Look at the accumulator (big cylinder) and watch it while the motor kicks on and off. You'll see a ring around it with little rubber bumpers. The whole thing will jiggle a little when the motor kicks on and off and the ring with bumpers keeps it contained. I'm just wondering if that jiggle is your clank, maybe the bumpers are missing or bent. No idea if that ever happens, though.
Any other warning signs / precursors to brake booster failure?
- Thread starter nukegoat
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2001LC
SILVER Star
First I'd save and clear dtc. Sneeze on the 100 series and Brake/ABS DTC sets-off.
Before clearing, I'd clock boost motor run time. 29 second new 40 max spec. Over 40 is leak or air in system.
forum.ih8mud.com
Before clearing, I'd clock boost motor run time. 29 second new 40 max spec. Over 40 is leak or air in system.
Brakes ...... Overdue write-up.
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...
forum.ih8mud.com
The engine wasn’t running during the video, so dash lights are on as normal, no codes.First I'd save and clear dtc. Sneeze on the 100 series and Brake/ABS DTC sets-off.
Before clearing, I'd clock boost motor run time. 29 second new 40 max spec. Over 40 is leak or air in system.
Brakes ...... Overdue write-up.
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...
I’m at 41 seconds with old black fluid, so a flush is definitely in order and hopefully new fluid will be slightly less compressible.
The accumulator bumpers are intact and doing their job. Would’ve been great if it was that simple!
I haven’t been able to replicate it again when parked & cold, I’ll check tomorrow after the truck is warm.
Hi friends, just hope to confirm, if my truck passes the following 2 tests:
1. Cold engine (parked overnight), turned ignition to ON but not Start, and measure the brake booster motor's run time, which is < 40sec;
2. Key out of ignition, pump brake 40 times, then turn key to ON, measure the booster motor's run time, which is also < 40sec.
With the above, does it mean the brake booster is most likely (above 99% chance) to be fine? And the shorter the above 2 times, the healthier the booster system?
Thanks!
1. Cold engine (parked overnight), turned ignition to ON but not Start, and measure the brake booster motor's run time, which is < 40sec;
2. Key out of ignition, pump brake 40 times, then turn key to ON, measure the booster motor's run time, which is also < 40sec.
With the above, does it mean the brake booster is most likely (above 99% chance) to be fine? And the shorter the above 2 times, the healthier the booster system?
Thanks!
JunkCrzr89
Competent Ignoramoose
Yeah
2001LC
SILVER Star
Run time is only one clue to health. It's important to note battery voltage at time of test. A new booster w/master and battery at or above 12.7V. We'll see run time of 28 to 30 second. Provide "no air" and "good" or fresh brake fluid.
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My LX makes a sound only when starting on cold mornings;
- like the booster is filling in short bursts of 1-2 secs
- the cycling lasts for a few minutes then completely stops after the car warms up
A couple of times on cold morning the Christmas tree of lights and tone has occurred. I pulled over, waited a few minutes, started the car and all is good. My mechanic did not see any error codes.
Should have added, it's not a daily driver and the more I drive it the less the sound occurs.
I have had the LX a few months ... just wondering if normal or???
- like the booster is filling in short bursts of 1-2 secs
- the cycling lasts for a few minutes then completely stops after the car warms up
A couple of times on cold morning the Christmas tree of lights and tone has occurred. I pulled over, waited a few minutes, started the car and all is good. My mechanic did not see any error codes.
Should have added, it's not a daily driver and the more I drive it the less the sound occurs.
I have had the LX a few months ... just wondering if normal or???
2001LC
SILVER Star
Running a few minutes at a time, is not normal and is not good. Booster motor should run less than 40 seconds. Indicates a pressure loss. When OAT cold the rubber seal shrink. If seal not in great condition, to begin with. Cold will make worst.
That sound at the 5sec mark is the sound I hear ... sometimes it cycles a few minutes when starting on cold mornings. I'll try to capture the sound and post a video.
I do not have the other sound that lasts the duration of the video.
2001LC
SILVER Star
My advise: Replace the brake master w/booster assembly. Then Flush & Bleed the system with Toyota brake fluid. Check all brake lines for age related damage/leaks. Replace all 4 rubber bleeder caps, when done bleeding. Tip: Blow out bleeders, before replace rubber caps.
As you video on a cold morning at first key on: You'll very likely see bubbles come up front of reservoir, at same time you hear the squeal
I'll bet your brake fluid reservoir is heavily stained and/or brake fluid is dark and/or darkens soon after flushing fluid?
Why:
A non replaceable (IMHO) seal within the master, is failing. When this seal is cold, brake fluid under pressure passes it. Once it warms by external heat of the day (OAT) or use, it expands and holds pressure. This is why, after using brakes or a day when OAT is high, brakes work as it should. But when cold, the shrunken seal can't hold full pressure. The booster motor will keep running, until the predetermined pressure reached, which signals booster motor to stop.
This seal fails, due to improper brake service. Number one is not regularly flushing. There is also concerns of which brake fluid used. Personally I only use Toyota brake fluid, out of abundance of caution.. Not even Toyota or Lexus Dealership, use their own brake fluid. They're seeing a very high failure rate across all makes!
The brakes will still work, for now! But over time/use, seal will get worst. Booster motor will run longer and longer. The booster motor is designed to run often, but only short duration. Booster motor running longer duration, will cause its premature failure. At some point, booster motor will fail to run. YOU'll LOOSE BRAKES, due to lack of brake pressure! You'll actually have about 2% to 20% braking, at bottom of pedal, with very hard foot pressure on pedal.
