1999 C6500 park brake???

[82355]

Anyone have any experience with this setup? It is the elecric/hydraulic/mechanical park brake on the out put of the transmission. On a gas burner with hydraulic brakes.

Martin

 

[Larry]

Anyone have any experience with this setup? It is the elecric/hydraulic/mechanical park brake on the out put of the transmission. On a gas burner with hydraulic brakes.

Martin

Yep, those are auto apply park brakes for units with Allison transmissions without park pawls. It’s a pain in the ass system we also used on RV chassis. Most times adjustment and relay issues cause most auto-apply woes. What’s the issue?

 

[82355]

Won't stay applied.

Martin

 

[82355]

I came in late to the game on this.

It already has a new actuator hung on the truck, and I installed a solenoid. Neither fixed the problem. From the reading I am doing on the internet, it looks like the pressure switch on the motor may be the problem.

Martin

 

[Larry]

But it does apply? Just don’t hold for long? Check the easy stuff like the adjustment and shoe condition? Any DTCs? Could be a pressure switch which would usually leave a code 9. Do you have access to All Data, Mitchell, GM SI2000 or some other type of service manual? These things can be a pain in the ass to work on without a book

 

[82355]

Won't stay applied.

Martin

Confusingly enough, by applied, I mean released.....

When pressure is applied to the system, it releases the brakes. Just like air brakes.

Martin

 

[82355]

Yeah, it applies (releases the brake). Then it starts making noise, and slowly the mechanical spring in the actuator overpowers the hydraulic pressure. As soon as it had completely let off the pressure, it applies again, and starts over.

I ordered a pressure switch for the motor.

Martin

 

[Larry]

Ya, it is backasswards like air brakes but you knew what I meant . I agree, I would suspect the pressure switch first. Good luck….these can be a hassle to mess with.