New Build/reno GMG940

[Macarrra]

Good afternoon to all

Thanks first of all for allowing me to be part of the forum, I hope it'll be helpful to learn from your group wisdom.

So last week I bought a 1969 GMC 940 2 ton dump truck.

She is a little tired and not working perfectly, but I have decided to try my best to bring her back to a great condition. While I have done some restorations in the past, it was all much smaller cars, so this is a new beast for me.

To my knowledge the GMC940 is a Canadian badge for the Chev C50 (or maybe C60?!?).

The engine needs some love, and the brakes dont work very well at all, so im starting by trying to learn exactly what's under the hood, so I can then learn how to research each aspect.

So my first questions, if you have the time to reply, are:
-exactly WHICH engine do I have under the hood?
-can you confirm if this is a vacuum brake system?

To my knowledge, its a V8 350, however upon some research it seems that there were three different models (307, 350, 396 cu in).

Can you tell from the pics below which one mine is? Otherwise any suggestions on where I can look further for identifying features.

The brake resevoir may not be the original one (it seems more modern that other parts under the hood). I'm told that this model should be a Vacuum brake system, but wonder if someone can confirm that. When I go to brake theres a loud hissing noise and the brake pedal eventually kicks back (and the truck really doesn't some to a standstill very quickly!).

Many thanks in advance for your time, I'm sorry for the lack of knowledge...but its never too early to learn new things, right?!?

I will occasionally post build updates if people are interested, perhaps people arent though

Thanks to all from British Columbia (CAN)

[Bob B.]

A Canadian 940 is the equivalent of a U.S. GMC C-4500 or Chevy C/40.

You have either a 307 or a 350, with the 350 being more likely. Look for a 2 or 3 letter code stamped in the block in front of the right cylinder head, and look the code up on line. Yes, that truck probably has vacuum boosted brakes. You cab see the vacuum hose going from the intake manifold to the pipe that goes to the booster next to the master cylinder. The vacuum booster is probably behind the left running board under the cab, and there should be a breather for it under or behind the driver's seat. It could be your booster has a bad diaphragm or control valve in it, which would explain the hissing noise and poor braking performance. These systems actually work very well if the booster is good and the brakes are adjusted properly.

Nice little truck!

[Macarrra]

Many thanks Bob,

As soon as I get to the truck (its up on jacks while I work on tires and rims) I'll take a look at the motor and look for the serial number you mentioned.

Ill also get to work on learning to diagnose that brake system fault.

Do you have a preferred resource online for finding spare/replacement parts, up in Canada there isnt much available, and what is is also more expensive.

Thanks again

[Bob B.]

Don't know beyond Rockauto or NAPA. Those boosters can be rebuilt if needed, try looking for a commercial truck parts house, preferably one that has been in business a long time.

I will place a little wager that engine isn't original to the truck. It is painted blue, and those particular valve covers were used a lot in the mid-to-late 70's. Doesn't matter though, '40' series trucks came with standard duty pickup engines in them.

[5Tractorguy]

If it comes down to having the booster rebuilt, I would highly recommend DS Parts Co. in Bluefield, VA. dspartscompany.com They rebuilt the Midland Hydro-vac booster in my '61 5000 three years ago. It was an oddball booster that I couldn't find any parts for. They had them in stock and it was shipped back within a week 'n a half. Excellent service....

Not sure how that would work shipping from North of the boarder, but if it's justifiable...

Almost guarantee if you get that booster working you'll have good brakes. I've come up on red lights quick with my 5000 and if I stomp that pedal it'll bring me to a halt real fast!

[Macarrra]

She (Donna) has been up on axle jacks for a couple of weeks while working on bringing the rims back from the past, as well as prepping drums and ordering the new tires. Soon she will be rolling again and i'll address the brakes.

I read that when the vac boosted is failing it can lead the engine to cut out when coming to a standstill...which does happen. So perhaps if I can fix/replace the booster ill address two problems!

Many thanks for the input, will keep posting for anyone interested

[Bob B.]

Looks like you have at least one busted leaf on your left rear spring. Might be a good time to deal with it. Make sure none of the leafs that are rolled around the front bushing are broken. Also, there is usually a half leaf at the bottom of the stack that is attached to it's own bushing. That one is very important, it locates the rear axle and counteracts axle torque when you accelerate or brake.