The Stovebolt Site Forums The Shop Area Engine Shop '55 3/4 ton transmission

I have just landed a two owner 1955 2nd series 3200 long bed pickup here in NZ for a friend of mine. It is 100% original as far as I know 265 V8 and 4-speed auto trans. The gear selector on the steering column has "R" at one end "N" at the other and
I2,I3,I4 in the centre. I have never seen one like this before. I thought that chevrolet only made a two speed powerglide back then. Can anyone out there in Stovebolt Land tell me what sort of trans this is?
Thanks
Kiwiwilly
New Zealand

Its a Hydra-Matic. GM's first automatic, used in Oldmobiles and Cadillacs starting about 1940 and trucks starting in '52 or '53. While they are not real common they are not exactly rare or popular either.

OK Thanks, the truck drives really well but the trans is very harsh when changing gears. Is this normal for this type of trans?
Are parts or rebuild kits available for them?

kw,

Remember your 3/4 ton is a truck and not a passenger car. The trans needs to shift firm so that it does not wear out when it is working hard. The firmness of the shifts can be adjusted in the shift rods. Small adjustments can make a big difference in the firmness of the shifts. It can be adjusted so that it feels like it is slipping into gear, unlike the banging into gear you are now feeling. Remember it shifts firm for a reason.

Also the firmness is regulated by throttle pressure. The harder you accelerate the harder the trans will shift. Do a search for the online chevy manuals and you will find instructions on how to adjust the linkage.

hydro manual

If the insides of the trans are working properly, the shifting is all related to the linkage and throttle pressure.

Part are available through a couple of vintage trans repair parts houses here in the States.

I thought a 3200 was a 1/2 ton.

Reverse is also the parking gear.
Yes, Ghostrider saw that. The 3200 is a long wheelbase 1/2 ton.

Yes, the 3200 is a 1/2 ton long wheelbase.
On the Hydra-Matic, it came out in Oldsmobile first, in 1940. Cadillac adopted it a year later. Truck use came in '53 in GMC, '54 in Chevrolet.

Oldsmobile, and a very few Buicks had a Hydramatic in 1938 and 39. Those transmissions had a manual clutch, however. It was necessary to disengage the clutch for stopping, but once in motion, the shifting was automatic. The 1940 models were the first to have a fluid coupling (not a torque converter). The fluid coupling locks up at almost 100% RPM with very little slip, whioch is one reason the shifting feels rough. Torque converters have 10% slippage built in by their design.

Throttle pressure adjustment is very critical. It's adjusted by changing the length of a rod or cable from the carb to the transmission. Too much, and the shift is harsh. To little, and there's a lot of slip (called "flare") on a shift, resulting in rapid wear on the multi-disc clutches inside the transmission. A little rough on the shift is better for long life of the trans.

A place called FATSCO Transmission Parts carries a good supply of rebuild parts, some of them original-equipment. They've got a website, so do a Google search for them.
Jerry

OK thanks to all for the information and sorry for the typo I meant to write 1/2 ton but must have suffered brain fade when typing.
Willy