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Have you called the dealership requesting and insisting an answer?
I personally will not drive the car until Lexus IS willing
to release all liabilities for the safety of your car..
lexus owes you an answer . I mean it could have been
very serious for you...
When I was driving today I was paying attention to how far my foot pressed the brake pedal during a “normal” stop. I would estimate I was moving the pedal about one inch.
If MJN331 was moving the pedal to the floor, I still stand by my assessment that he has a failure of the master cylinder piston seals.
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. 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.
To clarify, when this event happened, did the pedal travel completely to the floor? Or was it just rock hard at the beginning/middle of the pedal travel?
If you did have a failure if the vacuum assistance - whether from a malfunction/failure of a component, or the engine shutting off - pumping would be the exact opposite of what you want to do. Once the engine is off or there is no more vacuum being provided from the engine for other reasons, you have roughly 3-5 full pumps of the pedal until your vacuum reserve as all used up. So for future reference (which I hope you'll never need), if your engine turns off while driving, do not pump the pedal. Every depression of the pedal is going to use some of that reserve until it's all gone. You can see this for yourself just like BGW said - pump the pedal when the engine is turned off and notice how the pedal gets harder and harder with each application until it's gone completely and you're left with a rock hard pedal. (Yes I understand that the engine turning off is not strictly what happened in your situation; this is more of an aside)
Pumping the brakes is for when you're lacking pressure in the hydraulic side of the brake system, which results in a 'mushy' brake pedal, or a pedal that easily goes all the way to floor or ends up sinking to the floor as you're pressing it. If you had a failing master or slave cylinder causing pressure to leak past the piston or otherwise escape that specific part of the system, or any other pressure leaks elsewhere in the system causing pressure to leak out. Pumping the brake continuously adds more and more pressure, in the hopes that you can pump the pressure into the system faster than it's escaping.
Originally Posted by MJN331
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 thevehicle over.
Yes and no. This goes for all cars/SUVs/pickups with a traditional foot/floor or hand/console mounted emergency brake (not a button activated emergency brake like many new cars have today) - the foremost danger of a full application of the parking brake is locking the rear wheels while the car is in motion, especially at higher speeds 30-40mph and faster. The ability to lock the wheels depends on the adjustment and the design/components of your emergency brake. Out of the 10s of dozens of vehicles I've driven, some were completely unable to fully lock the tires while in motion (even with properly adjusted brakes), meaning they just didn't have the "clamping power" to overcome the tires' traction. If your rear tires lock while in motion, the vehicle will have propensity to slide sideways, where the rear of the vehicle is trying to trade places with the front of the vehicle. This is obviously very, very dangerous, and the risk of turning the vehicle over comes from one of two situations: in a tall/top heavy SUV or truck, just rolling over as it slides sideways due to the high center of gravity, or in any vehicle - even those with a low center of gravity - sliding sideways into a curb/pothole/other fixed object or the wheels and tires digging into dirt/sand while sliding sideways, which results in the same 'foot hole' effect as as hitting a curb/pothole, sending you on a not-so-fun ride.
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.
Huh? Are you saying the SC is unlike just about every car on the road with hydraulic brakes, and that the "assist" part of the SC's power assisted brakes rely on electrical power instead of vacuum created by the engine's operation?
Huh? Are you saying the SC is unlike just about every car on the road with hydraulic brakes, and that the "assist" part of the SC's power assisted brakes rely on electrical power instead of vacuum created by the engine's operation?
yes, goldwinger is correct. Vacuum is not used in this system and is that way on several Lexus models. It uses a pump and the energy is stored in a high pressure accumulator.
I used the GS430 in my search because it looks the same and operates the same as the SC430. Not sure about interchangeability.
yes, goldwinger is correct. Vacuum is not used in this system and is that way on several Lexus models. It uses a pump and the energy is stored in a high pressure accumulator.
I used the GS430 in my search because it looks the same and operates the same as the SC430. Not sure about interchangeability.
Nice write up. I would have answered sooner but still have my " Leaners" permit on the site so I like to take it easy.
If I'm recalling correctly, you can pump the brakes rapidly maybe a dozen times or so you can make the brake pedal sink. Then the brake light will come on. You can use that pressure of the pump faster than it can work. By no means am I saying this is what happened to the op! I'm saying that the loss of pressure from the pump in this car can feel the same as loss of brake fluid.
might be a dumb question but for
most everyday driver.. if you suddenly
lose “ Brake control with sudden failure”
regardless how the system mechanically function
I think most drivers will not know what to do but
react instinctively which is to immediately step
on the brakes a few times.
outside of downshifting , not on a busy highway or
going down hill at 30 mphs an hour in stop and go traffic
my feeling is a serious crash is still Iminiminent..
Not sure if the exact science of what the system should do
or not do will stop the serious accident.
Do I make sense? Not trying to be negative or
pesstimistic but this is what I think will still happen
might be a dumb question but for
most everyday driver.. if you suddenly
lose “ Brake control with sudden failure”
regardless how the system mechanically function
I think most drivers will not know what to do but
react instinctively which is to immediately step
on the brakes a few times.
outside of downshifting , not on a busy highway or
going down hill at 30 mphs an hour in stop and go traffic
my feeling is a serious crash is still Iminiminent..
Not sure if the exact science of what the system should do
or not do will stop the serious accident.
Do I make sense? Not trying to be negative or
pesstimistic but this is what I think will still happen
Actually, I think my first reaction would be to stomp on the brakes as hard as I can, After all the years of driving, it is just a reaction and my muscle memory is to apply more pressure if I need to stop quicker.
Does this mean we don't have to buy a new unit for $2500? If mine starts acting up, I was going to buy a used one from a salvage yard, but you never know if it as worn as yours (since it is the same age and all)
Being able to take the kit to a rebuilder would be a game changer
Does this mean we don't have to buy a new unit for $2500? If mine starts acting up, I was going to buy a used one from a salvage yard, but you never know if it as worn as yours (since it is the same age and all)
Being able to take the kit to a rebuilder would be a game changer
Since there is more to our MC, this kit does not address the booster pump or accumulator. It also does not address the ABS.
it provides a piston with seals, so yes, I guess you could take it to a shop or just do it yourself.
When my MC was leaking on my 2002, I think it was leaking from the ABS area.
Everything functioned normally but every morning I had to add brake fluid and wipe the garage floor. When I turned the key on, the boost pump ran for a long time.
i believe the boost pump and accumulator support both the power brake assist and the ABS.
Actually, I think my first reaction would be to stomp on the brakes as hard as I can, After all the years of driving, it is just a reaction and my muscle memory is to apply more pressure if I need to stop quicker.
If the Instinct is for anyone to just step on the brakes,
my original point then is an accident” not could happen
but will “happen. Outside of everyone just hoping
this sudden breakdown does not happen, Lexus need to
Adddress this issue. I have no problem replacing my
MC before if ever goes out but Lexus should offer
goodwill assistance or determine the probability of failure
and address accordingly.
If the Instinct is for anyone to just step on the brakes,
my original point then is an accident” not could happen
but will “happen. Outside of everyone just hoping
this sudden breakdown does not happen, Lexus need to
Adddress this issue. I have no problem replacing my
MC before if ever goes out but Lexus should offer
goodwill assistance or determine the probability of failure
and address accordingly.
I guess it comes down to whether he lost his brakes completely, in which case you would be correct that my solution would be a bad choice.
BUT if he just lost the Power Brake feature and still had a direct mechanical linkage to his brakes then my my solution would work.
07-11-18, 04:25 PM
