The main differences between 54/55 hydra-matic equipped trucks are listed below. If there is anything incorrect or omitted, please post this information. The following information might prove to be useful to someone who wants to convert a standard 54/55 truck to a hydra-matic-equipped truck:
1. There is a transmission-support frame cross-member for hydra-matic (the holes for this cross-member are in the frame side rail on all 54/55 frames).
2. The hydra-matic transmission floor cover is completely different is size and shape. A non-hydra-matic truck's floor board (and maybe part of the toeboard) can be adapted to use the hydra-matic's transmission cover.
3. The hydra-matic truck's gas pedal is attached to transmission floor cover.
4. The hydra-matic has a push-button starter on the dash (no foot-pedal mechanism) - it has an electric-solenoid-driven starter.
5. The hydra-matic truck has a different brake master cylinder and different routing of brake lines (an non-hydra-matic truck can be easily adapted).
6. There are no choke or throttle knobs/cables with the hydra-matic (but the dash holes are still there - with hole covers).
7. The entire shift lever, gear indicator, shift column, and linkages are all different.
8. The automatic-choke carburetor has linkage rods to the gas pedal and to the accelerator pedal. All these linkages, pivots, rods, clips are unique to the hydra-matic and should be carefully kept with engine. Many of the quirks mentioned above by Jim G are relative to the sensitive adjustments between the carburetor, the gas pedal, and the transmission. Having the original carburetor-linkage parts (and having a lot of patience when adjusting the idle and the linkages) are key to the proper adjustment of engine idle-speed, the adjustment of when the transmission shifts gears (mph range), and how smoothly the kick-down/down-shift works.
The engine and hydra-matic transmission were matched at the factory; however, people have matched up other 235/261 engines with a hydra-matic transmission. The 1954 Hydra-matic rear-end is however unique to the 1/2 ton hydra-matic, because it still has a torque-tube and the torque-tube length is shorter for the hydra-matic equipped truck.
As Greg Hill "pleaded", if you will doing a "restoration" in which you will not be using the hydra-matic drive-train, all of the above parts should be saved and kept with the hydra-matic drive-train (if you want someone to be able to use the drive-train in another 54/55 truck).
The original posting asked if a hydra-matic is a rare vehicle. It might not be rare but it is uncommon and it is a great conversation piece (it is too bad that Chevrolet had used Hydra-Matic hood side-emblems, as did GMC). Many people know about the 2-speed Powerglide but few know about the original 4-speed truck Hydra-Matic.
