I think I’ve verified it’s crosslinked. Plus the service manager says so too. I’ll know for sure later today. (it’s 2:14 am).
If you find out the real root-cause, please let us know.
Is your brake locking issue solved? What exactly was the problem?
It takes 10 minute to change the serpentine belt on my 99 Corolla.Just be careful not to damage the hydraulic belt tentioner because its expensive.
I meant to get back here and post that the problem was fixed by replacing the master cylinder.
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Glad to hear you got the problem solved OP. Best of luck.
You asked how the master cylinder could effect the system. There are 2 return lines to the master cylinders 2 return ports, each handling one of the diagonal systems. If either one or those ports gets clogged by dirt it has the same effect as two collapsed flexible lines not releasing the hydraulic pressure to those wheels.
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I suppose that could be yet but I’ve never seen inside a master cylinder like that to understand how else it could have happened. I’m imagining separate Pistons drive both sides and it would seem cuz though it would have to be pretty big dirt to clog it in that way and it doesn’t really address how the problem often didn’t occur until I driven many 2 miles and how it got progressively worse until I stopped and let it sit. My eye once remember going about 10 miles to a place and barely making it there then being inside for about out of, coming back out and they were freed up but then seized Again by the time I got home. It was always left front and right rear although I didn’t realize the right rear was involved until one time when I stopped for a traffic light and just before a complete stop I heard a squeak that I am immediately recognized as a pads squeaking on a drum, not a caliper on a disc squeak. Replacing the master cylinder fixed it but now I have a bit of disc warpage I can feel in the pedal under hard braking that is likely just the left front. I’m now just curious for Curious sake. Thanks very much for your input. The good news is I got to take all those brake parts that I had bought for the front back and get a full refund. I’m actually glad I waited until I was sure where the problem was because I had those brake parts in the trunk for at least a month. I’m always hesitant to hand my car to a mechanic unless I already know what’s wrong. I’ve been a service manager and I’ve known of unscrupulous service managers who would use what a customer thinks is wrong as an excuse to do more work than is necessary. It’s easy to use someone’s desire to be right against them. Personally, I’ve never had that in me.
Did you try cooling the MC off with a bag of ice to see how that affected the symptom? The clearances between the parts in a MC are necessarily very tight in order to contain the pressures involved , and the normal thermal expansion of metal could cause parts to bind, especially if they were already slightly corroded and/or the seals were degraded. And the point Oldtimer makes above about the fluid passages in the MC being very tiny is another possibility.
The dirt floats in the brake fluid which makes it intermittent but is too large to go through the jole in the port the return line screws onto.
All that can be said is the problem was in he mastercylinder and the exact cause is unknown.
Debris could be it but it’s not the only possibility, although the fact I remember finding something in the straining basket of the fluid reservoir well before this problem, probably give the idea more weight.
I first noticed front left. A couple of times both fronts were hot but the left would be hottest. But it didn’t occur to me to check the rears. Then one time when the right front was very very hot and dragging hard as I stopped for a light I heard a squeak that I recognized as a rear brake shoe squeak. I then found the right rear was hot.
Knowing the car had a dual brake system and the only way to safely do that is to crosslink side to side so it could be controlled with the other side out, I imitatively suspected the master cylinder as the only way the problem could be cross linked. I came her asking about it because I wanted to be fairly certain before handing it over to someone to check it out.