The solution to the problem was that one of the cups in the master cylinder was disintegrating. This debris made its way down the line and clogged the proportioning valve. Thus, when the brake pedal was released, fluid could not flow unimpeded back to the master cylinder and brake pressure built up. Replacing both the master cylinder and the proportioning valve fixed the problem. Thank you to all who contributed to helping me diagnose this problem.
When the master cylinder was suggested there was great howling from some corners.
Seems a bit doubtful there was anything at all wrong with the master cylinder. If there was that big of chunk of rubber missing from in the MC that would have produced a noticeable symptom (sinking brake pedal). They eventually found the problem after the master cylinder was replaced - that doesn't mean the MC was the cause or even a contributing factor. More likely whatever the "debris" was causing the blockage came from somewhere else. Since the problem started after doing the first brake job the debris probably came from the direction of the wheels when the fluid was forced back by retracting the wheel pistons.
-jim
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Glad you found it and let us know what had happened. Simple replacement of the master cylinder would have, I guess, availed little or nothing without going further and dealing with the proportioning valve. Congrats.
JESUS CHRIST!!!!!!
See what I mean?
with 265k miles on it. =A0There is a
Glad to hear the problem is fixed; however, can someone explain to me how this fix is possible? I have never seen a proportioning valve that in any way affected the operation of the *front* brakes, is there something I haven't seen before on the prop valve of the OP's car?
As an aside, if there's rubber debris in any brake component, it's
50/50 whether it came from the master cylinder or not. when I hear of something like this, my initial reaction is that it's likely rubber debris from the calipers/wheel cylinders or brake hoses forced backwards through the system by a technician who did not open the bleeder screws while pushing the pistons back when replacing the pads/ shoes. However, since as I recall you've already replaced both the calipers and the hoses, you ought to be good to go.Also, this whole exercise gives me an excuse to mention that I like to change the brake fluid in my vehicles every couple years, whether or not the FSM recommends it. This not only reduces corrosion but flushes all debris like this "downstream" and out, and most of the corrosion/rubber failures tend to happen closer to the wheels.
nate
Whatever howling you did or you thought some one else did that didn't fix the problem. Obviously a blockage blockage in the line to the wheel that had the problem is a reasonable explanation for the symptoms. Replacing the Master cylinder and proportioning valve may have resulted in a solution, but there isn't any clear evidence that there was anything wrong with those parts.
-jim
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Nate, The valve is weird in the 93 corolla. Basically, a line goes from the master cylinder DIRECTLY to the front driver's side wheel. Then a 2nd line comes from the master to the valve, which then proportions the pressure to the passenger side front wheel and BOTH rear wheels (you read that right... 3 wheels on the valve). Weird eh?
-Jon
I'd say so! but thanks for the reply, your explanation of the fix makes more sense now, esp. as I recall you stated that the problem appeared to be specific to the RF wheel. I wonder what the Toyota engineers' reasoning for doing this was?
nate
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