Brake Booster Problem

[fixit1070]

Can anyone tell me how to troubleshoot a brake booster for a 2001 SE model, I have had my van to the garage to have the brakes checked and the mecahnic told me the master cylinder was bad so I replaced that and still the pedal feels spongy.The car has new brakes all the way around and new rear brake cylinders ,the lines have been blead of all air and still the pedal is spongy.Some one mentioned to me if the booster is going bad it will leak to much air and the pedal will travel to far ,Is this correct and how do I tell if the booster is bad.Is there an easy way to check ?

Thanks

[LeSabre97mint]

Did you "bench bleed" the master cylinder before you installed it?

Dan

[garync1]

Most of the time if your brake booster goes bad it has a hard pedal. And are rare to go out unless the auto is old. I think unless the mechanic pulled the cowel off he did not bleed out the master properly. not too place blame you could check the proportion or equalizing valve under the driver side frame area under the van some times i have heard of them getting a slow leak almost not even noticed,just rub your fingers around it after pumping the brakes a few times also check around the ABS unit for slow leaks..If you want to check your booster pull the front cowel off pull the hose from the check valve and start the van push the pedal and you will notice a change. dont drive it because you will have to stand on the brakes to stop. over 20 mph.

[Rotorman]

Originally Posted by fixit1070

Can anyone tell me how to troubleshoot a brake booster for a 2001 SE model, I have had my van to the garage to have the brakes checked and the mecahnic told me the master cylinder was bad so I replaced that and still the pedal feels spongy.The car has new brakes all the way around and new rear brake cylinders ,the lines have been blead of all air and still the pedal is spongy.Some one mentioned to me if the booster is going bad it will leak to much air and the pedal will travel to far ,Is this correct and how do I tell if the booster is bad.Is there an easy way to check ?

Thanks

Sounds like nobody bleed the master cylinder before install. I would rebleed the back brakes using the gravity bleed way. Its safe , and slow , just use 2 qts of brake fluid and do each 10 minute slow drip method into a glass jar. I believe you a lot of high spots in your lines, this should help you to get a pretty good pedal.

[fixit1070]

Originally Posted by Rotorman

Sounds like nobody bleed the master cylinder before install. I would rebleed the back brakes using the gravity bleed way. Its safe , and slow , just use 2 qts of brake fluid and do each 10 minute slow drip method into a glass jar. I believe you a lot of high spots in your lines, this should help you to get a pretty good pedal.

The brakes were blead many times using several diffrent methods and still the pedal is spongy.The new master cylinder was thought to be defective and replaced a second time and the mechanic blead the lines for allot of hours and still no change.Everything seems to check OK for leaks. I was was told by another car guy that if the boster is going bad it could be spongy and then when it totally fails it will be hard.I'm not sure , the only thing left to change is the booster or the porportioning valve. I am tending to beleive that the master cylinder was not bad from the start but that's water under the bridge at this point,I just want the brakes to work normally.IF you have nay ideas please let me know.

Thanks

[MT-2500]

Originally Posted by fixit1070

The brakes were blead many times using several diffrent methods and still the pedal is spongy.The new master cylinder was thought to be defective and replaced a second time and the mechanic blead the lines for allot of hours and still no change.Everything seems to check OK for leaks. I was was told by another car guy that if the boster is going bad it could be spongy and then when it totally fails it will be hard.I'm not sure , the only thing left to change is the booster or the porportioning valve. I am tending to beleive that the master cylinder was not bad from the start but that's water under the bridge at this point,I just want the brakes to work normally.IF you have nay ideas please let me know.

Thanks

If a vacume booster system
A brake booster will give you a hard pedal when it goes out.
To check brakes or master cylinder with engine off pump brakes several times to remove vacume from booster.
The pedal should be hard and full pedal if master cylinder and regular brakes are good.

If you have ABS brakes and have let air into the system it may have to be bleed with a pressure bleeder and a ABS scanner with the special bleeding procedure in the scanner.
MT

[garync1]

I will also say to add as well to the top post that you should have no spongey pedel if you unhook the booster from the system although it will be hard there still should not be a spongey pedal. Your Abs is non intergrated system. If it fails braking should be normal. fluid should pass through when bleeding from wheels from master to ABS system to proportion valve. I pulled this up to help you trouble shoot the booster and check valve.To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced.

Vacuum boosters also have an external one-way check valve at the hose inlet that closes when the engine is either shut off or stalls. This traps vacuum inside the booster so it can still provide one or two power assisted stops until the engine is restarted. The valve also helps maintain vacuum when intake vacuum is low (when the engine is under load or is running at wide open throttle). You can check the valve by removing it and trying to blow through it from both sides. It should pass air from the rear but not from the front.