Brakes & Vacuum Troubleshooting

[Wire89]

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.

[Wire89]

So I ended up plugging the vacuum line for the AC and made my way down to Agile this weekend (another pleased RIP customer), 180 miles+ each way. On the way down, late night no traffic, the brakes were very consistent. On the way back, daytime lots of traffic, the brakes would slowly tighten up in the lower speed frequent use traffic situations, then return to normal after increased speed and/or no use. However, they were much better than previous, and they didn’t seem to keep contact and heat up. So I’m back to wondering if I should look further at booster or master cylinder? Maybe this isn’t so out of ordinary?

Any feedback appreciated.

[Bbasso]

Vacuum pump might be taking a dump, rather easy and affordable for DIY.

[Ben10281]

Just had my vacuum pump go. I have no idea how many miles mine had on it, but if anyone out three hasn't changed theirs in a while, or has a new to them diesel van, it may be worth swapping it out. When it goes, you have no power brakes and there is NO backup system other than stepping on the brake pedal hard, and even then I doubt my van would stop coming down a mountain pass!

As Bbasso said it is a pretty easy fix that can be done in the field with a few tools(10mm wrench, serp belt tool, pliers), as long as you have a spare pump, or can get to an auto parts store to get one.

Just thought I would toss that out there as a PSA!

[JWA]

Originally Posted by Ben10281

As Bbasso said it is a pretty easy fix that can be done in the field with a few tools(10mm wrench, serp belt tool, pliers), as long as you have a spare pump, or can get to an auto parts store to get one.

Just thought I would toss that out there as a PSA!

Good advice and I'll add all of us should carry a spare serpentine belt regardless of fuel---neighbor just recently blew one in his F-Series diesel that cost in excess of $600 to replace out on the road---not counting his down time.

The all time best too (IMHO) is this one: http://www.gearwrench.com/gearwrench...-tool-set.html Affordable, convenient to stow out of the way until needed and very usable on most every vehicle out there.

HTH