Tail shaft parking brake

[Brian48]

On my 1991 Safari Serengeti, 460 ford gasser, Osh Kosh chassis, the tail shaft parking brake is no longer working. My owners manual states "the parking brake is applied by means of a control valve activating a relay valve which activates the spring-set parking brake chamber. The spring chamber pulls a cable engaging the drum brake on the transmission tail shaft". Everything appears to move with exception of the spring-set chamber. It does not appear that chamber is getting the hydraulic pressure required. Any ideas where the control valve and relay valve mentioned above is located? Any info or schematics of the system would be greatly appreciated. Thank you.
Brian48

[Brian48]

I received a much appreciated e-mail from Mr. Haag, but he stated his expertise was more with the chevy workhorse chassis. I need to figure out where the actuator on this ford is and why it is not "actuating". Thanks. Brian

[Dennis4809]

Little off topic but be sure to check the fluid in that tail shaft. Parking brake almost covers it but that housing is separate from the transmission. Only function seems to be to house the speedo drive. Don't ask me how I know that no lube means seized bearings, a tow, and a very expensive part.

[fischer]

there was a guy called " old used bear " that was a guru for auto parking brakes for rv's try googling him. I have read that there are brake shoes that wear out in the hub , but maybe I am thinking of something else. also google auto parking brake ....

after you google old used bear select : Oemys web Site j71 auto park
good luck and keep us informed