You can try adjusting the Ubolt that connects to the pedal, loosen the 14mm nut behind it then spin the ubolt counter clockwise to lengthen it, this would give the piston a head start.
Master Cylinder Rebuild - DIY (1 Viewer)
- Thread starter Skidoo
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
@2001LC Helped me R&R on the MC a couple months back. We couldn't see any issues with the taken out MC, but it has now been two months and replacing that piece has completely eliminated the issue.
2001LC
SILVER Star
Just cylinder kit.
I use Valvoline DOT 3 or 4. Not totally sold on it, but they're basically all the same. The best may be Toyota. But that's very pricey and not same formula that ship in system from factory.
If rubber bleeder caps are bad or missing, get 4 of those.
One thing I've just started doing is: If I see corrosion on brake control wire. I'll replace it and the 4 nuts and screws that hold in. I believe corrosion is from the all to often overfilling brake reservoir. That the wire builds excessive resistance and causes the copper of commutator of booster motor to wear prematurely.
I use Valvoline DOT 3 or 4. Not totally sold on it, but they're basically all the same. The best may be Toyota. But that's very pricey and not same formula that ship in system from factory.
If rubber bleeder caps are bad or missing, get 4 of those.
One thing I've just started doing is: If I see corrosion on brake control wire. I'll replace it and the 4 nuts and screws that hold in. I believe corrosion is from the all to often overfilling brake reservoir. That the wire builds excessive resistance and causes the copper of commutator of booster motor to wear prematurely.
Last edited:
I did the MC rebuild due to double pumping the brakes (no CEL codes) and they worked well for awhile. Then I started to get the ABS Brake light again and the pedal went soft. I thought maybe I hadn't bled the brakes well enough. I timed the booster motor and was getting intervals all over the place with it turning on and off in like 4 and 5 sec intervals. I read that could be air in the system triggering the sensor to shut off. It would still pressurize the brakes sometimes but not all the time. So I bled the brakes again and now the motor is not kicking on at all and the brakes will not pressurize. Do I need a new motor or new motor and accumulator?
2001LC
SILVER Star
I'd test booster motor next. By jumping with your 12V car battery. Be advised that sometimes motor brushes land on bad spots on commutator, other times on good spots. This makes motor seem bad than good (doesn't work than does work).
I read through the thread but would like some help figuring out if I am a candidate for MC rebuild.
Few years ago, I used to get squealing/scraping noise from the MC/ABS unit that turned into everything lit and buzzer going. Had the Booster pump replaced, calipers cleaned out and system bled - fixed the issue for about three years.
Fast forward to couple months ago, about 20k miles later, the pedal started going soft, but only sometimes, when I stopped at a light. The pedal would sink slowly while the pump comes on. But otherwise, no problem in braking. Took it to a local shop - they replaced ABS sensors on the theory that bad sensors can cause the ABS to act up but they did not do a flush/bleed. The soft pedal went away for couple of weeks but returned again and this time, the ABS/VSC lights are on. No buzzer and truck brakes just fine. When I start the truck, the dash is normal but drive a few feet and the ABS/VSC lights come on. I can hear the pump kick in like always - no funny squealing/scraping noise.
Will appreciate any pointers on where to look next. Thanks.
Few years ago, I used to get squealing/scraping noise from the MC/ABS unit that turned into everything lit and buzzer going. Had the Booster pump replaced, calipers cleaned out and system bled - fixed the issue for about three years.
Fast forward to couple months ago, about 20k miles later, the pedal started going soft, but only sometimes, when I stopped at a light. The pedal would sink slowly while the pump comes on. But otherwise, no problem in braking. Took it to a local shop - they replaced ABS sensors on the theory that bad sensors can cause the ABS to act up but they did not do a flush/bleed. The soft pedal went away for couple of weeks but returned again and this time, the ABS/VSC lights are on. No buzzer and truck brakes just fine. When I start the truck, the dash is normal but drive a few feet and the ABS/VSC lights come on. I can hear the pump kick in like always - no funny squealing/scraping noise.
Will appreciate any pointers on where to look next. Thanks.
2001LC
SILVER Star
What year how many miles?
Check for codes?
Sound like a leak, or bad fluid (moisture). If fluid good and level not dropping, then "maybe" master cylinder seal leaks and needs rebuilding.
Whats is and ABS sensor? Are you talking about a wheel speed sensor, pressure sensor or what?
Was booster pump (did you mean booster motor?) new OEM, rebuilt or used back 20K ago? ?
Was anything else replaced with it? Like booster motor, pump, accumulator, control wire.
Posting picture of invoice may be helpful.
Check you brake fluid level, and note the level. Don't just add fluid. Read embossed instruction on the brake fluid reservoir on how to check level. It will set you up for booster motor run time test.
Once done, before putting IG key in. Get out stop watch for next test.
Put IG key in and turn to on. Time how long the booster motors runs, to fill accumulator bring pressure back up. Hood should be open and don't start the engine. That way you can easily hear the booster motor run and stop. It may pause momentarily a few time before stopping. Was time within 30 to 40 seconds? Good idea to re-time, two or three times.
Check for leaks right after active hard braking. Check entire brake system end to end. Key points being around master and at each wheels brake caliper and all brake lines and flare nut fittings..
Check for codes?
Sound like a leak, or bad fluid (moisture). If fluid good and level not dropping, then "maybe" master cylinder seal leaks and needs rebuilding.
Whats is and ABS sensor? Are you talking about a wheel speed sensor, pressure sensor or what?
Was booster pump (did you mean booster motor?) new OEM, rebuilt or used back 20K ago? ?
Was anything else replaced with it? Like booster motor, pump, accumulator, control wire.
Posting picture of invoice may be helpful.
Check you brake fluid level, and note the level. Don't just add fluid. Read embossed instruction on the brake fluid reservoir on how to check level. It will set you up for booster motor run time test.
Once done, before putting IG key in. Get out stop watch for next test.
Put IG key in and turn to on. Time how long the booster motors runs, to fill accumulator bring pressure back up. Hood should be open and don't start the engine. That way you can easily hear the booster motor run and stop. It may pause momentarily a few time before stopping. Was time within 30 to 40 seconds? Good idea to re-time, two or three times.
Check for leaks right after active hard braking. Check entire brake system end to end. Key points being around master and at each wheels brake caliper and all brake lines and flare nut fittings..
Year: 2000, Miles: 211,000. No codes on the OBD2 reader and I don't have access to a ABS/MC reader (yet).
I haven't seen any fluid drip down on the street/driveway but haven't very closely looked underneath or under the hood.
Sorry - I believe it is sold as "ABS Speed sensor"
Yes, the booster motor, rebuilt. AFAIK, nothing else was replaced. Didn't get an invoice. There is a guy in Sacramento who drives around (all the way up to the SF Bay Area) and will replace the motor with a rebuilt one, in your driveway.
So if the motor runs 30-40 seconds each time, does that mean the motor isn't the issue most likely? Off the top of my head, 30-40 seconds is about how long the motor runs each time I turn the IG key (before starting the engine). That said, I haven't run tests of trying to activate the booster motor, over and over.
Thanks for all the pointers, I guess I have some homework for the long weekend
2001LC
SILVER Star
They all will momentarily stop a few times while doing test. Doesn't hurt to do test three times in a row.
FWIW - I test in under 40 secs.
My brake master assembly is pissing fluid at this point, all in inside the engine compartment. Its bad. The reservoir is definitely not overfilled.
I've been fighting with this thing on and off for almost 18 months now. Master Cylinder and pump motor have been replaced.
I think the next step is replacing every seal I can get to in this thing. Anyone have a list of every seal we can replace?
Edit:
Ordered these from a post that @BigZPatt made a few months ago. I looked at a bunch of diagrams and couldn't find anything else that applied. Also bought a new cap, just in case. Will update the thread with my results.
Grommet / Seal part #'s:
4725516010 2qty
3141735010 1qty
Last edited:
2001LC
SILVER Star
With booster motor stopping under 40 sec, indicates leak not on pressure side. My best guess would be the grommets or a cracked reservoir.
When master and pump replace. If the old reservoir and grommets used. Chance grommet were mixed up.
When master and pump replace. If the old reservoir and grommets used. Chance grommet were mixed up.
(Posted this to the stickied brake failure thread but didn't get a response)
So it finally happened to me - 03 LX, 289k miles, ABS, VSC/TRAC lights on, alarm blaring, and brake pedal went to the floor. Luckily I was in my driveway so I just used the e-brake to maneuver it out of the way of my other car. I had just taken it on a 400 mile round trip with zero issues, went to get in it the next day, and as soon as it turned on, the alarm sounded. Fluid level in the reservoir is fine, no leaks at the lines or calipers, brake fluid is about a year and a half old. I pulled these codes:
C1256 - Accumulator Low Pressure
C1223 - ABS Control System Malfunction
I'm not sure whether the ABS pump is bad or if the master cylinder needs a rebuild? The truck is for sale, so I want to make sure this gets fixed correctly so her next owner doesn't run into this again.
So it finally happened to me - 03 LX, 289k miles, ABS, VSC/TRAC lights on, alarm blaring, and brake pedal went to the floor. Luckily I was in my driveway so I just used the e-brake to maneuver it out of the way of my other car. I had just taken it on a 400 mile round trip with zero issues, went to get in it the next day, and as soon as it turned on, the alarm sounded. Fluid level in the reservoir is fine, no leaks at the lines or calipers, brake fluid is about a year and a half old. I pulled these codes:
C1256 - Accumulator Low Pressure
C1223 - ABS Control System Malfunction
I'm not sure whether the ABS pump is bad or if the master cylinder needs a rebuild? The truck is for sale, so I want to make sure this gets fixed correctly so her next owner doesn't run into this again.
2001LC
SILVER Star
First thing I'd do, is check booster motor. The FSM has a procedure outlined for this. If you're planning on diagnosing and repair yourself?
I think I found that section of the FSM, but it only explains how to check the booster motor using a Toyota SST. Any ideas how to check it without it?
- Thread starter
- #318
Doubt a master cylinder rebuild will address those codes.
Have you double checked wiring and that connectors are clean and well seated?
Have you double checked wiring and that connectors are clean and well seated?
2001LC
SILVER Star
No Toyota SST needed.
First evacuate accumulator (IG key off, pump pedal 40 times). Then, Turn on IG key to ON (do not start engine) booster motor should run. If not move to jumping with 12Volt battery.
You'll see a way to jump pump from 12Volt battery. It will show you which wire lead gets positive and which negative in wire block on ABS unit (black unit on side of master). This passes current through ABS, through wires attached to bottom, into motor.
If it does not start motor from first point (wire block on ABS), than you'll jump directly onto wires at motor. Again FSM show which is + which -.
It is possible to jump at each point (ABS wire block, Wires at bottom of ABS unit and wires where they attach to motor) with care before any disassemble.
Look at wire end to see if wires and screws are corroded. By just peeling back boots at each end. If so commutator of motor is likely worn out.
Note: Motor can have a dead spot(s) on commutator. This gets tricky. As test by jump 12V to it, may start motor one time and then not another as brush land on dead spot or not. So you may get motor to start every time just by chance.
Note: FSM states brake control wire, nuts and screws are non replaceable. This wire is a resistance wire and very pricey.
First evacuate accumulator (IG key off, pump pedal 40 times). Then, Turn on IG key to ON (do not start engine) booster motor should run. If not move to jumping with 12Volt battery.
You'll see a way to jump pump from 12Volt battery. It will show you which wire lead gets positive and which negative in wire block on ABS unit (black unit on side of master). This passes current through ABS, through wires attached to bottom, into motor.
If it does not start motor from first point (wire block on ABS), than you'll jump directly onto wires at motor. Again FSM show which is + which -.
It is possible to jump at each point (ABS wire block, Wires at bottom of ABS unit and wires where they attach to motor) with care before any disassemble.
Look at wire end to see if wires and screws are corroded. By just peeling back boots at each end. If so commutator of motor is likely worn out.
Note: Motor can have a dead spot(s) on commutator. This gets tricky. As test by jump 12V to it, may start motor one time and then not another as brush land on dead spot or not. So you may get motor to start every time just by chance.
Note: FSM states brake control wire, nuts and screws are non replaceable. This wire is a resistance wire and very pricey.
Year: 2000, Miles: 211,000. No codes on the OBD2 reader and I don't have access to a ABS/MC reader (yet).
I haven't seen any fluid drip down on the street/driveway but haven't very closely looked underneath or under the hood.
Sorry - I believe it is sold as "ABS Speed sensor"
Yes, the booster motor, rebuilt. AFAIK, nothing else was replaced. Didn't get an invoice. There is a guy in Sacramento who drives around (all the way up to the SF Bay Area) and will replace the motor with a rebuilt one, in your driveway.
So if the motor runs 30-40 seconds each time, does that mean the motor isn't the issue most likely? Off the top of my head, 30-40 seconds is about how long the motor runs each time I turn the IG key (before starting the engine). That said, I haven't run tests of trying to activate the booster motor, over and over.
Thanks for all the pointers, I guess I have some homework for the long weekend
My friend managed to find and hookup the ABS diagnostic computer to the truck. Looks like the ABS/VSC light-up is unrelated to the soft pedal issue. The ABS unit kept throwing the Front Left Speed Sensor malfunction code. We put the sensors in streaming mode, drove around and found that - the front left sensor would drop to zero mph when turning right. Going straight and turning left, it stays in sync with rest of the sensors. Been reading this post and the fact that the sensor doesn't drop to zero when turning left gives me hope that it isn't a wheel bearing issue but I guess I will find out tomorrow what's causing the sensor to malfunction when turning right.
Tomorrow, the shop that did the speed sensor replacement will diagnose and fix the issue with the front left speed sensor and maybe that makes the ABS/VSC circuitry happy and with that out of the way, we can focus on the MC.
