Brake booster test
#2
Team Owner
Member Since: Aug 2006
Location: Columbia Missouri
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Yep. This is what it should do if it's working properly.
With the engine off:
Pump pedal until it gets hard and won't depress any further.
Start engine while pressing brake pedal.
(Pedal should get soft and stop at the point where your brakes normally lock up at.)
If the pedal never gets hard or if it doesn't get soft, then you have some sort of problem.
Look at and replace if needed the check valve and filter in the vacuum lines.
Also, an always mushy pedal could mean air in the system or a bad master cylinder.
#3
Team Owner
Yep. This is what it should do if it's working properly.
With the engine off:
Pump pedal until it gets hard and won't depress any further.
Start engine while pressing brake pedal.
(Pedal should get soft and stop at the point where your brakes normally lock up at.)
If the pedal never gets hard or if it doesn't get soft, then you have some sort of problem.
Look at and replace if needed the check valve and filter in the vacuum lines.
Also, an always mushy pedal could mean air in the system or a bad master cylinder.
With the engine off:
Pump pedal until it gets hard and won't depress any further.
Start engine while pressing brake pedal.
(Pedal should get soft and stop at the point where your brakes normally lock up at.)
If the pedal never gets hard or if it doesn't get soft, then you have some sort of problem.
Look at and replace if needed the check valve and filter in the vacuum lines.
Also, an always mushy pedal could mean air in the system or a bad master cylinder.
OR a bad booster.....I proved that one on my own car....
nothing good as Hydro Boost....nothing, not any vacuum assist system that is....
#4
Yep. This is what it should do if it's working properly.
With the engine off:
Pump pedal until it gets hard and won't depress any further.
Start engine while pressing brake pedal.
(Pedal should get soft and stop at the point where your brakes normally lock up at.)
If the pedal never gets hard or if it doesn't get soft, then you have some sort of problem.
Look at and replace if needed the check valve and filter in the vacuum lines.
Also, an always mushy pedal could mean air in the system or a bad master cylinder.
With the engine off:
Pump pedal until it gets hard and won't depress any further.
Start engine while pressing brake pedal.
(Pedal should get soft and stop at the point where your brakes normally lock up at.)
If the pedal never gets hard or if it doesn't get soft, then you have some sort of problem.
Look at and replace if needed the check valve and filter in the vacuum lines.
Also, an always mushy pedal could mean air in the system or a bad master cylinder.
I get a very hard pedal with the car off. Start it and then press the brakes and it goes straight to the floor. Is this right and how sure are you this is a correct method? Sorry to second guess you, but swapping out the booster is not an easy thing if you know what I mean.
2 months now it has been up on jacks
#5
is there any way to bench test a power brake booster?
i know the one i currently have is leaking, and ive got another one sitting on a shelf here that im assuming is good but dont know.
i know the one i currently have is leaking, and ive got another one sitting on a shelf here that im assuming is good but dont know.
#6
Le Mans Master
Member Since: Sep 2001
Location: Wellington, FL
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St. Jude Donor '11-'12-'13-'14-'15-'16-'17-‘18-'19-'20-'21-'22-'23-'24
Okay guys...you may have just solved my problem with brakes and I just want to confirm if you don't mind.
I get a very hard pedal with the car off. Start it and then press the brakes and it goes straight to the floor. Is this right and how sure are you this is a correct method? Sorry to second guess you, but swapping out the booster is not an easy thing if you know what I mean.
2 months now it has been up on jacks
I get a very hard pedal with the car off. Start it and then press the brakes and it goes straight to the floor. Is this right and how sure are you this is a correct method? Sorry to second guess you, but swapping out the booster is not an easy thing if you know what I mean.
2 months now it has been up on jacks
#7
New everything except the booster. Gravity bleed a solid qt per caliper over the last week. Used the Motive bleeder on each calip while tapping the calip and pulling on the pads to remove any additional internal air. Tried speed bleeders, and the manual 2 man bleeding job.
At this point no matter how much I bleed not a buble of air come out.
This is why I am thinking it is the booster as I have nothing else to lean on.
Does anyone have any other ideas to try?
#8
Le Mans Master
Member Since: Sep 2001
Location: Wellington, FL
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St. Jude Donor '11-'12-'13-'14-'15-'16-'17-‘18-'19-'20-'21-'22-'23-'24
Sorry I did not do a good job explaing my pre bleeding and brake replacement process so I will be quick.
New everything except the booster. Gravity bleed a solid qt per caliper over the last week. Used the Motive bleeder on each calip while tapping the calip and pulling on the pads to remove any additional internal air. Tried speed bleeders, and the manual 2 man bleeding job.
At this point no matter how much I bleed not a buble of air come out.
This is why I am thinking it is the booster as I have nothing else to lean on.
Does anyone have any other ideas to try?
New everything except the booster. Gravity bleed a solid qt per caliper over the last week. Used the Motive bleeder on each calip while tapping the calip and pulling on the pads to remove any additional internal air. Tried speed bleeders, and the manual 2 man bleeding job.
At this point no matter how much I bleed not a buble of air come out.
This is why I am thinking it is the booster as I have nothing else to lean on.
Does anyone have any other ideas to try?
#9
I kinda agree with the air, but then why do I have a hard as rock pedal with the engine off?
#10
Melting Slicks
The pedal is hard with the engine off because the booster has no vacuum to provide assist; you're basically operating the brake system manually at that point. The master cylinder in a power brake system is not designed to operated manually, and therefore there is high effort required to try to operate the brakes-rock hard pedal. The fact that you pedal drops when you start the engine tells me the booster is fine. If the pedal truly goes to the floor, you have a another problem. Does the car stop?
A booster problem causes a hard pedal and the car is difficult to stop.
A booster problem causes a hard pedal and the car is difficult to stop.
Last edited by 69autoXr; 01-26-2008 at 02:19 PM.
#11
The pedal is hard with the engine off because the booster has no vacuum to provide assist; you're basically operating the brake system manually at that point. The master cylinder in a power brake system is not designed to operated manually, and therefore there is high effort required to try to operate the brakes-rock hard pedal. The fact that you pedal drops when you start the engine tells me the booster is fine. If the pedal truly goes to the floor, you have a another problem. Does the car stop?
A booster problem causes a hard pedal and the car is difficult to stop.
A booster problem causes a hard pedal and the car is difficult to stop.
Another question if you don't mind. With the car off I can stand on the pedal hard..make that very hard and the pedal will not move more than 1/2". So even if the booster was bad I would just have a rock hard pedal that would require a lot more force to engage the brakes correct?
#12
Burning Brakes
It sounds to me like the actuator rod that runs from the booster to the master cylinder could be out of adjustment. Maybe someone else can chime in here that knows more about this. I've never made the adjustment myself.
#13
I just remembers another funny thing that happened. My friend and I finnished off the old manual way press the pedal to build pressure and open the bleeder to remove any remaining air. However, a few times as he was pumping the pedal it would go straight to the floor (no pedal pressure) when everything was closed tight. When that happened we let it sit for 5 min came back and the pedal was hard again so we had to do that a few times until all the air was out.
I am so fricken tired of this ****... 3 months now and can't get a pedal to go half way
#14
Melting Slicks
If the booster is bad (providing no assist) the pedal would be hard all the time, and you'd have a sore leg from trying to stop the car. If the pedal drops when you start the car, that indicates to me that the booster is holding a vacuum. Try pulling the check valve from the booster and start the engine (plug the vacuum line); the pedal should remain rock hard as though the engine were off and not supplying vacuum-this would simulate the condition if the booster could not hold a vacuum.
#15
Le Mans Master
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Location: Wellington, FL
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St. Jude Donor '11-'12-'13-'14-'15-'16-'17-‘18-'19-'20-'21-'22-'23-'24
now you can see the delima that I am having It is adjusted with no preload at all, but enough to just touch the MC upon install.
I just remembers another funny thing that happened. My friend and I finnished off the old manual way press the pedal to build pressure and open the bleeder to remove any remaining air. However, a few times as he was pumping the pedal it would go straight to the floor (no pedal pressure) when everything was closed tight. When that happened we let it sit for 5 min came back and the pedal was hard again so we had to do that a few times until all the air was out.
I am so fricken tired of this ****... 3 months now and can't get a pedal to go half way
I just remembers another funny thing that happened. My friend and I finnished off the old manual way press the pedal to build pressure and open the bleeder to remove any remaining air. However, a few times as he was pumping the pedal it would go straight to the floor (no pedal pressure) when everything was closed tight. When that happened we let it sit for 5 min came back and the pedal was hard again so we had to do that a few times until all the air was out.
I am so fricken tired of this ****... 3 months now and can't get a pedal to go half way
#16
Melting Slicks
#17
If the booster is bad (providing no assist) the pedal would be hard all the time, and you'd have a sore leg from trying to stop the car. If the pedal drops when you start the car, that indicates to me that the booster is holding a vacuum. Try pulling the check valve from the booster and start the engine (plug the vacuum line); the pedal should remain rock hard as though the engine were off and not supplying vacuum-this would simulate the condition if the booster could not hold a vacuum.
#18
You must be sucking air into the system when you and your friend are trying to bleed the brakes. Try the gravity bleed again and make sure all lines and hoses are tight. Open up one or more of the bleeder screws at a time and let the fluid drip until you have about a halve cup of the fluid from each caliper and taping them lightly in the process. Be sure to keep the m/c pretty much full. With Vettes, you're supposed to work from the closest caliper from the m/c and work towards the one the furtherest. I went thru this once and the only thing that got all the air out was with the gravity bleed. Good luck and don't give up. You'!l get it.
I am going to gravity bleed them again today and see what happens stay tuned and pray for me.
#19
Melting Slicks
#20
I have heard that a lot of air can get trapped in the calip and to tap on them and to pull and or push the pads away from the rotor, which helps remove any remaining trapped air. I did this a few times after I thought all the air was out and it actuallly worked. I was gravity bleeding and I pulled on the outer pad hard and a few more air bubbles came out so I continued around the car and 2 more wheels had air within.
I am heading out there again now to gravity bleed again.
I am heading out there again now to gravity bleed again.