The Stovebolt Site Forums The Parking Lot Big Bolts 1950 GMC Fire Truck

Hi, I just purchased a 1950 GMC Fire Truck Model: 9783 (3-ton). I'm trying to ID the axles so I can start working on the brakes. I've read the canadian 3-tons were the same as the us 2-tons?

Rear Axle

Rear Hub

Hy 1950firetruck, welcome, as far as I know there were differences between Canadian three tons and American two tons. Canadian frames and suspension had to be heavier to achieve the three ton rating. As to the brakes, before 1951 there wasn't a lot of difference in the braking equipment in the heavier GM truck line, if you take your rear brakes apart and ask us specific questions about parts we will do our best to answer them, hope that helps.

1950firetruck
Welcome to the group!
I cannot answer your question, but I'm sure there will be some experts chime in.
Post your questions in the right category and you will get a response.
By the way, Firetrucks are the coolest.

Don

A picture of the truck itself, and maybe a pic. of the ID plate in the driver door jamb would help us, help you better.

I'm looking for anyway to help identify things like the drive train. I've search around and can't find any rear axle that matches what I have. I'd like to know what gearing I have and where to locate parts.

The Truck

Serial Number

Looks like wheels are 5 on 8" bolt pattern, tubeless wheels were made with that pattern in the late '50's, so check around-verify first.

Is trans a 4 or 5 speed?

Is engine a Chevy(235 or 261) or a GMC? GMC engines SN start with the displacement, stamped on cast pad behind starter, starboard side, I. e. 248xxxx.

Px of engine/trans would help.


Ed

welcome to the site, cool truck!

Engine SN: G25268 ...is that the right one?

Engine ID

4spd. Havent driven the vehicle yet but fired it up and used the clutch and gears and they seem free and clear.

Tranny 1

Tranny 2

Brakes. The pedal is frozen which has to do with a stuck brake cylinder. The wheels move but you come to a stop pretty quick. Parking brake is also non functional.
Brakes

Hy 1950firetruck, your engine is a 248 GMC, for some reason Canadian 248s were not identified the way their American cousin engines were with the C.I.D. as the first three digits of the engine number, but rather the letter G was the first digit of the engine number. Is your truck equipped with a single speed or two speed rear axle? Your transmission is an SM420, and your truck has five bolt Motor Wheels, hope that helps.

Since it is a 248, then any 256, 270, 302 GMC engine will bolt in.

Ed

Welcome! Ive got at shop manual for the Canadian trucks, will see what I can dig up for you. Right ow you want brake info, right?

My goal is to get it on the highway so I'd like to figure out if I can change the gearing in the rear or need to swap it out completely.

I know the rest of the drive train needs to be addressed with a gearing change. Since I need tires and brakes figure its a good time to look at the axle.

PTO

Eventually this will be removed and we will be replacing it with a wood flat bed.

Highest ratio available might be 6.6 if you can find one. Might be best to find a modern rear axle(2speed) with juice brakes, although that bolt pattern is uncommon on modern trucks. There is a six lug bolt pattern that is common, so, if you find a whole truck, would be able to use two matched axles with tubeless tires. Just depends on how original you want to be and your intended use.

Best use for the pump assembly is to replace it with a Brownie. Takes care of too low rear axle plus low gears for creeping,

Ed

The power tower is fire truck specific. I have sold several of them for scrap iron. You are going to have to build a driveshaft anyway when you remove the power tower. The power tower's sole function was to drive the pump. The easy way to get a little more speed would be an auxiliary with OD. The hydrovac brakes will be adequate if you rebuild all the components. The small block GMC engines, 228 through 302, are comfortable running 3400 all day long. We ran them like that 50 to 60 years ago when we used them to haul gasoline. There is no reason to run them any slower today. A .80 OD will make the thing go faster than you probably want to drive it any way.

Interesting, I've never heard of running and OD. Anymore information on that would be great!

Google 'Brown Lipe Auxillary transmission.'

Probably a good start would be to figure out your diff. ratio, jack up one wheel and count driveshaft revs. vs. tire revs. X 2.

Ed

The typical auxiliaries came in two basic configurations: one is referred to as a progressive with ratios such as 1.24 low 1:1 direct and 0.86 overdrive. The other has a deep under with 2:1 ratio under, 1:1 direct and maybe a .80 overdrive.

The progressive units are best mated with an SM420, which you have, because you already have a compound low for crawling and you don't need 2x that ratio in low. Aside from that the progressive was designed to split the main box ratios three ways so you have about a 400 RPM drop between gears as opposed to about a 1500RPM drop on the main box that you now have. It makes the truck much more drivable on the road.

Look for tandem-axle trucks. Single axle rigs usually had 2-speed axles. The 5800 series transmissions were often used on gas powered tandem-axle dump trucks. The 6200 series were used on diesels mostly and would work fine on the 2-ton GMC, and the 8000 series were used on big over-the-road tractors behind big cummins engines. They are too big for our purposes.

Whatever you get make sure you get ALL the linkage and the cross member and rubber mounts if any. Get the ends of the driveshafts that hook to the transmission too. The big u-joints and slip-joints are expensive to buy new.

The interesting thing about wanting to make your truck go faster is you still have the same brakes and suspension. I don't think I want to drive my '56 faster than 50-60 mph and hit any kind of a large bump at speed, especially empty.

There is also a 5531 box that would work for your application. Many farm trucks have an earlier Watson box that would also work for you. Many have an attached Tru-stop brake that really works. Place here in Denver reclines shoes. Rubber mounts are easily made with neoprene grader blade mat'l

Ed