The Stovebolt Site Forums The Shop Area Engine Shop Hydramatic trans

I've been reading up on old treads about the hydramatic trans. I'm going to look at a parts truck tomorrow for my 55 1st, and the guy says he thinks it's the original automatic trans,my original plan for my truck was a t-5 swap with my 235, because i wanted to run a little faster, whats the best way for me to go? If i wanted to go a little faster with this?

The hydro will not give you any more top end speed, than any other stock trans for your truck. Final gear ratio is one to one. The rear end will have to be upgraded with taller gears or changed to a later model rear end with taller gears. 3.33 to one gears are available for the 55.1 rear axle which will net you more top end than the stock 3.90 gears.

If you get the truck and decide that the hydra-matic must go, let me know. I may be interested in some of the parts and linkage. Thanks, Greg H.

Another option would be to add an overdrive. I have an overdrive ( Hone-o-Drive) in my 55 coupled to a Th400. I put this in in 1970, and I have never regretted it. I have run it with gears as high as 4.57 and still got good gas mileage. I am presently running 3.73 gears.
Those Hydramatics are an excellent strong transmission.
Bob

The Hydro has a really low first gear, so another option would be to change the rearend to something like a 3.08, then you don't need an overdrive but you will be able to get off the line just fine.

The hydra-matic is a 4 speed auto. It has as mentioned a real short first gear. They do not use a torque converter rather than a torque coupler. They actually have 100% efficiency where a modern auto has between 5 and 10% slippage. That is the reason for the low first gear. You can push start a hydra-matic where you can't a modern auto trans. The shifts are firm and crisp. There is no park. You start the truck in Neutral and park in in reverese which has a locking pawl when there is no fluid pressure. They are not for everyone but I enjoy the one in my truck.

Just to add to Greg_H's posting for general knowledge. I believe all the truck Hydramatics had the forward and rear pump which enabled push starting, but some of the later car transmissions only had the front pump. (The rear pump was driven by the output shaft ) It isn't a big deal as long as you know that you have the original transmission in the truck, but the newer transmission could be damaged by attempting a push start. ( Not to mention the fact that it wouldn't start).
Bob

hey bigblockcameo, do you have any pics of your 55 ?
leonard

What do you want to see in the pictures? I have a '55 1st GMC 1-ton with a Hydra Matic. I found mine in a barn and it still has the patina it showed that first day.