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vacume booster

O

Old Roy

Well-known Member
1993 Chev 1500 I still need to check on the pads on the front, but when I push the peddle down, I get a very loose peddle that goes clean to the floor and a big Whooshing sound.

Upon checking prices for the booster its self I see there is also a check valve.

I am guessing either the diaphragm is gone or the check valve may be sticking .

is it possible a bad check valve may cause the peddle to go to the floor
 
First off, the check valve isn't the problem. It's purpose is to hold vacuum in the booster for one or two brake applications with the engine stalled or shut off.

Secondly, even if the booster fails, the pedal shouldn't go to the floor... that is a sign of brake problems. It should simply lose the "boost" function, making for a "hard" pedal.

As to the whooshing sound, that does sound like a failed booster, but doesn't explain why the pedal goes all the way to the floor!

Perhaps there is BOTH a booster problem and a brake system problem.
 
There is no broken of leaking booster that will allow a pedal to go to the floor. The mechanical linkage in the booster has, at the max, 3/16 travel such that your brakes are still available W/O boost. If the pedal is going to the floor, it is from either the Master cylinder (possible), a failed line, Probable, blown cylinder or caliper, or stuck caliper mounts not allowing self adjusting. There is no way chevy would put the booster in a position of eliminating the brakes. The booster is basically a solid rod with a valve in the middle. It is not your issue, even if the booster is bad. Jim
 
I have heard a booster make noise like that when it had full travel and no pressure against it. I believe he needs brake hydraulic parts if not mechanical as well. Jim
 
Ok thanks guys ! It'll be a couple days before I can get it inside. I'll keep ya posted
 
The wooshing sure does sound like a bad booster.. But, as the others said, you should have a stiff pedal.

HOWEVER.. on my dorF, it had a leaking booster for a long time, and it was strange.. sometimes, it would be really stiff, sometimes it would do like yours and go nearly to the floor, like you mentioned. I ended up getting a booster/master cylinder combo from NAPA (the booster was 115, or with the master cylinder it was 125.. Kinda a no brainer for me)

I cannot say however, that it was my problem in it's entirety, as I also put new rear shoes, drums, lines, wheel cylinders, spring and adjuster kits, etc. as one side was quite worn and I had warped drums as well.

I do, as the others, recommend checking lines for leaks (or the master cylinder to see if you appear to be "losing" fluid), and look at your calipers and make sure they are adjusting accordingly, and check the rear brake adjustment.. Just because it has "self adjusting" does not mean at all that it is in fact adjusting like it should.

GM trucks are kinda known for calipers sticking.. I've owned a few, and had the problem with every one, new and used.

Brad
 
The truck was on loan.

I don't feel it was my friends fault they failed, because he told me a day before he brought it back there was a grinding noise in the front.

Last inspection I had about half worn pads on the front and I don't think I put a thousand miles on the truck since then

I took for granted it must have been a stone.

upon reading another post awhile back the hot and cold weather may have contributed to the lining to come loose from the pad itself ,. I know they are bonded.
 
Bleed the brakes and keep the master cylinder full of fluid. If you don't see any brake fluid on the floor of your shop from any fluid leaking. If your pedal still goes to the floor replace the master cylinder. Hal
 
The whooshing sound might well be normal.

The booster works by having a diaphragm attached to the brake rod in the middle of the vacuum chamber with vacuum on each side. When you step on the pedal you allow air to enter the pedal side of the booster. Since the atmospheric pressure is greater than the vacuum the diaphragm assists in pushing the rod into the master cylinder to give you the assist with braking. A lot of trucks had the air inlet for the vacuum booster under or behind the drivers seat so hearing the noise would not be unusual.
 
The vaccum valve retains vacuum in the booster for power assist in case vacuum levels drop too low, like the truck dies suddenly. Test the pedal quality with the engine not running. Destroy the vaccum in the booster by applying the brake several times and see if the pedal is high and hard. If not look for hydraulic/mechanical concerns. If it is, start it up and the pedal should drop 1-2 inches when the engine starts and achieves at least 15 inches of vaccum at the booster. Hope this helps. Gerard
 
It ain't the booster. Don't know why but "whooshing" is fairly common especially when the pedal hits the floor. Could be the master cylinder but my guess is the noisy caliper got too hot or overtraveled & got a little air into the system.
 
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