The Stovebolt Site Forums The Shop Area Driveline 1954 GMC vs Chevy hydramatic

Backstory: I finally disassembled my stock 54 3100 with hydramatic. I listed the non body parts for sale locally. For obvious reasons and based on guidance from members here, I tried to sell the motor, hydra tranny with starter, as a matched set. Had a buyer ready… he needed my exact motor/tranny for his 1954. I offered the combo for a fair price, IMO, and came down a lot because I really wanted to help him replace what I destroyed…a factory hydra rig. But he kept low balling me. I eventually took an offer I could not turn down for my 235 motor, $2,100.

Today, I received an inquiry about my Hydramatic. He sounds like a newbie, so I am doing some due diligence. He has a 1954 GMC panel delivery that had a factory hydramatic. The motor and tranny are missing. I looked through several threads here, but nothing finite. My questions are:

Is a GMC 248 block “bell housing” bolt pattern the same as a chevy 235 block?

Is a GMC 248 crank pattern the same as a chevy 235?

Will my torque tube and rear end benefit him?

I know the tranny “flexplates” were machined to the block, but there’s a process to verify and set the runout, set the studs,etc. And the linkages are different, but again, that’s solvable. I just need to be able to tell the buyer with confidence that my 54 3100 hydra will bolt up to a 54 GMC 248. Normally, my motto is “buyer beware”, but as a responsible stove bolter, my standards are higher.

Thank you for your input.

Scott,

Just a note that I am going to move this post over to the Driveline forum as the better place to get an answer on your transmission question.

Am sure folks with more knowledge than I have on Hydramatic transmissions will chime in soon.

Dan

The bell housing bolt pattern on the Chevy and GMC engines are the same for standard trans applications. I can't think of a reason the H-M equipped blocks would have a different bolt pattern. I believe the H-M equipped engines had eccentric dowel pins that located the adapter ring for the transmission, and the ring needed to be checked for runout with a dial indicator bolted to a fixture attached to the crankshaft hub. That was done at the factory, which was why an engine block and adapter ring needed to stay together. The same procedure can be done in the field, but only by someone who knows how to use a dial indicator to check runout when installing the adapter ring between the block and the transmission. The fluid coupling (NOT a torque converter, BTW) is very sensitive to alignment with the crankshaft.

Your buyer could contact FATSCO transmission parts in New Jersey for a lot more accurate information about the differences in Chevy and GMC H-M transmissions. They specialize in obsolete automatic trans parts and repair manuals.
Jerry

The flywheel bolt pattern is not the same between chevy and gmc. It would take some work but could be done

Thanks! I will pas ps this along to him!

Thx!

Thx!

Scott from Idaho I had a hydramatic 54 chevy in 82 it had been mistreated and the flywheel torque springs just a handful of shrapnel in the cover below. Could not find springs so filled the holes with lengths of black pipe,that truck road and drove fine,real stump puller in low. My wife loved that little "automatic"truck. Your buyer will have a dandy suburban with that tranny. Our automatic trans specialist told me they demolished most of those drag racing them in California. He was old in 82 for 75 dollars he would have you take your tranny apart lay clean parts on cardboard,next evening put it togrther for you in about an hour. When he put the converter in would tell you not to dump it out in the floor,never had many come-backs either.

Thx Dan!

I think the buyer is holding out for a 1954 GMC 248 with a matching hydramatic. I tried to explain he will most likely never that, especially at the price he expects. It would probably be easier to buy my hydra and look for a 235 from a Chevy. IMO, period correct (1954) is the best he can get.

Too bad your tranny guy isn’t around. I doubt his knowledge was passed down.