[Cerry]

Hello guys!

i have a problem with my ' 81 k5 Chevy Blazer, could you help me???

when i push down brake pedal, i hear a sound of air come out.

could be a brake booster leak?

thanks guys!

Fabio

[Nsomnia]

Air or fluid squishing sound?

[fast68]

hi there

if you hear it under the dash inside the truck then its the booster or possibly the cruise vacuum switch mounted on the brake pedal arm bracket.

you will have to look and see while engine is running to figure it out.

or unplug the booster hose, and plug off the hose, and then try. if there is still the vacuum sound from under the dash then its the cruise switch.

if its not from under the dash then its either air in a line, or a hole in a line.

but then your pedal would be either all the way to the floor, or be very soft spongy

[Jmark]

Originally Posted by fast68

if you hear it under the dash inside the truck then its the booster or possibly the cruise vacuum switch mounted on the brake pedal arm bracket. you will have to look and see while engine is running to figure it out. or unplug the booster and plug the hose and then try it and see. if still the sound from under the dash then its the cruise switch.

Very good call! (and vise versa too on the booster/cruise test)


Mark

[Cerry]

yes exactly under dash!
as if i push down an air pump

[Jmark]

Originally Posted by Cerry

yes exactly under dash!
as if i push down an air pump

Usually, it is a bad power brake booster. Hissing under the dash when you step on the pedal. Changing the booster is probably in order.

Does it have cruise control too? If yes, it's possible that the cruise vacuum switch is bad. (never seen it but very possible)

IF you have cruise, find the big hose on the transducer that goes through the firewall and either clamp it off or remove it from the transducer and cap the fitting, then start and press the pedal again. If the hissing is gone, the cruise switch is bad. If the hissing is still there, the booster is bad.

If you don't have cruise, you need a new booster! LOL

Mark

[Cerry]

i'll check out later thanks!
i can say that brake system has never been checked or replaced.
30 years without maintenace! i thought at least worn brake pads or disks!

booster is a big problem!

[Cerry]

thanks guys for answers!
so i told you when i push down brake pedal i hear as air come out under dash.
today i checked the system.
1° - i depressed brake pedal several times with engine stopped. with pedal depressed i started the engine and pedal gone down, so i think this test has been good.
2° - i started engine and lei it run for 3 minutes then i shuted it off, i depressed brake pedal several times and sinceraly i realized that pedal reserve distance has not increased every time brake pedal is depressed, or better not so much! (maybe 'cause brake pad are used)
3° - i realized that when i depress brake pedal the reservoir assembly rises from master cylinder body, but not simple a littel, it seems to escape from holes, precisly the part near the cab body!

[68NovaSS]

I've merged yesterday's thread and todays, no reason for two posts, same issue. Also moved to the brake forum, you may get more responses there.

[Cerry]

sorry nova!