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hanover_fisk

Brake Problem

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I'm having brake problems with my 99 626ES 5 speed. At 120,000 miles the brakes were shot especially the front right wheel. It was dragging intermittently and pulsating when it got hot from dragging. So I order up a nice set of cross drilled and slotted rotors and Akebono ceramic brake pads. The caliper on the front right wouldn't press back it so I figured it was seized and bought a new one, not rebuilt, sliders were good and I used a special slider grease. Also did a bunch of other maintenance at the time like, centerforce clutch, new axles, and front struts. Sucked all of the old brake fluid out of the reservoir and filled with Valvoline DOT4 fluid. Everything seemed to have gone very well for a short while then the front right wheel starts intermittently dragging again as before! I take a look at the caliper and the piston won't push in again until the bleeder is opened. Advice from various sources recommends replacing the brake line on that caliper so I do so. No change and it doesn't want to bleed. With a vacuum bleeder and pumping the pedal fluid won't come. Had to start the car and use the brake booster to get it to grudgingly bleed. When the car is cold the pedal is soft. As it heats up the pedal gets hard, high, and very sensitive. The brake drag can get so bad that you can't maintain speed and a nasty vibration builds up. Then over 15 - 30 seconds it will rapidly diminish and disappear with out having touched the brakes. Funny thing is I would expect the car to pull to the left when this is going on but it doesn't. The car brakes straight without pulling and the ABS seems to be working normally. There obviously is something upstream that is check valving me and causing pressure to build up to that wheel. I plan on inducing the condition repeatedly and working up steam cracking fittings to relieve the pressure so the wheel will turn free. I am wondering if any one has heard of a proportioning valve, ABS, or master cylinder doing anything like this? I have also seen a recall for the brake reservoir cap but no explanation why. Any ideas?

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Someone on the forum had this exact same problem a few months ago, turned out to be his ABS unit.

He replaced the caliper, brake line, proportioning valve....and finally the ABS unit (which fixed the problem).

This is the 2nd time I've ever heard of this happening, so I'd say it's not common :huh: My guess is one of the solenoids inside the ABS unit jammed up.

If you want more info, try searching for "proportioning valve" for the past few months in the tech sections (not sure if he had a 4 cyl or V6, but the brake systems are identical for most years).

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Hi, I have the exact same problem with right front  brake sticking on and being unable to push back the piston unless the bleed valve is loosened. Replaced seals in caliper first as thinking piston was jamming. I did suspecr the ABS unit as my issue occurred after doing an emergency stop where brakes seemed to have remained locked on. I turned the ignition off and car became mobile again except for issues with right front brake was overheating. This indicates that the ABS unit is the culprit so will get a replacement from the local wreckers.  Thanks for the posts as it was very helpful.

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