Air Brake Plumbing Mix-up

[martinf]

Hey All,

I've recently got a 1971 MAck R series truck, set up for logging with a self-loader. The hydraulic grapple had busted off the air brake line Tees at the rear axle. WHen I got it, things were pretty messed up and disconnected. SO here's my questions:

Which chamber does the air brakes line connect to? I know there's a spring brake chamber and the air brake chamber, but I don't know which air fittings is for which. Do the air brakes connect to the front (smaller) chamber and the spring brake is the larger (rear) chamber?

Also, I'm assuming that the air supply line to the spring bake chamber is supposed to be ON as long as the truck is running. Ther eare two suppluy lines coming back there. One is on when I press the brakes, the brake line, of course. But the other one is not ON when the truck is fired up. Am I missing something here? Like a switch up front I must first engage. Obviously, I'm showing you all that this is my first MAck truck!

ANy help with this would be greatly appreciated.

btw, I know all about the dangers of opning up the spring brake.

thanks,

~martin

[Bollweevil]

You have pretty much figured it out by yourself. The front side of the chamber is the service brake, which is supplied by the foot valve. The rear part of the chamber is the parking, or spring brake, which is supplied through a valve inside the cab. Parking brakes are released by air pressure, not applied.

[martinf]

Parking brakes are released by air pressure, not applied.

SO, since the parking brakes are released by air pressure, I should have a source of air coming out of one of the supply pipes (the one other than the brake source that supplies air when I hit the brake shuttle) all the time the truck is running, correct?

I don't have any air coming and that's what I am wondering about.

Ideas?

~martin

[Bollweevil]

The only time you should have air to the parking brake chamber is when you have manually released the parking valve. It should be located in the dash or possibly between the seats, below the rear window. Normally you would need 60 to 70 lbs. air pressure to actuate the release valve, and keep it open. It should go without saying, that you should block the wheels if you are going to be under the truck testing these lines with the engine running. Since these lines were torn off, quick release valves on service and parking brakes, may further complicate or confuse the issue. you could e mail a phone number, and I'll try to talk you through this. James

[martinf]

The only time you should have air to the parking brake chamber is when you have manually released the parking valve. It should be located in the dash or possibly between the seats, below the rear window. Normally you would need 60 to 70 lbs. air pressure to actuate the release valve, and keep it open. It should go without saying, that you should block the wheels if you are going to be under the truck testing these lines with the engine running. Since these lines were torn off, quick release valves on service and parking brakes, may further complicate or confuse the issue. you could e mail a phone number, and I'll try to talk you through this. James

That makes sense. It'll be a week or so until I've got some time to investigate all this.

Thanks for the phone help offer, James, I'll take you up on it if I need it and will report back later.

~martin

[martinf]

That makes sense. It'll be a week or so until I've got some time to investigate all this.

Thanks for the phone help offer, James, I'll take you up on it if I need it and will report back later.

~martin

James,

Got it all hooked up and the brake adjusters set and I'm good to go. Loosing some air pressure somewhere, gotta track that one down next.

thansk for the assistance.

~martin