Tractor parking brake.

check for bad wires. Start from lights and go up

 

Check spring brake relay valve and/or quick release valve. Might be sticking and not dumping air fast enough.

 

Twice on current truck the parking brake for tractor and trailer would not operate,,,learned this as I was stepping out of truck.(this was at the top of a 2 mile 5% decline) Not sure what the shop did. On a grade I always wait a few seconds before exiting to make sure both brakes apply.

 

If taking awhile to exhaust air to apply springs then i’d look for a line restriction, bad quick release valve, or plugged exhaust in dash valve or quick release valve.

If exhausts air and applies springs like normal but takes awhile for shoes to grab and lock down drums to stop a rollaway. I’d look at possible broken springs in chambers, bad slacks/ or out of adjustment, camshafts defective, lack of grease or grease turned to glue, shoes and drums beyond service size and wear tolerances or getting oil contamination.