The subject is a crusty old Jeep pickup that doesn't get driven often enough for wear to be a real factor. The system is entirely conventional: front disc and rear drum with factory vacuum power assist, no hydroboost, no trick parts other than braided lines. All hydraulics were replaced several years ago - not to say that they are all confirmed good, but judging by brake feel and action, they are all doing their job.
The brake pedal is no longer returning to the upright position upon release. It stays down just far enough to impart a little drag on the brakes and keep the rear lamps lit.
I have power assist, and attempting to wiggle the check valve free of the booster results in a sharp hissing, ergo I believe the vacuum booster holds vacuum and the check valve functions correctly. If I purge vacuum pumping the pedal with engine off, and then start the engine with pedal depressed, vacuum assist pulls the pedal down farther as vacuum comes in.
When I push on the pedal, I can hear the control valve whooshing as it lets atmospheric pressure in on every stroke. This is disasppointing, as I was hoping the control valve was stuck and could be freed up with a few shots of throttle body cleaner, but it seems not to be the problem.
This is a dry west coast truck with no rust. I initially thought the pedal bushing was just sticky, but there is no real change after soaking the pivot with WD40 and working it in. The factory catalog does not list a pedal return spring. For now I'm just pulling the pedal up with my toe. Modern problems, modern solutions, and so on.
It's possible the rear shoe return springs could have broken or gotten soft, or maybe the master is sticky, but the pedal does return and there doesn't seem to be any braking action when the pedal is pulled up. I'm inclined rebuild the MC in case it's become sticky. Any other guesses before I just fire the cannon?
