Important warning / notice: 100% brake system failure lexus sc430
07-07-18, 10:07 AM
#46
The question then is can one stop the car fully with both legs
with 90-95% loss of brake hydraulics?
Not to say anyone of us would want to ever had to test
this theory going downhill but I still think the likelihood of
A serious accident is imminent.
Most drivers will not know about this approach let along
be fast enough to even remember to downshift as your mind
is probably in a state of sudden shock to react fast enough
with 90-95% loss of brake hydraulics?
Not to say anyone of us would want to ever had to test
this theory going downhill but I still think the likelihood of
A serious accident is imminent.
Most drivers will not know about this approach let along
be fast enough to even remember to downshift as your mind
is probably in a state of sudden shock to react fast enough
07-07-18, 10:43 AM
#47
Instructor
Mbodall
The problem is how many typical everyday driver will
know about this approach when there is a sudden failure
of brake control?
For a few seconds, you might not be able to react fast enough.
I am glad to know about this method. Regardless,I still
believe a imminent serious accident is waiting to happen
if there is a sudden brake failure as the human mind
cannot react fast enough.
The problem is how many typical everyday driver will
know about this approach when there is a sudden failure
of brake control?
For a few seconds, you might not be able to react fast enough.
I am glad to know about this method. Regardless,I still
believe a imminent serious accident is waiting to happen
if there is a sudden brake failure as the human mind
cannot react fast enough.
07-07-18, 02:01 PM
#48
Mbodall
The problem is how many typical everyday driver will
know about this approach when there is a sudden failure
of brake control?
For a few seconds, you might not be able to react fast enough.
I am glad to know about this method. Regardless,I still
believe a imminent serious accident is waiting to happen
if there is a sudden brake failure as the human mind
cannot react fast enough.
The problem is how many typical everyday driver will
know about this approach when there is a sudden failure
of brake control?
For a few seconds, you might not be able to react fast enough.
I am glad to know about this method. Regardless,I still
believe a imminent serious accident is waiting to happen
if there is a sudden brake failure as the human mind
cannot react fast enough.
With that said, I do want to commend MJN on how they handled this situation. Many other driver's likely would have panicked and ended up getting into a serious accident. It's absolutely awesome that you kept a level head, analyzed the problem, thought about (and executed) an appropriate solution, and safely stopped the car without incident.
07-10-18, 02:36 PM
#49
Driver School Candidate
Thread Starter
MJN your car most definitely does have a brake booster, so your mechanic must know this part by another name... but having worked as a mechanic myself I can’t imagine what other name this would be.
Either way, as others have said, it’s either a failure of the master cylinder/booster/some other type of loss of power assist. As someone else stated above, all cars on the road have hydraulic brakes which are assisted by vacuum created by the engine. If you lose this power assist, it will feel like your brakes aren’t working. You say in your title “100% brake system failure” but then say that you still had about 3%-5% braking power. That means you didn’t quite have 100% brake failure. Yes, I understand having even 5% braking power is far too little braking power for just about every situation, but it isn’t 0% braking power/100% braking failure. This again reinforces the notion of loss of power assist. Pushing your brakes with what is normally ‘100%’ effort which would normally resulting 100% stopping power of vehicle, feels like basically 0% when you lose power assisted brakes. I’m having trouble putting into words what I’m trying to say.... let’s try it this way. When your brakes are working properly, let’s say you only need to apply 7lbs of pressure on the brake pedal for them to go to the floor and active ABS fully. Now, you’re used to that amount of pressure (7lbs) being needed for full stopping pressure and full stopping power. However, after losing power assisted brakes, you basically can’t apply the required amount of pressure to recieve the same full ABS stop - you’d have to apply 150-250lbs of pressure on the brake pedal to achieve the same full ABS stop. So, with that in mind, you’re hitting the brakes with the same amount of force that you’re used to (7lbs) and getting all of 3-5% stopping power from them. Meanwhile, had you pulled on the bottom of the steering wheel with both hands to brace yourself in place while standing with both feet on the brake pedal like you were trying to rip off the steering wheel, you would have likely seen 30-70% stopping power, depending on how strong your legs, arms, and back were.
So, it’s not that there was a 100% brake failure, more that you were unaware that a malfunctioning component required you to apply 20-30x more effort to the brake pedal to have the desired stopping power. Granted, this is obviously far from safe, but I wanted to clear up the thought that you experienced “100% brake system failure”.
To try this out yourself as I have done many times in the last 15+ years of driving, find a small hill in a large, empty parking lot. Turn the engine off (just to accessory) with the transmission in neutral, then turn the key back to “on” but don’t engage the starter. Make sure your emergency/parking brake is working and adjusted properly since this will be what ultimately stops you at the end of this test unless the hill you chose is very, very slight (otherwise you might end up pulling a muscle or two lol). Pump the brake pedal 4-6 times until the brake pedal gets rock hard... you’ll notice the car is starting to roll down the hill even with you pushing the brake pedal quite hard. Push harder and harder on the brake pedal using the steering wheel and seat back as bracing to give you more leverage to push on the brake pedal. You’ll notice the braking of the car does increase, but the amount of effort required on the pedal is substantially more than you would expect.
Either way, as others have said, it’s either a failure of the master cylinder/booster/some other type of loss of power assist. As someone else stated above, all cars on the road have hydraulic brakes which are assisted by vacuum created by the engine. If you lose this power assist, it will feel like your brakes aren’t working. You say in your title “100% brake system failure” but then say that you still had about 3%-5% braking power. That means you didn’t quite have 100% brake failure. Yes, I understand having even 5% braking power is far too little braking power for just about every situation, but it isn’t 0% braking power/100% braking failure. This again reinforces the notion of loss of power assist. Pushing your brakes with what is normally ‘100%’ effort which would normally resulting 100% stopping power of vehicle, feels like basically 0% when you lose power assisted brakes. I’m having trouble putting into words what I’m trying to say.... let’s try it this way. When your brakes are working properly, let’s say you only need to apply 7lbs of pressure on the brake pedal for them to go to the floor and active ABS fully. Now, you’re used to that amount of pressure (7lbs) being needed for full stopping pressure and full stopping power. However, after losing power assisted brakes, you basically can’t apply the required amount of pressure to recieve the same full ABS stop - you’d have to apply 150-250lbs of pressure on the brake pedal to achieve the same full ABS stop. So, with that in mind, you’re hitting the brakes with the same amount of force that you’re used to (7lbs) and getting all of 3-5% stopping power from them. Meanwhile, had you pulled on the bottom of the steering wheel with both hands to brace yourself in place while standing with both feet on the brake pedal like you were trying to rip off the steering wheel, you would have likely seen 30-70% stopping power, depending on how strong your legs, arms, and back were.
So, it’s not that there was a 100% brake failure, more that you were unaware that a malfunctioning component required you to apply 20-30x more effort to the brake pedal to have the desired stopping power. Granted, this is obviously far from safe, but I wanted to clear up the thought that you experienced “100% brake system failure”.
To try this out yourself as I have done many times in the last 15+ years of driving, find a small hill in a large, empty parking lot. Turn the engine off (just to accessory) with the transmission in neutral, then turn the key back to “on” but don’t engage the starter. Make sure your emergency/parking brake is working and adjusted properly since this will be what ultimately stops you at the end of this test unless the hill you chose is very, very slight (otherwise you might end up pulling a muscle or two lol). Pump the brake pedal 4-6 times until the brake pedal gets rock hard... you’ll notice the car is starting to roll down the hill even with you pushing the brake pedal quite hard. Push harder and harder on the brake pedal using the steering wheel and seat back as bracing to give you more leverage to push on the brake pedal. You’ll notice the braking of the car does increase, but the amount of effort required on the pedal is substantially more than you would expect.
07-10-18, 02:37 PM
#50
Driver School Candidate
Thread Starter
The question then is can one stop the car fully with both legs
with 90-95% loss of brake hydraulics?
Not to say anyone of us would want to ever had to test
this theory going downhill but I still think the likelihood of
A serious accident is imminent.
Most drivers will not know about this approach let along
be fast enough to even remember to downshift as your mind
is probably in a state of sudden shock to react fast enough
with 90-95% loss of brake hydraulics?
Not to say anyone of us would want to ever had to test
this theory going downhill but I still think the likelihood of
A serious accident is imminent.
Most drivers will not know about this approach let along
be fast enough to even remember to downshift as your mind
is probably in a state of sudden shock to react fast enough
07-10-18, 02:39 PM
#51
Driver School Candidate
Thread Starter
Oh I totally agree with you. I'm just clarifying that this sounds like it wasn't a "100% brake system failure" and instead was a total loss of power assisted brakes. I completely agree that I may be splitting hairs here when it comes to your average driver's reaction to this happening and the potential outcome of this, but that it is different than a complete loss of braking ability.
With that said, I do want to commend MJN on how they handled this situation. Many other driver's likely would have panicked and ended up getting into a serious accident. It's absolutely awesome that you kept a level head, analyzed the problem, thought about (and executed) an appropriate solution, and safely stopped the car without incident.
With that said, I do want to commend MJN on how they handled this situation. Many other driver's likely would have panicked and ended up getting into a serious accident. It's absolutely awesome that you kept a level head, analyzed the problem, thought about (and executed) an appropriate solution, and safely stopped the car without incident.
07-10-18, 02:40 PM
#52
Driver School Candidate
Thread Starter
Mbodall
The problem is how many typical everyday driver will
know about this approach when there is a sudden failure
of brake control?
For a few seconds, you might not be able to react fast enough.
I am glad to know about this method. Regardless,I still
believe a imminent serious accident is waiting to happen
if there is a sudden brake failure as the human mind
cannot react fast enough.
The problem is how many typical everyday driver will
know about this approach when there is a sudden failure
of brake control?
For a few seconds, you might not be able to react fast enough.
I am glad to know about this method. Regardless,I still
believe a imminent serious accident is waiting to happen
if there is a sudden brake failure as the human mind
cannot react fast enough.
07-10-18, 03:17 PM
#53
just to be clear on some of the early posts some of the system descriptions are not correct. The system does not use engine vacuum for a boost of the power brakes. Its an electrical system over a pressurized system. You can feel the booster engage when you turn the key on to start and have your foot on the pedal. When it drops down that is caused by the added pressure from the system applying the brakes harder ( more pressure)than you were. This happens before the car starts Before engine even has any vacuum.
It does need proper voltage, clean fluid and the correct signals to work. If your brake system set no diagnostic codes and all the data looks correct it could come down to an intermittent connection. A crack in a circuit board is very common for hard to find concerns.
Unless you have a hydraulic leak you will still have brakes. Just takes a lot of effort to stop.
Just my thoughts and opinion. I work on this stuff every day and like other to understand how things they are driving work.
It does need proper voltage, clean fluid and the correct signals to work. If your brake system set no diagnostic codes and all the data looks correct it could come down to an intermittent connection. A crack in a circuit board is very common for hard to find concerns.
Unless you have a hydraulic leak you will still have brakes. Just takes a lot of effort to stop.
Just my thoughts and opinion. I work on this stuff every day and like other to understand how things they are driving work.
07-10-18, 03:40 PM
#54
Lexus Test Driver
Thank you for taking the time to send this and I wanted to reply. Everything you say is helpful and all I know is there was no way my car was going to slow down (no matter how many times I pumped that brake to the floor) unless I started the downshifting/emergency brake functions. Today I'm really happy I remember you push down the emergency brake "gently" because if you slam down on it (for some cars) you can literally turn the vehicle over. And it wasn't like the more I pumped down on the pedal the more pressure or braking power I obtained. Didn't go down or feel that way at all.
If you are saying the pedal was going all the way to the floor then you had a hydraulic failure somewhere in the brake system.
i believe you said somewhere that the master cylinder was still full. If that is the case, then I would think the master cylinder is the problem.
Again, if the pedal was going to the floor, I would think the seals on the Brake piston failed, allowing fluid to bypass the piston.
what do you think Goldwinger?
when I bled the brakes on this car, it was different from other cars.
the front bleeding is the same as other cars, but the rear was different.
Front Brakes, two person method, Pump the pedal several times, while holding the pedal down, release the bleeder plug, tighten and repeat.
Rear Brakes, all you do is turn the key on, depress the pedal, then release the bleeder plug. The system will pump fluid to the rear brakes.
Last edited by Bgw70; 07-11-18 at 03:17 AM.
07-10-18, 05:32 PM
#55
[QUOTE=Bgw70;10247285]
I have been wondering about the travel of the pedal and I think you answered my question in your second sentence.
If you are saying the pedal was going all the way to the floor then you had a hydraulic failure somewhere in the brake system.
i believe you said somewhere that the master cylinder was still full. If that is the case, then I would think the master cylinder is the problem.
Again, if the pedal was going to the floor, I would think the seals on the Brake piston failed, allowing fluid to bypass the piston.
what do you think Goldwinger?
when I bled the brakes on this car, it was different from other cars. In this car you bleed the front brakes like other cars.
two person method, Pump the pedal several times, while holding the pedal down, release the bleeder plug, tighten and repeat.
on the rears, all you do is depress the pedal, then release the bleeder plug. The system will pump fluid to the rear brakes.
I would say you are correct. If the pedal goes all the way to the floor you have a hydraulic leak. Maybe not an external leak. The master cylinder can bypass meaning the seals let the fluid leak by. Its always hard to remember what happened after a scary panic stop. Could the car have stopped if your legs belonged to the Hulk? If so you did not have a leak.
I have been wondering about the travel of the pedal and I think you answered my question in your second sentence.
If you are saying the pedal was going all the way to the floor then you had a hydraulic failure somewhere in the brake system.
i believe you said somewhere that the master cylinder was still full. If that is the case, then I would think the master cylinder is the problem.
Again, if the pedal was going to the floor, I would think the seals on the Brake piston failed, allowing fluid to bypass the piston.
what do you think Goldwinger?
when I bled the brakes on this car, it was different from other cars. In this car you bleed the front brakes like other cars.
two person method, Pump the pedal several times, while holding the pedal down, release the bleeder plug, tighten and repeat.
on the rears, all you do is depress the pedal, then release the bleeder plug. The system will pump fluid to the rear brakes.
I would say you are correct. If the pedal goes all the way to the floor you have a hydraulic leak. Maybe not an external leak. The master cylinder can bypass meaning the seals let the fluid leak by. Its always hard to remember what happened after a scary panic stop. Could the car have stopped if your legs belonged to the Hulk? If so you did not have a leak.
07-10-18, 05:56 PM
#56
Lexus Test Driver
I would say you are correct. If the pedal goes all the way to the floor you have a hydraulic leak. Maybe not an external leak. The master cylinder can bypass meaning the seals let the fluid leak by. Its always hard to remember what happened after a scary panic stop. Could the car have stopped if your legs belonged to the Hulk? If so you did not have a leak.
This might be a good time to ask anyone reading this to do yourself a favor and make yourself familiar with the feeling of no power assist.
Before you turn the key in your SC430, press the brake five times. It will either be hard right away or it will get harder with each press. When it gets really hard, note the pressure you must apply.
Now turn the key on or start the engine and press the brake pedal again, note how easy and more importantly note how far you pressed the pedal to apply those brakes. If you ever loose the assist while driving, you will need to make the pedal move that far for the brakes to stop the car.
Okay, now we just need to hear back from MJN331
The following users liked this post:
Goldwinger (07-10-18)
07-10-18, 09:21 PM
#57
Instructor
At the end of the day, I think what it boils down to
is I hope knock on wood brake “ failure” never
happento one of our SC brothers but what this
Discussion tells me I at least know I have maybe
3-5 seconds to react to down shifting immediately
if loss of brake pressure in the SC.
Now would someone who does not know much about
the SC430 know what to do at a quick sudden brake
failure?? My bet is No . I don’t even know if anyone of us
other than MJN today could react within a split second
know you must immediately down shift..
I have owned 4 SC’s and I would say this is the first
Time I am concerned about the safety/reliability of the SC.
is I hope knock on wood brake “ failure” never
happento one of our SC brothers but what this
Discussion tells me I at least know I have maybe
3-5 seconds to react to down shifting immediately
if loss of brake pressure in the SC.
Now would someone who does not know much about
the SC430 know what to do at a quick sudden brake
failure?? My bet is No . I don’t even know if anyone of us
other than MJN today could react within a split second
know you must immediately down shift..
I have owned 4 SC’s and I would say this is the first
Time I am concerned about the safety/reliability of the SC.
07-11-18, 03:49 PM
#58
Driver School Candidate
Thread Starter
just to be clear on some of the early posts some of the system descriptions are not correct. The system does not use engine vacuum for a boost of the power brakes. Its an electrical system over a pressurized system. You can feel the booster engage when you turn the key on to start and have your foot on the pedal. When it drops down that is caused by the added pressure from the system applying the brakes harder ( more pressure)than you were. This happens before the car starts Before engine even has any vacuum.
It does need proper voltage, clean fluid and the correct signals to work. If your brake system set no diagnostic codes and all the data looks correct it could come down to an intermittent connection. A crack in a circuit board is very common for hard to find concerns.
Unless you have a hydraulic leak you will still have brakes. Just takes a lot of effort to stop.
Just my thoughts and opinion. I work on this stuff every day and like other to understand how things they are driving work.
It does need proper voltage, clean fluid and the correct signals to work. If your brake system set no diagnostic codes and all the data looks correct it could come down to an intermittent connection. A crack in a circuit board is very common for hard to find concerns.
Unless you have a hydraulic leak you will still have brakes. Just takes a lot of effort to stop.
Just my thoughts and opinion. I work on this stuff every day and like other to understand how things they are driving work.
07-11-18, 03:51 PM
#59
Driver School Candidate
Thread Starter
This might be a good time to ask anyone reading this to do yourself a favor and make yourself familiar with the feeling of no power assist.
Before you turn the key in your SC430, press the brake five times. It will either be hard right away or it will get harder with each press. When it gets really hard, note the pressure you must apply.
Now turn the key on or start the engine and press the brake pedal again, note how easy and more importantly note how far you pressed the pedal to apply those brakes. If you ever loose the assist while driving, you will need to make the pedal move that far for the brakes to stop the car.
Okay, now we just need to hear back from MJN331[/LEFT]
Before you turn the key in your SC430, press the brake five times. It will either be hard right away or it will get harder with each press. When it gets really hard, note the pressure you must apply.
Now turn the key on or start the engine and press the brake pedal again, note how easy and more importantly note how far you pressed the pedal to apply those brakes. If you ever loose the assist while driving, you will need to make the pedal move that far for the brakes to stop the car.
Okay, now we just need to hear back from MJN331[/LEFT]
07-11-18, 03:56 PM
#60
Driver School Candidate
Thread Starter
At the end of the day, I think what it boils down to
is I hope knock on wood brake “ failure” never
happento one of our SC brothers but what this
Discussion tells me I at least know I have maybe
3-5 seconds to react to down shifting immediately
if loss of brake pressure in the SC.
Now would someone who does not know much about
the SC430 know what to do at a quick sudden brake
failure?? My bet is No . I don’t even know if anyone of us
other than MJN today could react within a split second
know you must immediately down shift..
I have owned 4 SC’s and I would say this is the first
Time I am concerned about the safety/reliability of the SC.
is I hope knock on wood brake “ failure” never
happento one of our SC brothers but what this
Discussion tells me I at least know I have maybe
3-5 seconds to react to down shifting immediately
if loss of brake pressure in the SC.
Now would someone who does not know much about
the SC430 know what to do at a quick sudden brake
failure?? My bet is No . I don’t even know if anyone of us
other than MJN today could react within a split second
know you must immediately down shift..
I have owned 4 SC’s and I would say this is the first
Time I am concerned about the safety/reliability of the SC.