Master Cylinder Rebuild - DIY

[dwh13]

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.

That's a lot of great info, thanks! Seems a little beyond my skill level at first glance, but I'll give it a try. I'm guessing I'll end up buying a used MC assembly to swap in.

 

[2001LC]

Testing is easy. You just need FSM to show which point to touch with pos and which neg.

It's likely the motor, if motor dose not come on with IG key ON and brake pedal goes to the floor.

 

[dwh13]

Testing is easy. You just need FSM to show which point to touch with pos and which neg.

It's likely the motor, if motor dose not come on with IG key ON and brake pedal goes to the floor.

Got a page number in the FSM that shows where to hook up 12v too? I'm looking at the section starting on page BR-40 but not seeing where to connect it. I just went out and poked around it, I had some corrosion on the screws but nothing major. Pumped the brake pedal 40 times, turned IG to on, and no sound came from the MC assembly at all. Maybe just a brake booster rebuild or replace?

 

[2001LC]

Look in Diagnostics. Start at DI-416 also D-433. There is other place/pages, but this should get you into right area of FSM as a place to start reading.

To jumping directly on to motor while still in. I used some long bars (screw drives) insulated. By understanding which is positive and which negative before hand.

Fist thing is to look at wire under the boots.

 

[2001LC]

Are they corroded? If so 9 out of 10 time commutator of motor has dead spot. Motor and wires need replacing. Once motor pulled it can be disassemble to confirm.

 

[2001LC]

But be advised: FSM has brake control wire, screws and nuts as non reusable.

 

[dwh13]

But be advised: FSM has brake control wire, screws and nuts as non reusable.
View attachment 2080746

This is awesome, thank you! I just ordered a new brake booster.

 

[2001LC]

You mean the whole booster assembly new OEM. What did that cost?

 

[slangdog]

I have the same issue as @FxFormat but the screech only happens when it's been sitting outside overnight and temp has dropped a little. Very rarely happens again during the day (unless cold).

No leaks, no soft pedal. When the pump runs too long I do get ABS warning for a little bit. Auto-electrician rewound the motor which he said didn't look that bad.

I have a second unit from a rolled cruiser that failed. Any suggestions on parts to use on current one?

 

[SJWantsADiesel]

I have the same issue as @FxFormat but the screech only happens when it's been sitting outside overnight and temp has dropped a little. Very rarely happens again during the day (unless cold).

No leaks, no soft pedal. When the pump runs too long I do get ABS warning for a little bit. Auto-electrician rewound the motor which he said didn't look that bad.

I have a second unit from a rolled cruiser that failed. Any suggestions on parts to use on current one?

Mine started the same way, about 3 years ago. Would screech when cold but everything worked alright - braked good and had no soft pedal. One trip to Tahoe in the winter, I had the christmas tree dash - drove for a little bit and returned to normal. A flush/bleed later, it was happy for about a year. Then, recently, developed a soft pedal issue.

This past weekend, had the MC rebuilt with a new piston, new wheel speed sensors (turns out, weren't actually needed) and flush/bleed and everything seems good now. I can tell the difference between how the pump sounded before/after the MC rebuild.

 

[2001LC]

Mine started the same way, about 3 years ago. Would screech when cold but everything worked alright - braked good and had no soft pedal. One trip to Tahoe in the winter, I had the christmas tree dash - drove for a little bit and returned to normal. A flush/bleed later, it was happy for about a year. Then, recently, developed a soft pedal issue.

This past weekend, had the MC rebuilt with a new piston, new wheel speed sensors (turns out, weren't actually needed) and flush/bleed and everything seems good now. I can tell the difference between how the pump sounded before/after the MC rebuild.

Interesting.

I recommend rebuild master as a first step for this issue. It seems 50/50 if it fixes issue. If not, second step is R&R booster assembly.

 

[dwh13]

You mean the whole booster assembly new OEM. What did that cost?

Whoops, just saw this - I got a refurbished OEM unit for $380.

 

[2001LC]

NP, I appreciate you getting back to me.
But what was it that you replaced. The booster assembly which is three parts or just the booster motor?
Do you have the old part?.

 

[dwh13]

NP, I appreciate you getting back to me.
But what was it that you replaced. The booster assembly which is three parts or just the booster motor?
Do you have the old part?.

I'm replacing the whole booster assembly - it should come in today and will be swapped out tomorrow. I'll have an old part if anyone wants to dissect or rebuild it!

 

[SJWantsADiesel]

Interesting.

I recommend rebuild master as a first step for this issue. It seems 50/50 if it fixes issue. If not, second step is R&R booster assembly.

Sorry, forgot to mention - at some point in the beginning, I had the pump motor replaced but when the existing/old motor was taken out, it didn't look like it needed replacement. And, recently, when doing the MC rebuild, my friend checked the motor and aside from rust flowers on the terminals, everything else seemed good with the motor.

 

[2001LC]

I'm replacing the whole booster assembly - it should come in today and will be swapped out tomorrow. I'll have an old part if anyone wants to dissect or rebuild it!

I'm am interest in all old brake master parts. I've been dissecting looking for cause and clues in how we can inspect for failure preemptively.

I need all of these I can get my hand on.

Anyone that has old parts and willing to help out with my research, please PM me. Will work it out!

Sorry, forgot to mention - at some point in the beginning, I had the pump motor replaced but when the existing/old motor was taken out, it didn't look like it needed replacement. And, recently, when doing the MC rebuild, my friend checked the motor and aside from rust flowers on the terminals, everything else seemed good with the motor.

Thanks for updating.

Wish I saw that commutator and wire. Even rebuild shop will say okay if ~30% remaining. How much wear interest me. Most look a two things; brushes and bearing. Unless commutator worn through, most do not give second though. But I find brushes usual have plenty of life left and not seen a bad bearing yet.

 

[SJWantsADiesel]

I'm am interest in all old brake master parts. I've been dissecting looking for cause and clues in how we can inspect for failure preemptively.

I need all of these I can get my hand on.

Anyone that has old parts and willing to help out with my research, please PM me. Will work it out!


Thanks for updating.

Wish I saw that commutator and wire. Even rebuild shop will say okay if ~30% remaining. How much wear interest me. Most look a two things; brushes and bearing. Unless commutator worn through, most do not give second though. But I find brushes usual have plenty of life left and not seen a bad bearing yet.

Yep, so to summarize: I have new-ish/refurb motor, rebuilt MC with new piston, new wheel speed sensors, bled and coming weekend, I am putting in new rotors/pads (EBC 3GD series and YellowStuff pads). Hope nothing lights up on the dash for the next 50k miles

 

[2001LC]

With front calipers I like to replacing pins if they're scored at all. Rear I make sure slide pins are moving freely and boots good. If not recondition or just replace.

Good time to do front wheel bearing service, during rotor R&R.

 

[SJWantsADiesel]

Yep, so to summarize: I have new-ish/refurb motor, rebuilt MC with new piston, new wheel speed sensors, bled and coming weekend, I am putting in new rotors/pads (EBC 3GD series and YellowStuff pads). Hope nothing lights up on the dash for the next 50k miles

Not so great news. Few days after rebuilding the MC, it leaked. My friend put in a new piston kit and that didn't help either. Looks like I am going to have to fork over $$$

 

[QBLX470]

Hi I have a 1998 LX470 with 180K miles. The abs light and buzzer came on and gave C1251, the terminals look bad!
Took it to the mechanic, he thinks the whole unit needs to be replaced. I have ordered a refurbished booster motor from ebay for 185$. Will be delivered in a few days.
The brakes are working fine, no other codes. The pump works fine without any noise or squeaking. It takes it 35 seconds to make the pressure if I pump the brakes 40 times . The mechanic was convinced that the pump alone wont fix the issue. Any feedback will be appreciated. Thanks