when i come to a long stop, i lose pressure and the pedal goes all the way down to the floor... and sometimes to the point theres no pressure at all if i sit on the brakes long enough... if i let off the pedal and press again i get pressure... awhile back my brakes were locking up and it turned out to be the master cylinder, and since then the pedal had been a lil soft i suspected that the booster was also bad but wasn't sure... any thoughts or suggestions?
my old one's bleed circuit was clogged causing the lock up... mechanic said it could have also damaged the booster in the process, gonna go to another mechanic tomorrow... this would really suck for a brand new MC to fail so quickly, makes me wonder if theres something causing the failures
booster CAN NOT effect the hydraulic brakes. it can basically leak vacuum, and/or fail to provide boost on the brakes. boosters seldom make problems.
if your pedal falls after engaging the brakes your master cylinder is allowing fluid to flow past the piston. that does not necessarily involve a leak. though sometimes it will.
The Following User Says Thank You to bob2 For This Useful Post:
You can drain the fluid from the master cylinder when you change it out. The rest of the fluid will be left in the brake lines from the master cylinder to each brake caliper. You can bleed them out after you replace the master cylinder. After bleeding and installing the master cylinder, bleed each brake line starting with the right rear, left rear, right front, and left front in that order. Have a small piece of tubing attached to the bleeder screw and insert the other end into an empty bottle (20 oz. pop bottle works great). Open the bleeder screw as someone pushes on the brake pedal. As they finish their stroke, close the bleeder screw and allow the brake pedal to return up. Repeat this process until all of the air and fluid have been removed and clear new fluid flows into the bottle. After 10-15 strokes, remember to replace the fluid in the master cylinder. If you allow it to go dry, you'll have to repeat this process all over again. The RR will take the longest and the LF will be the shortest.
SOMETIMES you can attach the m/c, pump the brakes up really well, then loosen one of the two brake lines on the m/c. repeat for the other line then repeat the whole process, several times. this will eliminate the need to push that air all the way to the wheels... SOMETIMES. it's worth a try .)
SOMETIMES you can attach the m/c, pump the brakes up really well, then loosen one of the two brake lines on the m/c. repeat for the other line then repeat the whole process, several times. this will eliminate the need to push that air all the way to the wheels... SOMETIMES. it's worth a try .)
lol thats what we did, worked like a charm... gonna fully bleed when i get rotors and pads
if your pedal is full up and does not pump up the only reason you would want to "fully bleed" is to renew the fluid in the system. the avalon is much more forgiving when bleeding brakes than most
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losing brake pressure
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