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  1. #1

    Default Difference Hydramatic 55 & 56 ?


    Apparently on the '56 Safari of a friend, there is a small radiator for the hydramatic oil ! Does anyone know if there's a possibility to add that radiator to my '55 Starchief HT Coupé ?
    I noticed that the hydramatic doesn't shift as smooth anymore as soon asthe oil gets warm.

    Glad for any help !


  2. #2


    Yes a small radiator can be installed on your 55 dual-range Hydramatic transmission but I doubt that is the source of your problem. External cooling was an option for the dual-range Hydramatic, recommended for severe driving conditions such as in Police cars, taxis and such. I've never seen it installed on a stock 55 Hydramatic. The stock Hydramatic without the external cooling did not have a problem with heat under normal conditions. I suggest your first check the oil. Change the oil if it is old. Check for a burnt smell of the oil which would indicate some internal problem. Insure oil level is correct and that you are checking the oil using the proper procedure. Adjust the bands, the dual-range requires periodic adjustment for good performance and smooth shifting.

    Your friends 56 Safari does not have the same transmission, assuming it is original. It has a "Strato Flight" Hydramatic which is considerably different than your 55 dual-range Hydramatic and not comparable. The 56 (and later) Strato-Flight Hydramatics all had external cooling but not with a small radiator -- cooling was done though an external heat exchanger that was cooled with radiator water.

    The Strato-Flight was a little smoother shifting and required less maintenance (band adjustments) than the dual-range. The dual-range was stronger and preferred for racing so it has advantages. The dual-range was used in Lincolns, Rolls Royces, GMC trucks through '59, tanks, and other applications requiring a strong automatic transmission.
    Larry Gorden, POCI 1956 Tech Adviser

  3. #3


    My Starchief doesn't have the dual range, but the four gear hydramatic. Is that not the same than the 56-modells? I just did an oil-change. It wasn't burned, an after a few hundred miles of driving it's still red, not dark or dirty.
    My hydramatic only starts these hard shiftings after I've been driving for a longer time!

    Last edited by Sethos; August 8th, 2011 at 05:59.

  4. #4


    All 55 Pontiac automatic transmissions were the dual range 4-speed Hydramatic, also called the "slant pan" Hydramatic. In 56, the dual range Hydramatic was used in Pontiac Chieftain models only and it was the last year Pontiac used the dual range Hydramatic (GMC trucks continued to use it though 59). The 56 dual range Hydramatic was same as the 55 transmission with minor upgrades.

    In 56, the newly designed Strato-Flight Hydramatic was used in all Star Chiefs, including Safaris. It is also 4-speed. The dual range Hydramatic does not have a Park (P) position and the Strato-Flight does so they can be quickly identified by looking at the shift indicator.

    I am not an "expert" on these transmissions so I can't say for sure if installing a cooler would solve your problem. If the transmission is overheating then I would suspect some internal problem. Regardless, if the bands haven't been adjusted for some time, then it should be done and you might find that that helps with your problem.

    You might try directly contacting the POCI transmission Tech Advisor. For more "expert" advice, I suggest you join the 1950s Pontiacs Yahoo Group and ask your question there.
    Larry Gorden, POCI 1956 Tech Adviser

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