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Old 11-09-2004, 07:36 PM
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brake booster gone?

this is a 72 chevrolet with drums all the way around. i started the car yesterday and heard air leaking so i popped the hood and saw the hose from the booster to the intake manifold had come off. i turned off the car and reattached the hose. now i have no brakes what so ever. Could this be the booster diaphram has busted or i have air in the brake line and need to bleed the system. im not sure what it is all help is needed thanks

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Old 11-09-2004, 10:23 PM
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It's most likely the check valve located at the end of the hosr where it plugs into the booster. A bad diaphram in the booster usually makes a sucking sound. Also make sure a piece of the hose didn't come off when you reattached the hose and is plugging the valve.
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Old 11-10-2004, 04:29 PM
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the check valve checked out ok and there is no sounds fron the brake booster at all. im guessing the master cylinder is shot!
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Old 11-10-2004, 07:03 PM
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Quote:
Could this be the booster diaphram has busted or i have air in the brake line and need to bleed the system.
If you do not understand the difference between a hydraulic problem and a lack of assist, you should look up some basic troubleshooting sites and/or literature before attempting any diagnosis or service yourself. The symptoms are VERY different, and easy to differentiate.

Here are some sites which may help with the basics.

http://www.mpbrakes.com/troubleshooting.htm

http://autorepair.about.com/cs/troub...g/a/bl302a.htm

http://www.babcox.com/editorial/bf/bf60133.htm
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Old 11-11-2004, 08:46 AM
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this is my question again

i just want to know how could my brakes go out when nothing major has happened to them only that the hose from the intake had fell off. and it was replaced. i started the car. i heard air sucking. the hose had come of the intake. i turned car off. replaced hose. no brakes why?


the sites told me what i already knew. they dont answer my question in deatil or answer it at all really. they just tell me the same things i asked. master cylinder? air in line? booster?
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Old 11-11-2004, 09:55 AM
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even with that hose off you should still have brakes they should just feel like manual brakes


if you have no brakes at all sounds like you have a more serious issue rather than that hose
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Old 11-11-2004, 12:07 PM
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the sites told me what i already knew. they dont answer my question in deatil or answer it at all really. they just tell me the same things i asked. master cylinder? air in line? booster?

BOOSTER
HYDRAULIC (master/air)


You tell me.
I'd tell you, but my foot wont reach your pedal.

Lack of assist is much harder than manual brakes.
Air wont enter without an opening, which means the master is probably bad if it is pic #2, or there is a fluid leak.
If it is pic#1, you have a bad booster, or vacuum is not reaching it, or staying in it. You have done no basic troubleshooting yet. We cant do it for you. Throw us a bone, and help will be available in buckets.

Last edited by yesgo; 11-16-2004 at 05:55 PM.
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Old 11-12-2004, 03:52 PM
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yesgo
i understand the pic dagrams now and didnt on the site. the pedal goes to the floor with ease. the pedal doesnt fell hard so sounds like a fluid leak or a master cylinder problem. i just wonder how it went out! the master is about a year old but if it was a cheap advance part that could explain it! ill be sure to get under it to check the lines. sorry for being impatient with this question. thanks
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Old 11-14-2004, 10:17 AM
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73... There are many people here to HELP you. No one here can do it for you over the NET. Do a little basic troubleshooting, provide the information you have, and then ask the question. You will usually get all of the information that you need and then some.

If the pedal goes to the floor, no work has been done to the hydraulic system, and the MC is full, I would suspect the MC is bad. The 2 things that MC does best is they stop a car, and they go bad.
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Old 11-16-2004, 03:47 PM
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Ok, The brake sytem has been checked out over and through. No fluid leaks anywhere. The master cylinder replaced today and The lines were blead numerous times to ensure the air is out of them. but the pedal still went to the floor but not as far as before; i have enough brake to drive and stop but still want better brakes.
I have been told that i may have a bad combination valve. i was told if the pressure was slow out of the bleeder holes when bleed the combination valve could be bad. When the brakes were being bleed they seemed to squirt equally the same after a few times of bleeding. so it may not be the combination valve.
I next took the wheels off to inspect the shoe wear any adjust the brakes. two were perfect. one was very loose and one the brake pad was shot and the drum has a 1/8" groove in it about 1/4" wide on the back shoe and not the front shoe; the front show had normal slight wear, but the rear was almost gone.
so im guessing i have more than a master cylinder problem on my hands. seems the wheel cylinder on that wheel isnt working correctly! maybe this is my problem with the brakes!
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Old 11-16-2004, 05:50 PM
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Sounds like you may have found it. Verify that all the adjusters work. If this was on a rear brake, check parking brake operation and make sure it is not overadjusted.

Inspect the backing plates for grooves and straightness, and check and/or replace all hdwre when doing the shoes. On 4whl drum systems, it is an excellent idea to replace front drums in pairs if one is bad. On rears it is not as important.

With 4 wheel drums, you probably dont have a combo valve. Just a splitter with a warning light. Either way, it is impossible for one to cause a low pedal unless it has a leak allowing fluid out or air in.

If it blocks fluid flow, which they sometimes do, the pedal is the opposite of low... like if you hammered the lines shut. It has to do with hydraulic principles. The fluid needs to find an outlet to an unpressurized source to drop the pedal, like when a master bypasses thru the compensating ports, or an ABS module is stuck open. The splitter or combo valve is a sealed unit with no bypass resivoirs, and only the ability to block flow, possibly bypassing it to another part of an already pressurized and sealed system.

I suspect, as do you, the unevenly worn shoe is the culprit, along with whatever caused it, allowing the wheel cyl to extend further (more fluid displaced=lower pedal). Makes sense anyway.

One of those links I gave has some good advice on curing a low pedal on a chevy truck. Some of it applies to yours... like pinching all the hoses shut to check the master before replacing it If you pinch the line shut to the suspect wheel, and the pedal feels good, you found the problem. Just remember to take the pinch off before driving. You can buy hose lock tools at a parts store usually.
http://www.gwrauto.com/phoenix/Line_Lock_Pliers.gif
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Old 11-17-2004, 03:33 PM
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one thing i wonder is why do the brakes pump up tight when the car is off but when started the pedal goes to the floor?
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Old 11-17-2004, 03:39 PM
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My experience tell me a bad booster will give you a hard pedal..won't push almost at all...so a soft pedal after startup is a bad master cylinder. Please keep us informed as to your progress...everyone is learning something from your problem.


Tazz


Rat Rods Rule!
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Old 11-17-2004, 11:26 PM
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Quote:
The master cylinder replaced today
You did bench bleed the master? If not, you likely would have continued to get air, or no pressure from the cylinders.

Dont concern yourself too much yet with what you are describing on the pedal right now. Power brakes can often make you think it is fine until you start it, and realize the extra pressure makes it go to the floor. When off, you may not even be overcoming the return springs on the shoes until it is started, so the cylinders just dont move much. Power brakes have about half the mechanical advantage of manual until you add the booster.... (Some systems still feel kind of soft anyway until you drive it and realize it stops easily, but it should not go to the floor.)

Make sure all 4 wheels' brakes are in good shape, and adjusted up, and that you can get a good, solid stream of fluid when bleeding. If the pedal still feels like crap, use the hose-lock diagnosis to eliminate the wheels as a cause. Let us know what happens, and details of what you did if it is still not working. There are other possibilities, but you need to fix the obvious problem first. The way you described that shoe, you need to take care of that.
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Old 11-21-2004, 01:00 AM
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The brakes pump up tight when engine is off because you are using up the reserve vacuum in the booster. Once that is gone, the brake pedale will feel high and hard. Upon startup, vacuum ia applied to the booster, allowing it to assist braking effort. If an internal hydraulic leak or loose adjustment condition is pre-existing, the force multiplication of the booster will allow you to push the pedal to the floor. The brakes pumping up hard with engine off, however is not an indication of malfunction.
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