I responded to PM, Thank You!
Okay, here goes yet one more of my long post, as I get on my soap box!
I've posted in a few threads, where you'll see I punch a hole and also fill boot(s) with dielectric grease.
But I feel
number one prevention is do not Overfilling reservoir. Don't Do IT! Brake fluid is
hygroscopic.
Here is my thinking and why:
I first thought just as you, water getting in the boot. Although driving through rain, snow, deep water it doesn't really get up to area. So I assumed it was from washing engine bay. But no wire corrosion on my 01LC (The King) which I washed engine bay at least once a year for 14 + years, you could eat off engine. Also drove in the rain and snow. No corrosion on wires.
I now inspect for this corrosion condition on brake master wires always. I've see engine bays of low miles rigs (50 to 130K 05-07), that look like engine bay never washed. No real way to known if ever washed, but clues said not washed. Yet found corrosion. How did moisture get in wire boot(s). Yet in early stage of corrosion I find thick wet gunk. Remove boot leaving off and it hardens and corrosives action goes to work.
First inspection of a 2007 from GA/TX. You're looking at reflection in inspection mirror of boot pealed back and wires exposed.
View attachment 1952874
I thought perhaps leak from ABS unit was getting through leads internally, then into boot. But I took/smashed apart the ABS unit. I really don't think fluid can get through ABS into boot. Plastic is cast around leads and snake up through the ABS plastic. Leads are deeply in-bedded in plastic.
When I considered it coming through the ABS. I realized brake fluid is
hygroscopic. Brake fluid attracts and holds moisture. But how could it be getting into boots. I'm 99.9% sure it's not leaking from ABS. So how then is brake fluid getting to the area? Leaks, spillage, what???
Over-filling of reservoir is second common thread (1st corroded wire) I'm finding to these failures. I find about 30% of all rigs over-filled. This includes Toyota or Lexus Dealership maintain with spotless service records. Shop tech's see reservoir low and tops with best of intentions. They think fluid low due to pad wear, which is normal thinking. But they fail to read what Toyota felt so important they embossed on the reservoir. A procedure to evacuate brake fluid from accumulator into reservoir before topping.
During normal driving over-filled reservoir, excess fluid is pushed out cap and grommets. This gets on boots and IMHO into boots.
Now the second question I have is:
Does the change of resistance in the wire, damage ABS and reduce life of motor. This is why I'm asking those that have had failures.
"Is wire corroded"?
What failed on brakes master?
It's also why I'm asking for the old brake master parts. I take apart and inspect for what, why and common threads.
I've one of the highest mileage 100 series (00LX) in the country at over 350K miles, that I'm driving. It lived in CN first few years (late 99). Spent some time in Boston. Has more rust then I'll usually buy, work on or see here in the west. Not really bad rust, but works me harder and has gotten under sheathing of some wiring (blueing oxidation). I've door lock motor issues and hinges of DS door are worn out. Steering column needs work as it's loose. It was Lexus Dealer maintained. The records are the thickest I've every seen, and I've yet to get the first two years of records as it lived in CN. This rigs a good test bed. Yet it's
wires have no corrosion. Motor is still working and seems fine. I will be pulling the accumulator pump motor and inspecting brushes, bearings and commutator one day. But that means replacing the very expensive the wires, FSM states non re-usable. So it makes for a very price inspection. For now I just made sure brakes are in tip top condition and pass all test. I also PM the e-brake with new shoe.
If I get a brake light and or alarm. I'll pull off road at once. I know I'll have limited number of time I CAN pressing pedal before assistance pressure is LOST!