What does it mean when I hear hissing when I apply the brake?

Question

Today I had to make a hard tire screeching stop to avoid a rear end collision. About an hour later I was on my way to a friends house I heard hissing from my brake pedal when I applied pressure. At first there was no problem but I realized that more and more it was getting harder to stop when it eventually came to a point where (after I decided to cancel and come back home) the only way my truck would stop was when I applied a great amount of pressure since the pedal was hard to push down. Thankfully I made it home but I was wondering what the problem could be and if it's something I could fix on my own and if not would this be a big repair since I have little money to work with here.

1996 2WD Chevy Tahoe 4 door ABS brakes

Addition: how can I get to the booster, is it right under the carpeting?

Answer 1

Yes, it is the brake booster. It is not hard to replace, just takes a little bit of time. The booster itself is located under the hood on the driver's side. It is that large, round, black thing with a rubber hose going from it to the engine. Order a re-man booster from the parts store before removing it so that they can order it if they need to.

To remove the booster:
Remove the rubber hose (the one going to the engine)from the check valve mounted on the booster.

Remove the nuts holding the brake master cylinder to the brake booster. CAREFULLY move the master cylinder out of the way.

Go under the dash in the vehicle.

There will be a rod that goes from the firewall to the brake pedal, remove this from the brake pedal.
PAY ATTENTION, there may be a brake light switch mounted on the metal stud where the rod mounts, make sure that you reinstall this the same way as you take it off or your brake lights will not work properly.

Remove the 4 nuts at the firewall that form a box around that rod.

Get back out of the vehicle and grab the brake booster.
Carefully remove it from the vehicle.

Take the old unit to the parts store to match it up and they will need the old one or else you will have to pay a core charge.

Reverse the procedure to reinstall.

Answer 2

There can be a hissing when you first push the pedal, because you are opening a valve to let vacuum into the power brake diaphragm chamber. But it must stop as long as you do not apply more pressure to the pedal. If it does not stop, then the diaphragm has a leak, and should be replaced. But also notice the engine speed. It should change a bit when you first hit the brakes, but it should return to normal in a second or 2, unless you push down harder. If the engine always runs different when the pedal is down, then there is a leak.

Answer 3

The brake booster which boosts your braking effort has punctured its diaphragm and the hissing you hear is the vacuum line sucking air through the booster.

Get the manufacturer's model number and build date and try to source a replacement working booster from a wrecker.

Yuo will need to remove the master cylinder from the booster, disconnect vacuum hose and unbolt it from the firewall and release the pedal from the booster then remove and refit replacement.

Not really a big repair but awkward and sometimes frustrating. (1-2 hours upsidedown under dash) booster should set you back around $100 depending from a wreckers.

Tried to edit in time but failed r well

Booster is up against the "firewall" in the engine bay (steel wall between cabin and engine bay), is 6"-7" dia. round, black or silver and has steel piping/hoses connected to it.

Answer 4

You blew the diaphragm in your vacuum brake booster most likely. It is not too hard to change.

But if you do not have one go to your local parts dealer like Auto Zone, ABC, Advance, O'Reilley's and get a manual for your make and model car. The instructions will help a lot. You can also price another booster while there.

Answer 5

under the dash just about 4 inches to the left and 4 inches above the steering sector, there are four nuts in a square pattern on the fire wall about 3 inches apart. I don't think you have to move any carpet . just some wires have to be pushed out of the way. if still having trouble look for the brake pedal pushrod, the nuts are around it.

Answer 6

it sounds like you ruptured the diaphram in the power brake booster and the noise you are hearing is vacuum being pulled thru the unit.there is a small filter were the pedal push rod goes thru thr firewall and if you check that is probably were the noise is coming from,you will need a new booster

Answer 7

Your brakes have reached its minimum safe level where the metal strip is rubbing against the rotor. The hissing sound is an indicator for you to replace the pads.

Usually you still have about 4mm pads left. During this time, you can start saving some money and go buy the pads from the shop.

happy driving.

Answer 8

it is definetly the vacuum brake booster and it should be located betwwen the firewall and the brake master cylinder (engine side).The cheapest way is to get a second hand one and get it tested before fitting it.Any good brake specialist should test or know of someone that does.

Answer 9

air power assisted brakes....problem may be leek in air-line or rubber diaphragm in booster is perished or got a hole in it if you can track down where the hissing is from it may be very ezy to repair

ps brake shoes don't hiss (they squeal/grind)so no need to look there

Answer 10

check the brake shoes if they are still good or became thin so you must change them,in some cases these shoes are bad quality then became in their half age give hissing sound with weak breaking,also chech break pump oil level.then decide what you must do to clear this problem.