I changed the pads on my car, and the rear calipers wouldn't compress, so I opened the bleeder valve, so I could compress the calipers. Do I need to bleed/flush the brake system now?
by 
sbryant7
ANSWERS: 3
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Try this test: Turn on your engine, and depress the brake pedal. It should feel firm, and stay put under pressure. If it feels spongy, or slowly keeps going to the floor, the rear brakes probably do need to be bled. Another test: did you close the bleeder valve before any air could be sucked back into the cylinder? Like, the moment you finished compressing the caliper? If so, you may be alright. When you said "compressed" in your question, I'm suspecting you mean opening the caliper so it will accept the new pads. Bear in mind that when you compress the caliper, you're forcing brake fluid back up the lines and into the master cylinder. If the cylinder won't compress, that means you forgot to remove the filler cap on the master cylinder. Leaving the cap off allows the fluid to fill back into the master cylinder, so you can compress the calipers.
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I would like to add that the fact you had to open the bleeder to compress the caliper piston may mean you have a problem. When compressing a caliper piston you are in effect pushing the brake fluid behind it back up to the master cylinder, through your hoses, and lines. When a caliper piston cannot be compressed its usually a sign that there is a blockage / restriction in one of those hoses or lines, that lead to the master cylinder. If it was just one of the rear calipers, especially if the pads on that side were worn a lot more than the opposite side, that is probably true, if it was both, then most likely not. Also as far as your question goes, it all depends on how you did the process. There is only one way to be sure, push the pedal, and see if it goes to the floor. If it goes to the floor they need to be bled.
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as long as you closed the bleeder valve before you released the piston , it should not need to be bled. however the fact that you had to open the bleeder tells me that the caliper's piston may be bound. my wife's chev malibu's piston were frozen, she just doesn't use the brakes hard enough to keep them free. though it should not move easy a small pry bar when it is still attatched should move it.
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