What you are describing is exactly what happens when the rear drum brakes are badly out of adjustment. The brake pedal goes too far because it takes a real lot of brake fluid to push the rear shoes out far enough to contact the drums, then pressure will start to build up. When you release the pedal, it comes back up right away, but it takes some time for the shoes to slowly retract. If you press the brake pedal again before the shoes are fully retracted, they don't have to move so far to contact the drums again, so the pedal will be higher. With three or four pumps, the shoes will be all the way out to the drums and the brake pedal will be high and hard. If you release the pedal for about three to four seconds, that is enough time for the shoes to fully retract; then the pedal will be low again next time you push it.
Also consider that on vehicles with anti-lock brakes, some systems require a scanner to activate some of the valves to allow trapped air to be expelled from some chambers. That should only be necessary when the master cylinder was allowed to run empty.
If there is air in the hydraulic system, most trucks and minivans use a height-sensing proportioning valve near the rear axle. If the vehicle is up on jack stands and the rear suspension is hanging down, that mimics a light load and the need for that valve to reduce rear braking power. In that condition, you may not be getting any fluid flow to the rear wheels, so no air can be bled out.
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Friday, December 16th, 2016 AT 7:00 PM
