Poll on total brake failure in 100 series

[2001LC]

Brake fluid heats with active use. The older the fluid the more moisture in it, the low temp the fluid boils at. Fluid is good for 2 to 3 years, miles is secondary!

With age seals become worn and shrink. We've seals from end to end.

These may be your issue or part of.

 

[ShenValley100LC]

Brake fluid heats with active use. The older the fluid the more moisture in it, the low temp the fluid boils at. Fluid is good for 2 to 3 years, miles is secondary!

With age seals become worn and shrink. We've seals from end to end.

These may be your issue or part of.

Yeah, it seems like I'm not in imminent danger. So maybe I'll start off with another flush with Toyota brake fluid. Then maybe start replacing seals on the Brake Master Cylinder and Booster?

 

[abuck99]

At 505,000 miles- (impressive) the Master&Booster have exceeded their service life so anything you get from them at this point is a bonus.

Dont waste your $$ on Toyota fluid in a potentially failing system. Any good quality DOT 3 will do.

 

[D21FJ60]

The '99 truck I just picked up had the BMC done in 2006 at about 146k miles. If this helps at all. It is now at 295k.

 

[gil12]

Mileage on Car 504,XXX .....


Anyways, am I most likely a candidate for a MC/Booster rebuild? Or new unit (hope not)? Or might this simply be air in the lines and I need to bleed lines? Is this a ticking time bomb I should take action on?

In my opinion, if your 100 series reaches half a million miles, Toyota should give you a MC for free! I'm just saying. That kind of achievement sells some trucks just by word of mouth! Give it up Toyota!

 

[e9999]

^well, I'm thinking Toyota should give all of us a brake fix for free. That failure rate is unacceptable given the potential consequences, and especially so for the flagship vehicle in the lineup, IMO.

 

[gil12]

^well, I'm thinking Toyota should give all of us a brake fix for free. That failure rate is unacceptable given the potential consequences, and especially so for the flagship vehicle in the lineup, IMO.

I'd be good with that!

 

[nothappening]

The accumulator is bleed by depressing peddle 40 time key off. The FSM recommends pre -bleeding master when it's replaced or rebuilt. But not big deal. Just flushing the system bleeding all 4 generlly takes care of all that. Just keep fluid level above min as you work. brake peddle should feel firm and normal once you've air out. Remember, for first bleed of a front caliper, pump peddle 20 times, then about 5 pump thereafter. Front take about 7 to 10 bleeds each bleeder.

The booster may come on just from one push on peddle, 3 or 4 is fine. Most just never notice booster runs often.

I am almost hyper aware of the pump running because of the full failure potential. I have been wondering if mine has been running too often since it does run about every 4 pedal presses but if you say it's okay then I'll take your word for it.

 

[e9999]

you guys have better ears than I do, obviously, I don't hear that pump running, ever....

 

[nothappening]

you guys have better ears than I do, obviously, I don't hear that pump running, ever....

When I was reading through other replies, it seems that new vs. old brake components can make a difference in volume of the pump. I need to do a brake job, so I'll be interested to see if it makes a difference in the noise level.

 

[2001LC]

With ABS systems, we only depress and hold brakes on, we do not pump the peddle. That said:

I can say pump motor coming on every 1, 2, 3 or 4 times peddle depressed is normal. How long and hard peddle depressed makes a difference. Each time we use the brakes or just as time passes, pressure is lost. Sensors indicate pressure drop and at predetermined point, turns on power to the pump motor. Once pressure back to predetermined point, pump motor power is cut off (motor stops).

The older the system the fast the loss of pressure, due to aged seals and accumulator.

If pump runs longer than 40 sec., after pumping peddle 40 times to evacuate fluid form accumulator with IG key off. Than we've concern. If pump runs to long, 5 minutes IIRC. A DTC will come up and shut down ABS system. But brakes still work. Pumps motor running to long will prematurely wear out brushes and commutator of motor..

With brand new motors it is near impossible to hear it running, while in driver seat with window up and hood closed. The high mileage used/older motors, are easily heard form driver seat. Also, a new motor spins faster so it builds pressure faster and higher. Just replacing a bad brake control wire, we may see motor spin faster.

 

[nothappening]

I finally got around to testing my system. The pedal went soft at 29 depressions and the pump ran for 34 seconds after turning the key to "ON" position. The pump did cut out for a split second 3-4 times during the 34 seconds and did not run absolutely continuously. I assume that's normal.

I'm happy with the results. I saw earlier in the thread where you (2001LC) mentioned that you've experienced low mileage rigs only taking 22-28 depressions and weak systems taking closer to 40. I'm in an '06 so it's one of the youngest 100 series, but I'm over 190k miles at this point.

 

[100serieslover]

Welp, I've now replaced the master cylinder assembly, MINUS the accumulator and motor (the motor was replaced in April). I detailed my problem above (MC developed a leak).

I ordered the new MC from Toyotapartsdeal. It arrived damaged. The plastic surrounding the electrical connectors on the ABS computer (??) portion had taken a hit during shipping. The retailer refunded the majority of my money after they asked if I could use it still, and I determined that I could still use it with some ingenuity (welcome to ranch country, boys and girls!).

When I started swapping parts out between the old and the new assembly, I noticed that the wire connections on the bottom of the computer assembly were terribly corroded. This was something that I'd NOT noticed when I swapped out the accumulator motor last April. I still can't nail down the exact source of my brake fluid leak, but I now suspect a combination of the plastic tube on the MC, and the wiring on the computer portion of the MC based on where I saw brake fluid and the corrosion. I'm not about to spend $200 on a wiring pigtail, so I cut the connectors off that end, and peeled some insulation back to check the state of the wires. They weren't bad. I bought some new terminals, and put the wiring back together and reused it. Didn't fill it with dielectric grease, and I probably should have. Likely will do that soon (somehow, lol).

Got it all installed, brakes bled following this process: key off, RR, LR, key on, RF, LF, RR, LR. Drive it and get the ABS to kick in. Bleed it key on: RR, LR, RF, LF. Once I started the bleeding process, it took a while to get the pump to start pumping properly and the ABS warning lights to shut off. It was doing short spurts of running until I'd driven it a bit, and tried kicking in the ABS several times (by driving on gravel and slamming on the brakes). Once the pump started pumping for longer times, the alarms went off, I was able to get the ABS to kick on consistently a few times, and I did the final bleed. Pump was running for 30-35 seconds, and brake fluid was checked per procedure on the reservoir.

That was Sunday evening, and she still feels good! Need to adjust the pedal throw length, but other than that, seems that the MC was definitely the issue.

I PRAY that this is the LAST time I have to do this job. I'm so sick of this stupid master cylinder in these rigs.

 

[2001LC]

The brake control wire, is controversial. Toyota states non reusable, if just removed. It's believed to be a resistance wire. Meaning it has a specific resistance as current passes through. I've no doubt as resistance increase, commutator of booster motor wears excessively. Increased resistance of that wire, may also damage the electronics of the ABS unit (black box on master). Reduce resistance by replacing or shorting, may speed up motor. This increases brake pressure. Which some old master have trouble handling.

 

[100serieslover]

The brake control wire, is controversial. Toyota states non reusable, if just removed. It's believed to be a resistance wire. Meaning it has a specific resistance as current passes through. I've no doubt as resistance increase, commutator of booster motor wears excessively. Increased resistance of that wire, may also damage the electronics of the ABS unit (black box on master). Reduce resistance by replacing or shorting, may speed up motor. This increases brake pressure. Which some old master have trouble handling.

Interesting. I am somewhat concerned with the fact that the only terminals that I could find to replace the corroded ones were aluminum and not brass. It looks like aluminum has lower resistance than brass, and better conductivity. But I don't notice an increase in brake pressure at the pedal.

 

[2001LC]

You'll not likely notice in pedal. What we see, is when Master not replaced and or caliper piston seal old and worn in use. The system doesn't handle added pressure, as it's then closer to like when new from factory. You have new master, so will not likely have and issue. At least not with master.

 

[savirc]

With ABS systems, we only depress and hold brakes on, we do not pump the peddle. That said:

I can say pump motor coming on every 1, 2, 3 or 4 times peddle depressed is normal. How long and hard peddle depressed makes a difference. Each time we use the brakes or just as time passes, pressure is lost. Sensors indicate pressure drop and at predetermined point, turns on power to the pump motor. Once pressure back to predetermined point, pump motor power is cut off (motor stops).

The older the system the fast the loss of pressure, due to aged seals and accumulator.

If pump runs longer than 40 sec., after pumping peddle 40 times to evacuate fluid form accumulator with IG key off. Than we've concern. If pump runs to long, 5 minutes IIRC. A DTC will come up and shut down ABS system. But brakes still work. Pumps motor running to long will prematurely wear out brushes and commutator of motor..

With brand new motors it is near impossible to hear it running, while in driver seat with window up and hood closed. The high mileage used/older motors, are easily heard form driver seat. Also, a new motor spins faster so it builds pressure faster and higher. Just replacing a bad brake control wire, we may see motor spin faster.

This... so I finally gave up and bought the entire assembly together and its whisper quiet. I can still hear the motor if inside the engine compartment, but I'm noticing after a couple of bleeds the motor does run almost every depress or every other depress. I don't think that the previous set up was doing this, which leads me to my initial suspicion of a faulty pressure sensor on the old assembly hopefully. New assembly is detecting the slightest change of pressure? it takes 20+ depress to loose pressure when off.

@2001LC f you can confirm a brand new unit does this (go off every other depress) because of changes in accumulator pressure dropping I'll feel much better.

Look at this shiny thing made of gold and diamonds...

 

[2001LC]

This... so I finally gave up and bought the entire assembly together and its whisper quiet. I can still hear the motor if inside the engine compartment, but I'm noticing after a couple of bleeds the motor does run almost every depress or every other depress. I don't think that the previous set up was doing this, which leads me to my initial suspicion of a faulty pressure sensor on the old assembly hopefully. New assembly is detecting the slightest change of pressure? it takes 20+ depress to loose pressure when off.

@2001LC f you can confirm a brand new unit does this (go off every other depress) because of changes in accumulator pressure dropping I'll feel much better.

Look at this shiny thing made of gold and diamonds...

View attachment 2233859

Can't say I've noticed, but will watch for after next one.

 

[100serieslover]

You'll not likely notice in pedal. What we see, is when Master not replaced and or caliper piston seal old and worn in use. The system doesn't handle added pressure, as it's then closer to like when new from factory. You have new master, so will not likely have and issue. At least not with master.

Ahhh. So I should consider getting some caliper rebuild kits (are these even available for these rigs???) on hand. Got it.

Thanks for the help!

 

[2001LC]

Ahhh. So I should consider getting some caliper rebuild kits (are these even available for these rigs???) on hand. Got it.

Thanks for the help!

Yep. Seal Kits are available, piston are purchased separately. Also new calipers (still available) or rebuilt OEM.
One thing I'm finding, is pistons of calipers pitted. This happens from not flushing often enough. When new pads are installed, piston are full contracted. As pads wear the part of piston expose longest to moisture in fluid, get into seal area. So we see some pressure loss and a weep from caliper more as pads are worn down. Usual very minor but additive to pressure loose.