Power brake booster failure?
Thread Starter
Race Director
Joined: Mar 2001
Posts: 11,601
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From: San Francisco CA
St. Jude Donor '07
Power brake booster failure?
My brake pedal goes to the floor without stopping my car that well. I've replaced all the calipers and the front lines (due to previous bubba-ing) so I'm pretty sure it's not them. MC is new also. My Dad suggested to try the brakes w/o power assist and see how well the stop. It's hard as heck to push the pedal, but it almost seems to stop better with the vacuum line plugged. Still doesn't lock up the wheels like it used to, but it indicates to me something wrong with the booster. It seems that the booster isn't pressing on the MC hard enough to stop the car, despite the pedal going to the floor, possibly a torn seal or bad internals? Does this sound about right? Are there other test procedures? Any other ideas?
6th Gear
Joined: Mar 2004
Posts: 6
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From: Bethalto IL
Re: Power brake booster failure? (Buffalo Dude)
If your brake pedal is going to the floor and it does not stop the car, the booster is not the problem....has to be the master cylinder OR you got a bunch of air in the system and the brakes need to be bled...if the booster goes bad you have to press harder, but it won't affect how far the pedal travels.... :banghead:
Instructor
Joined: Aug 2000
Posts: 209
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From: Prescott Valley, AZ USA
Re: Power brake booster failure? (SCCACFC)
When my booster was beginning to fail, every time I pressed the pedal, I could hear a whistling sound, so at least I knew it was the booster.
Good Luck, bleed the system some more.
Josh
Good Luck, bleed the system some more.
Josh
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
Re: Power brake booster failure? (Buffalo Dude)
Your booster is working, but since it is probably 20+ years old, its probably not a bad idea to replace it. The Cardone rebuilds work great and can be had for $100 from an Autozone-Checker type store.
Mine was failing and causing intermittent hard pedal (no power assist).
If you cannot lock up your brakes with applying good pedal pressure, then you have air in the lines. After I tried unsucessfully to bleed mine by the gravity method, I used the pump and hold method 5X at each bleeder and went around the car 2X. I went from furthest to closest to MC and do the rear inner before the rear outer bleeders.
Brent...
Mine was failing and causing intermittent hard pedal (no power assist).
If you cannot lock up your brakes with applying good pedal pressure, then you have air in the lines. After I tried unsucessfully to bleed mine by the gravity method, I used the pump and hold method 5X at each bleeder and went around the car 2X. I went from furthest to closest to MC and do the rear inner before the rear outer bleeders.
Brent...
Melting Slicks
Joined: Jul 2000
Posts: 2,107
Likes: 14
From: Lancaster PA
Re: Power brake booster failure? (MN-Brent)
FWIW, I would not replace the booster unless it is bad. First of all they are a major PITA to replace and second, I toured the Cardone factory last year and was surprised to see that they do not replace the diaphragm unless they are bad. So the rebuilt one that you bought could have a 20 year old diaphragm. Craig
Thread Starter
Race Director
Joined: Mar 2001
Posts: 11,601
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From: San Francisco CA
St. Jude Donor '07
Re: Power brake booster failure? (SCCACFC)
I guess I should have stated that this was a problem before I touched anything on the car. It became a problem after I had to step on it in an emergency stop and locked up the wheels. Since replacing the calipers and MC, I've bled about 5 quarts through the entire system using every type of process, vacuum, pressure, old fashioned pumping, everything except gravity. After the manual pumping though, the pedal just seems to drop to the floor when everything is all sealed up, but after a few pumps it starts to firm up. What does that indicate? Is it possible the calipers are failing, despite being new? I'm pretty sure there's no air in the line due to the sheer volume of fluid I've put through it, but is there any 100% sure way to know?
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Instructor
Joined: Nov 2001
Posts: 143
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From: Sun Valley CA
Re: Power brake booster failure? (Buffalo Dude)
Sounds to me like lots of air in the system. I think you wrote that you replaced the master? If so, did you "Bench Bleed the master?
You need to do this before bleed the lines. If you dont get all the air out of the master, you will never get a firm pedal. The new master should have come with either plastic plugs, or plastic nipples with clear rubber hoses.
If it has the plastic threaded plugs, you will need to remove the brake lines and plug the out let ports from the master. Fill the master with fluid and pump the brakes slowly untill there are no more bubles comming up
If it came with the nipples with the clear hoses, you will need to fill the mater with fuild and feed the clear lines back into the resviors. Clip the hoses some how into the res. Pump the brakes slowly, untill there are no bubles comming through the lines.
Hook up your brake lines and bleed the wheels again.
Good luck! :thumbs:
You need to do this before bleed the lines. If you dont get all the air out of the master, you will never get a firm pedal. The new master should have come with either plastic plugs, or plastic nipples with clear rubber hoses.
If it has the plastic threaded plugs, you will need to remove the brake lines and plug the out let ports from the master. Fill the master with fluid and pump the brakes slowly untill there are no more bubles comming up
If it came with the nipples with the clear hoses, you will need to fill the mater with fuild and feed the clear lines back into the resviors. Clip the hoses some how into the res. Pump the brakes slowly, untill there are no bubles comming through the lines.
Hook up your brake lines and bleed the wheels again.
Good luck! :thumbs:
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: Power brake booster failure? (blackbirdpilot)
Sounds to me like lots of air in the system. I think you wrote that you replaced the master? If so, did you "Bench Bleed the master?
...
...
Even though you are moving fluid through the hydraulics in the bleeding process you can still have an air lock in the master cylinder that doesn't become apparent until you build operating pressure in the system. A thorough bench bleed is absolutely critical and many C3 owners put gallons of brake fluid through their system trying to get a good pedal and get frustrated, like you, that it seems impossible to get there. Then the tale of how hard it is to bleen C3 brakes gets reinforced.
Bleeding out the master cylinder can easily be done inadequately because you can be pushing the piston and see the fluid with no air moving through the lines, install it and still have a spongy pedal and, assuming the cylinder is bled, start perpetually bleeding out the lines and calipers. I pump the cylinder until all the easy air is out of the system and then I give it four of five hard, fast, a full pushes on the piston to push the trapped air out. If there is air in the cylinder the fluid flow is a bit anemic and will probably have some very small bubbles that just move back and forth on the piston strokes. If all the air is gone, you'll see the fluid is clear and has a lot of volume. This can be messy since it will spit fluid from the intake ports.
I do a bench bleed, install the cylinder, and use a vacuum pump to bleed out the lines and calipers. It's really not that hard...if the air is out of the master cylinder.
There are various methods for bench bleeding. Most of the variety is in the open tube methods (bleeder tubes from the outlet port feeding into the reservoirs). There is also a sealed port method that essentially pushes the air out through the fluid intake ports.
Just be sure that when you pull the cylinder off (again) that there is no fluid coming out of the back of the cylinder bore. It's not uncommon to have a bad seal there that pulls air.
Race Director
Joined: Oct 2002
Posts: 12,065
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From: Smalltownville Michigan
Cruise-In 5, 6 & 10 Veteran
St. Jude Donor '09
Re: Power brake booster failure? (Buffalo Dude)
That sounds like air. I had the same dilemma last year and found that i had gobs of air in my brakes. It was due to leaking calipers. Be sure to use the proper sequence in bleeding as well.
Instructor
Joined: Nov 2001
Posts: 143
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From: Sun Valley CA
Re: Power brake booster failure? (gerry72)
One more thing. It is not recommded that you bottom out the master when you pump the brakes for bleeding. There is a good possibility that you can damage the seals on the piston in the master.
Thread Starter
Race Director
Joined: Mar 2001
Posts: 11,601
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From: San Francisco CA
St. Jude Donor '07
Re: Power brake booster failure? (gerry72)
Sounds to me like lots of air in the system. I think you wrote that you replaced the master? If so, did you "Bench Bleed the master?
...
99.99 percent sure that is what your problem is.
Even though you are moving fluid through the hydraulics in the bleeding process you can still have an air lock in the master cylinder that doesn't become apparent until you build operating pressure in the system. A thorough bench bleed is absolutely critical and many C3 owners put gallons of brake fluid through their system trying to get a good pedal and get frustrated, like you, that it seems impossible to get there. Then the tale of how hard it is to bleen C3 brakes gets reinforced.
Bleeding out the master cylinder can easily be done inadequately because you can be pushing the piston and see the fluid with no air moving through the lines, install it and still have a spongy pedal and, assuming the cylinder is bled, start perpetually bleeding out the lines and calipers. I pump the cylinder until all the easy air is out of the system and then I give it four of five hard, fast, a full pushes on the piston to push the trapped air out. If there is air in the cylinder the fluid flow is a bit anemic and will probably have some very small bubbles that just move back and forth on the piston strokes. If all the air is gone, you'll see the fluid is clear and has a lot of volume. This can be messy since it will spit fluid from the intake ports.
I do a bench bleed, install the cylinder, and use a vacuum pump to bleed out the lines and calipers. It's really not that hard...if the air is out of the master cylinder.
There are various methods for bench bleeding. Most of the variety is in the open tube methods (bleeder tubes from the outlet port feeding into the reservoirs). There is also a sealed port method that essentially pushes the air out through the fluid intake ports.
Just be sure that when you pull the cylinder off (again) that there is no fluid coming out of the back of the cylinder bore. It's not uncommon to have a bad seal there that pulls air.
...
99.99 percent sure that is what your problem is.
Even though you are moving fluid through the hydraulics in the bleeding process you can still have an air lock in the master cylinder that doesn't become apparent until you build operating pressure in the system. A thorough bench bleed is absolutely critical and many C3 owners put gallons of brake fluid through their system trying to get a good pedal and get frustrated, like you, that it seems impossible to get there. Then the tale of how hard it is to bleen C3 brakes gets reinforced.
Bleeding out the master cylinder can easily be done inadequately because you can be pushing the piston and see the fluid with no air moving through the lines, install it and still have a spongy pedal and, assuming the cylinder is bled, start perpetually bleeding out the lines and calipers. I pump the cylinder until all the easy air is out of the system and then I give it four of five hard, fast, a full pushes on the piston to push the trapped air out. If there is air in the cylinder the fluid flow is a bit anemic and will probably have some very small bubbles that just move back and forth on the piston strokes. If all the air is gone, you'll see the fluid is clear and has a lot of volume. This can be messy since it will spit fluid from the intake ports.
I do a bench bleed, install the cylinder, and use a vacuum pump to bleed out the lines and calipers. It's really not that hard...if the air is out of the master cylinder.
There are various methods for bench bleeding. Most of the variety is in the open tube methods (bleeder tubes from the outlet port feeding into the reservoirs). There is also a sealed port method that essentially pushes the air out through the fluid intake ports.
Just be sure that when you pull the cylinder off (again) that there is no fluid coming out of the back of the cylinder bore. It's not uncommon to have a bad seal there that pulls air.
Hypothetically, if I hadn't bench bled it properly, wouldn't the bubbles come out of the cylinder and into the lines?
Also, I suppose it's always a possibility they sold me the wrong cylinder. How can I check to make sure this is the proper one?
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
Re: Power brake booster failure? (Buffalo Dude)
There is an odd chance that your new MC is screwed. I guess others on the forum have stated that this has happened to them, right out of the box.
I would remove and re-bench bleed if your in doubt and is the cheapest fix. Next would be new MC and try again. Last resort would be to go to a shop to have them power bled with air pressure or you can make you own power bleeder out of a air compressor and a plate steel peice with a rubber seal of some sort.
There is info on the web on how to do it and this generally gets rid of stubborn trapped bubbles.
Brent...
I would remove and re-bench bleed if your in doubt and is the cheapest fix. Next would be new MC and try again. Last resort would be to go to a shop to have them power bled with air pressure or you can make you own power bleeder out of a air compressor and a plate steel peice with a rubber seal of some sort.
There is info on the web on how to do it and this generally gets rid of stubborn trapped bubbles.
Brent...
