First and foremost: Brakes should only be worked by those, with high level of mechanical abilities and experienced with brake systems.
With the age of all 100 series today, in our aging fleet. Any issue, with brake master assembly. IMHO, best and safest course of action. Have the whole brake master assembly, replaced with new. If you have to ask question, on "how to", your not qualified to work on the master.
My hope is below link will give better understanding as to what we can do to reduce brake failure and what to watch for. The info is from my experiences and my thinking, as to what and why brakes fail on 100 and 200 series. As such, is subject to change, as I learn and others contribute!
IMHO most brake failures give us clues, and are preventable.
How many miles before failure, in a perfectly health brake system? Very hard to say, but likely around 500K miles, combined city & HWY. Some are constantly on brake pedal ever few feet (stop and go traffic). Whereas others may go ~200 or more miles without touching pedal on regular basis (HWY vehicle). The 1 million mile Toyota had no brake issues reported IIRC. So miles aren't the best indicator.
It is the sudden, zero pressure of brake fluid in brake master, that yields pedal to the floor. Which results in relatively no usable brakes. This happens from lose of fluid or brake booster pump motor failure.
Inspecting brake flexible and hard lines.
Just as it says, inspect them. Rusty rigs will eventually get holes metal lines. Kept clean and inspecting, is best PM. Flexible lines, which 98-99 have five of and 00-up have six. May show a bubble or swell, indicating failure. Typically if a front line leaks or burst, it's a slow leak. Leaking more each press of the pedal, holding pedal down it's not a continuous flow to front lines. Where as rears leak faster, anytime brake pedal held down, it is a continuous flow. We'll likely see dash brake lights and hear alarm, as level drops and system has difficult reaching pressure in allotted time. Pump may run excessively long. So watch for signs.
Caliper piston seal can leak, although rare and usually very minor weep. But do inspect for leaks at each of the four wheels. Some holes ture of bleeder and banjo fitting (where brake flexible line attaches to caliper)
Test your brake alarms, dash light & audible. Simply press brake pedal rapidly on continuously, with IG key on. May take 5 or 10 pumps. Then you see and hear alarms or should.
Eventually all brake booster motor will fail in all motorized brake systems. It's the motor failing to start/run that yields zero pedal more than anything else I've seen. As the motor turns the pump, pressurizing the accumulator.
A few tips:
First:
Never ignore brake warning lights or alarms.
Second:
Listen for brake booster motor, when you first key on, before starting.
After vehicle has sat with IG key off, for a few hours. The pressure in brake system bleeds down. The older the system the faster it bleeds down, primarily do to aging of a rubber seal or seals and depletion of nitrogen gas from accumulator. By turning the IG key to ON, the booster motor will activate once pressure sensors senses pressure below a preset level.
By listening before starting engine, brake booster motor can be heard running. Motor not running or run for more than 40 seconds is a warning. If not motor heard running. Press brake pedal a few times, it should than be heard. Since pressing brake pedal depletes stored pressure from accumulator. It then gets sensor input of low pressure, and turns on booster motor. If motor runs for longer than 40 second, before stopping. That should be investigated too. It indicates; 1) weak battery voltage. 2) Weak or slow booster motor. 3) Pressure loss. 4) Weak accumulator.
Third:
Periodically test booster motor run time. Do this by pumping brake pedal 40 times with IG key off or key out of IG. Than check level in brake master fluid reservoir. Which should be at or near max line but not over. Than turn IG key to ON, and time booster motor run time. 40 seconds is max. 28 second is a very health system (new or newer). 40 seconds is limit, but may indicate some weakness. i.e: low voltage/amp from battery, it likes about 12.5Volts, weak seals, bad fluid, air in fluid, etc. Over 40 second, service is necessary.
Prevent measures.
Brake failure:
Brake booster motor failure, is number one reason for no brakes!
I'll start with this, most common cause of brake failure. Which is loss of brake system booster pressure.
Other than no brake fluid in system, which one can easily see. Brake booster motor failure, is number one reason for no brakes.
These are my opinions, I drew from working on 100 series brake systems. Many, muds members help me gain understanding on the subject. Some with their posting in mud, others by sending their failed master to dissect. Thanks all of you
Overfilling brake fluid reservoir, "may" cause loss of brakes:
IMHO this is number one reason for sudden brake failure.
Over filling; Seems such a small thing. That most Toyota Master ASE certified mechanics, will say makes no difference. Most are not even aware; Toyota embossed instruction on topping procedure on the brake reservoir. Which if overfilled, fluid may come out the reservoir. Even spillage on reservoir can have same effect.
Why is fluid on out side of reservoir an issue. If brake fluid aloud to run down side of reservoir. Fluid may get on the wires and/or into its sheathing. Fluid may then travels along the wire(s) into the boots.
Brake fluid is hygroscopic (pulls moisture from the air). If brake fluid gets in the boots of the brake control wires, which are resistance wires. The wire terminals, nuts & screws will corrode from the moisture. This corrosion will increase resistance of wires, causing the commutator to prematurely wear out. IMHO: This is leading cause of motor failure. If bushes, fail to pass current to commutator/armature, motor fails to run. No brakes!
forum.ih8mud.com
Overfilled brake reservoir or fluid spillage, effect on wires, seen below.
A second cause for brake booster motor failure. Is excessive long run times:
Motor running excessively long, each time it is called (pressure in system low) on to run. This happens most often due to a leak or air in system. Leak is not always external (internal pressure leak). Internal pressure leak, will not cause fluid level to drop. Note: level drops naturally with pad wear. I'll touch on this subject later. But if we hear the screeching sound when motors is running and see bubbles (wake in fluid seen) come up front of reservoir. This is internal pressure loss. The master will need replacing, or pump will run excessively long. Pump is designed for short run time. Running to long each cycle, can overheat the motor. This heat too, cause premature wear of motors commutator and brushes.
A third cause for motor failure.
Brake fluid, gets in the motor from passive seal in the pump, which is not a pressure seal. This seal is seen, when motor pulled off the pump.
What happens is the motor air vent become clogged. The pump has weep drain canal on face of pump, where motor mounts to it. The pump also has a air vent with boot cover next to the drain canal. This air vent is designed to reduce the vacuum (negative air pressure), built up inside motor, as it spins at high RPM. If the air vent gets clogged, brake fluid is then sucked from passive seal weep area of pump, into motor. The brake fluid then soaks/damages the rubber insulation in the motor. This brake fluid can also damage motor bearings. It "may" also affect resistance within motor, by affecting contact between brushed and commutator and windings.
Pump and motor with clogged vent pictures:
Pump (side motor attaches to)
Motor
Motor & Pump
With the age of all 100 series today, in our aging fleet. Any issue, with brake master assembly. IMHO, best and safest course of action. Have the whole brake master assembly, replaced with new. If you have to ask question, on "how to", your not qualified to work on the master.
My hope is below link will give better understanding as to what we can do to reduce brake failure and what to watch for. The info is from my experiences and my thinking, as to what and why brakes fail on 100 and 200 series. As such, is subject to change, as I learn and others contribute!
IMHO most brake failures give us clues, and are preventable.
How many miles before failure, in a perfectly health brake system? Very hard to say, but likely around 500K miles, combined city & HWY. Some are constantly on brake pedal ever few feet (stop and go traffic). Whereas others may go ~200 or more miles without touching pedal on regular basis (HWY vehicle). The 1 million mile Toyota had no brake issues reported IIRC. So miles aren't the best indicator.
It is the sudden, zero pressure of brake fluid in brake master, that yields pedal to the floor. Which results in relatively no usable brakes. This happens from lose of fluid or brake booster pump motor failure.
Inspecting brake flexible and hard lines.
Just as it says, inspect them. Rusty rigs will eventually get holes metal lines. Kept clean and inspecting, is best PM. Flexible lines, which 98-99 have five of and 00-up have six. May show a bubble or swell, indicating failure. Typically if a front line leaks or burst, it's a slow leak. Leaking more each press of the pedal, holding pedal down it's not a continuous flow to front lines. Where as rears leak faster, anytime brake pedal held down, it is a continuous flow. We'll likely see dash brake lights and hear alarm, as level drops and system has difficult reaching pressure in allotted time. Pump may run excessively long. So watch for signs.
Caliper piston seal can leak, although rare and usually very minor weep. But do inspect for leaks at each of the four wheels. Some holes ture of bleeder and banjo fitting (where brake flexible line attaches to caliper)
Test your brake alarms, dash light & audible. Simply press brake pedal rapidly on continuously, with IG key on. May take 5 or 10 pumps. Then you see and hear alarms or should.
Eventually all brake booster motor will fail in all motorized brake systems. It's the motor failing to start/run that yields zero pedal more than anything else I've seen. As the motor turns the pump, pressurizing the accumulator.
A few tips:
First:
Never ignore brake warning lights or alarms.
Second:
Listen for brake booster motor, when you first key on, before starting.
After vehicle has sat with IG key off, for a few hours. The pressure in brake system bleeds down. The older the system the faster it bleeds down, primarily do to aging of a rubber seal or seals and depletion of nitrogen gas from accumulator. By turning the IG key to ON, the booster motor will activate once pressure sensors senses pressure below a preset level.
By listening before starting engine, brake booster motor can be heard running. Motor not running or run for more than 40 seconds is a warning. If not motor heard running. Press brake pedal a few times, it should than be heard. Since pressing brake pedal depletes stored pressure from accumulator. It then gets sensor input of low pressure, and turns on booster motor. If motor runs for longer than 40 second, before stopping. That should be investigated too. It indicates; 1) weak battery voltage. 2) Weak or slow booster motor. 3) Pressure loss. 4) Weak accumulator.
Third:
Periodically test booster motor run time. Do this by pumping brake pedal 40 times with IG key off or key out of IG. Than check level in brake master fluid reservoir. Which should be at or near max line but not over. Than turn IG key to ON, and time booster motor run time. 40 seconds is max. 28 second is a very health system (new or newer). 40 seconds is limit, but may indicate some weakness. i.e: low voltage/amp from battery, it likes about 12.5Volts, weak seals, bad fluid, air in fluid, etc. Over 40 second, service is necessary.
Prevent measures.
- Flush brake fluid often. No longer time period between flushes than 3 years, after first factory fluid flushed out.
- I've gone back to using only Toyota brake fluid. It's pricey and may not make any difference. But the extra cost worth it for piece of mind and many add years to life on master. Toyota states on the bottle "engineered to Toyota spec". Condition of seal is very important to heath of master. Bad seals can weep or even squeal under high pressure. Booster motor will then run excessively, as pressure keeps dropping. Use of non Toyota brake fluid, may damages seals.
- Inspect motor run time and listen for excessive running of motor.
- Never overfill brake fluid reservoir. Fluid may escape from cap or grommets at bottom. If fluid get on booster motor brake control wires, it may enter boots protecting wires at connection points under boots. The ensuing corrosion from hygroscopic action, will increase resistance of brake control wires. This will hasten motors failure, very rapidly.
- Debris may clog booster motor breather. Brake fluid may get into breather port for motor. The fluid/oil may attract dust, an may clog breather. The motor, creates a vacuum (high RPM spin). It will suck fluid from pump into motor, due to breather clogged. Also deep water reaching the breather may clog it. Also lack of splash protection in fender well, may contribute to clogging of breather. So inspect breather at bottom of booster motor annually, is not a bad idea. Also after deep water crossings, driving in tall grasses, muck, very dusty condition. Especially if missing fender splash shield or inadequate splash protection or undercarriage shielding. Note: lifted increasing opening area in fender well to engine bay. May all add to debris entering engine compartment. Be on the watch and check breather more often under these or extreme driving condition.
- Keep battery, battery post clamps and cables properly serviced. Volt/Amp drop from battery, will be the same as increased resistance in wires. This will also effects RPM (slowing) booster motor.
- Keep grounds to frame, body and engine properly serviced.
Brake failure:
Brake booster motor failure, is number one reason for no brakes!
I'll start with this, most common cause of brake failure. Which is loss of brake system booster pressure.
Other than no brake fluid in system, which one can easily see. Brake booster motor failure, is number one reason for no brakes.
These are my opinions, I drew from working on 100 series brake systems. Many, muds members help me gain understanding on the subject. Some with their posting in mud, others by sending their failed master to dissect. Thanks all of you
Overfilling brake fluid reservoir, "may" cause loss of brakes:
IMHO this is number one reason for sudden brake failure.
Over filling; Seems such a small thing. That most Toyota Master ASE certified mechanics, will say makes no difference. Most are not even aware; Toyota embossed instruction on topping procedure on the brake reservoir. Which if overfilled, fluid may come out the reservoir. Even spillage on reservoir can have same effect.
Why is fluid on out side of reservoir an issue. If brake fluid aloud to run down side of reservoir. Fluid may get on the wires and/or into its sheathing. Fluid may then travels along the wire(s) into the boots.
Brake fluid is hygroscopic (pulls moisture from the air). If brake fluid gets in the boots of the brake control wires, which are resistance wires. The wire terminals, nuts & screws will corrode from the moisture. This corrosion will increase resistance of wires, causing the commutator to prematurely wear out. IMHO: This is leading cause of motor failure. If bushes, fail to pass current to commutator/armature, motor fails to run. No brakes!
“Total” brake failure yesterday... accumulator pump motor CONFIRMED
I experienced a “total” break failure in my ‘00 Cruiser yesterday. I’ve had the truck since January. During the first couple of weeks of ownership, I got the ABS/TRAC/Brake lights on the dash with the alarm... always on a cold morning first start. It would typically go away after 30 to 40...
forum.ih8mud.com
Overfilled brake reservoir or fluid spillage, effect on wires, seen below.
A second cause for brake booster motor failure. Is excessive long run times:
Motor running excessively long, each time it is called (pressure in system low) on to run. This happens most often due to a leak or air in system. Leak is not always external (internal pressure leak). Internal pressure leak, will not cause fluid level to drop. Note: level drops naturally with pad wear. I'll touch on this subject later. But if we hear the screeching sound when motors is running and see bubbles (wake in fluid seen) come up front of reservoir. This is internal pressure loss. The master will need replacing, or pump will run excessively long. Pump is designed for short run time. Running to long each cycle, can overheat the motor. This heat too, cause premature wear of motors commutator and brushes.
A third cause for motor failure.
Brake fluid, gets in the motor from passive seal in the pump, which is not a pressure seal. This seal is seen, when motor pulled off the pump.
What happens is the motor air vent become clogged. The pump has weep drain canal on face of pump, where motor mounts to it. The pump also has a air vent with boot cover next to the drain canal. This air vent is designed to reduce the vacuum (negative air pressure), built up inside motor, as it spins at high RPM. If the air vent gets clogged, brake fluid is then sucked from passive seal weep area of pump, into motor. The brake fluid then soaks/damages the rubber insulation in the motor. This brake fluid can also damage motor bearings. It "may" also affect resistance within motor, by affecting contact between brushed and commutator and windings.
Pump and motor with clogged vent pictures:
Pump (side motor attaches to)
Motor
Motor & Pump
Last edited:
