Brake Pedal Sinks

1984 500 SEL. I replaced a rotor on the passenger rear wheel, and whenever I drive, if I press the brake pedal down at just the right distance, the pedal slowly sinks to the ground, all the way. And when
Im stopped at a light, it slowly starts to sink down to the ground. Any ideas?
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I. Air within the new caliper. Did you bleed it after installation and is the bleeder at or near the top of the caliper?
II. Low brake fluid level and / or defective master cylinder.
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I didn't replace the caliper, its the one that was on there before, the only thing I replaced was the rotor.
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OK, when you replaced the rotor did you support the caliper or let it hang by the brake line? If the latter I'd suspect the flex hose and replace it if there's any doubt for the alternative, brake master cylinder is more costly and therefore should be the second suspect.
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It is most likely your master cylinder is bad. I suggest you not drive the car anymore unitl you get new master cylinder. You will find it at one time, it will sink like crazy and you can't stop... unless you pump... but still, you don't want to be in that situation.
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The caliper was resting on something, not hanging. Ill check that flex hose. It doesn't leak fluid though, at all.
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The hose should be OK, go to the master cylinder.
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If the line is undamaged, the master cyl piston got some crud in it when retracting the pistons. Replace it. Just out of curiousity, why change only one rotor? They cost under $30.
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Long Story. Basically my wheel fell off one day, and it stripped the threads on the hub. So I had to helicoil the threads, and the new bolts were long enough to strike the parking brake mechanism. Overtime, it broke off inside the rotor, and slowly scraped the inside of the rotor. This eventually caused it to weaken enough until it cracked. So I just removed the parking break mechanism on that wheel, and replaced the rotor, and now I don't have any problems.
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That is except for the problem that you don't have a parking brake on one wheel, which would be nice to have if your brakes fail, which might happen if your master cylinder decides it doesn't want to play.
Please fix it correctly for everyone's safety, not just your own.
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Get the right lug bolt... doesn't the factory lugbolt fit? Unless someone put in the wrong one. Stick it into the wheel and look at the back side... it should extend like 1" nothing more than that... if more than one inch, then it is the wrong bolt and yes, will damage the parking brake.
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Well they didn't have the right metric size helicoil, so I couldn't use the original bolts. By the end of the month, Im having the hub replaced with a used one, so it will be original
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Ahh... I see now... okay. Just be careful when you drive.
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