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All four Brakes keep locking up on 96 Camry

I have a 1996 Toyota Camry, I was having a noise from right rear and every now and then the car would start slowing down like I was braking. I replaced all four calipers, rotors and the pads, then bled the whole system. The noise went away, but the car still seems to engage the brakes, but only after a few minutes of driving, but then it goes away. I thought it was a single brake line, but after not driving it for a week, yesterday I was driving it and after about 20 minutes it started again, when I pulled over all for wheels were smoking, after allowing it to sit for a few minutes, I was able to drive home 30 miles without it happening again. Would this happen with just one line bad, as someone suggested, or is this an issue with the master cylinder, bad brake fuild or something else? Any input would help…

I suspect that the master cylinder is hanging up; the brake booster is not releasing; or the pedal linkage is binding. I am sure that you would have noticed if the pedal was not returning to its rest postion i.e. brake lights remaining ‘on’ and pedal resting too far down. Anyway, try pulling up on the pedal to see if the brakes release. If you are willing to trouble shoot, unbolt the master cylinder when the brakes are dragging (don’t disconnect the hydraulic lines). If the brakes release, the problem is probably in the booster. If the brakes don’t release, crack the fittings on the master cylinder. If the brakes release, you have a master cylinder that is binding up.

I just had a thought. This Camary probably has ABS. So it could be something wrong with the ABS unit. Have you been diligent about flushing the brake system every 3 years or 30k miles. If cracking the master cylinder lines does not release the brakes try this. With the brakes locked up, crack the line going to each caliper. If that releases the brakes, it might be the ABS unit.

Hope this helps.

Researcher’s advice and instructions are excellent and I wanted to insure you that turning the fittings at the master cylinder and the bleeders at the wheels will not allow air to enter the system as long as the master cylinder is near full and the pedal is not pushed. I seem to recall someone with a similar problem who avoided opening any fittings because they were mistakenly concerned that air would enter the system. Good luck.

I also like Researcher’s post. I wanted to add a few other ideas.

Try also (first) disconnecting the vacuum line to the brake booster. Clamp the engine side of the line (to prevent a vacuum leak with the engine) and see if the symptoms disappear. You’ll take a bit more pressure to apply the brakes, but it’ll either confirm or eliminate the booster as a candidate.

The booster works by using the engine’s vacuum to helo apply the brakes by applying it to the front of a diaphragm. In normal mode, with the brake undepressed, vacuum should be applied to both surfaces of the diaphragm. If the valves are screwed up and vacuum is constantly being applied to the fromt side of the diaphragm, it can constatly apply the brakes.

I’m inclined not to suspect the ABS system. It functions bu interfereing with the hydraulics on a particular wheel when it senses that wheel not turning, but it really cannot apply hydraulic pressure in any way. It’s simply a set of solenoid-operated valves, one on each brake line, that pulsate and shut the line off & on for a wheel that’s slipping.