Brakes & Vacuum Troubleshooting
Back with another one...starting to seem like one thing gets fixed and another raises it's head. This time the brake peddle occasionally goes hard, other times it's a typical gentle push. On three occassions the front brake pads maintained contact with the rotors and began to heat up. This has been going on for approx. 3 months. The vacuum pump was replaced about 4 months ago when it went out on me along CA's 166. Pump still draws good vacuum and holds at 26 inches for a good long time. The brake system was also completely bled, including the ABS, and all calipers checked about two months ago.
Yesterday, I performed the simple brake booster check...pumping brakes with engine off to a hard state, then starting engine with slight pressure on pedal to see if descends under vacuum. That worked out fine. I then started a vacuum diagnosis on all vacuum connections and narrowed it down to a fairly rapid leak in the AC line. However, though leaking fast when I shut it down, it still pulled about 25 inches, a bouncy unstable 25 inches. The last easily accessible AC line connection (just behind the battery and above the heater core) holds vacuum, and the first easily accessible connection inside the cab does not hold vacuum. In fact it barely pulls 15 inches. So in reading other posts it sounds like a check valve or reservoir leak, which I've also read is an absolute PITA to access.
So, before I make the AC leak attempt, in the interest of resolving the brake problem first, can I safely plug the AC vacuum port on the vacuum manifold tree and run the vehicle to see if the brake problem is still present? I know a low vacuum will make the pedal hard to push, but is it reasonable that a low or unstable vacuum can also cause the pads to not fully disengage at times? Should I be looking elsewhere before tackling the AC leak?
thanks in advance.
2002 E350 7.3L