Mechanics

BRAKE PRESSURE

2000 Ford Focus • 90,000 miles


On my way home from work my brakes failed, luckily I wasnt far from home. I discovered the brake pipe had split and I have now replaced this. I have bled the brakes but the pressure isnt increasing. Is there a sequence I should be following? Started rigt rear caliper, left rear, front right, front left. Or is there any other tips you could give me to get this problem solved?

PLEASE HELP!
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Lee81
May 28, 2012.



If the brake pedal went all the way to the floor, either during the failure or while bleeding, there's a real good chance the master cylinder has been damaged. Crud and corrosion build up in the lower halves of the two bores where the pistons don't normally travel. When you run the pedal all the way down, the lip seals get ripped on that crud, then you have an internal leak that prevents pressure from building up.

Caradiodoc
May 28, 2012.
Thanks for you reply! Pressure is building up slightly but then seems to drop again. Could this also be a result of the master cylinder being damaged? It did look like the brake pipe had been rubbing against something which is what ive put the split down to, but would the split pipe itself not cause the problems with the pressure? Like I say, the pressure does seem to build a little but not to the required level.

Tiny
Lee81
May 28, 2012.
There's two hydraulic circuits and two pistons with lip seals in the master cylinder. If only one seal is damaged some pressure will build up against the brake pedal. There is a spring inside to create that pressure which forces some brake fluid to go out to the two working brakes.

What you should be able to do, with a helper, is to have them pump the pedal rapidly a few times, then hold it down with just normal foot pressure while you open a bleeder screw. You should get a little spurt of fluid and the helper should feel the slight movement of the pedal. Do that for each wheel. If you find one front brake and the opposite rear brake don't give you that nice spurt, suspect the master cylinder. If you DO get a good spurt from all four wheels, there is likely still air in the line.

You should only have to bleed the line that had the leak, not all four of them unless you let the reservoir run dry. Even then I never bleed at the wheels. No air is going to travel to the wheels that didn't have a leak. Simply working the brake pedal a few times will wash up any air bubbles that might have gone a few inches down those lines.

Caradiodoc
May 28, 2012.