Air brake can leaking

[Asymair95]

Was adjusting my brake shoes today (.030”) and came across a leak I had not noticed before because of the non standard configuration of the parking brake. Air tanks full, engine off, and parking brake disengaged with wheels chocked. The drivers side, rear tire, rear brake can leaks air from inside the can someplace.

This does not happen when I shut down the truck normally, air tanks full, engine off, parking brakes engaged...no leak.

Question is, is this something to worry about? I never park the truck with the parking brake disengaged.

 

[simp5782]

Was adjusting my brake shoes today (.030”) and came across a leak I had not noticed before because of the non standard configuration of the parking brake. Air tanks full, engine off, and parking brake disengaged with wheels chocked. The drivers side, rear tire, rear brake can leaks air from inside the can someplace.

This does not happen when I shut down the truck normally, air tanks full, engine off, parking brakes engaged...no leak.

Question is, is this something to worry about? I never park the truck with the parking brake disengaged.

Yes. Causes air loss while driving causing the air compressor to cycle more often to keep up. Causes more moisture in the system, wear on the dryer filter, etc. Replace the diaphragm inside and on the rest of them. Just dry rotted rubber inside from sitting

 

[Asymair95]

Ok, thank you Wes. I’m going to just replace the whole can then. I’m not comfortable opening them up.

Superman, do you have one of these?

 

[wandering neurons]

Based on my experience and documented on the site - you've got a spring in that spring brake chamber that has broken and punctured its diaphragm. Could possibly be dry rot only without a broken spring too. When spring brake button is pushed, air pressure into the spring brake chamber applies pressure to that diaphragm to compress the spring, releasing that brake. Pulling the button (or dumping your air tanks) dumps pressure in the spring chamber, the spring presses the diaphragm, and applies that brake.

 

[M35A2-AZ]

That looks like the same cans that are on the M939 5ton truck. The spring brake diaphragm is #16 and service is #12. Not sure your going to find a complete can. It is not hard to change just need to be safe, cage the brake and open it up, two bolts.

 

[simp5782]

That looks like the same cans that are on the M939 5ton truck. The spring brake diaphragm is #16 and service is #12. Not sure your going to find a complete can. It is not hard to change just need to be safe, cage the brake and open it up, two bolts.

They are a #9 on the service and #12 on the spring


They also crack, this one cracked on the brake release line.

 

[Asymair95]

Thanks guys, Bryce is going to hook me up with a new can.

 

[fasttruck]

From the description in post 1, parking brake released and service brake not applied, there is a leak in the emergency side of the dual brake chamber. Opening these up at home is hazardous to your health when what is left of the spring comes out and bites you. It is safer and more practical in the long run to replace the whole assembly for an issue on the emergency side. Single service brakes and the service side of a dual service chamber can be repaired by replacing the rubber diaphragm inside. As the bolt on the clamp is typically an odd size, when at the parts counter see if you can get that also. Pic of dual service brake chamber cut away and an example of a dual service chamber cracked from road salt induced corrosion attached.