from a blog post;
Recently, we stored our diesel pusher for 2 months. When “closing it up” for the extended storage, we put down the hydraulic jacks and engaged the air (i.e., parking) brakes. At the end of the storage period, the coach started up fine, the jacks came up, and then when getting ready to move, after putting the transmission into drive, the air (i.e., parking) brakes seemed to dis-engage (I pushed in the yellow button and heard the air system operate the braking mechanism), yet the coach would not move because the brakes had “frozen.” Very stressful time, yet after a bit of back and forth rocking, the brakes broke free and we were able to drive away.
We have again just put the coach into storage, yet this time, our plan was revised to NOT putting on the air (i.e. parking) brakes AND not putting the jacks down; although we did “lower the coach” by draining all the air from the air suspension system. We put lots of blocks in front of and behind all wheels. However, after we thought the coach was de-commissioned and ready for storage, we heard a strange noise, which turned out to be a “air leaking” noise which was the air (i.e., parking) brakes engaging automatically. IS THIS NORMAL? Is it even possible to store a coach with the air (i.e. parking) brakes not engaged?
The “parking/emergency” brakes on an air brake system come on via strong springs. It is the air pressure in the system that allows you to release the brakes by applying air pressure against the spring. It is designed so that if when operating the motorhome you start to lose pressure the emergency brakes will engage. This is usually around 45-20 psi. There is a warning buzzer that goes off indicating low pressure (around 60 psi) before the brakes engage
So yes it is normal for the “parking” brake to activate if the pressure in the system drops too low.
I encourage all diesel motorhome operators who have air brakes to review their manual to learn about the operation of the braking system. CDL drivers have to pass a separate test on air brakes to get an air brake endorsement (or in some states, to not have an air brake exclusion) on their license.
Normally you engage the parking brake by pulling a knot which releases the air pressure only at the brakes allowing the spring to release and set the brakes.