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Brake pedal soft, then hard

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    Brake pedal soft, then hard

    A week ago I installed new front calipers and ss lines. When we had the lines off the brake fluid drained out quite a bit and the resevoir may have been empty. Before the brake pedal was ever touched we added fluid to the resevoir.

    We bled the front brakes but did not do the rears.
    Driving around for the past week the brakes were pretty bad and felt as though there was air in the system. Had to press the brakes once, then release a bit and then repress to get good stopping power.
    We suspected that when bleeding we introduced a bit of air that made its way to the rear lines.

    Today I installed the new rear calipers and ss lines.
    Bled the whole system (rears and then fronts).

    Brakes are much better now but still can only get maximum braking by pressing a bit, releasing and then pressing again.

    Is this related to air trapped somewhere or is this just due to the design of the brake system on the E30 and the pistons/pads need to be seated up a bit first?
    If it is air, then how do I go about getting it out, as I went through 500ml today just bleeding.

    #2
    That doesn't sound exactly like air in the brake system, but a full bleed/flush that ensures that is no air in the system takes more than 500ml. See below.

    This sound more like a master cylinder or brake booster problem.

    A pressure bleeder, which isn’t expensive, makes this an easy one person job. One liter of ATE Type 200 fluid is more than enough for a full flush/bleed on a car with a three channel ABS.

    The ATE fluid has proved to be resistant to moisture absorption, by testing. Which means that there is little chance of rusting or boiling of the fluid under hard braking conditions. It also has a reasonable boiling point, high enough to make it suitable for track/race use in a stock E30. Whatever luid you use should be changed every other year.

    Start by sucking the old fluid out of the reservoir (a turkey baster or large syringe works). Then connect the filled bleeder and pump it up to about 15psi.

    On early cars with the three channel ABS system like an E30, push a measured 200cc of fluid through each rear caliper and a measured 150cc through each front caliper. Push a measured 100cc through the clutch system on a manual transmission car.

    It doesn’t matter which rear wheel you start with, but the last caliper should be the left front. When the flush/bleed is finished, turn the bleeder upside down and drain fluid from the bleeder to fill the line on the reservoir and clear the hose of fluid. Then when you remove the cap from the reservoir you won’t have fluid spraying out and making a mess.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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