kawilson918

The Haynes manual makes this look easy enough, replacing my rusted-out, leaking vacuum booster on a '91 F150/ I6-manual, but what it doesn't tell me is that when I go to various online sources (Murray's, the zone, etc.) for the part, I'm offered it "loaded" or "unloaded." The former has a master cylinder attached, looks like. But is there any other significance to the expression loaded/unloaded?

Haynes makes it look like you could do this, without the new master cylinder (I have no indication mine's bad), and could not only save bucks but avoid having to bleed the system. Can that be right? It sure is enticing with the temp out there hovering in the low teens and brisk wind, and me with no garage access (my son's dead '78 Econoline--rod knock--is eating up the space).

dewman

First, I would use my F150 to pull the van out of the garage.
Second, I would park my F150 in the garage so I could work on it in relative comfort, especially compared to the outside temps.

As for the booster, on rockauto.com, they list it for $60.99 w/o the master cylinder and $120.79 with the master cylinder. There is a $25 core charge w/o and a $40 core charge with the cylinder. For the relatively few extra dollars it would probably be a good idea to replace the master cylinder too. It would help reduce the likelyhood of future brake problems related to that part and you are already elbow deep replacing the booster anyway.

kawilson918

Yeah, I hear that! You genuinely got me to LOL. I just used the F150 to haul him (age 24, and has boomeranged on us twice now) and his junk out of my basement to his new apartment, Jan. 1. The E-van is the next target. I've got a one-lane driveway and my boat is in between me and the van, or it would be sitting out in the snow already. Complicated little game of vehicular Tetris to play.

You're probably right about it being wiser to do the master cylinder at the same time. I just keep thinking about busted bleeders in the cold and crud and wincing about it. One of my other sons has a friend in auto technician school who already has his brake certification...maybe he'd like to earn a few bucks on the side.

KAH

I have a bit of a question regarding your defective vacuum brake booster.

As of now, I have only replaced one and hope not to have to do another,
although it was not too bad as I was able to work around the master cylinder.

My questions though, involves the symptoms. In my case, every time I
put the brakes on, the leaky vacuum booster would let more air into the
engine by the vacuum lines.

This would make the car go faster. Incredible, put the brakes on and the
stupid car went faster.

I have no idea if this is a common sympton. Did yours do this also ?

I thought it was pretty scary and still do.

Thanks, Ken H.

kawilson918

No, mine doesn't do that. My truck has a manual trans, so I'm either downshifting to give the brakes a little help from engine compression or the clutch is in. Either way, the truck isn't going to speed up. It picks up revs, only a little, but that's normal with the clutch pedal in and your foot off the gas, therefore no-load on the engine.

It's leaking out the rusty body of the booster, anyway, not back through the line. Technically, if you're "leaking" vacuum, it means you'd really be sucking air in, but that just equalizes pressure on each side of the diaphragm in the booster so you don't have proper power assist. Did you have a bad vacuum line from engine to booster, too, or a flaw within the booster itself, such as a split in the diaphragm or a bad check valve on the line?

I've never encountered the situation you described, but if the prospect of a repeat really scares you and your vehicle has power steering, too, there's an alternative. Researching this online I found this tech article at a Bronco site, describing installation of a hydroboost unit from an old car (it uses your power steering pump to generate hydraulic pressure, rather than vacuum): http://classicbroncos.com/hydroboost.shtml

New cars with advanced ABS systems, and hybrids, use electrical pumps to pressurize power brakes, but that's way beyond the scope of your usual shadetree mechanic driveway mods.

You mention you worked "around" the master cylinder. One worry I have doing it that way, as the Haynes manual indicates, by pulling the m.c. forward a bit to clear the booster for removal and reinstallation, would be putting pressure on the brake lines coming off the m.c. Does it have to move very far? Cracking or kinking a line would be no fun. Anyone else done it this way, rather than replacing the booster and m.c. as a unit?

dewman

that is probably not a bad idea, let the kid get some experience and earn a couple bucks too!