This bus has Meritor WABCO brake chambers and sadly the parking brake springs in both chambers are worn, allowing the bus to move with the parking brake applied when given 1,300-1,500rpm. This is why I always do an air brake test. I want to make sure everything in the brake system is working. Interesting how this bus uses Meritor WABCO chambers when the parking brake valve is a Bendix part. Bendix EnduraSure chambers would be able to withstand a lot more than these pieces of junk.

04/16/2024 Update: Issue has been fixed.