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Discussion Starter #1
Hello, I recently picked up an 86 mr2 that has not been driven regularly for about 2 years. After driving to work a few times I started to have a pretty sever brake issue that I cant seem to figure out. Long story short, intermiddately while driving on the interstate there seems to be pressure building up in the brake system causing all 4 brakes to apply pressure to the rotors and heat up. When this happens the brake pedal becomes hard as a rock. I have tested the brake booster to the best of my ability and swapped the master cylinder with one from one of my other mr2s. After the pedal gets hard and the brakes are dragging I have cracked a bleeder valve and not much fluid comes out but that does unlock the brakes and free up the wheels. It seems to happen faster on hot days after sitting in the parking lot. Once the pressure builds I have a hard time accelerating but after stopping for a minute it gets better. Then after not driving it for 2 hours it is fine again. I am stumped. Please help. Sorry for the long post, ask away for more information. Tia
 

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Probably the master cylinder not releasing pressure. Maybe a good flush of the brake fluid would help, but likely just replace it with a quality part.
Good luck
Mike M.
 

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Discussion Starter #6
I've flushed the fluid so that's good and the master that I put in is good cause I took it off a car that I drive regularly with no issues. As far as pedal play?? What would cause pressure to build in the system and make the pedal super hard? Once it is hard and the brakes are on if I crack a bleeder valve, everything goes back to normal.

Could it be something with my brake booster? I'm not sure what can go wrong with those but when I removed the master cylinders from both cars the shaft that comes out of the booster in the 86 with the problem did seem to show noticable wear over the the one in the good car. Would it be worth switching the brake booster to see if it is the culprit?

Thanks for the replys!
 

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Discussion Starter #7
Anyone have experience with a collapsed brake line? Could that be the culprit? After the pressure builds and the brakes drag my passenger rear wheel is much hotter than the others...
 

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... As far as pedal play?? What would cause pressure to build in the system and make the pedal super hard?

...Could it be something with my brake booster?
Heat. That will make the fluid expand, and if it is in a closed system, it has to go someplace.

I suppose so. A defective valve could cause it to go berserk.
 

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You need to adjust the push rod in the master cylinder. The M/C piston must be able to retract pass an internal port to allow brake fluid to return to the reservoir after you apply the brakes. You need 1mm clearance between the push rod and the piston. Also verify that you have a return spring on the brake pedal lever. Davew
 

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If brakes hoses are in question at all, CHANGE them. I recommend stainless braided ones. You will love the feel. Also, I had a rear wheel get very hot from a stuck caliper. The caliper got seized on the upper pivot pin. I guess the last time I did the brakes I didn't lube the pin. What a pita that was. I would recommend a total brake system rebuild/upgrade if you have the money. If all of the components are original then the system will need to be over hauled. Because brake fluid is so corrosive it can eat hoses from the inside out. A hose can actually get like a flap internally from the rubber being eaten from the fluid. It can actually act like a check valve where it will hold pressure on the caliper.
 

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A blocked hose is possible, but a seized caliper is the most likely cause for a single hot wheel. They all seize sooner or later. If it is a rear wheel it is easy not to notice it while driving. Whatever the cause, it is probably unrelated to your larger problem.
 

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Discussion Starter #12
Thanks for your posts. I think I got it sorted. I ended up going to stainless steel brake lines and basically lubing up all the caliper slides while I was in there. I have put 150 miles on it with no problems.
 
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