The Stovebolt Site Forums The Shop Area Engine Shop 1955 truck 1/2 ton 4 speed automaiic tranny hunting info?

I have a basket case! I have a truck that someone installed a three speed manual with an overdrive. They cut the floorboard and put a crappy homemade shifter; but it gets better. They removed the shifter in the column. Then when you look at the steering box they cut the shaft going into the automatic shifting controller unit, with a torch. My question is how can I tell which transmission the truck had; and is it rare to have one with a 4 speed automatic ? If so where do I find one and what would the GM numbers be? Thanks for your help

I'm just going from memory here, so take it with a grain of salt: The auto trans equipped trucks had a badge on the fenders that said they were automatic. I believe the tranny GM used for the Chevy trucks is the same Hydra-matic that was used in Olds cars of the 50's. If there's a tranny rebuilder where you live with gray hair he could tell you exactly what to look for.

These were great trannys. No overdrive, but a "digger" first and second gear. My grandpa's '51 Olds could burn rubber clear across the high school parking lot but don't ask how I know that.

The 4-speed auto used in mid-50's Chevy and GMC trucks was a Dual Range Hydramatic. It's the same basic trans the 54 and 55 model Olds, Pontiac, and Cadillac passenger cars had. They're scarce, but not impossible to find. The bits & pieces to re-fit your truck back to original condition such as the bellhousing, crossmember, shift linkage, driveline, etc. will be harder to find than a suitable transmission.

I recently found a few factory service manuals for the dual range on ebay, to help out another bolter who was trying to get one rebuilt. BTW, the Controlled Coupling Hydramatic, used from 56-64 or so in Olds, Pontiac and Caddy IS NOT the same transmission. From 1940 to about 53 or so, the Hydramatic didn't have the Drive Right range which kept 4th. gear from engaging until the engine was in danger of floating the valves. It was the same basic trans as the 54-55 models, but it had a different valve body, and very few interchangeable parts. The truck shifter gear positions were labeled 1-2, 1-3, and 1-4, indicating how many shifts were possible for a particular shifter position. Reverse also served as Park, when the engine was stopped. Good transmission, but a little jerky on the shifts. I rebuilt my first one at age 12, as a student in an after-hours class my father used to teach for other mechanics in Nashville.
Jerry

Thanks for the info, but I cant stop their. In your opinion would it be something that I should start trying to hunt down; and would their be any data plate or other signs that would show what the truck had? The truck is in really good shape and it was a custom cab with a lot of accessories. Did the tranny have an oil cooler and lines to the radiator? I love a good hunt but I really have little to go here.

There won't be any data plate or identification other than the side badging. What engine does it have? The throttle linkage is different on a Hydro truck, it should have a linkage the would have gone to the kickdown on the trans.

On the 54 hydramatic, there was a solenoid starter instead of the foot stonper. There was also frame differences with hydramatic crossmembers that unbolt so trans can be removed from under the truck. Brake lines are routed differently for the same reason. There are other differences that you will find if interested by searching around the old topics. Hope this helps, G.H.

I have a '54 GMC 1-ton Hydra-matic truck. Is your '55 a 1st or a 2nd? If a 1st my '54 GMC should be almost identical.

The engine is a 235 and the truck does not have a push pedal start switch; but it does have the kick down switch for the 3 speed manual tranny. It still has the controls on the steering gear box that shows that it had an automatic. Their are two small screw holes in the steering column where a gear indacator might have been; and, they cut the floor to put a shifter in. The fenders have been replaced and the truck is a 3200 seres. I didn't see another shift linkages or tranny lines. Are their any old timer shops that post on this site that might have some books or info that would help?

2nd series

2nd series

Who knows where i can find one of the hydra matic tranny with all the things I might need to put this truck back to original?

Do you have a clutch pedal hole in your floor board?It sounds like your truck was a 3 speed on the tree.