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You still have air in the brake system. When I changed my first 240 rear caliper, I went through 2 quarts of brake fluid trying to get the last pocket of air out. I got it to the point where the pedal was hard, but there was still enough air in the system to illuminate the Brake Failure light. -then I drove on it for a few weeks, bled the system again, and the last of the air finally came out.
The Brake Failure sensor is simply a pressure differential switch. Since you have two seperate hydraulic brake systems on the car, it looks to see if one system has more pressure than the other (the circuit with less pressure is due to the air compressing). When there's more pressure in one circuit, it slides a pressure switch left or right and closes an electrical connection.
Personally I find "bleeding" the brakes on a Volvo to be a frustrating task, -especially on the non-ABS models which have 8 or 10 bleed screws. I spent the $50 for a Motive Pressure Bleeder (available from IPD or FCP Groton). Now, I toss in a quart of DOT 4 into the power bleeder, pump it up and open the bleeder screws one at a time until clear fluid comes out. By the time I'm done, I've used almost the full quart and I've got clean fluid in the lines and no air bubbles. I can't tell you how many hours this device has saved me. Worth every penny!!! -and no more Brake Failure lights.
FYI, a brake caliper will last almost indefinately, provided the brake fluid is clean. The auto manufacturers, including Volvo, advise flushing the brake fluid ever 2 years (not just bleeding it but flushing it clean). DOT 3 and DOT 4 brake fluid is almost chemically identical to Alcohol and it disolves moisture (it literally sucks the humidity right out of the air and disolves it in the brake fluid). The water is still chemically active and it begins to rust the steel brake lines from the inside out. The rust particles brake free of the lines and become suspended in the fluid, -thus changing color and causing the calipers to lock up (they're precision components and assembled in a clean room).
Additional information for anybody who is changing a brake caliper in the future:
If push the brake pedal down about 2 inches and brace it there so that it can't return upwards, you'll move the Master Cylinder forwards in the bore past the two resivouir ports and effectively "close" the brake system. This removes the atmospheric pressure from the system on the Master Cylinder end, and thus keeps the brake fluid from running out the open line when you disconnect a caliper. Think of it like you are dipping a straw in a glass of water. If you put your finger over the top, you can lift it up without the water running out of the straw. After you've got the new caliper installed, you only have to bleed a little bit of air instead of a lot. This also helps prevent air pockets getting trapped in the distribution block and the pressure limiting gates.
God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 251k miles.
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