Pres712

Yesterday driving home I pulled up to a stop light and there was a hissing sound (air escaping) coming from the brake pedal. Obviously there is a leak in the power brake system, somewhere. Before I get into it; has anyone had this experience?

antfarmer2

Need a new brake booster or your vacumme line came off or cracked.

WW7

....Yep......WW

Pres712

Checked under the hood all around the booster, no hissing. Can only hear the air escaping while in the car. Went under the dash and pressed on the brake and the sound is coming from under the dash? If I hold down the pedal the engine will want to stall. So vacuum is leaking from somewhere.

WW7

The back of the booster is under the dash , so don't rule out it being a bad booster yet ..Check the vacuum lines also....WW

antfarmer2

Is the brake harder to push? Pump up the brake with the car off while holding the brake start the car does the pedal go down a bit?

tgurnick

It definitely sounds like the brake booster. I had one in my S10 give similar symptoms. The booster might seal up when not bothered, but once you push the brakes the diaphragm could be losing it's seal internally.

Pres712

It has always gone down a little when starting. The brakes work fine except when it's hissing and then it seems to revert to "hard" brakes-no booster. I'm sure it's a bad seal or something in the rear. I found one on line for $112.00. Not to sure how to replace it.

antfarmer2

Take the old one off first. youtube is your friend. It is suppost to go down a little. Four nuts and a clip.

krackenvette

Check the booster closest to exhaust manifold cylinder #7. Thats usually crack central due to heat front exhaust.

gerardvg

Have had the same problem, hissing only when pressing the brake pedal.
Did not affect braking assistance much at first, turned out the diaphragm in the booster had torn.

You can get them repaired however most will not want to try, the plastic has hardened with heat over the years and can break when they try to open it.

I got a new one and make sure i do not bleed the brakes the old fashioned way, that extra travel usually does the diaphragm in my experience.

Is a fairly simple straight forward job to replace the booster.

scooter mcfly

You are in for a treat. You're gonna need lots of extensions for your ratchet. 1/4 inch will be easiest. There just isn't much room under the dash to work. Remove the drivers seat. I would tape either a towel or sheet of plastic to the firewall under the dash so when you drop the nuts, and you will, they won't disappear into the black hole the resides under the steering column. You're gonna be lying on your back trying to hold a flashlight in your teeth while trying to get your socket on the bolt with one hand and working the ratchet with the other. Plan on cussing a lot. Beer is your friend. Before you put yourself through this ordeal, and yes that is what this is, check the check valve on the booster. If it's bad you could save yourself a lot of time, money, and aggravation.

Pres712

I watched a video on YouTube and I think I will ask my Corvette garage what they will charge. They get $75/hr. Maybe 3 hours? Might be worth it. I'm 6'2" 250 lbs. Could be a squeeze?

antfarmer2

I am the same size just add two inches. Just have everything set up and a little head light will help wish I was closer $225 for a clip and four nuts. use some tape in the socket to hold the nut

Red86Z51

Have you checked the vacuum operated cruise disengage switch for leaks? It is mounted by the brake light switch, behind the brake pedal, under the hush panel. Remove the panel, start the car, press the brake pedal with your hand and listen. The switch is only activated when you depress the brake pedal. They are plastic and do go bad. It's a fast an easy check before tearing out your booster.

If it leaks, you can hear a hiss when you press the pedal.

krackenvette

Thanks. Love learning new stuff. Now I need to check mine

scooter mcfly

Don't give up so fast. If a mechanic can do it, you can. No special skills required. You'll actually be pretty comfortable down there. And the convertible makes it easier to get in and out. The hardest part will be finding a combination of extensions that will work. Cover the studs the seat attaches to with a towel so they don't dig in. A helper would be nice for when you drop something. And lots of beer. And music. You'll be fine.

antfarmer2

The hardest part will be trying to drink beer under there LMAO

scooter mcfly

Only if you haven't stocked up on vacuum hose! 4 or 5 ft should do.

antfarmer2