Do i have a bad brake booster????
12-17-2010, 06:35 PM
#21
Race Director
The procedure with clamping off the hoses is the method they train new mechanics with, they don't have time to guess.
If you haven't done that, then you don't positively know.
Realize it's also going to take a few miles to bed in the new pads, that will affect braking distance.
Going about 10 mph, step very lightly on the pedal and see how far down it goes before you can feel the brakes starting to drag. It should be withing the first inch.
Also check the booster to master rod for proper length.
Lengthen rod until there is a hairline space between booster and master flange, then shorten until it just disappears.
To loosen tough air bubbles another method is to oscillate the lines and calipers while bleeding. Maybe you can borrow your wifes vibrator.
As far as the booster R&R, jack up the front of the car as high as you can, kneel beside it, remove the lower a/c vent if an air car, use a 2 foot long 3/8" extension and ratchet with a deep 9/16" socket and universal. Takes less than 10 minutes to remove or install, clip on the clevis is the worst.
If you haven't done that, then you don't positively know.
Realize it's also going to take a few miles to bed in the new pads, that will affect braking distance.
Going about 10 mph, step very lightly on the pedal and see how far down it goes before you can feel the brakes starting to drag. It should be withing the first inch.
Also check the booster to master rod for proper length.
Lengthen rod until there is a hairline space between booster and master flange, then shorten until it just disappears.
To loosen tough air bubbles another method is to oscillate the lines and calipers while bleeding. Maybe you can borrow your wifes vibrator.
As far as the booster R&R, jack up the front of the car as high as you can, kneel beside it, remove the lower a/c vent if an air car, use a 2 foot long 3/8" extension and ratchet with a deep 9/16" socket and universal. Takes less than 10 minutes to remove or install, clip on the clevis is the worst.
12-18-2010, 04:22 PM
#22
Intermediate
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OK well this morning i went out and picked up another BRAND NEW master cylinder since im getting alot of people saying thats what my problem is. I bench bled it and installed it and bled the entire system using my Motive power bleeder, and i am still having the same issue. The pedal is firm with the engine off, and goes nearly to the floor with the engine running. I dont know what else to do other then try changine the booster? I am now on my FOURTH master cylinder. Any other thoughts?
12-18-2010, 05:14 PM
#23
Race Director
OK well this morning i went out and picked up another BRAND NEW master cylinder since im getting alot of people saying thats what my problem is. I bench bled it and installed it and bled the entire system using my Motive power bleeder, and i am still having the same issue. The pedal is firm with the engine off, and goes nearly to the floor with the engine running. I dont know what else to do other then try changine the booster? I am now on my FOURTH master cylinder. Any other thoughts?
but i had the same symptoms... after replacing everything (my culprit was my proportioning valve) but still had to bleed it over a period of 1 month... a little air here and a little air there,,, finally all gone...
BUT you will always have a mushy peddle with the vacuum booster, if you want a firm peddle there in no option other than Hydroboost,,, and if you are going to pull the VB anyway if you feel its bad (probably not) then I and most all others that have converted will tell you the same... go hydorboost.....
12-18-2010, 05:31 PM
#24
Racer
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i say air in system too then if your on your 4th master. hope when your bench bleeding master your dont push all the way in until it stops, the cups in there prone to messing up when you do that. gravity bleed couple hours then vacuum bleed a couple quartz threw. guess i got lucky when i replaced all 4 calipers, flex lines and master quick bled all 4 corners and was in business.
12-18-2010, 06:40 PM
#25
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i say air in system too then if your on your 4th master. hope when your bench bleeding master your dont push all the way in until it stops, the cups in there prone to messing up when you do that. gravity bleed couple hours then vacuum bleed a couple quartz threw. guess i got lucky when i replaced all 4 calipers, flex lines and master quick bled all 4 corners and was in business.
12-18-2010, 07:24 PM
#26
Burning Brakes
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12-18-2010, 08:48 PM
#27
Race Director
When I bleed the master, I just bolt it on the car and pump the pedal instead of using a vise and doing it by hand, I don't think that would make it go too far. I am using a SYNTHETIC Dot 3 fluid, could that be causing any of my problems? Thanks again everybody for ur help.
BENCH bleed the mc... and then power bleed for a week....you got air
12-18-2010, 09:16 PM
#28
Race Director
Here is how you have to bench bleed it and why.
The ports are not at the top of the bore and the angle mount installed in the car makes it worse. If memory serves me correctly the top of the ports are approx 0.060 below, leaves quite an air gap.
Second pic shows a master I cut apart, was in a car with decent brakes for at least a couple years. Notice the corrosion from the air bubble.
Third pic is another way to bleed, moving the master around a bit to remove the air space.
Here are some other instructions
http://www.filesend.net/download.php...718e5f56411c63
The ports are not at the top of the bore and the angle mount installed in the car makes it worse. If memory serves me correctly the top of the ports are approx 0.060 below, leaves quite an air gap.
Second pic shows a master I cut apart, was in a car with decent brakes for at least a couple years. Notice the corrosion from the air bubble.
Third pic is another way to bleed, moving the master around a bit to remove the air space.
You can use any of a dozen methods to bleed and unless you bench bleed the master properly and test it, you can fool around forever.
Bleed it properly, test it properly and then go to the rest of the system.
In the pic, you can see the top rusted trail in the bore that is caused by air from normal level bleeding.
Bleed it properly, test it properly and then go to the rest of the system.
In the pic, you can see the top rusted trail in the bore that is caused by air from normal level bleeding.
Here are some other instructions
http://www.filesend.net/download.php...718e5f56411c63
12-19-2010, 12:02 AM
#29
Race Director
Here is how you have to bench bleed it and why.
The ports are not at the top of the bore and the angle mount installed in the car makes it worse. If memory serves me correctly the top of the ports are approx 0.060 below, leaves quite an air gap.
Second pic shows a master I cut apart, was in a car with decent brakes for at least a couple years. Notice the corrosion from the air bubble.
Third pic is another way to bleed, moving the master around a bit to remove the air space.
Here are some other instructions
http://www.filesend.net/download.php...718e5f56411c63
The ports are not at the top of the bore and the angle mount installed in the car makes it worse. If memory serves me correctly the top of the ports are approx 0.060 below, leaves quite an air gap.
Second pic shows a master I cut apart, was in a car with decent brakes for at least a couple years. Notice the corrosion from the air bubble.
Third pic is another way to bleed, moving the master around a bit to remove the air space.
Here are some other instructions
http://www.filesend.net/download.php...718e5f56411c63
12-19-2010, 07:32 AM
#30
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When I bleed the master, I just bolt it on the car and pump the pedal instead of using a vise and doing it by hand, I don't think that would make it go too far. I am using a SYNTHETIC Dot 3 fluid, could that be causing any of my problems? Thanks again everybody for ur help.
12-20-2010, 09:45 PM
#31
Le Mans Master
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I would suspect it is a synthetic made like synthetic oil vs using actual oil based products. The DOT 5 is Silicon and is not hygroscopic like regular brake fluid is.
12-20-2010, 10:46 PM
#32
Melting Slicks
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St. Jude Donor '11-'12-'13,'19-'20
In my experience, a bad booster gives you a hard pedal, not a soft one. You still have air some where. This worked for me, may or may not work for you, pump the brake pedal voilently 3 or 4 times and hold it down while the bleeder is opened. Sometimes this will move the air through to the bleeder. Do this several times per caliper and see if you get more air.
or.. got time?...try gravity bleeding...one bleeder at a time for at least 1hr each...furthest to the closest.. MC cap off...keep it topped off and let er drip! Make sure to fill and cap MC before touching the pedal.
Also make sure p-valve is in good working order.
