brake issues

[lak2004]

So i did my rear drums a couple weeks ago when I had to change wheel seals. I bled the brakes and my pedal still felt spongy. So I noticed that I could hear an air noise when I push the brake pedal so I went ahead and replaced the master cylinder, but I am starting to think the power booster is leaking?

I did bench bleed the master before putting it on.

SO now when I push the pedal when my blazer is running it makes a loud air noise "whooooosh." When I turn the truck off it doesnt do that when I pump the brake. Is that normal? I am going to make a homemade power bleeder today or tomorrow and try bleeding all the lines again as well.

But what I really need to know is if the booster is failing me? Thanks

 

[diesel4me]

Vaccum boosters do make some "whooshing" noise normally,when they fail you'll first notice a lack of power assist,or the vacuum boosters diaphram might cause a rough idle or staling when you apply the brakes if it is ruptured..

One way to see if the diaphram is OK is to run the engine for a few minutes,shut it off,then apply the brakes--the first two pumps should still have power assist,then the pedal will get much harder to depress...another way is to idle the engine a minute or so and shut it off,then wait 15 minutes--and pull out the check valve that plugs into the grommet on the booster that the vacuum hose goes too--it you hear a suction as its being pulled out,the diaphram is OK..

My guess is your brakes are still in need of bleeding or the rear drums (if so equipped) are not adjusted correctly..excessive brake pedal travel makes the booster have to travel further and that can cause more "noises"..

 

[lak2004]

hmmmm i was getting a surging in the engine when I applied the brakes at stop lights. so maybe the diaphragm is fubrd. ill try to bleed them again with a power bleeder and if that doesnt work ill check the vacuum lines and make sure those are not leaking.

 

[diesel4me]

You'll get "some" change in the idle when you apply the brakes normally,it's when the engine wants to stall or barely idle with the brakes applied, that's when the booster's diaphram is faulty..some engines will speed up for a second when the brakes are let off,thats considered normal...sometimes you'll hear vacuum leaking under the dash when the diaphram is bad too,with the brakes applied..