My daughter's '92 4runner (V6, 4wd) suddenly has really hard brakes as if there's no power boost. I have very good vacuum at the pwr booster nipple.
Is there a simple fix like a blown fuse? I don't have the fuse box cover to see if one works the pwr brakes. I figured I'd ask the collective wisdom before I start yanking fuses or pulling wheels.

Thanks in advance,

 

Do you have good vacuum at teh booster end of the large black vacuum line? There's a oneway valve that may be clogged/failed about halfway along that. If you have good vac at the booster end of the line, you may have a leak in the booster, or perhaps the MC seals need to be replaced.

Just a couple of thoughts

 

Sorry for the threadjack. Does anyone have a link to how a brake booster works, or would care to explain it.

 

Big, large surface area diaphram on a light spring, just enough to hold it agianst the vacuum, connected to the MC shaft. When you press the pedal, you overcome the spring tension, and the engine vacuum "helps" pull the shaft in, or apply the brakes. Think of it as the engine vacuum pulling on the pedal to help your foot pressure.