5 ton new brake problems

[RRdr]

I had previously posted some issues with brakes on my m813a1. Since then I have rebuilt the air pack and installed it, and installed a new master cylinder today, then I bled out the master cylinder, and air pack then the axles according to the pubs, I started and operated my truck. Previously the brakes on the front and middle axle would stick because air pressure wasnt being relieved and the fluid pressure was stuck at the brakes locking them up. Now since the install of the new master cylinder and rebuilt air pack, the truck will move and then once I press the brakes it stops, and when I let go of the brake pedal there is a time delay sometimes between ten to twenty or more seconds before the brakes release. During this ten to twenty seconds when I try to let out the clutch, the brakes will kill the motor until the air pressure makes a clicking sound and it gets built up to 120 psi on the dash pressure gauge farthest from the drivers seat, is there some sort of valve or check ball that is supposed to relieve air pressure in the system from the brake pack which would in turn release the fluid pressure from the wheels once the brake pedal is let go of? What component or part controls the air pressure relief once the brake pedal is released? I am thinking that the air pressure relief is delayed and causing the fluid pressure to keep the axles locked up. If anyone has encountered this and know how to fix this issue please , I could use some insight on this issue. Thanks in advance.

 

[Ajax MD]

Sounds like the air is slow to bleed off. I'm not an expert on the air pack. I'm replying to bump this thread to the top so that someone more knowledgeable will contribute.

 

[G744]

Open the rear gladhand yellow valve and try the brakes.

That should allow the application pressure to immediately release.

If not, there is an internal problem in the airpack.

DG

 

[RRdr]

Thanks for the advice, I am wondering if it might be a switching valve in the air pack, now the glad hand and valve your talking about would be the service glad hand or the emergency glad hand valve? The rear service glad hand on the passenger side of the truck in the back, when I open the valve and remove the glad hand cover it immediately dumps system air pressure out, because nothing is connected to it. I didn’t know which one you were referencing ?

 

[msgjd]

When you replaced the master cylinder it is critical to have the linkage and pedal adjustment within the correct tolerances per TM... There is a possibility the MC piston is not returning all the way, even if the pedal travel seemed adequate when you first started out .. therefore, it will be slow to release pressure ... In my case the pedal free play became less and less with each application to the point the brakes would not release until I let it sit awhile.. I have experienced this on the M817 .. Just another thing to be sure of

 

[RRdr]

When you replaced the master cylinder it is critical to have the linkage and pedal adjustment within the correct tolerances per TM... There is a possibility the MC piston is not returning all the way, even if the pedal travel seemed adequate when you first started out .. therefore, it will be slow to release pressure ... I have experienced this on the M817 .. Just another thing to be sure of

thank you I will def check that and make sure it is within specs.

 

[G744]

The service line only carries metered pressure when the brakes are applied.

If air comes out continuously, there is a upstream problem.

The previous posts have good advice for the fix.

DG

 

[RRdr]

So you believe the problem lies in the air pack? The only moving part in it is a switching valve in the back of the air pack besides the piston and rubber bladder, I don’t know a whole lot about the air pack but it did receive a fresh rebuild very recently, would the problem possibly be in any other part of the air system?

 

[G744]

The airpack may not be at fault.

Not releasing could be a bad adjustment on the MC pushrod, or the plumbing was reconnected in error.

DG

 

[Brutacus]

You could have a multitude of problems adding up to the big problems you have now. Once you rule out the air pack, check your brake cylinders. I went through similar problems with my brake system. After replacing the master cylinder, another air pack, replace the hoses and most of the rusted out hard lines, I found that some water had found its way into some of the brake cylinders causing problems as well. Also, half of the brake shoe return springs were rusted beyond being operational. That caused some of my brakes cylinders to operate normally, and others to act as if the air pack is acting strange.