Master Cylinder Rebuild - DIY (2 Viewers)

[nckwltn]

@silveradofab I agree with @Skidoo and @2001LC could be problematic. Perhaps look for a part number or something in the casting to confirm they are different or the same.

@2001LC my brake fluid wasn't discolored, but there was something suspended in the brake fluid that was depositing itself in the reservoir, and I noticed the same particles located in the brake fluid as I was flushing/bleeding. I agree that those particles could very well be a seal being damaged and the remnants remaining in the fluid. But looking at the diagram, it seems like the relief valve should be opening and preventing an over-pressure, and should be preventing seals from being damaged (unless the relief valve itself is what was being damaged).

I do think that there isn't as much risk in examining or replacing (could be impossible to replace) the high pressure switch. This switch is telling the pump when enough pressure has built up and it should stop pumping. I suppose on one side of it, you could send a signal before enough pressure has built up, but I think you can mitigate that by monitoring the amount of fluid that drops from the reservoir. If that drop remains consistent, I would think that the pressure has built up correctly.

I agree that it is unlikely the switches are replaceable. With the design being 20+ years old, it seems unlikely that we are going to stumble across the solution. However, I don't think I've seen anyone else (or too many others) come to the conclusion that the high pressure switch is malfunctioning causing a build up of pressure. So who knows, we could be on to something new! (trying to remain hopeful in the face of $$$-$$$$ to replace )

 

[2001LC]

@silveradofab I agree with @Skidoo and @2001LC could be problematic. Perhaps look for a part number or something in the casting to confirm they are different or the same.

@2001LC my brake fluid wasn't discolored, but there was something suspended in the brake fluid that was depositing itself in the reservoir, and I noticed the same particles located in the brake fluid as I was flushing/bleeding. I agree that those particles could very well be a seal being damaged and the remnants remaining in the fluid. But looking at the diagram, it seems like the relief valve should be opening and preventing an over-pressure, and should be preventing seals from being damaged (unless the relief valve itself is what was being damaged).

I do think that there isn't as much risk in examining or replacing (could be impossible to replace) the high pressure switch. This switch is telling the pump when enough pressure has built up and it should stop pumping. I suppose on one side of it, you could send a signal before enough pressure has built up, but I think you can mitigate that by monitoring the amount of fluid that drops from the reservoir. If that drop remains consistent, I would think that the pressure has built up correctly.

I agree that it is unlikely the switches are replaceable. With the design being 20+ years old, it seems unlikely that we are going to stumble across the solution. However, I don't think I've seen anyone else (or too many others) come to the conclusion that the high pressure switch is malfunctioning causing a build up of pressure. So who knows, we could be on to something new! (trying to remain hopeful in the face of $$$-$$$$ to replace )

The pressure switch(s) in ABS unit, I'd not try to fix. I've busted one ABS unit to pieces to examine. Stuff is molded into.

But it's easy to toss on a used ABS unit. Most are good. I've seen one bad, and it gave DTC that indicated it was bad. We swapped with a $100 recycled one, and worked just fine. Local Dealership wanted $5,500 for the job. I did for $500. Included restore of brake control wire. I've more experience with these now. Today I would pull motor apart make sure it's good, R&R plunger and replace brake control wire at minimum.

But; When I see a bad brake control wire. Where I was recommending we replace the wire and do other stuff. Today I like to flush first. If color of fluid was bad, and then turns dark again fast (in months). I don't like to touch it master. Reason is, we increase pump speed (either just new wire and both wire and motor) and we get increase in pressure. If seal bad, we may than get the screeching and bubbles, form increasing pressure.

This is one reason a the Dealership nor shop on the corner or Slee will repair a Master. Most, even senor mechanic at Toyota, don't even know Toyota sell the master plunger. They do one thing, replace the whole assembly. Otherwise the customer may have to repeatedly return for same issue or what is perceived same issue. Additional there is a liability. If they change one part of the master, and another fails they'll end up in court.

The bad fluid with pieces you have, is the clue. I'll bet your inner seals are shot. Likely your caliper piston seals are also bad and/or piston pitted.

 

[Eyedaho]

When cold OAT, rubber seals shrink. Very common in colorado winters, to have brake warning sound, on cold mornings. Then as we use brakes, seal(s) heat and expand, alarm turns off. If fluid has been in too long, it can damage seals and pit piston. We put on new pads and no more warning. Than as pads wear, worst of pitting on piston get exposed to the seals and pressure warning again (cold morning alam)

Not flushing brake fluid regularly is damaging to all seals. This includes master. If your fluid turns dark quickly after flushing, this is a bad sign of seal damage.

If squeal sometimes referred to a screaming banshee. Is also accompanied by air bubbles in reservoir. Only thing that can be done is replace master. There is a seal we can't get to. This "seals damage" allows pressurized brake fluid past it. That's what we hear. The bubbles in reservoir is the fluid released into from seal under pressure.

What I can not say, is which fluid is best. Toyota fluid has seal modifiers others may not. Toyota fluid in the can, is not same mix as what comes in the rig from factory. But is or was the same manufacture making it.

Your brakes will still work, provided squeal from bad seal in master or leaks at piston calliper seals, not so bad you lose most all pressure or fluid.. But, the constant excessive run time of pump, do to pressure lose. Will cause pump to wear out prematurely. Than we lose brakes, as we no pump to bring up pressure.

The HP switch can be tested along with pressure of system. But good luck finding a gauge to do the job. I have replaced the HP switch seal(s). I did get some improvement. But this seal we can't get to. That squealing. Is deep inside master cylinder behind plunger, which is the one we can not replace.

Note: The HP switch was first used in the 2000 USA models. In mid 2000 they change the switch. They are not interchangeable, the seal(s) are. But FSM states in the second gen switch, they are not reusable.

So do the '98-'99 model years not use an HP switch? If not then how does the booster pump turn off? Or do you mean prior to 2000 was a different switch?

 

[PabloCruise]

So do the '98-'99 model years not use an HP switch? If not then how does the booster pump turn off? Or do you mean prior to 2000 was a different switch?

As a '99 owner I was wondering the same!

 

[Skidoo]

So do the '98-'99 model years not use an HP switch? If not then how does the booster pump turn off? Or do you mean prior to 2000 was a different switch?

Don't know about HP switch but the ABS valve matrix and ABS computer is different as rear brakes are on a common brake line for those years.
So only 3 lines come out of valve matrix LF, RF and Rear common. 2000 on has a separate brake line for each wheel.

 

[Eyedaho]

Don't know about HP switch but the ABS valve matrix and ABS computer is different as rear brakes are on a common brake line for those years.
So only 3 lines come out of valve matrix LF, RF and Rear common. 2000 on has a separate brake line for each wheel.

That makes sense with the addition of traction control, since you would need independent braking control at each wheel.

 

[PabloCruise]

That makes sense with the addition of traction control, since you would need independent braking control at each wheel.

Ah yes! ATRAC started in 2000?

 

[Eyedaho]

Ah yes! ATRAC started in 2000?

Not sure, but I don't have it in my '99.

 

[2001LC]

It's my understanding the booster motor is control by pressure switches in the ABS unit (black box on side of master). The 12v battery current flow through the ABS unit to the booster motor via the brake control wire.

99-98 does not have the replaceable sensor ( I called HP switch) thread in the front of master. The FSM calls this a Master Cylinder Pressure Sensor (MCPS). I referred to a HP switch, which it's not really a switch. I call it that, because it's under very high pressure. This was add in 2000. The seal in it is a high pressure double seal setup. In mid 2000 they change this MCPS, which has a different shaped wire housing connector. The new MCPS connection, will not fit the early 2000 wire harness. The FSM states the newer MCPS is non reusable.

This is 98 with reservoir removed. Notice no MCPS

In 2000 they added ATRAC and a MSCP. Notice the oblong housing for wire harness.

In mid 2000 they change the MCPS.

 

[nckwltn]

If you load tech-stream and monitor the data on the MCPS, it is a sensor that detects how much pressure is being applied to the brake pedal. My understanding is that if it detects a quick change in pressure, it can apply additional braking force beyond what is being applied by the pedal.

You'll see it read 1 volt (no pressure) to near 4 volts (as far as I could push the pedal in).

This is a different sensor to the switches for high and low pressure in the system. Sadly those read only on and off in tech stream... so you get very little feedback of how they are operating.

 

[Eyedaho]

That makes sense about the pressure sensor. Thanks guys!

 

[silveradofab]

So I swapped the accumulator and pump from my 4 runner. No dice. Still screeching. From reading the thread and thinking about it it mus be the internal pars that are failing. I later sourced a used master(complete) from a lx470 out of a yard in OK. I installed it last Sunday and it has been great so far. Did a manual bleed procedure and it is working well.

 

[nckwltn]

So I swapped the accumulator and pump from my 4 runner. No dice. Still screeching. From reading the thread and thinking about it it mus be the internal pars that are failing. I later sourced a used master(complete) from a lx470 out of a yard in OK. I installed it last Sunday and it has been great so far. Did a manual bleed procedure and it is working well.

Hold on to that motor and accumulator, you may need it someday! I also have a new (to me) master, should be arriving Friday.


One work-around I've found that works 75% of the time. Turn the key to the on-position, but don't start the car. Let the pump build up pressure, once/if the screeching happens, turn the key off and let the car sit for 5ish minutes. Turn the key back to the on-position and listen for screeching. Rinse and repeat if it doesn't work the first time.

I've found that this seems to get the screeching to stop for the day (usually mostly). Not super convenient, and not good if the wife wants to drive the car somewhere and doesn't know the start up procedure.

 

[mderrick]

so i found a puddle of brake fluid under my truck the other morning... I haven't had any soft pedal or what i would consider weak brakes. I figured that i may need to rebuild my master cylinder so i ordered the parts from Cruiser Outfitters and pulled the unit out. once it was out there was no weeping from the shaft end but the under side of the MC was soaked in fluid. it looks like the puddle was dripping off the frame after the fluid had run down the top of the inner fender. this is the ifrs time i have been into the brake system on my 2000 100 series. my question is are the plastic pieces at either end of the hose supposed to wiggle? and should there be brake fluid in that hose? I am thinking not. what would cause the fluid to get there?

 

[YardPig]

Has that brake fluid ever been changed...? Yikes. Looks like a ton of moisture.
Would like to see some more detailed pictures of the bore and piston. Thanks for sharing.

 

[mderrick]

Has that brake fluid ever been changed...? Yikes. Looks like a ton of moisture.
Would like to see some more detailed pictures of the bore and piston. Thanks for sharing.

I have not changed it since i purchased it 3 years ago, i was planning to flush it before winter..... the PO would have replaced the fluid at least once since he purchased it with a bad booster.

 

[2001LC]

so i found a puddle of brake fluid under my truck the other morning... I haven't had any soft pedal or what i would consider weak brakes. I figured that i may need to rebuild my master cylinder so i ordered the parts from Cruiser Outfitters and pulled the unit out. once it was out there was no weeping from the shaft end but the under side of the MC was soaked in fluid. it looks like the puddle was dripping off the frame after the fluid had run down the top of the inner fender. this is the ifrs time i have been into the brake system on my 2000 100 series. my question is are the plastic pieces at either end of the hose supposed to wiggle? and should there be brake fluid in that hose? I am thinking not. what would cause the fluid to get there?

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If you're asking about the white plastic tubes. One on master and one on pump with black hose between them. Yes they are kind of loose or wiggle. That is feed line to pump from reservoir. It's a low pressure line.

There are a few places leak may be from. One could be the red line. That is the highest pressure line in the system. Yours is wet and rusty!

Another overlooked leak point. Is at bottom of pump, at weep hole. If motor air vent plugged you may have suck fluid from the pump into motor. It would fill weep cavity and pump and leak at bottom.

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

Leaks, I suppose, can happen at grommets at bottom of reservoir.

BTW: That is the worst (gunky) master plunger, I've ever seen. I'd start looking for a replacement master and save the master plunger kit.

 

[hickuptruck]

That looks like y

so i found a puddle of brake fluid under my truck the other morning... I haven't had any soft pedal or what i would consider weak brakes. I figured that i may need to rebuild my master cylinder so i ordered the parts from Cruiser Outfitters and pulled the unit out. once it was out there was no weeping from the shaft end but the under side of the MC was soaked in fluid. it looks like the puddle was dripping off the frame after the fluid had run down the top of the inner fender. this is the ifrs time i have been into the brake system on my 2000 100 series. my question is are the plastic pieces at either end of the hose supposed to wiggle? and should there be brake fluid in that hose? I am thinking not. what would cause the fluid to get there?

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And thats from Cruiseroutfitters old 100 series? No way. I think the master cylinder unit is just too far gone to save. Best off to just fork the $2k for a new unit!

 

[hb1980]

Hi, guys,
Firstly I'd like to thank Skidoo for this write and all the members who've contributed to this post.
So I have a 2007 LC100 and I had a complete Master cylinder assy replacement 3years back when I got the vehicle (PO had really no sense of PM or any maintenance at all.) Just 2 weeks back i started experiencing the soft pedal and no brakes issue, no codes, decided to pull the trigger on a piston replacement. Now I have brakes, pedal is rock hard with about 1" travel and it brakes fine. But I still feel I braked better before when the MC was new.
Issue now is it takes a bit longer to stop and when I out the car on a lift and put in in drive and press the brakes, the fronts catch instantly and the rear has a slight delay. Anyone notice this? I'm wondering if I need to adjust the rod, not sure in which direction.
Any suggestions? Still running OEM brake parts.
Thanks

 

[2001LC]

That is interesting. I've never look at front and rear brake caliper, during brake pedal push. Seems, it would be very difficult to visually time front to rear.

Can I ask: How did you see this sit happened?

Did you test booster motor run time, from evacuation (IG key off, pump pedal 40 times) of accumulator?

As for fronts, moving first. They have 4 piston, whereas rears one piston in caliper. They also have shorter brake lines to front. Additional the rear have two sets of flexible lines each side, which flex/expand more with time/age. But still, I'd think, all should move at same time.

Interesting also. My 01, the fronts lasted 90K+ miles and rears ~45K miles. Yet time and time again. Reading vehicle histories at Lexus, Toyota and/or car fax. I see very often fronts wear faster than rears in the newer models. The only difference I know of, is pads. They all are interchangeable, but the PN's different. IMHO this is different brake pad material to meet newer EPA standard.


Your left 98-02.

Did you make sure your clips and slip pins in rear caliper move freely, and flex line are not swelling. Air in lines or damage line, could account for this also.

This very clean 06 w/150K. I found RH slave slid pin frozen in. Also found clip trashed and pack with crud. The LH anti squeal shim damage. The read pad on RH had ~7mm. One pad on LH ~1mm.