Master Cylinder Rebuild - DIY

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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)


mastercyl01_1.jpg
 
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Move emission charcoal canister to top of engine cover. By disconnecting two connectors, one hose on lower front (2nd photo) and one bolt, then sliding it up. Other hoses are long enough.

Disconnect all the connectors to master cylinder assembly (bottom photo).
mastercyl02_1.jpg
mastercyl03_1.jpg
mastercyl04_1.jpg
 
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Place rags or paper toweling under Master Cylinder Assembly to catch brake fluid when lines are disconnected.
Unclip brake lines from clip, need something to wedge open clip to get line out. I used an Allen wrench, but you might want to order a new clip just in case.

Disconnect brake lines (green arrows) from master cylinder, if you have ATRAC, will have 4 lines, otherwise 3 lines. Carefully pull them out of MC, and move slightly out of way, you DO NOT want to kink them.
Master Cylinder Assembly comes out by moving forward and towards fender (blue arrow). The red high pressure line will try to catch on disconnected brake lines, so keep an eye out to guide things.
mastercyl08_1.jpg
 
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From here on you do not want any dirt getting into MC assembly, if it gets in and jams the ABS valves, MC is toast. So make sure work area and outside of MC are clean. Some brake cleaners are not safe on rubber and plastic, do not use them.
Drain fluid out of brake fluid reservoir into a container. Remove brake fluid reservoir by removing 3 screws and pulling up. NOTE: There are two different sizes of grommets on reservoir so keep track of which ones go where. Clean inside with denatured alcohol, shake and dump, repeat if not clean. Dry and then pour in a cup or so of brake fluid, shake and dump. Reservoir in photo has been cleaned, before cleaning it had dark deposits in reservoir near grommets.
BTW, will have a half gallon or so of used brake fluid to recycle when done with rebuild.
mastercyl09_1.JPG
 
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You may want to make up bracket to hold master cylinder in a vise out of some slotted steel. (this photo taken later in disassembly)

Don't have a photo, remove clevis and nut from shaft, then remove rubber dust boot.
2nd photo shows the snap ring retaining MC Piston.
mastercyl11_1.JPG
mastercyl10_1.JPG
 
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The FSM, at this point, removes pump, accumulator and pressure switch from Master Cylinder Assembly. I did, but not sure if you need to.
Do this work over something to catch fluid.
To remove snap ring. Push in piston enough to clear snap ring, a deep socket and a few taps with hammer if it is sticking.
2nd photo shows hole used to push end of snap ring up so it can be pulled out. When reassembling position snap ring so end is just past hole.
mastercyl12_1.JPG
mastercyl13_1.JPG
 
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Put clevis back on and insert rod or screwdriver through clevis on shaft to pull out piston assembly. PULL STRAIGHT OUT, to not score bore. Expect more fluid to come out.
Remove clevis.
The rebuild kit is the parts you see here.
mastercyl14_1.JPG
 
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In the back of the master cylinder bore there is a spring and small piston (green arrow 1st photo), they do not come out. I used new brake fluid to clean inside of MC, it has ports into booster section and did not want to get cleaners in there.
Inspect the master cylinder bore, it must be clean with no corrosion. If is pitted or scored, a rebuild is not the answer, order the whole assembly.

Lubricate new parts with brake fluid to assemble. Hold MC assembly upright (bore facing up) to center as much as possible the spring and small piston fixed in bottom of bore. If the spring and small piston can not be centered, it may be damaged and require the entire master cylinder assembly. When inserting piston assembly rotating it can help it seat with small spring at bottom. Make sure it goes STRAIGHT IN, to not score MC bore.
mastercyl15_1.jpg
mastercyl16_1.JPG
 
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Included for your viewing pleasure is photo with cover plate off to show top of solenoid valves. Do not do this, not required for rebuild, I was just curious.
mastercyl17_1.JPG
 
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Assembly is reverse order.

I bled the brakes in this order.
With key off, Right front, then Left Front. This is to get fluid into MC.
With key on, Right rear, then Left rear.
With key on Right front, then Left front.
Don't be shy about bleeding, long run to rear.

Two options at this point.
1. Carefully drive it to dealer for full system bleed.
2. Do some braking that activates ABS, gravel road, etc, then bleed again, rears then fronts.

I did option 2 and it seemed to be working fine, but then chickened out and did option 1. ;)
 
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Awesome pics and writeup.

I don't own a 100 series but the master cylinder on my 01 4Runner is extremely similar, if it isn't the same exact one. :cheers:
 

e9999

You want to do what...?
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excellent detailed write up! way to go.
Good for FAQ.
 
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Considering the ABS system will costs $1700 with c dan discount it is worth trying to rebuild the mc your self if you dont trust your mechanic read the codes correctly.
 

bluecruiser

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great step by step...I am a 2:banana: mechanic at best and I was able to complete this exact job over a year ago...over 20k of miles since and still working well.

This was my alternative to entire replacement when I started getting spongy braking and a pedal that would not return. I also replaced all of the grommets...they looked fine but since I bought them, I did it.

nice work.
 
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Great write-up!

Skidoo - Was the problem with the old piston obvious ? Was the problem wear limited to the plastic seals ?

Maybe someone could post up the parts numbers for the rebuild kit. Are there different numbers for different years?
 
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No visible wear on seals. Then again my issue was brakes dragging, I have always had a good solid pedal. I think there are more seals and/or valves inside piston assembly that might be the issue for me, have not taken it apart to look. Most of the folks who have rebuilt, are addressing soft pedal, 2nd pump issue and sticking pedal. For those would expect to see wear on seals, if it is not worse case scenario of corrosion or scoring of bore. Reminder, flush that brake fuild every 5 years max.
Added part number I used to first post.
 
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