Help! Rear Brakes Locked Up

I got a '86 420SEL. The rear brakes locked up 3 times. All after a while driving, and when applied brake then resume driving, the gas pedal felt heavy and it could only move at most 20 mph. then braked to full stop, found the rotors coal-red hot, and the car wouldn't move at all. But after about 30-60 minute, everything normal again. Brought to mechanic, he said he founf a metal stuck in parking cable, and i drove home. Two days later, it stuck again. Went to another experienced mechanic, he drove two days, found nothing. I drove back, and the next driving only took 10 minuted to happen again. I saw someone here with same problem, but anwered with a opinions, parking cable and master cylinder, and sort of believing it's master cylinder, but should I buy one or rebuild one? Any idea welcome as well as procedure.

I find your post confusing because:

[QUOTE]Originally posted by zebra100
[B]I got a '86 420SEL. The rear brakes locked up 3 times. All after a while driving, and when applied brake then resume driving, the gas pedal felt heavy and it could only move at most 20 mph. then braked to full stop, found the rotors coal-red hot,
and the car wouldn't move at all. But after about 30-60 minute, everything normal again. Brought to mechanic, he said he founf a metal stuck in parking cable, and i drove home.

An 86 420SEl has a drum/shoe parking brake, this would not heat up the rotor to red hot, so what did the mechanic do? My guess, nadda

Two days later, it stuck again. Went to another experienced mechanic, he drove two days, found nothing. I drove back, and the next driving only took 10 minuted to happen again. I saw someone here with same problem, but anwered with a opinions, parking cable and master cylinder, and sort of believing it's master cylinder, but should I buy one or rebuild one? Any idea welcome as well as procedure.

Symptoms indicate a locked up caliper(s). I suggest replace calipers/rotors/pads, since you have fried them, the pads and rotors.

Suggest you get caliper rebuild kit and rebuild caliper. Be sure to clean all rust off the slide areas where the caliper slides back and forth and coat with caliper grease for smooth movement. Replace brake pads and rotor.

[Kestas]

Perhaps a flexible brake hose is disintegrating from the inside, acting as a one-way valve.

[jcyuhn]

It seems rather unlikely that both calipers failed in exactly the same way at the same time, or that both flexible brake hoses failed in exactly the same way at the same time. What are the chances? You need to go back to the point at which one failure can cause both rear brakes to lockup. That point is the master cylinder. Simultaneous lockup of the rear brakes is in fact a known failure mode of MB master cylinders from that timeframe. I've been there, done that. Replace the master cylinder and you'll have fixed the problem.

That said, a thorough inspection of the rear brake system is now in order. You probably do need to rebuild the calipers, as the dust boots have likely melted from the heat. The rotors are probably warped, and there may be some collateral damage. You almost certainly need new brake pads.

- JimY

[sbourg]

My first inclination would be to say your parking brake is the problem. In my experience, a locked-up caliper is a rarity, but brake shoes are a different story. Since the brake drum and rotor are the same part, the rotor would heat up even if the drum and shoes are the culprits. This is why the first mechanic found a problem with the parking brake cable.

Steve

Thanks, guys!

I think my first choice is master cylinder like Jcyuhn said. He poined out for the same problem for someone with exact locking and the problem was solved. Also, my parking brake is pretty loose and take 5-6 clicks to barely hold. And the symptom always automatic solved after 30-60 minutes may suggest master sylinder will release the pressure of the fluid in time. But parking brake is total mechanic system, and it unlikely auto release every time. And I will definitely change the pad (though I hate the dust thing) and check rotors and cater. And all your posts gave me valuable respect to consider. Thanks again.

Another thing is where to find a good deal on master cylinder and rebuit cylinder is reliable? Or repair kit is workable? Is there anyone have any comment on this?

[Kestas]

Click on the FastLane button on top of this page. It'll take you to a place where you can get all you need for your vehicle.

Exchange or rebuild?... What you could do is take apart the calipers and assess their condition. If you find pitting corrosion on the critical slide surfaces or frozen bleeder screws, then you're forced to exchange calipers. Otherwise you can rebuild. Another factor to consider is how much you save by rebuilding yourself. For some cars it's not much savings.