Slim Jim Tran.

[Guest proxie35]

Hi, Could someone tell me when Pontiac first used the Slim Jim Tran. & which model was it used in? Thanks

[poci1957]

It was used in Pontiac Catalina and Grand Prix from 1961-64. Bonneville and Star Chief still used the larger (and better) Jetaway/Super Hydramatic.

[Guest]

Roto is the second and last generation of Controlled Coupling Hydramatics. The first Controlled Coupling was called just that from Hydramatic Division, sometimes they called it 315 Hydramatic. Pontiac called it Strato-Flight and later called it Super Hydramatic. Oldsmobile called it Jetaway Hydramatic, finally Cadillac called it 315 Hydramatic. This trans mission used two fluid couplings, the small coupling was used instead of the front clutch in the old "D" type Hydramatic.

315 Hydramatic was a expensive 4 speed unit and so a replacement was sought. Cadillac used this transmission from 1956- 1964, some 1964 Cadillac models use the new T-400. Pontiac uses this trans from 1956-1964. It was Pontiac's only auto trans from 1957-1960. It was used in 1956 Starchief, while 870 and 860 models used the old "D" type. In 1961-64 it was used in Star Chief and Bonneville. 1961-1964 Catalina, Ventura, and Grand Prix use Roto. Olds used Jetaway from 1956-1960. 1956 88 used the old "D"type. 1961-1964 all Olds went to Roto.

This 2nd generation controlled coupling was cheaper and used less parts, but in some ways more complicated because it eliminated the large fluid coupling and bestowed it's duties on the little coupling. This little coupling is used as a coupling devise between the engine and transmission ( the old transmissions large couplings job ) and the front clutching of the planetary gear set ( like the old 315's small coupling ). Roto is a three speed unit and to make up for the loss of the 315's 3.97 first gear a torque multiplier is used in the coupling to increase torque multiplication.

Most people consider the 1-2 shift to be the most pronounced because the coupling drains and goes into direct mechanical connection between engine and transmission and this is a almost severe R.P.M drop. It's not so much a problem at wide open throttle because the stator helps, but at light throttle it's very noticeable.

Don

[Guest 4896]

helfen: Please address the question as to how much horsepower is consumed or lost through the 1959 Hydromatic in the Bonneville.

Thank you

[Guest]

helfen: Please address the question as to how much horsepower is consumed or lost through the 1959 Hydromatic in the Bonneville.

Thank you

________________________________________________________________________

I have no idea how much horsepower it takes to run a Super-Hydramatic. I'm sure Hydramatic Division did calculations, but it's not in any GM Hydramatic manual that I've seen.

I do know when Roto is in second gear ( drive range 3 ) the whole trans is in complete mechanical lock up.

I know when "D" type (original single coupling Hydramatic), "P" 315 type (Dual Coupling Hydramatic or Super Hydramatic/Jetaway) are in fourth gear, and Roto is in Third gear ( drive range 4 ) that the power flow from the engine to the tailshaft is only 25% handled by the fluid coupling.

This makes all three Hydramatic's the most efficient automatic's made before the addition of a lock up converter was used. This is because in a automatic with a torque converter ALL the power from the engine goes through the converter. Therefore all three coupling automatic's are more efficient than ST300, STH 400, TH350, Buick Dynaflow (both types) Chevrolet Powerglide and Turboglide, Chrysler TorqueFlight, Ford C-4, C-6. AMC

I left out Nash, Hudson, Lincoln, Frazer-Kaiser, Willys, and Rolls Royce- Bently groupe because they were smart enough to buy the single coupling Hydramatic from GM.

There is one automatic transmission in the fifties that in theory that was more effecient in high gear and that was Packard's Ultramatic which did have a lock up Torque converter, but because this trans started out in high gear it was very inflexible. It was a two speed automatic, but if you wanted first you had to manually pull it down to the L position to get it---just like the early Chevy Powerglides did, but this type of shifting the automatic greatly wore it out prematurely the same as Powerglide and Dynaflow wore prematurely with this type of driving-plus by doing so you were doing the first to high gear shift.... so it wasn't being used as a automatic!

As far as horsepower goes or is wasted I only have one figure, It takes 35-40 horsepower less to run a T-350 than a T-400.

Don

[Guest 4896]

Don: Thank you for answering my question. John (4896)

[PONTIAC1953]

hi, i studied automatic transmission in college for a year, it takes 40 horses to operate a turbo 350 trans, 65 horses for a turbo 400 trans. don helfen is very correct that the single and dual range D type hydra-matic are the most efficent automatic back then, very little slippage in the fluid coupling. in 1956, the pontiac 316 V8 made 20 more horsepower than the 1955 287 V8, but the new strato-flight hydra-matic transmission (controlled coupling) took 20 more horses to operate than the D type hydra-matic. charles coker, 1953 pontiac tech advisor.

[Donald_G]

I have a 1956 pontiac 870 model Built with controled coupling transmission

Is it a fact or guess about only "D" type transmission usage on 1956 Pontiac 870 or 860 models?

Tonight I looked at several 27 series cars Non Safari most had Park position on column indicator (Controled Coupling)

Edited January 6 by Donald_G (see edit history)

[PONTIAC1953]

On 1/5/2024 at 9:09 PM, Donald_G said:

I have a 1956 pontiac 870 model Built with controled coupling transmission

Is it a fact or guess about only "D" type transmission usage on 1956 Pontiac 870 or 860 models?

Tonight I looked at several 27 series cars Non Safari most had Park position on column indicator (Controled Coupling)

in 1956, with Pontiac having both version of the Hydra-Matic transmissions, if you were buying a Chieftain 860 or 870 series model, you were offered the Dual Range Hydra-Matic option for $175.00 extra, if you were buying a Starchief, the Strato Flight Hydra-Matic was a $190.00 option, I don't doubt for one second, that many of Chieftain buyers were able to pay the $15.00 difference, and get a Strato Flight added to their Pontiac order.

[Donald_G]

8 hours ago, PONTIAC1953 said:

in 1956, with Pontiac having both version of the Hydra-Matic transmissions, if you were buying a Chieftain 860 or 870 series model, you were offered the Dual Range Hydra-Matic option for $175.00 extra, if you were buying a Starchief, the Strato Flight Hydra-Matic was a $190.00 option, I don't doubt for one second, that many of Chieftain buyers were able to pay the $15.00 difference, and get a Strato Flight added to their Pontiac order.

Thank you for your reply.

There have been several cases of bad information given on this topic related to which neutral safety switch part number to use based only on pontiac model and not transmission type.

You have verified what I suspected was the case.

[PONTIAC1953]

5 hours ago, Donald_G said:

Thank you for your reply.

There have been several cases of bad information given on this topic related to which neutral safety switch part number to use based only on pontiac model and not transmission type.

You have verified what I suspected was the case.

1953-1956 Pontiac Dual Range Hydra-Matic Neutral Safety Switch p/n 1998039

1956-1957 Pontiac Controlled Coupling Hydra-Matic Neutral Safety Switch p/n 1998129