The Stovebolt Site Forums The Parking Lot Big Bolts 1955 GMC 550

My dad had an old GMC 550 they have owned many years. I really want to restore it. When it was new it had a V-8 with a Hydramatic that was equipped with a two speed gearbox behind it. The transmission has been removed, but the reduction gearbox is still in it. I was wondering what the trans looked like or what kind of numbers it would have had on it. It must have been a heavy duty unit for at truck that size. Finally, does anyone know how many large trucks like this would have been equipped with the hydramatic? Any help would be appreciated.

I think a truck that size would have had the Allison transmision that GMC called the TorqMatic.

On the hood it has Hydramatic just like all of the smaller series trucks. The original transmission was removed because of oil leaks and replaced by a muncie 5 speed manual. I would like to find the original auto trans to restore the truck though. The truck was originally purchased by the Caterpillar dealership here in Greenwood in 1955 and was their lo-boy truck, so they told me it had a hydramatic. The engine is either an olds or pontiac V8, it has air brakes, and power steering. I am not familiar with the hydramatic, so were there different size tranmissions for the larger series trucks or were they all the same? Does anyone know where I can find any information about 550 series GMC's on the internet. Thanks for any replies.

I just got a book from '60 that shows a Torquematic, really an Allison auto. It was on bigger trucks and engines. What engine do you have? Could be some oddball. Pontiac 322 is listed in this book or Motors manuals. Not sure on olds ID. I'ld say, if the trans and box work now, leave it alone. I bet the orig trans set-up would be "Unobtainium" material. Even the old 60's GMC's had adapters and such needed to use that trans on their V-6's. But yours would have to be for that pontiac engine then? Don't see it being easy at all. The manual is probly far less trouble too, that's why they changed it. Those old autos weren't as trusty as new ones today.

dont know about the trans, but do you have pics, those trucks look so cool. I love the big grills and general shape of the front ends, wish I could find one out in the north west.

The truck has a 324 olds engine, and it had the 245G hydramatic trans. I really would like to find that original trans, but I am going to fix the truck no matter what. Maybe I can post some pictures soon.

we have the sfm 460 with an inline 302 & 245g hydramatic trans. We had work done on it last year and we were told it came from a 40's Army Duck.
There is a 550 parked in our town, I haven't found the owner yet, we want to take our bus down for a side by side photo shoot, darn sexy looking vehicle.

Well the GMC 2 1/2 ton 6X6 army trucks (CCKW?) had 302's with dual range Hydramatics. Maybe you should look for a military truck as a trans donor. If you find one you take the trans and I'll get the motor..... Have you looked on the oldgmctrucks.com site. Good GMC info there and they have a friendly discussion board. Good Luck.

55-550 I think I have a hydramatic from a 54 GMC 470 I have here, it had a emb on side of hood stating hydramatic, I'll look this week, if you still need on let me know. 1-918-542-3871 week days or E-mail [email protected] Thanks Tom