Master Cylinder Rebuild - DIY (1 Viewer)

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An update to my post #476:

At this point I've rebuilt the master cylinder, replaced the accumulator o-ring, spring and pipe, cleaned out the motor, and replaced the unit on the vehicle. I bled the system pretty thoroughly using techstream and pedal, and then actuated the VSC solenoids (SRMF & SRMR). Can someone confirm this is correct? I have a very firm pedal.

I'm still getting the same cycling from the pump/motor/accumulator.

Before I order a new pump/motor/accumulator, does anyone have any thoughts on other solutions/troubleshooting steps? Since I'm not getting a soft pedal, I'm wary that the issue is not mechanical but electrical, and that replacing the pump/motor/accumulator won't address whatever it is that's signaling the motor to keep turning on and off. I might be better off replacing the entire assembly but that's way more money.

Would I get a soft pedal if the accumulator wasn't holding pressure? Do the accumulators go bad?
If by cycling, your hearing the "screaming banjo" and see bubbles coming up front of reservoir at same time. With brake pedal not being depressed, and the frequency is increase with time. You'll need a new brake master.

BTW: Looking at your picture of motor front bearing and commutator. They look wet. If it came apart wet, and wet not from silage or you wetting. It's a sign the air vent is clogged. Clogged vent leads to vacuum of spinning motor sucking fluid from pump. This will damage the motor. Motor vent and pump drip ort need to be keep clean.
Hey man, I did this check the bolts in the rubber cover and it looks good, but I did that pump timing test twice, I got 50seconds and 52 seconds. what I did is I hit the brake pad 40+ then turn the key on (not start engine), then it starts the pump, no warning sound, the car sit there overnight before I do the test.

So is it bad? or I did the test in the wrong way? If it is bad, will a dealer brake flush help?
Make sure to check your battery voltage. A good booster motor time test, is take at ~12.4V or better. Lower voltage, motor turns slower and motor run time goes higher.
Check voltage on battery post, and than on positive battery clamp and a ground point. Volts should be the same from all points.

Over 40 seconds, and you have and issue that needs correcting. Most common: air in system or weep/leak in system. It can also speak to heath of booster assembly i.e motor, pump and/or accumulator.
 
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If by cycling, your hearing the "screaming banjo" and see bubbles coming up front of reservoir at same time. With brake pedal not being depressed, and the frequency is increase with time. You'll need a new brake master.

BTW: Looking at your picture of motor front bearing and commutator. They look wet. If it came apart wet, and wet not from silage or you wetting. It's a sign the air vent is clogged. Clogged vent leads to vacuum of spinning motor sucking fluid from pump. This will damage the motor. Motor vent and pump drip ort need to be keep clean.

Make sure to check your battery voltage. A good booster motor time test, is take at ~12.4V or better. Lower voltage, motor turns slower and motor run time goes higher.
Check voltage on battery post, and than on positive battery clamp and a ground point. Volts should be the same from all points.

Over 40 seconds, and you have and issue that needs correcting. Most common: air in system or weep/leak in system. It can also speak to heath of booster assembly i.e motor, pump and/or accumulator.

The battery is 14v, new battery and alternator. And the pump charging is also a little weird, it always charges 4 times to complete the charging. The First 3 times are about 8 seconds each, then the last time will be around 30 seconds, there are significant stops between the chargings. then it becomes quite/fully charged. I plan to do a full flush first, if still can not pass the 40 seconds test, I will change the whole unit, what the hell...

Thanks for you mentioned this 40 seconds test in many posts, without reading them I don't even know there is this kind of thing...
 
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The battery is 14v, new battery and alternator. And the pump charging is also a little weird, it always charges 4 times to complete the charging. The First 3 times are about 8 seconds each, then the last time will be around 30 seconds, there are significant stops between the chargings. then it becomes quite/fully charged. I plan to do a full flush first, if still can not pass the 40 seconds test, I will change the whole unit, what the hell...

Thanks for you mentioned this 40 seconds test in many posts, without reading them I don't even know there is this kind of thing...
Brake failure is very dangerous, obviously. Keep in mind working on your own brakes is at your own risk. Any advise or help I offer is your sole responsibility to evaluate risk. Most any INDY shop or Dealership, will only do one thing with any brake master issue. They just replace the whole unit, and for good reasons.

I've only seen for one reason for brake failure. "Loss of brake system pressure".
Which happens for two reasons. 1) Booster assembly fails. 2) Loss of brake fluid.

@zhloea
This "long charging" with extra long pause, is after evacuating (key off pump pedal 40 times) accumulator, right!
How many pumps on pedal before pedal back pressure drops?

Clues:
With a NEW OEM booster assembly I get about 22 to 24 pumps on pedal, before pedal back pressure drops off (IG key off). With aged accumulators, I get 26, 28, 30, 32, 34, 38 even 40 pumps. IMHO, the higher the number of pumps of pedal, indicates the weaker accumulator. It can to lessor extend IMHO, indicate bad seal(s) in master. Some of which we can not replace.

Look for weeps/leaks:
I'd re-bleed, make sure fluid level stay above minimum line of reservoir at all times. Than dry each bleeder with can of brake cleaner and high pressure air or a de-greaser and dry. Look for any sign of weeps/leaks at bleeder right after using brakes aggressively. Check hard brake lines and each flare nut for leaks. Check all 6 (5 in 98-99) flexible lines for leaks or bulging when under pressure (key on pedal pressed hard)

Bleed the accumulator:
Which is just pumping pedal 40 times key off. Then key on, let accumulator charge. Repeat five times. Testing "time to motor shut off" each time key turned on.

When I'm evaluate a brake master. I look at clues and rate them.
Is fluid dark, Yes very -3, somewhat -2, mild -1.
Is reservoir stained. Very -3, somewhat -2, mild -1
Does fluid darken soon after a flushing system, which includes flushing accumulator 5 times. Yes very -3, somewhat -2, mild -1.
If I get a high negative count. This makes a good case for replacing the master. It indicate fluid not properly flushed often enough, which damages seals. There's a seal or seals in master than are not serviceable. We boost pressure, by even just replace a bad wire, delivery more AMP to motor (spins faster) and seals fail. If internal seal are weak, we get a pressure lose at times. Typically this is when we hear a screeching sound and see bubbles come up inside front of reservoir, during brake booster charging (booster motor running)

Any weeping at bottom of ABS unit. Replace master. This is difficult call as to where fluid from. If just grommets than just replace grommets, but I've not found those bad yet.

Also FSM has some test for ABS unit. Been awhile since I ran through them. But it's using a multi meter at wire contacts coming off black box on side of master. It must pass all. In addition resistant of brake control wire can be test through ABS unit. Again been awhile since I did this test, so you'd need to figure it out.

Booster assembly clues:
Fluid is or was over filled. Yes -1
Is wire corroded. Yes -3.
How many pumps on pedal. 38 to 40 -3, 34 to 37 -2, 30 to 33 -1.
Time until accumulator charged. 28 seconds new (new booster assembly with good seal and lines throughout system, including caliper pistons) 30 to 34 second average good system 13 to 20 years old with good voltage from battery. 36 sec -1, 38 sec -2, 40 sec -3.

You may also want to check voltage at Master/ABS unit. See FSM for which points to check.

Wire corroded and resistance test higher than test wire (OHM's as compared with New OEM wire). Yes-3 (wire replaced and motor should be opened and inspect at minimum).

Any weeping at bottom of pump. Replace motor, pump & wire. Motor air passages and pump weep passage must be clear of obstruction! Some very very minor weep occasional, at pump weep passage, is okay. But no brake fluid should be found inside motor ever.

I'd say this to everyone reading here:
Bottom line: In our aging fleet, if in doubt for good reasons, replace the whole master assemble. But don't even touch master, without good understanding and mechanical skills. Lives are at stake!
 
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Brake failure is very dangerous, obviously. Keep in mind working on your own brakes is at your own risk. Any advise or help I offer is your sole responsibility to evaluate risk. Most any INDY shop or Dealership, will only do one thing with any brake master issue. They just replace the whole unit, and for good reasons.

I've only seen for one reason for brake failure. "Loss of brake system pressure".
Which happens for two reasons. 1) Booster assembly fails. 2) Loss of brake fluid.

@zhloea
This "long charging" with extra long pause, is after evacuating (key off pump pedal 40 times) accumulator, right!
How many pumps on pedal before pedal back pressure drops?

Clues:
With a NEW OEM booster assembly I get about 22 to 24 pumps on pedal, before pedal back pressure drops off (IG key off). With aged accumulators, I get 26, 28, 30, 32, 34, 38 even 40 pumps. IMHO, the higher the number of pumps of pedal, indicates the weaker accumulator. It can to lessor extend IMHO, indicate bad seal(s) in master. Some of which we can not replace.

Look for weeps/leaks:
I'd re-bleed, make sure fluid level stay above minimum line of reservoir at all times. Than dry each bleeder with can of brake cleaner and high pressure air or a de-greaser and dry. Look for any sign of weeps/leaks at bleeder right after using brakes aggressively. Check hard brake lines and each flare nut for leaks. Check all 6 (5 in 98-99) flexible lines for leaks or bulging when under pressure (key on pedal pressed hard)

Bleed the accumulator:
Which is just pumping pedal 40 times key off. Then key on, let accumulator charge. Repeat five times. Testing "time to motor shut off" each time key turned on.

When I'm evaluate a brake master. I look at clues and rate them.
Is fluid dark, Yes very -3, somewhat -2, mild -1.
Is reservoir stained. Very -3, somewhat -2, mild -1
Does fluid darken soon after a flushing system, which includes flushing accumulator 5 times. Yes very -3, somewhat -2, mild -1.
If I get a high negative count. This makes a good case for replacing the master. It indicate fluid not properly flushed often enough, which damages seals. There's a seal or seals in master than are not serviceable. We boost pressure, by even just replace a bad wire, delivery more AMP to motor (spins faster) and seals fail. If internal seal are weak, we get a pressure lose at times. Typically this is when we hear a screeching sound and see bubbles come up inside front of reservoir, during brake booster charging (booster motor running)

Any weeping at bottom of ABS unit. Replace master. This is difficult call as to where fluid from. If just grommets than just replace grommets, but I've not found those bad yet.

Also FSM has some test for ABS unit. Been awhile since I ran through them. But it's using a multi meter at wire contacts coming off black box on side of master. It must pass all. In addition resistant of brake control wire can be test through ABS unit. Again been awhile since I did this test, so you'd need to figure it out.

Booster assembly clues:
Fluid is or was over filled. Yes -1
Is wire corroded. Yes -3.
How many pumps on pedal. 38 to 40 -3, 34 to 37 -2, 30 to 33 -1.
Time until accumulator charged. 28 seconds new (new booster assembly with good seal and lines throughout system, including caliper pistons) 30 to 34 second average good system 13 to 20 years old with good voltage from battery. 36 sec -1, 38 sec -2, 40 sec -3.

You may also want to check voltage at Master/ABS unit. See FSM for which points to check.

Wire corroded and resistance test higher than test wire (OHM's as compared with New OEM wire). Yes-3 (wire replaced and motor should be opened and inspect at minimum).

Any weeping at bottom of pump. Replace motor, pump & wire. Motor air passages and pump weep passage must be clear of obstruction! Some very very minor weep occasional, at pump weep passage, is okay. But no brake fluid should be found inside motor ever.

I'd say this to everyone reading here:
Bottom line: In our aging fleet, if in doubt for good reasons, replace the whole master assemble. But don't even touch master, without good understanding and mechanical skills. Lives are at stake!

Thanks for the detailed reply.

1. I am so sorry, I did not understand your answer about the pauses during the pump charging. are these pauses normal or not?
that long charging is after I turn the key off and pump the pedal 40 to 50 times. the pause during the recharge is about 1 second each time (did that test twice, every test have 3 pauses), the pedal drops after 30 to 35 pump.

2. Thanks for the warning "But don't even touch master, without good understanding and mechanical skills." did you also mean "don't try to replace the whole assembly"? If you what you said "touch the master" and "replace the whole assembly" are a different thing (my understanding of this "touch master" is disassembly the unit and repair the part of cylinder master), will replace the whole assembly is relatively less risky than touch the master?

I totally know it is all at my own risk, and I consider myself is an entry-level DIYer, so I don't even have a plan and guts to disassembly this thing then replace the master cylinder.
The only thing I want to do is flush the brake then replace the whole assembly, the reason is I don't want all that dirty fluid involved in my new assembly.
 
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Thanks for the detailed reply.

1. I am so sorry, I did not understand your answer about the pauses during the pump charging. are these pauses normal or not?
that long charging is after I turn the key off and pump the pedal 40 to 50 times. the pause during the recharge is about 1 second each time (did that test twice, every test have 3 pauses), the pedal drops after 30 to 35 pump.

2. Thanks for the warning "But don't even touch master, without good understanding and mechanical skills." did you also mean "don't try to replace the whole assembly"? If you what you said "touch the master" and "replace the whole assembly" are a different thing (my understanding of this "touch master" is disassembly the unit and repair the part of cylinder master), will replace the whole assembly is relatively less risky than touch the master?

I totally know it is all at my own risk, and I consider myself is an entry-level DIYer, so I don't even have a plan and guts to disassembly this thing then replace the master cylinder.
The only thing I want to do is flush the brake then replace the whole assembly, the reason is I don't want all that dirty fluid involved in my new assembly.
Yes a pause is normal. I hear 1, 2 or 3 pauses, most times. But it's very brief, usually a second or less. So we do not stop timing during pause. It's the total time we need to know. I misunderstood, thinking you were getting longer pauses. Over 40 seconds total with good voltage to pump motor, indicates a pressure problem. Air in system after bleeding or leak most are common reasons.

30 to 35 pumps is wide spread. Cold we get higher number of pumps. Each time we repeat, it warms seals. But I typically I only see ~2 to 3 pump spread. I'd not be overly concerned with spread. Only note as -1 in overall rating.

I assume you've good skills and followed FSM steps. Replacements of master assembly w/booster not a big deal. But for most shade tree mechanics it best they don't touch, not even flush or bleed brakes. For that mater most shops. I say that because I do so much corrective work, due to some shop touching any part on our 100 series.

BTW: I've use only Toyota Brake fluid these days. Out of fear any other may damage seals. Most Toyota/Lexus dealership do not use it, they use bulk. But the number of masters being replace in all Toyota/Lexus, is staggering.
 
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Yes a pause is normal. I hear 1, 2 or 3 pauses, most times. But it's very brief, usually a second or less. So we do not stop timing during pause. It's the total time we need to know. I misunderstood, thinking you were getting longer pauses. Over 40 seconds total with good voltage to pump motor, indicates a pressure problem. Air in system after bleeding or leak most are common reasons.

30 to 35 pumps is wide spread. Cold we get higher number of pumps. Each time we repeat, it warms seals. But I typically I only see ~2 to 3 pump spread. I'd not be overly concerned with spread. Only note as -1 in overall rating.

I assume you've good skills and followed FSM steps. Replacements of master assembly w/booster not a big deal. But for most shade tree mechanics it best they don't touch, not even flush or bleed brakes. For that mater most shops. I say that because I do so much corrective work, due to some shop touching any part on our 100 series.

BTW: I've use only Toyota Brake fluid these days. Out of fear any other may damage seals. Most Toyota/Lexus dealership do not use it, they use bulk. But the number of masters being replace in all Toyota/Lexus, is staggering.

Thanks for the reply. " But for most shade tree mechanics it best they don't touch, not even flush or bleed brakes." If so, what should I do after I replace the whole assembly? there will be some air get into the system during the replacement right? Could I just top off the fluid and manage to drive to the dealer or some shop for a flush and bleed?
 
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If you can replace the whole assembly, I'd think you can also bleed. But if lacking the understand to bleed, well I'd not want you replacing my master.

No, don't just top and drive.
 
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Thanks. I think I understand the bleed/flush and reviewed most posts from the forum about this, but just never did one. I do think that the bleed process need more experience than the whole assembly replacement (watched some video from youtube, the replacement seems not that hard)...
 
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Not sure why your replacing master. I'd be digging more to see if "long test time" is other components first.

But in the end if replacing master. It's not hard for me, but then I've R&R a lot of them. I've bleed about 12 system already this year. I've been buying Toyota brake fluid by the case. In fact going to pick up a 1/2 case now,. Second time in a week Dealership did have a full case for me.

Few tips:
Pre-prime master with brake fluid. By just adding a can of fluid, and work plunger until fluid flows out brake line ports.
During assembly, I clean and lightly oil pipe and threads of flare nuts. I than thread on each all the way by hand. Working hard line so I'am sure to seat flare of pipe squarely in port. I torque them each to 7ft=lbf, after master mounted completely.

Sometimes to get pedal to firm up during bleed is a pain. In those I use my hand vacuum pump, drawing fluid to each caliper/bleeder.

I always test time of booster charging 5 times, and check for leak before driving. Pedal must feel good and firm on every press. I then drive on dirt road and slam on brakes. I do this at least 3 times. I must hear ABS kick in.
 
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Well, I picked my new "kidney" from the dealer today, they ordered this from other dealer, and it took 3 days shipping to the local, but seems the plastic mounting foot is broken, no issue other than that, should I ask them for an exchange?

Screen Shot 2021-05-24 at 10.31.15 PM.png
 
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Well, I picked my new "kidney" from the dealer today, they ordered this from other dealer, and it took 3 days shipping to the local, but seems the plastic mounting foot is broken, no issue other than that, should I ask them for an exchange?

you can swap out that plastic cover from your old one... but it is a bit of a shame to have it damaged as much as it costs... perhaps you can get a few $$s back vs having the entire thing being sent back?
 
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you can swap out that plastic cover from your old one... but it is a bit of a shame to have it damaged as much as it costs... perhaps you can get a few $$s back vs having the entire thing being sent back?

I checked my truck, that leg actually not been used..I don't know if it supposed to not been used or my truck missing something before my ownership.

I a little concerned if there is anything inside this box is damaged during that "breaking leg hitting" and I hesitant to return it because I am not sure how good the next one will be...

Screen Shot 2021-05-24 at 10.52.57 PM.png
 
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I checked my truck, that leg actually not been used..I don't know if it supposed to not been used or my truck missing something before my ownership.

I a little concerned if there is anything inside this box is damaged during that "breaking leg hitting" and I hesitant to return it because I am not sure how good the next one will be...

Inside the cover is pretty robust... probably unlikely anything is broken. If that clip hole isn't used, I'd put the part in and not think twice.
 
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I returned it back for exchange...let's see next...well for this price, I will forgive my little obsessive-compulsive disorder~
 
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Yes a pause is normal. I hear 1, 2 or 3 pauses, most times. But it's very brief, usually a second or less. So we do not stop timing during pause. It's the total time we need to know. I misunderstood, thinking you were getting longer pauses. Over 40 seconds total with good voltage to pump motor, indicates a pressure problem. Air in system after bleeding or leak most are common reasons.

30 to 35 pumps is wide spread. Cold we get higher number of pumps. Each time we repeat, it warms seals. But I typically I only see ~2 to 3 pump spread. I'd not be overly concerned with spread. Only note as -1 in overall rating.

I assume you've good skills and followed FSM steps. Replacements of master assembly w/booster not a big deal. But for most shade tree mechanics it best they don't touch, not even flush or bleed brakes. For that mater most shops. I say that because I do so much corrective work, due to some shop touching any part on our 100 series.

BTW: I've use only Toyota Brake fluid these days. Out of fear any other may damage seals. Most Toyota/Lexus dealership do not use it, they use bulk. But the number of masters being replace in all Toyota/Lexus, is staggering.
I got a weird thing yesterday, it is a pretty hot day yesterday, about 104f. I drive my truck about 1 hr for shopping around, then I think I accidentally hit the center diff lock button when I left Walmart, then I got "center diff", "VSC off", "VSC track" light on after about 5 mins driving, those lights went off after I restart the truck engine when I back to home. I hooked the code reader and I got code "C1340 opn ckt in ctr diff lck signal ".

Then I did a master cylinder pump timing test twice right after this, it only takes 30 to 33 secs at this time... (which always take 50 seconds before). Any ideas, suggestions?

Thanks!
 
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CDL has nothing to do with booster time test.
Two thoughts:
1) Battery Voltage up do to driving.
2) Seal expand when they get hot.

Thanks, good points! so that CDL issue, accurately, it is "VSC trac on when CDL engaged", I am thinking, could it be a "Zero point calibration" issue?
Since I did so much parts replacement (steering rack, cv axles, control arm joint, rotors) and never did that. I just read from some posts and video, if we have that "Zero point calibration" issue, then the main symptom is "VSC trac" on after short driving...
 
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Hi, just saw some threads talked about adjusting the " padel push rod" on the master/booster assembly to enhance the brake, I am wondering that "do we need to adjust the brand new master/booster assembly before the installation"?

Or, to ask, will the new master/booster assembly come will a properly adjusted push rod?

Thanks.
 
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flintknapper

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Hi, just saw some threads talked about adjusting the " padel push rod" on the master/booster assembly to enhance the brake, I am wondering that "do we need to adjust the brand new master/booster assembly before the installation"?

Or, to ask, will the new master/booster assembly come will a properly adjusted push rod?

Thanks.

Its one of those things that you'll probably have to 'adjust' to suit you. Install it as it is.....drive it and see. IF it needs to be adjusted, just remove the hairpin clip and cross pin, move the clevis in or out (as needed) and try it out. Don't tighten the 'jam nut' so much that is it hard to loosen...in case you need to adjust the push rod.
 
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Order correct rebuild kit. Part number for 2000 US model w/ ATRAC is 04493-60330
[edit 6/2018 - this part number is correct for all US 100s. Checked with @beno and while online it will only be listed for 2003-2007, its correct for all US 100s.]

Kit is around $50, so a bunch cheaper than ~$1500 Master Cylinder Assembly. Rebuild will not fix everything, but for the price it is worth a shot. Brake fluid, think I used around 2 qts.
Would be a good idea to have FSM, since this is written assuming you have it.

Tools: 10mm flare wrench, 3/8" socket set w/ 12mm deep socket, long 3/8 extensions, 3/8 u-joint. Brake bleed kit, torque wrench, usual hand tools...
Photos are 2000 LC w/ ATRAC


Would be good at this point to pump pedal 40 times with key off. Will release pressure in high pressure accumulator and return some fluid to reservoir. Don't turn key back on until you have MC out or you will re-pressurize it.
Remove driver side lower dash, has a few layers, plastic skirt, sheet metal plate, plastic heater duct.
After removing dash components it should look like this photo. (green arrow shows one of the nuts for ABS ECU bracket)


View attachment 442106
Firstly, great knowledgeable post! Thanks!

Do I really have to remove all those internal panels to remove the 4 nuts on the mounting bolt? I just start to do this...don't know where to start and end, thanks!
 

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