GmanSC

Of course, nothing lasts forever. But for the brake, the manufactures should think harder. At least, the warning system should alert the driver long before the brake fails not a moment before. In the cace of MJN331, he had no time at all to react. Suddenly, bunch of warning lights lit up from dashboard and next thing he knew that he had no brake. Imagine you were in that situation and at the busy intersection.
The SC is built in 2001, not 1920. Toyota have experiences and thing like this happens is unexceptable.

Seattle SCone

I would propose that owners of the older SC's monitor how their boost pump is behaving to avoid being caught out. Maybe we should periodically turn on the key without starting engine or pressing brake pedals and tabulate how long it takes before the boost pump activates a second time or third time. If internal leakage is worsening, I would expect that interval to decrease. Also, would be good to become familiar with how the boost pump sounds. You can hear it quite readily upon turning the key on. This would probably need to be done in as repeatable a condition as practical - maybe after an overnight park.

Maybe log the interval every six months as a prelude before oil changes?

Might also be enlightening if we could compare that the brake boost re-pressurize interval amongst SC430 owners here.

degmla

iTrader: (1)

I guess I can summarize my response with: vehemently disagree.

Seems you want to put the burden of wear-out and eventual scrap on Lexus, or any manufacturer? If this failure was occurring during a warranty period, then by all power and fervor, seek blame. But on a 16 year old car with 135k miles, owner beware. Forever and always. When a warranty runs out, the owner interpretation should be "the manufacturer no longer has confidence that this vehicle will operate reliably." Now, you and I are lucky in that we can reap the benefits of an amazing car at a fraction of the manufacturer's price...but now you know why. Because we are taking the burden of continued reliability.

If that doesn't set well with someone then, like I already suggested, they need to get a newer vehicle.

MJN331 was not at a busy intersection, but on freeway -- but your point has already been acknowledged: it's scary regardless of where you are. And it has happened to me (on my previous LX450). I was on the freeway. Guess what, no lights came on! Nothing! That was the old vacuum assist system. The brakes were just suddenly hard as crazy to stop (as was MJN331's). A very stressful drive the rest of the way home. At least MJN331 received a rather extreme warning notifying of the failure BEFORE needing brakes, not DURING actual brake usage.

And, ultimately, that is one of the extreme benefits of these forums: to educate, make aware, help us keep our cars safely on the road and know what to look for. And kudos to those like MJN331 that take the time to share.

But, those of you that want to try and assemble against Lexus and place blame on them for a partial brake failure 16 years and 135k miles down the road? -- sorry, I just have to respond. And, my opinion, these forums aren't the place for that. In warranty period, sure. Out of warranty period, no. And since all SCs are out of warranty period, then I'd rather these threads concentrate on higher value topics -- like why did the brake failure SUPPOSEDLY fail 100% (as opposed to just having a hard brake like some of us continue to speculate).

degmla

iTrader: (1)

IIRC, there are 2 types of failures that I have experienced with these designs. 1 has warning, 1 doesn't. As the motor wears out, it'll usually develop a noise. Eventually, the brushes will wear too far. The motor might cycle more frequently (i think this can indicate an accumulator failure as well). Whatever it is, you usually sense it.

But the other failure is instant. The ECU rubber grommet on the large wires that go from the brake ECU to the brake motor corrode so heavily such that either (1) suddenly can't get electricity to the motor, or (2) there is so much rust trapped in the grommet that it shorts the ECU (this happened on my LX470). However, these failures always throw codes (but that won't help you stop any quicker!).

If you haven't already, either remove the grommet, or put a small hole in the bottom so it won't collect air moisture and trap it against the terminals, or rub a bunch of heavy non-conducting grease on the terminals and pop the rubber grommet back on.

I'll try and find a pic.

degmla

iTrader: (1)

In the pic, the rubber grommet is already pulled off some. Obviously, only do this with vehicle off, since the brake motor can start any time key is on.

Seattle SCone

Great tip regarding the grommet and corrosion! Will have to look at mine. Thanks.

degmla

iTrader: (1)

What a bad one might look like (I think this is from ih8mud)…

Wilson2000

Owners should have recourse regarding "total brake failure." Brake systems are designed to be "fail-safe," which means, they fail in a manner which still allows the operator to stop the vehicle. No amount of miles or age should result in a total brake failure. That's why this phenomenon is so rare, because manufacturers go through great lengths to ensure it doesn't happen.

jonas's RX

How do you take that grommet apart again? Do you need
to pull the entire ABS unit apart to get to it?
And what does applying extra grease there do again?

thx

GmanSC

Well said.

Bgw70

thanks for providing the answer to the brake failure problem...awesome.

I am not going to rule out a seal failure.
https://repairpal.com/recall/10V499000

Here is a good thread with many examples of the brake power assist (booster) system failure...
https://www.clublexus.com/forums/sc4...l#post10240122

Bgw70

I agree with you...I think a total brake system failure would mean fluid is getting past the piston seals...seal failure caused by age, dirt, corrosion etc.

Also wonder if it is two problems or just one and one is confused for the other.
Is it a pedal to the floor zero braking problem or a power assist (booster) problem?

Bgw70

agreed...

here is another recent article, same subject.
https://www.carcomplaints.com/news/2...-lawsuit.shtml

Harold57

This is all good stuff. But to take it a step further:

Is there a way to test for the compromised (leaking) seal? What would be the symptoms of the failing brake booster pump motor?
Or taking a different tact, what are the part numbers of the seal and motor so that preventative maintenance could be performed? (A diagram would be great, if you have one.)

Seattle SCone

Trying to think how a boost pump failure could make the system go completely non-functional. Unfortunately, without actually knowing internal plumbing, it is a bit of conjecture.

1. Pressure in normally operating accumulator helps deliver increased hydraulic pressure beyond that manually generated by the master cylinder pistons.

2. VSC system is able to pulse accumulator pressure to calipers under electronic control

3. There must be a valving system that directs accumulator pressure to calipers instead of against master cylinder.

4. If one pumps the brake pedal while key is off (accumulator has not yet pressurized), a normally functioning brake system does push brake fluid to front brakes. There must be a valve that under normal circumstances, excludes master cylinder pumped volume from accumulator. Otherwise, pumping the brake pedal would drop pedal trying to fill accumulator.

5. There must be hydraulic pathways that interconnect master cylinder, accumulator, and calipers. Otherwise, no brake fluid/pressure would transfer.

Given the above, one would need to lesion the valving system in such a way that the master cylinder piston volume is able to flow into accumulator in addition to calipers. If boost pump also fails, accumulator pressure goes to zero, master cylinder pushes fluid preferentially into accumulator. Non-pressurized accumulator returns zero fluid. Near zero resistance and no fluid return from accumulator, so fluid from reservoir is only source of fluid possible for master cylinder to refill. If you also somehow slow brake fluid flow from reservoir, MC cannot fill and pedal drops completely to floor.

It would need a chain of three failures to completely knock out the system. At least one reports suggest that brake operation can return to normal after a total failure. Getting all three failures in a reversible manner would be most easily accomplished by making the electronics or solenoids ruin coordination of the valving on top of the pump motor failing.