Hard brake pedal,hissing sound, rpm drop....

[gunhound]

Did a search but couldn't find anything on this issue.

Have a 97 Blazer 4x4. Today as the wife was driving home, the pedal became hard to press. I checked it out and noticed a hissing sound such as an air leak when applying the brakes, and as I applied more pressure, the engine rpm drops and nearly cuts out.
It actually cut out on her while stopped at a traffic light. I really need to find the problem since its the wife's car.
Any information will be greatly appreciated.

[DINO55]

If your hearing a hissing sound inside your blazer when you push down on thebrake pedal, The most likely cause would be a brake booster failure.

[drdd]

check for vacuum leaks ... particularly at the vacuum ball and the "three way splitter" ... look for dry-rotted rubber at all connections ... see if you can hear where the hiss is coming from ... check all vacuum fittings ...

Originally Posted by gunhound

Did a search but couldn't find anything on this issue.

Have a 97 Blazer 4x4. Today as the wife was driving home, the pedal became hard to press. I checked it out and noticed a hissing sound such as an air leak when applying the brakes, and as I applied more pressure, the engine rpm drops and nearly cuts out.
It actually cut out on her while stopped at a traffic light. I really need to find the problem since its the wife's car.
Any information will be greatly appreciated.

[JA no Y]

Does the hissing sound stay even when stoped?. My booster went out and the pedal was hard like you described. Sounded like air brakes on an 18 wheeler. Long as I had the brake pedal presssed the sound stayed. I replaced the booster and problem went away.

[Rmbodie]

I agree , it sounds like you will be pulling off the power brake booster . Since it is losing all the vacuum when you apply brake , it probably means the rubber diaphram is torn on the inside seal . I dont think it is user rebuildable but you will have a core charge for the exchange . You can remove the vacuum line from the engine compartment side and temperarely plug it up so your engine will run correct and pretent you are driving a 50 year old car when you want to stop(until you can replace it) . Good luck ,Rob

[wolfox]

A stuck open EGR can create a hiss that can be heard in the air intake and make braking hard. Had that happen to me twice until all the carbon gunk got swept out of the EGR passages on my '95. Food for thought.

[BlazerLT]

I don't understand why people instantly run to their computer instead of at least checking where the noise is coming from.

OPEN YOU HOOD AND LOOK!

[gunhound]

JA no Y-
The sound of rushing air only occurs when I press the brake pedal, and it does seem to sound like air brakes.
Looks like I will be replacing a brake booster. Any tips on replacing it?

BTW, I did check under the hood, but the sound was more pronounced inside.
I do have some mech experience, but have never had this occur.

Thanks to everyone for the quick responses.

[BlazerLT]

Mine always sounds like air is moving when I oress the brakes.

Did you chack the vacuum hose going to the brake booster and make sure it is attached?

[gunhound]

There is usually a slight sound of air (such as an air leak) when brakes are applied. But now it is VERY noticeable with an extremely hard pedal feel. Rusing air sound is loud, like air brakes.
I am going to check vacuum lines, but I suspect the booster is shot after reading the posts. I will probably replace the master cylinder while I'm at it.

[BlazerLT]

Check the hose before anything.

[JA no Y]

The rushing air sound only happened on my bad booster when I pressed the brake pedal. On a normal brake it only occured for a second or two. When my booster went it stayed no matter how long I had the brake pressed and was alot louder. Wasn't the quick little hiss on a normal opperating pedal.

The hardest part of replacing the booster was getting to the nuts attaching the booster to the firewall. They are behind the drivers dash but can be gotten to from underneth. Just make sure you have a universal and some extensions. Have to pull back the carpet and remove the access pannels under the dash also.

To remove the bnooster, remove the nut attaching the master cylinder to the booster and carefully pull the master cylinder along with RWAL control module and isolation/dump valve forward until it clears the mounting studs. Be carefull not to bend or kink the brake lines.

Disconect the vacuum hose.

Inside the vehicle, remove the clip and remove the power brake pushrod from the top of the brake pedal

Remove the nuts attaching the booster to the firewall

The carefully remove the booser form the engine compartment.

To intall the new one just do the reverse of removing it

Unless there is a problem with the master cylinder, I wouldn't change it. Can be a pain to get out any air in your brake lines from changing it out if you don't have someone to help you. Especialy with an ABS system.

[gunhound]

JA no Y-
Thanks a bunch - the booster was the culprit.
It was a PITA to change it out, but was done in a couple of hours.

Thanks to everyone and this board as well.

[BlazerLT]

Glad you are back on the road.

[D_M]

HI to everyone!
gunhound, what did you did to fix the this issue, replace the booster?
I have same problem...(