The brakes on my '90 4Runner make a loud hissing noise, but it goes away when the brake pedal is pushed down all the way. When you let up it starts hissing again.

They aren't mushy but they move a lot farther than they used to. When I first got the truck about a year ago, they were real touchy (you only had to push them about an inch or two to get full stop, it made people who weren't used to driving it look retarded) but now they move almost all the way to the floor. Plus, I slammed on the brakes going about 25 on a gravel road and there is no ABS action at all.

Oh,and I recently got a lot of stuff on it fixed (vacuum solenoid, fuel leak, new water pump, other small stuff) if any of that make a difference. I thought fixing whatever vacuum problem was in there because of that solenoid would fix the brakes, but I guess not.

So any ideas why they do this?

 

Check the adjustment of the rear shoes, also check the drums for being out of round.

 

Sounds like you have a vacuum leak. It's most likely a bad diaphragm in the brake booster. Does the engine stumble when the brake pedal is pressed?

 

I am having the same problem on my 93 3vze 4x4. I'm going to replace the bbooster. my question is, what is causing the hissing noise when the brake is being presssed? if it is a faulty diaphragm in the bbooster, would a faulty master cylinder cause this to fail? should i replace the master cylinder as well?

 

my engine does stumble a little when the brakes are starting to be pushed down. It's especially bad when approaching a stoplight or stop sign. guess im going to take apart the brake booster today.

 

Be warned, the booster has a big spring in it. Mind your teeth!!!!