The Stovebolt Site Forums The Shop Area Driveline Hydramatic Transmission

Hi Team,

I have a 54-55 GMC series 1, 100 series with a hydramatic transmission. It was working fine when I parked the truck in 1985 outside. It has not been run since what is the best way service it? I will be pulling everything out of the truck - rebuilding the engine since it was missing on one cylinder. Should I send the transmission out for a rebuild or can I just clean it up and put in fresh fluid and go with it? Does it have a filter that I should change or should I remove and clean the pan? Obviously I am not very familiar with this transmission and have not done anything to it since I have owned it. What fluid would you recommend for this?

Originally the Hydramatic used "Type A- - -Suffix A" fluid, which is no longer manufactured, mostly because it contained a small percentage of whale oil and the bunny huggers got their drawers in a bunch about that! One of the best sources of information and parts on vintage automatic transmissions is FATSCO transmission parts in New Jersey. Check out their website and give them a call- - - -I've been doing business with them for 30-something years. They're good guys, even though they speak funny! A phone conversation between a Noo Joisey yankee and a Tennessee redneck is quite an experience!
Jerry

If you post this on the oldgmctrucks.com website, there are members who have extensive personal experience with that make/year GMC Hydra-Matic transmission.

It might be the same-as (or, quite similar-to) the Chevrolet H-M transmission.

This old iron was build very well. However, anything that has been sitting that long could be marginal at best. It would be a lot of extra work to service and install it and then find out it had some leaks or didn't shift well. The recommended fluid for the early hydramatic transmissions was Type "A". If it is still available it would be quite pricey. I believe it crosses to a newer product in the Dexron series. It also takes about 10 quarts.
Fred

You might want to look for a 1954 GMC Maintenance Manual - reproduction manuals are available.

Here is the H-M section in the Chev Truck manual.

Thanks for all of the information, I will reach out to Fatsco and see what they advise. I have ordered the GMC manual and Supplement covering the transmission so that should help. Looking at the H-M manual for the Chevy and there isn't any filters for the fluids and they recommend changing them on a regular basis, every 25k. I remember when driving it that first to second was very smooth but second to third seemed like a big jump and was very noticeable. I thought that it was due to the gearing and that there was a big jump, plus the motor had a miss on one cylinder which I thought also contributed. However it was smooth from third to fourth so maybe it was the trany? I am going to continue my research and get an estimate to rebuild it. Thanks a lot for the help.

Was Type "A" was replaced by Dexron?
If so, as per G.M. bulletin: DEXRON®-VI can be used in any proportion in past model vehicles equipped with an automatic transmission/transaxle in place of DEXRON®-III (i.e. topping off the fluid in the event of a repair or fluid change). DEXRON®-VI is also compatible with any former version of DEXRON® for use in automatic transmissions/transaxles

The 2-3 shift on a Dual Range is always firm- - - - -don't expect to be able to adjust it out. That's one reason Hydramatic developed the Controlled Coupling transmission in 1956- - - -smooth shifts, but sort of flimsy. That one didn't get used in the trucks at all.
Jerry