minitech

I have searched several threads on brake problems but just want a confirmation that my booster is bad.

Last season the brakes were soft, pedal went down far before brakes engaged. I took it in to one shop and they said the master cylinder might be bad and changed it. That may have made some difference but not much. I don't trust this shop did a good job because of something they did with another issue on the car.

Took it to another shop and asked them to bleed the brakes. They did and that seemed to make some difference but the pedal never was up where it should be.

Months go by and brakes are acceptable and safe.

Last weekend I took the car out and the pedal seems even softer and even with pedal max pressure the wheels don't lock up. "Couldn't lock the tires when I tried." Not safe for road now.

So I jacked the car up and took off the tires to check for leaks and none found. Master cylinder has maybe half inch low fluid, not indicating big sudden leak.

So I'm looking at the booster. Engine running I pull off the vac to the booster and it has pressure there. (Seems likes strong vac pull to the fitting.) When someone is in the car and presses the brake pedal and then I pull off the vac fitting and pressure much less as if the booster is leaking. Should the booster hold pressure at all times? i.e. with the pedal pushed it still holds pressure or is it supposed to bleed off vac with pedal pushed?

Is there anything else to check before buying the new booster and putting it in?

my 76 ray

When a booster fails it usually results in a hard brake pedal and requires a lot of pressure on the pedal to stop.

It could be a bad master cylinder. They can leak out the back (if the rear reservoir was low that might be the problem) or they can just fail to push the fluid due to a bad seal.

minitech

So if the booster failed it would be a hard pedal but hitting it real hard the brakes would lock?

If the master cylinder failed it would not let the fluid go and not let the calipers have oil?

Still could be the master cylinder then. The reason I don't trust the first shop is I dropped the car off early, drove to work and 10 minutes later called to mention something else. The boy they had working said he found a loose hose causing a leak and already fixed it for the tranny leak I had. Couple minutes. I called later and the owner now arrived and told me the tranny leak would cost $80 to fix and I knew the boy saw the simple thing and did it already.


So the #@%!&ng shop may have not done good work with the master cylinder.

mrvette

All GM cars have a large amount of pedal travel in the brakes, just one of their things I have never understood, now in the shark boosters, look at an assy diagram of the thing, as I tore my old booster apart, I noted a stupid spring between the input and output shafts......my pedal could always be forced to the floor, and it always stopped the car more or less ok, but that excessive pedal travel was flat irritating to me, the booster checked good no matter how I checked it, and when torn apart it looked fine inside, except for that spring/design flaw.....

I put on a Hydroboost system, and Sharkey stood on the nose, and my nose went into the steering wheel.....CASE CLOSED@!@!!!!

minitech

Thanks I am glad you replied. You seem to get the practical bottom line on things.

dochorsepower

Have you inspected your flex hoses? Over time they degrade and will expand under pressure like a balloon giving you a soft pedal feel.

briankeery

You didn't say which reservoir was half empty, front or rear. If no visible leaks are present and your pedal isn't hard, I'd be looking at rotor run out as your cause. Also, suggest you pick up a Motive Power Bleeder and bleed your own brakes.

minitech

It was the front one that was a bit low.

The car slows but no grab and no ability to lock the wheels with hardest pushed pedal. Also no pull to one side or the other, don't think one caliper is not working.

I have a power bleeder for my C5. Need the right adapter to work on C3 but I should get it and be able to do my own.

minitech

I'll post this for anyone in the future searching

Diagnosing brake booster failure:

Instructions
1
Turn off your car and pump your brake pedal five times. Push the brake pedal all the way down and turn the car on, keeping the pedal pushed down while starting the car. If your brake booster is functioning normally, you should notice that the pedal goes further down and the resistance will immediately decrease. If the pedal's position does not change and the resistance does not change, this indicates a faulty power brake booster.

2
Leave your car running for five minutes. Turn it off and immediately push the brake pedal five times. If the brake booster is functioning normally, you should notice that the resistance increases each time you push the brake down. In addition, the pedal should come to a rest at a higher level after each push of the brake pedal. If you do not observe this happening, the power brake booster is malfunctioning.

3
Listen for any whining noises that occur when you apply the brakes while driving your car. If you notice this, the vacuum line that connects to the power brake booster is punctured and is letting air out, resulting in whining when the brake is applied. In this case, the vacuum line must be replaced to prevent the brake booster from failing.



Read more : http://www.ehow.com/how_7591240_diag...-problems.html

minitech

I have an EARLY 77. It had a 76 A/C system under the hood, fender alarm switch. These were changed mid year 77 to "77"

Brake booster comes as 68-76 and 77-82

Did the booster change for all 77? What difference is there between the two types?

Stewart's74

My Brakes are really poor as well. No visible leaks but I do hear a significant air leak noise coming from somewhere under the dash when i push the brake pedal (with car running)
Could this be the booster?
In the meantime, I'll follow Minitech's advice above for additional clues.

Cheers,

Stu

RMJ11949

Was your problem your booster?
My pedal goes to the floor when the engine is running. No leaks, no air in lines, all components checked or replaced except for the booster. I get a whooshing sound when brakes are applied with the engine running.
I suspect my booster.


QUOTE=minitech;1587841608]I have an EARLY 77. It had a 76 A/C system under the hood, fender alarm switch. These were changed mid year 77 to "77"

Brake booster comes as 68-76 and 77-82

Did the booster change for all 77? What difference is there between the two types?[/QUOTE]

minitech

[/QUOTE]


Yes it was the booster. I changed it and now it is fine. I waited a long time to change it because I heard it was difficult to get to the nuts to change it but it was not really difficult at all. Two 12 inch extensions for the 3/8 ratchet and a swivel joint on the socket was the way for me.

RMJ11949

You must own an automatic. The pedal brackets are different and there is no way I'm getting to that nut unless I remove my clutch pedal and all the related parts and brackets. I've done it before, but it's a pain in the ***. I guess I answered my own question, found out what that unknown part was as well.
Best regards,
Rick


QUOTE=minitech;1590530777][/QUOTE]


Yes it was the booster. I changed it and now it is fine. I waited a long time to change it because I heard it was difficult to get to the nuts to change it but it was not really difficult at all. Two 12 inch extensions for the 3/8 ratchet and a swivel joint on the socket was the way for me.[/QUOTE]