Thanks for the information, I have thoroughly cleaned with the whole assembly, removed the plastic cover and re-torqued the six bolts and all the other screws/torx and filled the fluid reservoir. Will give it a few days to see if it still is leaking and post my findings.
Master Cylinder Rebuild - DIY (2 Viewers)
- Thread starter Skidoo
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Thanks for the excellent write up. Replaced the abs motor, put in the new piston, haven't bled it yet but it'snot working quite right.
The brake feels like it has very little pressure, and at full depression, the pedal gets stuck all the way in. II disconnected the clevis pin and it's definitely the piston that is getting stuck. I can't remember now if it was doing that before I put it back in the truck, but I feel like I need to fix the sticking piston before bleeding the brakes.
Had anyone else seen this?
The brake feels like it has very little pressure, and at full depression, the pedal gets stuck all the way in. II disconnected the clevis pin and it's definitely the piston that is getting stuck. I can't remember now if it was doing that before I put it back in the truck, but I feel like I need to fix the sticking piston before bleeding the brakes.
Had anyone else seen this?
First of all i would like to thank Skidoo for the excellent write up.
I followed the procedures exactly and had no issues removing the M/C and replacing the piston.
The reason I performed the piston replacement due to sticking pedal issues. I always had good pedal feel just a sticky pedal.
However, after replacing the piston my pump is no longer working and i have zero pedal pressure and the brake and ABS lights are on and the buzzer is going off. I know that the pump should run for 40 seconds to pressurize the system, however mine only runs for approx 3-5 seconds then cycles off and then about 10 seconds later it cycles on again for another 3-5 seconds. I never get any pedal pressure at all.
I know others in this thread have stated that it is a bad pump and have either replaced the pump or the entire master cylinder assembly with accumulator, pump, M/C, etc. My concern is that the pump was working fine until the piston replacement. Is there any electrical trouble shooting that can be performed, other than checking the fuses which all checked out fine?
I followed the procedures exactly and had no issues removing the M/C and replacing the piston.
The reason I performed the piston replacement due to sticking pedal issues. I always had good pedal feel just a sticky pedal.
However, after replacing the piston my pump is no longer working and i have zero pedal pressure and the brake and ABS lights are on and the buzzer is going off. I know that the pump should run for 40 seconds to pressurize the system, however mine only runs for approx 3-5 seconds then cycles off and then about 10 seconds later it cycles on again for another 3-5 seconds. I never get any pedal pressure at all.
I know others in this thread have stated that it is a bad pump and have either replaced the pump or the entire master cylinder assembly with accumulator, pump, M/C, etc. My concern is that the pump was working fine until the piston replacement. Is there any electrical trouble shooting that can be performed, other than checking the fuses which all checked out fine?
If it cycles on for 3-5 then off, then on again, it sounds like there's something telling the pump to turn off, like a sensor. Could be a pressure sensor that's getting tripped because there's air in the system.
Did you fill up the master cylinder assembly with brake fluid after performing the rebuild? Not just the reservoir, but the entire assembly. It's been a while since I did this job, but I remember having the reservoir off and filling up the entire assembly with brake fluid and pushing the master cylinder in and out by hand to move the fluid and air around. Since the system was open, the air just bled right out in the form of bubbles. I also did a brake bleed at each wheel after getting pressure in the system, just to get fresh fluid in there.
Did you fill up the master cylinder assembly with brake fluid after performing the rebuild? Not just the reservoir, but the entire assembly. It's been a while since I did this job, but I remember having the reservoir off and filling up the entire assembly with brake fluid and pushing the master cylinder in and out by hand to move the fluid and air around. Since the system was open, the air just bled right out in the form of bubbles. I also did a brake bleed at each wheel after getting pressure in the system, just to get fresh fluid in there.
I did not fill up the master cylinder after the rebuild. I can have the M/C out fairly quickly so I can try that tonight. Just remove the reservoir and pour fluid down the three holes and then work the piston by hand?
I plan on performing a full system brake bleed once i get some pressure.
I plan on performing a full system brake bleed once i get some pressure.
Yes sir, that's what i did. Since you have everything installed, I'd just pull the cap off the reservoir and start pumping the brake pedal (with the ignition off). It may take a while, but the assembly should build up pressure. Make sure there's always fluid in the reservoir so you don't pump air into the assembly. You may have to pull the brake pedal off the floor, since there is currently no pressure. Pull it and push a few times to see if you can build up pressure.
If you can't get pressure, check for any fluid leaks by where the piston connects to the pedal. When i first did this, I couldn't build up pressure and noticed fluid leaking in this area. Root cause: I had one of the piston seals in the wrong direction. These seals came separate from the piston and had to be installed on the piston. I didn't realize they were directional, and I put it on backwards. Had to disassemble and flip the seal.
If you can't get pressure, check for any fluid leaks by where the piston connects to the pedal. When i first did this, I couldn't build up pressure and noticed fluid leaking in this area. Root cause: I had one of the piston seals in the wrong direction. These seals came separate from the piston and had to be installed on the piston. I didn't realize they were directional, and I put it on backwards. Had to disassemble and flip the seal.
2001LC
SILVER Star
Make sure all flare nuts seated squarely (not cross threaded) and torqued to spec.
Did you remove or disturbed the red & blue wires connecting ABS to booster motor?
Where those wire (red & blue) ends clean and shiny or corroded?
Are all WIRE BLOCKS firmly attached including under dash near pedel?
Is your battery fully charged?
Zero pedal pressure mean pedal goes to the floor?
You can jump the booster motor. It's first done at wires block going into ABS (ABS test), then done at pump (direct pump test). But if pump coming on and was working, it's probably ok. There's many test that FSM has for; pressure switch, ABS, motor, pump, etc. But before going this route double check everything and the try this.
After double checking everything: Make sure all bleeders closed. Repeatedly pull pedal out by hand and press in (to floor) with key on. Keep key on and look very closely for leaks at boot, flare nuts and from under reservoir.
Then try opening a rear caliper bleeder with key on pedal held firmly to the floor. See if you can get fluid/air to run out bleeder.
It may just be switch coming on and off due to zero fluid/pressure on it. Gravity, moving pedal in and out and bleeding off some air may correct your issue.
Did you remove or disturbed the red & blue wires connecting ABS to booster motor?
Where those wire (red & blue) ends clean and shiny or corroded?
Are all WIRE BLOCKS firmly attached including under dash near pedel?
Is your battery fully charged?
Zero pedal pressure mean pedal goes to the floor?
You can jump the booster motor. It's first done at wires block going into ABS (ABS test), then done at pump (direct pump test). But if pump coming on and was working, it's probably ok. There's many test that FSM has for; pressure switch, ABS, motor, pump, etc. But before going this route double check everything and the try this.
After double checking everything: Make sure all bleeders closed. Repeatedly pull pedal out by hand and press in (to floor) with key on. Keep key on and look very closely for leaks at boot, flare nuts and from under reservoir.
Then try opening a rear caliper bleeder with key on pedal held firmly to the floor. See if you can get fluid/air to run out bleeder.
It may just be switch coming on and off due to zero fluid/pressure on it. Gravity, moving pedal in and out and bleeding off some air may correct your issue.
I will try the cap off and pump method tonight.
All flare nuts were able to be 95% threaded by hand so I do not think i have any issues there.
I did notice that the red and blue wires inside the rubber housing were somewhat corroded (like a bad battery terminal). I did not remove or mess with those connections other than visual inspection.
Not sure what wire blocks you are referring to?
Battery is fully charged
Yes, zero pedal pressure means pedal to the floor. It does rebound but there is no pressure when stepping on the pedal.
I will follow your suggested procedure tonight and see if i can build up some pressure.
Thank you and Elliot for your help and suggestions. I was getting pretty frustrated yesterday when i get it all put back together and then felt like i might have messed up the system way worse than it was before.
All flare nuts were able to be 95% threaded by hand so I do not think i have any issues there.
I did notice that the red and blue wires inside the rubber housing were somewhat corroded (like a bad battery terminal). I did not remove or mess with those connections other than visual inspection.
Not sure what wire blocks you are referring to?
Battery is fully charged
Yes, zero pedal pressure means pedal to the floor. It does rebound but there is no pressure when stepping on the pedal.
I will follow your suggested procedure tonight and see if i can build up some pressure.
Thank you and Elliot for your help and suggestions. I was getting pretty frustrated yesterday when i get it all put back together and then felt like i might have messed up the system way worse than it was before.
2001LC
SILVER Star
All the wire blocks connect to master.
I'd don't leave cap off for to long, mouture becomes a concern also affects pressure in reservoir.
I'd don't leave cap off for to long, mouture becomes a concern also affects pressure in reservoir.
All four of the connections to the M/C are all reconnected. I did not remove any from under the dash, but i will ensure that they are all connected tightly. Did not think to check under there.
Good point about the cap on the reservoir, i have not had it off since refilling with fresh fluid so hopefully just long enough to get pressure will not result in too much moisture.
Thanks again
Good point about the cap on the reservoir, i have not had it off since refilling with fresh fluid so hopefully just long enough to get pressure will not result in too much moisture.
Thanks again
2001LC
SILVER Star
I'd Keep cap on while pumping pedal with pump on. Cap off may help when just sitting full of fluid and letting gravity trickle fluid down into master. (Edited) But that expose brake fluid to air (moisture), so don't do for long.
Last edited:
Thank you again 2001LC and Eliot. I was able to gradually get some pedal pressure back with just constant pumping. I then bled the rear passenger side brakes and when i finished that wheel, the pump kicked on and stayed on long enough to pressurize the system. Immediately the alarm, ABS, and Brake lights went out. I was then able to repeatedly bleed the brakes to remove the old fluid and remaining air. Took it to a wet field to activate the ABS and it worked like a charm. So thankful that you both were able to help.
Last edited:
2001LC
SILVER Star
You rebuild master "due to sticking pedal issues" did this totally clear that up?
BTW: FSM states to test system: Pump pedal 40 time key off. Then; Turn key on and time booster pump run time, spec is 30 to 40 seconds. If not to spec: Pump pedal 20 times key on. Then bleed starting at front followed by rears with key on pump several times on each bleed of fronts, just hold pedal down for each rear (no need to pump for rears). I do this (starting at front) for a finally bleed, after a full flush. I'll drive on dirt road stomping on brake 5 or 6 times to activate ABS, before and after final bleed.
Side note: Because bleeder and inlet line at top caliper, fluid doesn't move out of caliper as we like to see unless forced to.
If you really want to flush as much dirty (mosture) old fluid out as possible. You can compress brake pads/pistons into caliper with corresponding bleeder open, to push/force fluid out of calipers.
BTW: FSM states to test system: Pump pedal 40 time key off. Then; Turn key on and time booster pump run time, spec is 30 to 40 seconds. If not to spec: Pump pedal 20 times key on. Then bleed starting at front followed by rears with key on pump several times on each bleed of fronts, just hold pedal down for each rear (no need to pump for rears). I do this (starting at front) for a finally bleed, after a full flush. I'll drive on dirt road stomping on brake 5 or 6 times to activate ABS, before and after final bleed.
Side note: Because bleeder and inlet line at top caliper, fluid doesn't move out of caliper as we like to see unless forced to.
If you really want to flush as much dirty (mosture) old fluid out as possible. You can compress brake pads/pistons into caliper with corresponding bleeder open, to push/force fluid out of calipers.
Last edited:
Yes, the rebuild completely cleared up the sticking pedal issue.
I had to manually pressurize the system (via pedal pumping with key off) and bleed the rear passenger brake. Once this was done there was enough pressure in the system for the electric pump to run a full cycle instead of the intermittent 3-5 second cycling that was occurring prior.
I did follow the 40 pump/20 pump procedure after the electric pump began working properly. I also went into a wet field and activated the ABS a number of times in the midst of the numerous bleeds.
Good point about old fluid retained in the caliper. I will probably do another bleed after driving around some today and tonight. Would love to get as much of the old green coffee looking fluid out of the system.
I had to manually pressurize the system (via pedal pumping with key off) and bleed the rear passenger brake. Once this was done there was enough pressure in the system for the electric pump to run a full cycle instead of the intermittent 3-5 second cycling that was occurring prior.
I did follow the 40 pump/20 pump procedure after the electric pump began working properly. I also went into a wet field and activated the ABS a number of times in the midst of the numerous bleeds.
Good point about old fluid retained in the caliper. I will probably do another bleed after driving around some today and tonight. Would love to get as much of the old green coffee looking fluid out of the system.
2001LC
SILVER Star
Good job!
Interesting you said "green". I found this before on older rigs and only after factory fluid remove and a second flush years later of aftermark fluid. I now have found the 98-02 have copper washer/gaskets and copper coated union bolt. Copper reacts with moisture!
Interesting you said "green". I found this before on older rigs and only after factory fluid remove and a second flush years later of aftermark fluid. I now have found the 98-02 have copper washer/gaskets and copper coated union bolt. Copper reacts with moisture!
Well my 1999 with 180K miles fits perfectly with your findings.
My problem of leaking fluid turns out to be one the 3 rubbers on the mc resoviour .
When the weather warms up it does not leak but anything near freezing and it drips away .
Meantime I have a brake fluid puddle and top it from time to time .
Does any body know where to buy these ?
Or is there away to revitalise the rubbers?
When the weather warms up it does not leak but anything near freezing and it drips away .
Meantime I have a brake fluid puddle and top it from time to time .
Does any body know where to buy these ?
Or is there away to revitalise the rubbers?
2001LC
SILVER Star
Any Toyota or lexus parts department. About $2 ea. Call ahead to order in.
Just wanted to see if anyone was interested; I got frustrated about a month ago when the grinding noise came back after 3 months of rebuilding the ABS motor and decided to buy a used complete unit online. Not sure if that was the best idea, but it’s installed and working. If anyone is interested in my old one, which didn’t show any signs of being soft, and has the rebuilt ABS motor on it, let me know with a PM and I’ll send pics. I would like to get $500 out of it, which is about what I have into the core charge PLUS the motor rebuild. I’m pretty sure the problem I was having as with the Acccumulator, but not 100%. I just got frustrated and didn’t want to mess with it anymore.
Anyone ever have any issues removing the hard brake lines from the master cylinder/abs assembly?
I have done this 3 times now so you would think I am a pro, but the head of one of them actually started to strip a little and it scared me. The other 2 came out fine.
I hit it with a penetrating lube and it still didnt want to budge, so I am leaving it overnight.
I have done this 3 times now so you would think I am a pro, but the head of one of them actually started to strip a little and it scared me. The other 2 came out fine.
I hit it with a penetrating lube and it still didnt want to budge, so I am leaving it overnight.
