air lost when truck put I drive

[Tinydragon2001]

air lost when truck put in drive

I been using my m931 on a job to move trailers around an old fleet yard that's over grown and muddy. I noticed while using it today that the truck would build air a bit slow, and once I'd put the trans in gear the secondary air system would start loosing pressure. Needless to say, I spent most of the day listening to a low air buzzer. I wouldn't lose all air. It would stay around 60 until I'd put the truck back in neutral. It would build fine when in neutral. Any one have this happen before?

 

[Suprman]

Was it loosing air when you took your foot off the brake? You could have a bad brake chamber.

 

[Jeepsinker]

Take a hammer to the air dryer just in front of the inter axle. Probably got mud in the bleed off valve. You could also remove the three 5/16 bolts from the bottom of it and take the plastic cover off then tap the plastic valve up and closed.

 

[Tinydragon2001]

I'll give that a try.

 

[goldneagle]

If that is not the problem you may have a torn diaphragm in one or more of the brake chambers. I had to replace both front ones on my M923. They are about $5 each at NAPA.

If the leak is in the spring brake chamber do not attempt to open it. The spring can kill you! Only the ones in the front wheels and matching ones in the rear can be opened safely with air pressure drained.

 

[Suprman]

Could be a leak in one of the airbrake lines also. A good way to diagnose would be to park on level ground and chock the trucks wheels very very well. Start it with the brake lever on and build air to 120psi. Turn off truck and release brake lever. Make sure truck is chocked well and does not move. Walk around truck and listen for air leaks. You should hear a leaky brake chamber and if it's a line you can hear it and spray a little windex around till you see it bubbling where air is escaping.

 

[Tinydragon2001]

I'm pretty sure it's a leaking diaphram. I built air, shut the truck off, and released the parking brake. Heard a hissing coming fron an air canister.

Goldeagle... you got a part number for the replacement diaphram from napa?

 

[goldneagle]

I'm pretty sure it's a leaking diaphram. I built air, shut the truck off, and released the parking brake. Heard a hissing coming fron an air canister.

Goldeagle... you got a part number for the replacement diaphram from napa?

I'll check and add to this reply.

Type 12 Air Brake Chamber Diaphragm (part # 234226 / AD17544)