Hey guys does anyone know what trans will mount up to a 1957 347 GMC? It has a Hydra-Matic in it now. Also would a tri-power set up work with that motor being its a truck motor with a long stroke? What are my options? I would like to keep it as original as possible but able to run hwy speeds.
For transmission options, I think you are pretty well stuck with the stock automatic or the factory stick shifts used in GMC and Pontiacs of that era UNLESS you buy a trans adapter. Try Bendtsens www.transmissionadapters.com or Wilcap www.wilcap.com . As for the "long stroke truck motor".......it's the same bore/stroke 347" used in the '57 Pontiac cars. Compression ratio and camshaft specs may be differ from the car applications, but not the stroke. Ray
If the speeds are a problem, change the rear gear. '57 Pontiacs set speed records for the flying mile at Daytona that year around 140 MPH. The trans and the intake certainly aren't causing the problem; I had a '60 with a 2-bbl 389 and hydramatic and that car would fly like nobody's business; it had a 3.08 gear in it and 75, 80 was no problem at all.
The hydramatic has 4 forward speeds and an extremely low 1st gear. They are strong and work well. You can also use any later th 400, th 350, 700r4, etc with an adaptor. In the intake- direct interchange using a factory intake is 1955-1960. Pontiac made 2bbl, 4bbl, 3-2 bbl and 2-4 bbl. Most aftermarket intakes fit 1955-1964. You can also fit later heads and use later intakes with them. Lots of options for the wonderful Pontiac V8.
The shift from third to fourth gear locked the forward gear assembly, producing 1.00:1 transmission.[5] The fluid coupling now only handled about 25 percent of the engine torque, reducing slippage to a negligible amount. The result was a remarkably efficient level of power transfer at highway speeds, something that torque converter equipped automatics could not achieve without the benefit of a converter clutch.
What gear ratio should I run in the rear differential for that Hydra-Matic that I could run highway speeds?
If it's a dual range hydro, low gear is around 4.11.....my 60 w dual coupling trans has a low gear of 3.97 and the rear end ratio is 3.08....you could even go lower than that...a lot of the early 60s pontiacs had rear ends between 2.69 - 3.00 .....no problem with that low 1st gear in the trans
Yezzi, you are stuck with the old hydro unless you buy the Bendsten adapter but the fellow that said you have the same bore/stroke as a stock 57 passenger car 347 is wrong. I know this for a fact. I have a stock 57 GMC block I don't need and it is a weird displacement in the 330 something cubic inch range. I don't feel like measuring it now, but the guy I got it from confirmed that the truck engines were in fact different with a longer stroke and he owned his truck a long time. 55yak
I am sorry, but I think you are misinformed. In '55 GMC used the Pontiac 287 (GMC ads called it a 288), in '56 they used Pontiac 316 (GMC ads called it a 317), in '57 GMC used Pontiac 347. In '58/'59 GMC used a smaller bore version of the Pontiac 370 that was 336 cubic inches. That is, apparently, what you have, but it is not likely a '57 unless there was a change late in the '57 model year that carried into '58. I stand by my statement that a '57 GMC (Pontiac) 347 is the same bore/stroke as the passenger car 347, but may not be the same compression ratio or hp rating. Ray
If I remember correctly, the 347 and 370 have the same stroke. Also seems like either the early dual range hydro or dual coupling hydro (w park) would bolt up....not sure about flywheel spacing etc, but you can go to the PY site, join up and you will be able to search for all kinds of info on this...I'm sure it's there!
i dissambled my trans from a 1958 gmc and not the same as a pontiac 1957 trans mount not the same as passenger car and converter not the same but it will bolt on a 347 engine .what i can see converter is the same as my cadillac 1949 where you have a gasket behind all bolt in flywheel not every second as in pontiac 1957
First off I am far from being an expert and can only offer an opinion. A few years ago I looked at a longbed GMC (I think it was a '57) that had a 347 with Tri-Power, complete with the fender badges. It appeared to be factory(?) as the truck seemed pretty much original. It was a beautiful 2 tone Iris/Rose(?) The truck also had the Hydro-matic and I was surprised how well it worked. I was also surprised how brisk the truck was !!!
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