Master Cylinder Rebuild - DIY (8 Viewers)

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Yes pump can leak. #1 reason it leaks, is due to air vent at bottom of pump getting clogged. Than as motor spins, it creates a vacuum in motor housing and sucks fluid from pump. The seal in the back of pump is not a pressure seal. This seal in back of pump, can also leak/weep on it's own. Seal just leaking on it's own is not all that common, but does happen. Toyota put a canal from seal to daylight (bottom of pump). I presume this canal is to allow minor seepage to just drip out, rather than pool and get into motor damaging it.

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@2001LC

As always, thank you for your informative post, that is very helpful. Do you have any insight into how much fluid would leak from there, if that were to be my situation? Also, do you have any other guesses as to what could possibly be causing my leak, given what I have already replaced (or anything else I could replace to try to solve the issue)?

I know its very hard to assess a vehicles issues from 1000 miles away, but anything helps at this point!
 
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@2001LC

As always, thank you for your informative post, that is very helpful. Do you have any insight into how much fluid would leak from there, if that were to be my situation? Also, do you have any other guesses as to what could possibly be causing my leak, given what I have already replaced (or anything else I could replace to try to solve the issue)?

I know its very hard to assess a vehicles issues from 1000 miles away, but anything helps at this point!
How much could be leaking, you tell me! It is a weep hole (pump drain) to keep small amounts from puddling and getting into motor. But if seal bad it could be a constant drip. If this the case, it's very likely pump bearing has or is going bad. Cruddy brake fluid may have something to do with damage to bearing. Was fluid dark and reservoir stain before all this. Clues!

After cleaning. Take a mirror and look if fluid coming from pump weep "drain".

Was vent clogged, which then sucks out brake fluid of pump. Since you replaced the motor, I'd assume you checked the vent. Did pump come with motor.

You now know the reason, most Dealerships and INDY shops will only replace the whole Brake master w/booster assy. We fix one issue and another crops up!
 
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How much could be leaking, you tell me! It is a weep hole (pump drain) to keep small amounts from puddling and getting into motor. But if seal bad it could be a constant drip. If this the case, it's very likely pump bearing has or is going bad. Cruddy brake fluid may have something to do with damage to bearing. Was fluid dark and reservoir stain before all this. Clues!

After cleaning. Take a mirror and look if fluid coming from pump weep "drain".

Was vent clogged, which then sucks out brake fluid of pump. Since you replaced the motor, I'd assume you checked the vent. Did pump come with motor.

You now know the reason, most Dealerships and INDY shops will only replace the whole Brake master w/booster assy. We fix one issue and another crops up!

My buddy has a shop and he still only wants to deal with this if he can replace the whole booster assembly LOL!

I did test it with a mirror, there were drips but it was very hard to tell from where. It leaks a good amount, I have to top off the fluid every 50-80 miles and you can visibly see it drip after driving (sometimes, doesnt happen every time which I find weird).

Sounds like I might have gotten a bad pump when it was rebuilt. I went for a rebuild from an ebay seller, if I remember correctly people on this forum had used him, but maybe I should DIY it or look for another source.

I will have to investigate more - as you know its next to impossible to see things under there, lol, and I wanted to do my best to have this thing partially figured out before I took the damn booster assembly out again. Out of curiosity, are there any other ancillary o-rings that could cause a leak such as I am experiencing? I'd like to replace them as well.
 
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My buddy has a shop and he still only wants to deal with this if he can replace the whole booster assembly LOL!

I did test it with a mirror, there were drips but it was very hard to tell from where. It leaks a good amount, I have to top off the fluid every 50-80 miles and you can visibly see it drip after driving (sometimes, doesnt happen every time which I find weird).

Sounds like I might have gotten a bad pump when it was rebuilt. I went for a rebuild from an ebay seller, if I remember correctly people on this forum had used him, but maybe I should DIY it or look for another source.

I will have to investigate more - as you know its next to impossible to see things under there, lol, and I wanted to do my best to have this thing partially figured out before I took the damn booster assembly out again. Out of curiosity, are there any other ancillary o-rings that could cause a leak such as I am experiencing? I'd like to replace them as well.
That is a very bad leak, and wired! But use would have more to do with leak than miles. Clean spotless, than have friend press brake pedal with key on, as you look with a mirror. Or setup your smart phone video under the master. You can place phone on a towel under master. to get a good shot. Just try and place at point it will not get brake fluid on it. With good lighting you may get lucky.

So you bough a motor with pump off ebay. I had client bring me one from and ebay seller not long ago. Upon inspection, to make sure motor commutator and brushes good. I found the pump leaking and Styrofoam packing in vent and drain of pump/motor, which was plugging/stopping leak. I had also notice excessive brake fluid in box/bag it came in. We sent it back.

If no leak before install of used pump/motor. It's either a bad pump or bad install.

Yes, leak can be from:
Pump seal.
Accumulator O-ring.
Actuator Hose, (comes from reservoir to pump).
Actuator tube (High pressure hard line (red))
Grommets under res.
Cracked reservoir.
Pressure sensor seal on 00-07
Where ABS unit bolt to master.
Brake master assembly FSM.JPG
 
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Hoping the brake booster experts here can shed some light on the issue I'm having... There's a periodic chugging/cycling noise coming from the brake booster/accumulator/reservoir area that happens constantly when the ignition is turned to ON or the vehicle is running. Brakes work fine and there are no warning lights, but the vibration from the pump/motor can be felt through the pedal. At this point, I've tried flushing and bleeding the fluid using Techstream and I've rebuilt the master cylinder, but it still sounds the same. I think my next option is to buy a new accumulator/motor assembly but want to see if anyone knows what's going on here or if that will help solve it.

Here's the video of the sound:

 

flintknapper

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Hoping the brake booster experts here can shed some light on the issue I'm having... There's a periodic chugging/cycling noise coming from the brake booster/accumulator/reservoir area that happens constantly when the ignition is turned to ON or the vehicle is running. Brakes work fine and there are no warning lights, but the vibration from the pump/motor can be felt through the pedal. At this point, I've tried flushing and bleeding the fluid using Techstream and I've rebuilt the master cylinder, but it still sounds the same. I think my next option is to buy a new accumulator/motor assembly but want to see if anyone knows what's going on here or if that will help solve it.

Here's the video of the sound:



That's what mine did before it started not coming on AT ALL. I could tap the motor and it would run just a bit, then it just died altogether.
 
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That's what mine did before it started not coming on AT ALL. I could tap the motor and it would run just a bit, then it just died altogether.
Did you end up replacing just the motor, or the motor and accumulator, or the whole master cylinder assembly as well?
 

flintknapper

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Did you end up replacing just the motor, or the motor and accumulator, or the whole master cylinder assembly as well?

Motor and accumulator. Also rebuilt the Master Cylinder while I had it all out.

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flintknapper

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Thanks flintknapper - fairly certain the motor/accumulator is my next step. Where did you get yours and what did you pay? Looks new OEM.

I got mine from McGeorge Toyota. Got it in about 4 days. It was right about $800.00 (shipped). Be sure to rebuild your Master Cylinder while you have the whole thing out. Kit is about $80.00 and is just a piston and cup and some seals. Also look to see if the grommets between the brake fluid reservoir are leaking. Good time to replace them too (very easy).

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I got mine from McGeorge Toyota. Got it in about 4 days. It was right about $800.00 (shipped). Be sure to rebuild your Master Cylinder while you have the whole thing out. Kit is about $80.00 and is just a piston and cup and some seals. Also look to see if the grommets between the brake fluid reservoir are leaking. Good time to replace them too (very easy).

Thanks for those grommet part numbers. I already did the master cylinder rebuild so I should be good to go there.

Has anyone had luck finding a reman'd part?
 

uHu

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I'm guessing the commutator bar has to be pulled off and pressed back on. Could be very difficult to do for a home-gamer. I'm not seeing an obvious keyway on the armature shaft or in the image of the replacement commutator.
You may have a point there - I'm not seeing an easy way of getting them on and off.

My motor doesn't look great, but it also doesn't appear to be the cause of my issues. The brushes and commutator still have some life left, though one of the bearings is nearing its end. I'm thinking a likely culprit of the constant cycling is the o-ring at the accumulator. I will probably end up replacing the motor anyway but will go with an already-refurbished unit.

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Sorry for taking this thread in perhaps an odd direction, but I've been working on adapting this MC/Booster to a Tacoma. Does anyone know if it's possible to completely eliminate the ABS control module? My application doesn't require ABS... and frankly, I need the room (i.e. the control model hits my coil over mount).. And I'm also just curious if I can make this work for my application.
 
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I don't think you'll go into limp mode. But you'll likely get dash lights and possibly alarm.

Unplug wires from ABS unit on brake master and CPU near brake pedal and see what happens :hmm:
 
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I don't think you'll go into limp mode. But you'll likely get dash lights and possibly alarm.

Unplug wires from ABS unit on brake master and CPU near brake pedal and see what happens :hmm:
that won't work. I physically cannot install the unit w/ the ABS control module attached. So i need to find a way to convert the MC to non-ABS. But looking at the hydraulic diagrams, I'm not sure it can be done??
 

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