Yet another brake thread...sorry folks (1 Viewer)

[KliersLC]

Hey all,

1999 LC with 220k. Mostly stock Alabama car with the last 8 years in Virginia Beach
I have watched the brake failure threads with very closely but have not seen this particular issue come up.

My daughter reported that her brakes "failed" resulting in a minor fender bender a couple months back. I was skeptical as a typical father is, but put the car through a pretty rigorous set of tests and the brakes performed wonderfully. It has been DD'd from then till now, and today she called to say that she had been pulling up to a light and the brake pedal was hard, but not effective. She was able to get stopped via strong legs, and then pulled off into a parking lot. There was not a brake alarm or dash light in either case.

I drove it home today and it drove just fine. I pumped the pedal to failure with the key off and upon starting, the pump ran smooth and quiet for ~20 sec. I application of the brakes=no action. Holding brakes=no action. 3 subsequent pumps and the motor ran for 3-4 seconds. Subsequent testing revealed that the third distinct application of the brakes with a full release in between always triggers the pump, and motor always runs smooth and quiet.

So, my question is, what else should I look at? I am easily able to rebuild the MC, but it does not appear to need it. Any issue on the pump/motor/accumulator side should be accompanied by the warning light and buzzer, so that shouldn't be the issue (verified both light and alarm work). I am planning on a full flush/bleed of the system including the abs pump, but wanted to check in here to see if the gurus had any tips.

Thanks!


Dan

 

[ramangain]

Mr. Dan,

Have you thought about trying a simple brake bleed at all 4 corners to start, along with the procedure to properly bleed the ABS portion using Techstream?

 

[AlpineAccess]

Mr. Dan,

Have you thought about trying a simple brake bleed at all 4 corners to start, along with the procedure to properly bleed the ABS portion using Techstream?

 

[ramangain]

Just providing the gentle nudge, that is all

 

[AlpineAccess]

Just providing the gentle nudge, that is all

 

[KillerBox]

Every time that I read a brake failure post, I always wonder if they have ever changed out the brake fluid?

On my 2001 LX that had 107,000 miles in 2017, the brake fluid was very dark. This LX had been mostly dealership worked on & one owner.

Soon after I bought it, one of the rear calipers were sticky. I replaced both rear calipers, brake pads on all 4 corners & flushed out the old fluid. Since then the brake fluid has been in great shape but, I changed out 1/2 of it again this year just to check to make sure.

 

[JunkCrzr89]

The pump motor or accumulator failing don't always cause the alarm + lights.

 

[flintknapper]

The pump motor or accumulator failing don't always cause the alarm + lights.

^^^^^

Correct and the issue is apparently 'intermittent' in this case...(making it hard to reproduce and diagnose).

When checking my pump motor (on vehicle) it would run (smoothly) several times, then not at all unless I tapped on it, then eventually quit altogether.

Not saying this is the OP's issue....but worth looking at. Not worth taking any chances with braking.

 

[AlpineAccess]

Sounds like a big part of the failures can also be traced to people not filling the brake reservoir using the FSM and it ends up overfilled. It then dribbles excess fluid on the electrical contacts and corrodes them. That creates resistance, motor is worked too hard, etc.

 

[flintknapper]

Sounds like a big part of the failures can also be traced to people not filling the brake reservoir using the FSM and it ends up overfilled. It then dribbles excess fluid on the electrical contacts and corrodes them. That creates resistance, motor is worked too hard, etc.

I don't think leaking brake fluid is necessarily the cause. You'd have to grossly overfill the reservoir for that to happen and/or be in a really off-camber or steep incline/decent to have that happen. Even then.... the boot makes a pretty darn good seal (if mine was any example). My guess....is that its simply condensation and the boot seal contributes to holding in the moisture. I could see no evidence that mine had been subjected to brake fluid.

IMO the issue is the material the screws and nuts are made. No excuse for them to become corroded to that degree. Either use stainless or brass. The 'bean counters' were probably responsible for that choice.

 

[thebeedeegee]

I'm still amazed there was never a recall on this. Is the same system still in use on the 200?

 

[427060]

Just some musings from an 80 owner curious about this system: It seems like there's an electric vacuum pump, a vacuum accumulator, and then that drives the brake master cylinder like a typical brake booster.

If your brakes are intermittently 'wooden', then you do not have an appropriate difference in pressure across the booster to drive the master cylinder. Logically, that could be loss of accumulator vacuum, or a rear air inlet valve issue. Accumulator pump still works intermittently, so it's less likely that it's the pump circuit and not the sensing/logic circuit.

When it comes to intermittent failures, I think an electrical failure on the sensing side is more likely than a rear inlet valve failure. So, unless someone close to you is into electronics, I'd replace entirely and practice electronics diagnosis on the radio!

 

[JunkCrzr89]

So, unless someone close to you is into electronics, I'd replace entirely and practice electronics diagnosis on the radio!

Do you have $2,500 to give each of us so we can buy said entirely new unit? There’s a reason why we try to diagnose the electronics on these booster assemblies...hell, some people bought their 100s for less than a new booster assembly costs!

 

[JunkCrzr89]

I'm still amazed there was never a recall on this. Is the same system still in use on the 200?

Why would there be a recall? Traditional vacuum boosters and master cylinders fail, too, and most of these electronic booster assemblies are lasting 200k miles or more before failing. Yes, the 200 uses a similar system...so do most other Toyota/Lexus 4x4s produced after 2000.

 

[Skidoo]

Just some musings from an 80 owner curious about this system: It seems like there's an electric vacuum pump, a vacuum accumulator, and then that drives the brake master cylinder like a typical brake booster.

If your brakes are intermittently 'wooden', then you do not have an appropriate difference in pressure across the booster to drive the master cylinder. Logically, that could be loss of accumulator vacuum, or a rear air inlet valve issue. Accumulator pump still works intermittently, so it's less likely that it's the pump circuit and not the sensing/logic circuit.

When it comes to intermittent failures, I think an electrical failure on the sensing side is more likely than a rear inlet valve failure. So, unless someone close to you is into electronics, I'd replace entirely and practice electronics diagnosis on the radio!

Incorrect.
The electric pump pressurizes brake fluid, the accumulator is for high pressure brake fluid.

 

[Skidoo]

I would check the wires to the booster pump on both ends of the wires, these are prone to corrosion and could cause an intermittent failure.
Also take a look at the pedal linkage under the dash to see if anything is loose or something is jammed in there.

 

[thebeedeegee]

Why would there be a recall? Traditional vacuum boosters and master cylinders fail, too, and most of these electronic booster assemblies are lasting 200k miles or more before failing. Yes, the 200 uses a similar system...so do most other Toyota/Lexus 4x4s produced after 2000.

Maybe you're right, but I had never heard about brakes failing like this on a car until I started kicking around here. Maybe they do, but I personally had never heard of it before.

 

[flintknapper]

I would check the wires to the booster pump on both ends of the wires, these are prone to corrosion and could cause an intermittent failure.
Also take a look at the pedal linkage under the dash to see if anything is loose or something is jammed in there.

^^^^^

Exactly right. This is where to 'start'.

 

[AlpineAccess]

Why would there be a recall? Traditional vacuum boosters and master cylinders fail, too, and most of these electronic booster assemblies are lasting 200k miles or more before failing. Yes, the 200 uses a similar system...so do most other Toyota/Lexus 4x4s produced after 2000.

Toyota replaced a Tacoma frame for a buddy at 230k when it had rusted through. I don't see how an unnanounced failure of a braking system would be less dangerous than a perforated frame.

They recalled hundreds of thousands of Takata airbags for failures as well.

Most likely, this hasn't been addressed because folks have fixed it without reporting it, and/or Toyota made few enough 100s that they see it as a reasonable risk.

 

[flintknapper]

Just some musings from an 80 owner curious about this system: It seems like there's an electric vacuum pump, a vacuum accumulator, and then that drives the brake master cylinder like a typical brake booster.

Nope.