question about brake master cylinder and brake fluid change or flush (1 Viewer)

zhloea

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Hi, I read a lot of posts talking about master cylinder replacement I have some questions below, thanks for any suggestion.

1. Currently I have no issue with the brake, but I know the master cylinder in lc100 could be a common issue finally. So, what will happen when we get this issue? will we lose brake immediately (on the highway :eek: )? or it will give us some time to tell there is a problem?
2. will suck out most of the brake fluid from the reservoir and top off with new fluid regularly (every 5000 miles) help to prevent this issue?
3. I saw many o people did brake flush, I am not so confident to do this, so will replace the fluid in the reservoir like 4 times in a month have the equal effect as flush?
 
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That will only replace a small amount of the fluid. Need to replace fluid by bleeding system.
If you are not up for it, have a dealer or good shop do it, brake system will last longer, cheaper in long run.
 
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What happens if/when the master cylinder fails depends on why it failed. You may experience a gradual loss of braking power, or it may fail all at once, leaving you dependent on the transmission and handbrake to slow and stop you.

Replacing the fluid is a good idea because the hydraulic fluid reacts with the metal in the braking system and becomes saturated with copper, which lessens its ability to resist compression. There are cars and trucks on the road which still have the factory fluid in them and the brakes work. They just don't work as new.

Replacing the fluid will likely not save a failing master cylinder. The seals are, IME, usually the failure mode and they fail due to age, not contaminated fluid.

HTH
 

zhloea

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That will only replace a small amount of the fluid. Need to replace fluid by bleeding system.
If you are not up for it, have a dealer or good shop do it, brake system will last longer, cheaper in long run.
thanks, how much will the dealer normally charge for this?

Nevermind, I figured the dealer will charge almost 600 to do this ....
 
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Don't confuse master cylinder failure with ABS motor/accumulator failure (which is attached to the master cylinder, and often replaced together). When the ABS motor fails, you should get a loud beeping and ABS/brake lights on dash, at which point you should have some braking still, but need to pull over and stop immediately. If you ignore the beeping, you'll probably lose almost all braking power. When you slam your foot through the floor, you'll get just a tiny bit of braking, but it won't do much.
 

zhloea

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I think based on all of this suggestion, I should replace a new set of hand emergency brake firstly:bang::bang:

My lc has 170k now, so it will happen soon?
 

87warrior

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I think based on all of this suggestion, I should replace a new set of hand emergency brake firstly:bang::bang:

My lc has 170k now, so it will happen soon?
My booster failed at 320k miles. I started the vehicle with my foot on the brake, foot went to the floor and the dash warning sounded/illuminated. Turned it off, then back on and drove 20 miles home (slowly) with full brake functionality.
 

zhloea

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My booster failed at 320k miles. I started the vehicle with my foot on the brake, foot went to the floor and the dash warning sounded/illuminated. Turned it off, then back on and drove 20 miles home (slowly) with full brake functionality.
I would save money from now for that 3000 dollar repair, I will replace that whole thing when my lc pass 200k even though it still work...
 

JunkCrzr89

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Don't confuse master cylinder failure with ABS motor/accumulator failure (which is attached to the master cylinder, and often replaced together). When the ABS motor fails, you should get a loud beeping and ABS/brake lights on dash, at which point you should have some braking still, but need to pull over and stop immediately. If you ignore the beeping, you'll probably lose almost all braking power. When you slam your foot through the floor, you'll get just a tiny bit of braking, but it won't do much.
x2 - the master cylinder is typically not problematic, and if it is, it’s remedied by a simple $55 rebuild kit from Toyota. In contrast, The hydraulic booster assembly, including the pump motor and accumulator, are typically the failure points.
 

zhloea

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x2 - the master cylinder is typically not problematic, and if it is, it’s remedied by a simple $55 rebuild kit from Toyota. In contrast, The hydraulic booster assembly, including the pump motor and accumulator, are typically the failure points.

could we replace the hydraulic booster assembly, including the pump motor and accumulator separately? And what is the symptom of those parts falling?
 
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likely in the salvage yard
could we replace the hydraulic booster assembly, including the pump motor and accumulator separately? And what is the symptom of those parts falling?
The symptoms are when they fail you lose braking power and get the lights on the dash. Not many symptoms to warn impending failure it happens quickly. Save some money and buy the pump and accumulator for when the time comes to replace them. GENUINE Toyota LEXUS BRAKE BOOSTER W/ACCUMULATOR PUMP 47070-60010 OEM | eBay - https://www.ebay.com/itm/352587611156
 

zhloea

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Yea i think preventative it's not necessary unless you are traveling in a remote desert soon and want to rule out it failing soon. I plan to have one on hand for when mine fails. If for some reason i decide to sell my truck before that i can sell the pump and accumulator to the new owner or someone here.
 

JunkCrzr89

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could we replace the hydraulic booster assembly, including the pump motor and accumulator separately? And what is the symptom of those parts falling?
Yes, you can replace the pump motor and accumulator separately. Pump motor will most often scream at you when it starts failing.
2B485A57-5C52-4ECF-9C79-2858CDF14240.jpeg
 

zhloea

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Yea i think preventative it's not necessary unless you are traveling in a remote desert soon and want to rule out it failing soon. I plan to have one on hand for when mine fails. If for some reason i decide to sell my truck before that i can sell the pump and accumulator to the new owner or someone here.
I don't really go anywhere off-road, I just a guy driving locally and high way and enjoy other people assuming I am a off-road guy~୧( "̮ )୨✧ᐦ̤
 

zhloea

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I just bought an electric brake fluid tester and a pack of brake fluid testing strips yesterday. The electric tester show I have less than 1% moist in the fluid and strips shows everything normal. So I probably don't need a brake flush. I plan to just change the brake fluid in the reservoir this weekend. Thanks, guys!
 
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What happens if/when the master cylinder fails depends on why it failed. You may experience a gradual loss of braking power, or it may fail all at once, leaving you dependent on the transmission and handbrake to slow and stop you.

Replacing the fluid is a good idea because the hydraulic fluid reacts with the metal in the braking system and becomes saturated with copper, which lessens its ability to resist compression. There are cars and trucks on the road which still have the factory fluid in them and the brakes work. They just don't work as new.

Replacing the fluid will likely not save a failing master cylinder. The seals are, IME, usually the failure mode and they fail due to age, not contaminated fluid.

HTH
My master brake cylinder failed coasting to a flat intersection in a very hilly area. Someone was watching over me.
 
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Don't confuse master cylinder failure with ABS motor/accumulator failure (which is attached to the master cylinder, and often replaced together). When the ABS motor fails, you should get a loud beeping and ABS/brake lights on dash, at which point you should have some braking still, but need to pull over and stop immediately. If you ignore the beeping, you'll probably lose almost all braking power. When you slam your foot through the floor, you'll get just a tiny bit of braking, but it won't do much.
Wow that sounds like a design defect and a huge lawsuit against the manufacturer should that caused the major accident.
 

flintknapper

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Wow that sounds like a design defect and a huge lawsuit against the manufacturer should that caused the major accident.

It's not really unlike any other braking system that is 'boosted' (Whether Vacuum or Hydraulic). When you lose 'boost/assist' your braking ability is compromised.

With our system (Toyota) when/if you have booster pump or accumulator failure....you still have some residual pressure to work with. BUT.....it requires the driver to pull over right away.

When boost/assist is lost...it happens quickly, meaning you don't gradually lose brake pedal pressure which would be a more tactile way of knowing something was wrong.

Instead....when the pressure is gone, its gone! The pedal will drop dramatically toward the floor. It is this action that prompts folks to describe it as 'losing all brakes' which is not technically true.

**Provided your master cylinder is not leaking**.


IF your master cylinder is leaking AND you lose boost....you are definitely in a bad situation.

Losing boost alone is not a great thing to happen either since any braking you have will be purely manual and at that point the vehicle has the mechanical advantage.

You have to really stand on the brake pedal to get any results and frankly....for some folks it just wouldn't be possible to bring the vehicle to a quick stop (if that were needed).

Bottom line here is: DO NOT ignore any warning lights/tones associated with the brake system.
 

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