All of a sudden my brake pedal is very soft, and makes a hissing noise when it's pressed. The hissing seems to be coming from that diaphram area above the brake pedal.

The master cylinder is full and there don't appear to be any fluid leaks. When I turn the engine off though and pump the brakes, the pedal will get firm again. It's only with the engine on that is goes soft.

Any ideas? Brake booster maybe?

Thanks

 

With the truck off, pump the pedal until hard. Push hard on pedal, keep pressure on it and start truck. If it's working, the pedal will move down. If it stays "high and hard" the booster system ain't workin.

This is from alldata...

Remove the vacuum booster hose from check valve connection. Manifold vacuum must be available at the check valve end of the vacuum booster hose with the engine at idle speed and the transmission in NEUTRAL. If the manifold vacuum is available to the power brake booster, connect the vacuum booster hose to the power brake booster check valve and do what I have above.

CHECK and if no downward movement of the brake pedal is felt, replace the power brake booster

Operate the engine a minimum of 10 seconds at fast idle. Stop the engine, and let the vehicle stand for 10 minutes. Then apply the brake pedal with approximately 89 N (20 lbs) of force. The brake pedal feel should be the same as that noted with the engine operating. If the brake pedal feels hard (no power assist), replace the check valve and retest. If the brake pedal feels spongy, bleed the hydraulic system to remove air.

 

Sounds like the booster is done.

 

Well I took it to a shop for a "free" brake inspection, and they said when they inspected the rear drums the shoes just fell apart and that was the cause of my soft pedal. They said the booster was fine. Well $250 later to replace the shoes I still have the soft pedal and "hiss" noise from the brake pedal!

 

my pedal has been soft since I changed out my rear axle. i think it is due to air in the system. take it somewhere and have them professionally bleed the brakes.


$250 for rear brake shoes? are they like regular ol' Duralasts or are they good ones? seems like a lot?

 

Wirelessly posted (Android)

They always charge an arm and a leg for brake work.

 

Why take it somewhere? All you need is the right size wrench for the bleeder valve and a friend to pump the pedal while you bleed them...

 

I've noticed that. I wonder why. It's so simple and the parts are cheap. I think they are just banking on the fact that people don't know how it works.

I said professionally because I never seem to bleed them right. I've bleed my brakes 3 times since I've had the truck (first was after front pads, second was after rear shoes, and third was when I swapped my axle) and I have yet to get them right the first time around. Maybe due to lack of experience.

It sounded like he was tired of dealing with the issue and since he had already taken the truck to have the brakes done, which can also be done in ones driveway with minimal toolage, I thought it pertained better to him if I said to have someone else do it.

 

eh, brakes only slow ya down.

 

Yeah the $250 definitely seemed high, but I was stuck paying it because when they inspected the rear brakes the shoes pretty much just fell apart. They had about 90k miles on them...

Can anyone do me a favor, and start their truck and listen to hear if there is a hiss noise from the brake pedal/booster diaphram area when the pedal is being pushed down? Just trying to figure out if it's normal or not...

Also is it possible to replace the booster without having to bleed the brakes?

 

My brake pedal does the same thing and it's been that way for as long as I can remember. It sounds like something being deflated, and it happens when you first push the brakes then the pedal stiffens up, right? I've never really paid any attention to it because my brakes have always worked just fine.

 

Mine does it to dude. Rangers are known to make a bunch of noises all the time. Power steering is whines, brake booster makes noise. Drive shafts clunk. Engines idle loud. Exhaust rattles. Tranny shifts rattle. Just runs in the trucks.

 

if the OPs truck doesnt have 4 wheel ABS then yes that will work but you cant do that with 4 wheel ABS equipped trucks...need a vac. bleeder