The Stovebolt Site Forums The Shop Area Engine Shop Guys with 1953-59 Hydramatics

Just wanted to know what it was like to drive a Hydramatic equiped truck? I have read that the fluid coupling is not a torque converter and when you come to a stop it won't creep forwards. I would like to know how it shifts? What you like or don't like about it? How much is it like a regular automatic?

Thoughts, Opinions,

Thanks

I drove a deuce-and-a-half in the Army that had a hydramatic. They banged on the 2-3 shift, and was rough during other shifts. I'm pretty sure that's the nature of the beast. Yeah, they had a fluid coupling, and they did "creep". Maybe this will help.

http://en.wikipedia.org/wiki/Hydramatic

The Dual Range is a 4-speed automatic, and yes, it shifts hard. Instead of a torque converter it has a fluid coupling, which transmits torque, but does not multiply it when gertting moving from a dead stop. On the upside, there is almost no RPM loss through the coupling, instead of the 10% slip that's built into all torque converters.

Throttle valve pressure is critical to good shifting on a hydramatic. It's controlled by the linkage from the carburetor to the transmission. Adjusting the length a tiny bit will make major differences in shift points, and it can go from a slip to a slam-bang shift with little room for error.
Jerry

Hey Hotrod, thanks for the post. My only experience with hydramatics was in the old Army trucks. Wikipedia isn't always reliable and that's all the technical info I could find.

Check Ebay motors for oldtime service manuals and operators' manuals. There's usually a bunch of them out there. The HydraMatic was used in a lot of cars besides GM, even Lincoln, Hudson, and Nash used them in some applications. Pontiac, Oldsmobile, and Cadillac used one version or another from the late 1930's to the mid-1960's. The 38 and 39 Oldsmobile had a 4-speed auto, but used a manual clutch. By 1940, they added the fluid coupling and started calling it the HydraMatic. WW II trucks and some tanks used the same transmission, (Cadillac engine in the tank) and there was a double-transmission rig with one trans on top of another that used a torque splitter to adapt to an engine too powerful for one Hydramatic to handle. I don't remember the application on that one.

I grew up around one of the two shops in Nashville that began working on automatics in the late 1940's. The other guy besides Dad who dit transmission work had been a tank mechanic in WW II.
Jerry

Thanks again. I hope Texasdeere is taking all this in!

I have a 54 3100 that has been in the family for almost 45 years now. My dad had it, I learned to drive in it, and now my kids have their eyes on it. It was originally a 3 speed on the column. When I learned that 54 was first year for hydra-matic in Chev half ton, I researched all the differences and started collecting pieces for the conversion. It wasn't easy as even the frames are different due to heavier and bolt in crossmembers so that trans can be removed from bottom side of the truck. After the change over, I can't imagine the truck any other way. It used to be that you were grabbing a different gear as you were turning a corner. Now the steering wheel is the only concern. 1st gear is real short as it is just to get the truck moving due to the previously mentioned lack of torque converter slippage. The trans shifts quick and crisp. The throttle pressure adjustment is as sensitive as mentioned. You can soften the shifts but lose the downshift as you round a corner. My truck has dual carbs and a little lumpier cam than is ideal for the hydra-matic as it also likes a pretty low idle speed for proper operation. I feel that there is room for improvement in my setup but still favor it greatly over the old manual transmission. You can push start a hydra-matic truck where you can't a modern automatic. There is no park. You park it in reverse and when the engine is not running and there is no fluid pressure, a lock pawl drops into a large gear on the mainshaft and locks the trans like a park position. You lose the foot stomp starter in favor of a solenoid starter. There is also an automatic choke on the stock carb. vs. the manual choke on a manual trans. Bottom line is that it feels like an older automatic transmission before they went to a part throttle downshift. You actually have to stab it pretty good to get a downshift and it shifts like an automatic trans that has been treated to a shift kit as related to the harshness of the shifts. Hope this helps.

Great stuff guys,

I am considering buying a 58 6 cyl auto truck and swaping out transmissions and all the other associated parts. I think this truck has the posi rear as it doesn't look like the round Eaton style cover in my 59.

I thought about the adapter plate/TH350 route, but then I need to side mount my 6 and I haven't found a kit for that yet.

I have read the Wikipedia link before. I was a little suprised how little info there is on these transmissions online.

I have a 1954 GMC 100 pickup that was equipped with a Hydramatic from the factory. It was so bad that I went to a lot of trouble to convert it to a 3 speed column shift. The Hydramatic was a real PITA to drive, it shifted when it got good and ready, now I can choose what gear I want when I want it. I am completely satisfied with the 3 speed standard shift. I have an overdrive transmission I plan to install soon to make it more freeway friendly.

I would be more inclined to think the diff wasn't original if it isn't an Eaton, as the Posi option wasn't available until '59. The '59 Posi trucks did use a different rear diff, the Spicer 45 that was also used in GMC 1/2 tons.

I read that before about the posi option. It looks like a Dana 44 rear in the pictures. Maybe it is a very late 58, or who knows. The truck is about to sell on ebay right now. You don't see this setup too often but I don't really don't want to dump $1500 plus into a parts truck.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=320347157733&sspagename=STRK%3AMEWAX%3AIT&viewitem=

Someone got a bargain.