You're try to diagnose and repair something you don't likely understand. Even techs at Toyota, don't. They just replace the whole master. For good reason.
My write up on brakes (master). Is to help all understand, how to care from them. Also, what clues to look for, that tells us, we may be heading for issues. I do not advocate repairing, brake master or the ABS unit.
I may recommend service the booster assemble. Which depends clues as to heath of masters. But replacing the master, is less labor than R&R of any part of it. With exception of the accumulator and reservoir.
Hi ! I spend the whole last night read up this thread since the beginning till now and 1st off I just wanted to say I really appreciated your time and effort on trouble shooting this well know issue on our vehicle since there is not much information on the ABS system on these rigs, so I have a 1998 with 270k miles on it I purchased 2 years ago, the original ABS pump on it was running very loud but at the time it was working and I thought it supposed to run like that, fast forward to last winter the dreadful ABS light and brake alarm is on but brake still work at that time, I swapped it out with a used unit on eBay and bleeded the system and everything was great, the original unit was in very bad shape like completely dusted and rusted out on the outside let alone internal, the new unit that I put in look very decent shape with unknown miles but it run very quite compared to the old one, I almost can't hear it running if I was in the rig, fast forward 2 months after it happened again and this time I COMPLETELY LOST BRAKE WITH OUT EBRAKE, luckily I made it home safe and parked the rig, let it sit for 2 days come out to start it lights went away and I can hear relays clicking and the pump is running fine, test drove around the blocks a few times nothing, than I drove a little farther and at a random parking lot it HAPPENED AGAIN brake pedal sink to the floor and completely no brake pressure, I parked the truck turned it off and turn it back on and it went away very strange, shut it off again turn it back on and the alarm went on and no pedal, which almost made me believe there is a short in the system cause no power to the pump but I'm not expert, I did a quick test around with my vol multimeter for fuses and relays and they seem to be working fine, I almost think it was the ABS module under the dash on driver side was bad or lose a ground or sth, but after founding this thread and spend the last night gathering information I got a few things down
Bottom line. Get a new brake booster assy with master (the whole brake master).
- look like I overfilled the system, when the pump shut off completely and brake fluid return to reservoir, it's above max
Overfilling, will not affect brake master operation, in the short term. But, it mayl in the long run.
- look like there is no thread about the ABS module is the cause for this, 9/10 is the whole pump itself
- I will try to get to my truck today and correct the fluid level, check for the brake wires control condition (I didn't check it when I swapped it in) and try to move the rig home for further diagnostics
I still have my original unit that I took out from the rig laying at my other house's garage, if this unit I just swapped in 2 months ago is indeed bad too, would you be interesting on 2 cores for more documents on the issue and I would definitely thinking about getting a rebuild unit from you directly,
No thanks you.
I'm done with my research (data point collection) on brake master booster motors.
At this time, I do not rebuild booster motors.
I would never buy or recommend, rebuilt brake master.
I don't want to go with eBay route or possibly salvage yard, want something reliable and well rebuild by experience tech
Booster motor, can be rebuilt. But so often, old brake master or its other components will fail shortly after a new or rebuilt booster motor installed.
Brakes are, the most important safety device. Your life and the lives others depend on them.
Nice picture possier picture, of your 100 series. But pictures of brake master reservoir and control wires, would have been more helpful here today.
Bottom line. Get a new brake booster assy with master (the whole brake master).
Brake booster motor:
I've seen, more than once. Where the brake booster motors' commutator, has worn thin and has dead spots. The motor runs fine, when running. But sometimes, when it's time for motor to start running (fire-up). A brush happens to land on a deads spot, so booster motor will not fire up (run).
Overfilling the brake fluid reservoir a little, is not going to directly affect motor or operation or the ABS unit. Not in the short term. But, it will affect the booster motor and may affect ABS unit, in the long run.
The issue with overfill. Is when brake fluid comes out the cap/top. May even force brake fluid out the grommets in bottom of reservoir. The fluid may then travel down to brake control wire (resistance wires). Brake fluid once on wires. Then travels along wiresir, into its boot covering the contacts (contacts, leads, washers and screws). Brake fluid attracts moisture (hygroscopic) from the atmosphere. The moisture, being held in boot, results in corrosion of contacts.
The corrosion, on brake control (specific resistance) contacts. Increase resistance of wires. This result, in excessive heat between commutator and brushes. Which heat cause excessive wear of commutator. Premature failure of motor.
Seals within master:
When pressure drops within brake master. Brake booster motor gets signal to run. It turns the pump, forcing brake fluid into accumulator. If the non replaceable seals within master, are weak. They'll not hold full pressure. The loss of pressure, results in brake booster motor running. This may result in booster motor running excessively long. The booster motor is designed to run often, for short burst. If it runs continuously or prolonged periods. It creates excessive heat. This also will cause premature failure of motor (wear of brushes & commutator). These seals, are weakest when cold.
The ABS unit (black box) on master. Can also fail. The ones I've seen fail, have had very stained reservoir's and often corrosion on brake control wire.