Bgw70

I just thought you might be interested in seeing any maintenance performed by Lexus, if any...it’s a nice service provided by Lexus. I have the Lexus service history on both of my SC430s.
The service history could show if the brakes were ever bled. Never bleeding brakes could be the reason you had brake MC failure.

Why do you say it is electronics?

dbryan

It wasn't soft like brakes that hadn't been bled. It was a momentary grab followed by complete to the floor failure. They would have been soft long before you'd have a failure. I know what air in the lines feels like. In addition, once I started the car to move it, the brakes were fully functional again.

Bgw70

What do you think failed?

Never had major brake failure like you and others, but did have a bad leak on my 2002 SC430 BMC shortly after I made the purchase.
Replaced it with a $100 unit from a 2005 in a salvage yard. Still good several years later.

Here are my two cents...When the fluid is never changed and the fluid is black, caused by water/condensation entering the system, the seals in the MC piston can fail which allows fluid to pass by them causing the pedal to move to the floor rapidly.
or the lack of fresh fluid in the ABS controller causes a similar problem with the ABS valves sticking open.
I say that because in three cases I know of, the driver pressed the brakes very hard...perhaps enough to engage the ABS.

dbryan

First, I was using normal pressure when they suddenly failed. Secondly, they functioned properly when the car was turned off and then back on again. Thirdly when I have the oil changed, the shop always examines all the fluids and it was fine. Finally the first time I brought it in I specifically had the brakes checked as per usual whenever I buy a car. It was not brake fluid. I am certain.

If you check one of the first links on this thread you will see a similar issue reported..

JTho

Dbryan, so glad you are okay. That sounds terrifying. I remember the other post from a couple years back.
I w/ ask about brake bleeding w/ my mechanic. Is there something to proactively check w/ the MC? I will go back to those links and re-read.
What would happen if one tried to pull up the parking brake should something like this happen? Providing one had the wherewithal!

Bgw70

not our model or year but it is happening...
https://www.aboutlawsuits.com/toyota...-recall-99756/

https://www.mechanicsdirect.com/blog...us-is-failing/

http://www.diy-time.com/automotive/t...ta-lexus-cars/

dbryan

This describes it pretty well

Popping/Clicking Sound

There have been various loud sounds reported to occur immediately preceding brake actuator failure. Though the descriptions of the sound may vary, they are all loud and consistent. The loud sounds likely result from the pressure leaking rapidly from the brake system, as the brake actuator fails to regulate the pressure.

Sudden Brake Failure

The worst and eventual result of brake actuator failure causes a sudden failure in the braking system. Since the brake actuator is responsible for both immediate braking and the parking brake, this can occur at nearly any time. Owners have reported the sudden failure at many different speeds, including braking to slow a vehicle as well as intentional stop braking. Failure, while parked with the parking brake engaged, has also been reported to result in diagnosing brake actuator failure.

DshngDaryl

Hey BGW, didn't you once say that Lexus has a rebuild kit for the master cylinder? Something relatively new, since you had to buy a used one the time you had a problem.

Though the master cylinder is expensive to replace, it might not be too bad for people to have their cylinder "rebuilt"

Ah heck, I guess I should just google "Sc430 master cylinder rebuild kit" and see for myself
https://www.lexuspartsnow.com/oem-le...epair_kit.html

Bgw70

yep, that would be the one...a new BMC piston and O-rings.
I never bothered to purchase one since I was able to locate the salvage yard BMC. But I almost did because I was desperate. Never could locate the source of the leak.
I still believe one of the contributing factors for failure is not keeping the fluid serviced.
It seems this only happens to the first generation SC430s.
Does anyone remember any 2006-2010s failing?

dbryan

Fortunaely I'm big into servicing. I've notified Lexus and they are looking into it.

Bgw70

good call, please let us know how everything turns out...very interested to hear what Lexus has to say.
I should add that I also believe Toyota had some issues with our SC430 BMCs but there just weren’t enough malfunctions or enough people shedding light on the problem.
Our BMC is complex and expensive because it does it all in one unit...BMC, ABS, pump and accumulator all in one. I want to say the GS430 had an identical unit with its own share of failures.
I believe One of the articles I posted was a class action lawsuit for another Toyota model.
Lets face it, Toyota only uses so many subcontractors to produce their parts.

718SC

Really sorry to hear about this and am also glad your okay. It's a scary thought to even have about any vehicle yet alone one being serviced regularly by the dealership. I also have an 02 sc430 and am concerned as well. I have had mine since a little under 100k miles and am up to about 175k miles. I did the supra tt front brake upgrade along with the stainless steel lines and saw a major improvement in braking.

DshngDaryl

According to the Lawsuit links you had sent, it is the "O" ring that is either defective or goes bad.

Bgw70

I just wish we knew exactly why this happens in our cars.
What years, is it the O-ring, is it contamination, does it happen more to cars in a certain climate, etc.
We just know it happens and the only answer I have seen is Toyota telling people they need a new $$$$ BMC.

dbryan

What's worse is why does the computer sensor disable the brakes? Even mushy brakes would be better than no brakes. If this is Toyota's/Lexus' attitude maybe there is a class action suit waiting for someone to take on. This seems more deadly to me than the airbag issue