A couple of months ago I posted on some observations on the
state of my rear brakes when I remove the IRS for some
extended service work.
The passenger side pads were worn to the shoes and the disk
was about half the size of the other side’s disk. Caliper
leaking fluid. The parking brake fork was broken and the
parking brake pads were worn to the point of needing
replacement. Driver’s side looked good.
These brakes had been completely rebuilt (calipers, new
disks, pads, forks, all of it) about 20K mi ago, about 12
I concluded, after tearing this down and attempting a
caliper rebuild, that moisture had somehow gotten into the
system and that this had been responsible for the
extraordinary wear (a lister mentioned that the moisture,
as the brakes get hot, vaporizes, and pushes the pads out,
causing premature wear…don’t know if that is really what
happened, but it is certainly plausible given the
So, yesterday, as part of the last steps in getting the car
back together (many many changes and upgrades done- renew
brakes and hand brakes, 3.54 diff, suspension changes,
incl. addco rear bar, new exhaust system design, bored
throttles, etc., etc.), I bled out the brakes. The rears
produced an incredible amount of white-ish yellow-ish
sludgy slop, and eventually ran clear, indicating that the
system was flushed.
I am guessing that this slop was not only held in the lines
but also in the accumulator and switch, given the volume
that came out. I can also see that this slop probably
contributed to the premature brake pad wear and caliper
I had not flushed the brake system since that total rebuild
about 10-12 years ago.
After finishing the rears, and moving to the fronts (these
both ran clear from the start), I was working on the last
caliper (driver’s side) when the ABS pump tone changed, and
the pump continued to run. Then, after turning off the
ignition and turning it on again, the pump did not come
on. But, I now have an ABS and brake warning light lit,
and the pedal is high and rock hard.
I am strongly suspicious of a brake pressure switch
failure, from the gooey fluid that must have been laying in
that switch body. I pulled the pump assembly and opened
this to examine the internal filter, but this is clean.
Clear fluid. I replaced that switch and the accumulator
when I last rebuilt the brakes.
Lesson learned: flush this system regularly per the manuals!
But, as to the symptoms and root cause: anyone care to
hazard a guess? I am thinking switch right now.
Mike, 1990 5.3 XJS Conv., 5-speed, SE-ECU, TT Extractors
Lakewood, OH, United States
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