adapter rings. I've never researched doing this but it would make sense. 1965 and up transmissions also would work without the adapter plate but it is not a simple switch for the uninformed. 


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