My 1999 GMC Jimmy's ABS light comes on and off and then the car makes a humming sound. When I press the brakes the car begins to stop, but then the pedal drops to the floor and the car keeps going. I recently changed my front brakes and a rear brakeline that was leaking; However, when I check the brake oil level on the car it seems to be fine. Can the caliper or master cylinder be going out?

SOURCE: the brake light on the

There is a level switch in the master cylinder if the fluid level is low it will turn on the light and If you pressure or vacuum bleed the brakes you will center the proporting valve switch that warns of low brake pressure in either Front or rear.
Vacuum bleeding I have found to work the best.
Make sure the Park brake lever is all the way released. If you find this informationn helpful please leave me a favorable rating and by all means contact me if I can be of any further help.
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SOURCE: Anti-lock brakes come on just before I stop.

It might be a ALB sensor. Did you check to see if the sensor is operational? Its the cheapest place to check.

SOURCE: Brake problem

air in the lines,bleed them,check rear brakes

SOURCE: no brake pressure

There IS one place it can still leak. behind the brake master cyl - into (inside) the power brake vaccum booster, although that doesn't seem the problem. You first need to make sure your master cyl is bench bled. with a hose bleeder kit, you can bench bleed in-car. you should be able to bleed sys through abs sys with no problem. Sounds like the master cyl needs to be re-bled.

Ned C Cook

• 3433 Answers
• Posted on Jun 15, 2009

SOURCE: bad brakes on gmc suburban,

Gravity bleed your brakes starting at the wheel farthest from the master cylinder. No pweddle pumping. I Fill M/C and leave cover off. Then open the bleeder and watch what is coming out. Uou can see bubbles. When the fluid drips steady and without bubbles, cole and do the same to the other three. Don't let the master cykinder get low because thr fluid level helps move the fluid and air through the lines.Periodically tap the break lone with your wrench to keep everything moving.. When sll bleeders drip clean and steady. Make sore your rear brakes are adjusted to barely touch the drum. Then top off the master cylinder, cap it and give yourself a "break". :)