Some alarms are hard to hear (weakened with age) especially with stereo on. But most time there are warning signs, like booster pump sound changing. It's been my understanding we do have some brakes, just need a very hard push at bottom of peddle stroke. Unless fluid loss, then we've nothing as no hydraulic pressure can be generated.
When I bleed rear brakes I'll hear the alarm go off as I reduce pressure by bleeding off fluid, way before level alarm sounds.
Reservoir being full indicates fluid was not lost. To have over max line indicates system was overfilled. I see 7 out of 10 overfilled, even when dealer maintained. Seem no one reads the procedure stated right on the reservoir. Does this cause damage to booster, master or ABS IDK. I do know the cap seals the reservoir, and overfilling is not a good idea.
The newest thing I'm checking during my inspection is check the leads for the ABS to booster pump. Here is one ABS unit I swapped out for a mud member this summer.
Leads are in very bad shape (Rust) This was from a clean 98 no rust w/150K miles. Edit: After leaving exposed to air, it dried in a matter of hours. I'm now convinced after seeing 100rds of master. Rust (corrosion) is a result of brake fluid getting into boot and on wires. This increases resistance. Which damaged motors commutator, causing premature booster motor failure.
I use a mirror to check by pulling boot back. On The king which I had 14 years the leads were fine. I note that because I washed engine bay at least 7 times over the years, thought that washing may be cause. Nope appears not the case.
Here I found something on my 07 Unicorn, which is a supper clean rust free rig, but can't tell what it is. So I'll be pulling Master assemble to get a better look. May just be a protective grease, may be leak or may be rust.
I also know there was an issue with after market brake fluid being add to some 04-06 (not series 100). IMHO it was from change in rubber formula to cut cost:
Toyota DOT 3 Brake Fluid Composition ? I learned we can not get the same fluid that can with the 100 series from anywhere in the USA.
Safety Recall A0M – Preliminary Notice
2005 through 2006 Model Year Avalon Vehicles and
2004 through 2006 Model Year Highlander (Non Hybrid) Vehicles
Rubber Seal (Brake Master Cylinder Cup Replacement)
******URGENT******
On October 21, 2010, Toyota filed a Defect Information Report (DIR) with the National Highway Traffic Safety
Administration (NHTSA) informing the agency of our intent to conduct a voluntary Safety Recall on 2005 through
2006 Model Year Avalon Vehicles and 2004 through 2006 Model Year Highlander (Non Hybrid) Vehicles to
replace the Brake Master Cylinder Cup. This Safety Recall will also cover 2006 Lexus GS 300, IS 250, IS 350
and 2004 – 2006 Lexus RX 330.
Condition
• During vehicle assembly, Toyota uses brake fluids containing polymers that act as lubricants for certain
brake system components. If replacement brake fluid is used that does not contain such polymers, or
contain only small amounts, a part of the rubber seal (Brake Master Cylinder Cup) located at the rear of the
brake master cylinder may become dry, and the rubber seal may curl during movement of the piston. If this
occurs, a small amount of the brake fluid could slowly leak from the seal into the brake booster, resulting in
illumination of the brake warning lamp.
• If the vehicle continues to be operated in this condition, the brake pedal feel could change, and braking
performance could eventually begin to gradually degrade.
•
Toyota original brake fluid which is applied at the manufacturing plant contains polymers and does not cause
this phenomenon
This recall is why I now use only Toyota brake fluid. Not doing so may damage seals inside master. Then when booster motor replaced. The ensuing pressure increase reveals bad seals. We then must replace Master!
Holy cow...
