The Stovebolt Site Forums The Parking Lot Big Bolts Overdrive tranny?

Anybody have an Idea of what kind of overdrive 5 speed would be in a late 40's deuce and a half with a GMC 270 in front of it? Going to look at one New Year's Eve about 70 miles away. Man says it doesn't have the park brake mounted to it like my Clark. He also doesn't see any tags on it yet. Can park brakes be mounted on most trannies of that era. Thanks. Jim. This will be going in my 1950 GMC 450 firetruck if I get it.

If your truck has a mid mount pump the parking brake is located to the rear of the transfer case, if you have a front mount pump, disregard this statement.

I'm sure you could fabricate a drive shaft hand brake if one can't be found to fit what you're looking at.

Mike B

In a 4wd application the brake would be after the transfer case.

My firetruck is 2 wheel drive with the park brake attached to the back of the Clark 5 speed. It is a mid mount pump driven from a Waterous PTO. This will all be coming out eventually. Guess I'll see the OD tranny New Years Eve. Gotta crawl under mine and see how the brake attaches to the Clark. Never looked closely at it. Thanks. Jim

I guess the Duece and half would be 4 wheel or all axle drive. Didn't think of that.

If it doesn't have the drive shaft brake it would have the handle mounted to the transmission with levers. And cables to the rear wheels like mine has.

There were aftermarket park brake assemblies available for GM trucks back then. The most popular one was the Tru- Stop" park brake. One of my trucks had one on it. Mounted at the tail of the tranny. Looked like a large disc. brake rotor with either single, or double brake pads.

My GMC 450 has a drum brake on the tail end of the Clark 5 speed. I'll crawl under it tommorrow and get a good look at it. The gentalman that has the overdrive tranny hasn't called me back, so I guess he hasn't gotten it pulled or found a tag yet. Thanks.Jim

Deuce and a half should have a divorced transfer case.

Those divorced T/C's are popular with the monster-truck builders,at least they were last time I saw one for sale.
Speed

The parking brake is on the output shaft of the transmission (external band type). Since the GMC CCKW used two different transfer cases (Timken and Corporation for two separate axles aka 'split' and 'banjo')

All of the Chevvy 1.5 ton 4x4s had Corporation (or banjo) while CCKW 6x6s (2.5 tons) had both depending on model/configuration.

The 5 speed is SIGNIFICANTLY larger than the 4 speed (I have a G506 1.5 ton and G508 2.5 ton) and this topic comes up every so often. Its about 30% larger and much heavier.

You would need a few custom parts (the drive shaft from the tranny to transfer) and the floor pan and will need some major work. The bell housing should match up, but the frame mounts won't. The transfer case would also need to be moved about to line it up properly.

I've never actually seen or heard of anyone doing it... but floor pans are cheap... finding a useable 5 speed is not that big a deal (I have 3, two spares). They come up on ebay... unless it has been rebuilt, they are worth their weight in scrap... $200-300. If rebuilt (and the have papers/documentation) then well over $500-800 is not out of the question. It will all depend on the rebuild.