The Stovebolt Site Forums The Shop Area Driveline 1956 GMC V8 Hydra-Matic

I have a '56 GMC V8 Hydra-Matic that is having some problems. She isn't street legal yet (no working lights) so I had a friend tow it for me to my new house and we started smelling burnt oil and noticed that it was leaking fluid from the pan on the tranny and was overheating after being towed about two miles in Neutral. I have driven the truck around my old neighborhood prior to this without any problems. Unfortunately I don't know much about transmissions, so am not sure if I just need to replace the seal and flush it, or do I need to have it rebuilt. Any help would be wonderful! Thanks!

prolly best to have a rebuilder inspect for what damage you did - the rule is to never tow an automatic with drive wheels on the ground unless the driveshaft is removed, the pump isn't working

Bill

From the 1956 GMC Owner's Manual Hydra-Matic section...

"IF YOUR TRUCK IS TOWED
The rear wheels must be off
the ground-or disconnect the
propeller shaft at axle. The
transmission will be damaged
if towed in any other way."

Start there...

Hy pensbyjon, the Hydramatic is one of the last automatic transmissions that would allow you to push start the engine. It is equipped with two pumps, one in the front driven by the flywheel, and a second one in the back, driven by the driveshaft. I would drain the fluid, including draining the fluid coupling [there is a drain plug in it], and replace it and see how it performs.

Thanks 3B...I will start there. I have sent a few emails out to some rebuild shops in the area for some rough quotes, but hopefully there isn't too much damage and I can replace the gasket on the pan and fluids like you suggested.

Not too sure about the GMC truck hydramatics, but on Oldsmobiles and Pontiacs, the hydramatic transmission used from back in the 40s up through 1955 was what we called the "tilt case" hydramatic. In 1956 GM went to a different hydramatic in their cars. The tilt case unit had front and rear pumps and could be push started and also could be towed in neutral with the drive shaft in, as the rear pump circulated the tranny fluid. If the owner's manual for the 56 GMC says the driveshaft has to be removed for towing, it may be the later "slim jim" hydramatic. Probably just useless info, but I get a kick out of dragging some old car stuff out of my tired old brain.

Larry

Hy tarheel and guys, the Cadillac Hydramatic was always a flat pan type up to 56, the Chevrolet and GMC truck Hydramatic used this type of Hydramatic right up to 1962, they never changed to the much poorer design that they did in the cars from 56/57 on.

Pull the pan and look inside. drain the fluid and cross your fingers. I have several manuals and each one states a different warning. Caddy book says dont flat tow or push start with less than 5000 miles on the odometer. others say its ok at low speed for short distances. some say no no.older manuals say one thing new years say another

drain and inspect and cross your fingers. Good idea to use synthetic tranny fluid and adjust the tranny while the pan is off. Might squeez a few mor miles out of her

can i recomend the oldgmctrucks.com website