2003 T4R , brake master cylinder, ABS unit kaputt

[werminghausen]

Hi earthrealm,

The brake system is leak free since I fixed the rear brake line

Swapping motor/pump/accumulator with a reman unit.
I was removing the hydro booster unit today (lots of crawling under the dash, not very difficult but definetely not convenient). Working with brake fluid is always messy.

With the unit on the bench it its relatively easy to swap motor/pump and accumulator.
Then I installed the updated unit back into the car and filled the tank with fluid.
I did not bleed the system yet but wanted to see what happens when I start the engine

So I started the car and the dash was silent! Finally some success.

Okay something must have been causing the problem , either the old motor or the pump or the accumulator.... or a combination of these.

I opened the motor (just 2 allen screws) and to my surprise it looked almost new, there is no reason the motor was failing.

If the motor is good then the problem must be a failing pump or a failing accumulator.

My logic tells me that it must be a failing pump.

I am assuming that the brake alarm ((dash lights with the beeping) goes off if the system does not have enough pressure.
Pressure is built up by the motor and pump action. The accumulator is simply storing pressure and if the accumulator fails pressure cannot be stored.
(unsure what this means in regards to the alarm- does someone know?)

As the motor was tuning and is actually looking really good the problem could be the pressure pump.


The good news: I have no alarm.
Tomorrow I will bleed and test the brakes.


The confusing parts was that I obviously had two brake problems at once
1) the leak in the rear brake circuit which turned on 'Brake!' in the dash and then right after the full alarm went off meaning 2) the brake pump failed.

Is the brake pump prone to failure if the system is low on fluid?
If yes that would explain what happened.: First I ran out of fluid and then the pump failed because there was no fluid?

Martin

 

[werminghausen]

I was looking at the removed and obviously failing motor/pump accumulator unit on my bench.

I could easily run the el motor and fluid was squirting out at the pump outlet.
The pump could be a 3 cylinder piston pump but not 100% sure.

My theory so far: the pump was failing and could not deliver the required pressue. This lead to the dashlight not clearing.

Well I still have no proof but I might take the pump apart at some point.

Here is a picture of the motor inside... it looked pristine, like new, see picture.

Martin

 

[AuSeeker]

It could be something as simple as the O-ring that seals the accumulator being bad.

 

[earthrealm]

I was looking at the removed and obviously failing motor/pump accumulator unit on my bench.

I could easily run the el motor and fluid was squirting out at the pump outlet.
The pump could be a 3 cylinder piston pump but not 100% sure.

My theory so far: the pump was failing and could not deliver the required pressue. This lead to the dashlight not clearing.

Well I still have no proof but I might take the pump apart at some point.

Here is a picture of the motor inside... it looked pristine, like new, see picture.

Martin

yeah, the motor is in great shape, you can sell it for a couple of bucks on ebay. wish i could get my hands on the motor, my 2nd replacement unit is failing again and its either the motor or piston assy


the 2nd likely culprit is the oring on the piston assy. its a 60 dollar part.


the accumulator rarely goes bad, its just a metal cylinder and an o ring on top. its easy to see/know if the accumulator is leaking, as slight fluid would be seen leaking from the top/connection



anyway great news your brakes are working ok now

 

[werminghausen]

yeah, the motor is in great shape, you can sell it for a couple of bucks on ebay. wish i could get my hands on the motor, my 2nd replacement unit is failing again and its either the motor or piston assy


the 2nd likely culprit is the oring on the piston assy. its a 60 dollar part.


the accumulator rarely goes bad, its just a metal cylinder and an o ring on top. its easy to see/know if the accumulator is leaking, as slight fluid would be seen leaking from the top/connection



anyway great news your brakes are working ok now

Hi earthrealm,

Piston assembly.... you mean the accumulator? Is this a piston accumulator then?
[The accumulator is mounted onto the pump and the pump is holding the motor and the accumulator. ]

The o-ring potentially going bad is the one between pump and accumulator?

I don't see a shrader valve for filling the accumulator with nitrogen...meaning the accumulator is not to be refilled with nitrogen.
if the charge is gone.... it is not reusable.

What is the shut off pressure (pump shut off) of the brake fluid under pressure (accumulator filled) if charged?

Martin

 

[werminghausen]

Accumulator again. (I am in the hydraulic business and I know this stuff...at least).
If fluid is leaking through this o-ring... that is just a fluid leak... but the accumulator would still work. ( I had NO leak there at any time).
It would need to leak A LOT for a brake failure.

The more realistic option for an acculuator failure is the loss of nitrogen. I a piston accumulator the piston seals would be leaking and the loss would result in a gradual loss or reduction of pressure storage to a point when fluid pressure cannot be stored at all.

If fluid storage (volume of fluid under pressure) is reduced then then pump has to work mpre frequently to make up for the reduced storage.
If no pressure can be stored any more then the pump would run at all times.... which would be deadly.
I don't know how the Tooyota controls work for the hydro brakes but I guess the alarm would go off as soon as the motor runs too often?

I am still trying to analyze why my brakes failed or what exactly failed...

Best, Martin

 

[earthrealm]

Accumulator again. (I am in the hydraulic business and I know this stuff...at least).
If fluid is leaking through this o-ring... that is just a fluid leak... but the accumulator would still work. ( I had NO leak there at any time).
It would need to leak A LOT for a brake failure.

The more realistic option for an acculuator failure is the loss of nitrogen. I a piston accumulator the piston seals would be leaking and the loss would result in a gradual loss or reduction of pressure storage to a point when fluid pressure cannot be stored at all.

If fluid storage (volume of fluid under pressure) is reduced then then pump has to work mpre frequently to make up for the reduced storage.
If no pressure can be stored any more then the pump would run at all times.... which would be deadly.
I don't know how the Tooyota controls work for the hydro brakes but I guess the alarm would go off as soon as the motor runs too often?

I am still trying to analyze why my brakes failed or what exactly failed...

Best, Martin

in a normal brake system, you gotta depress the brake pedal for 2 or 3 times...before the pump kicks in to top up the system. in a failing system. just onetime depression of the brake pedal and the pump kick in. the pump isnt designed to run all the time or too frequently, hence if the failing pressure causes the pump to run too frequently, the pump may burn out, or the 40amps fuse powering the pump fails. then when u open the pumps, you will see debris inside the assy. your pump was squeaky clean, so your failure must have been something else in the assy. the piston assy is connected directly to the brake pedal...and has an oring which traps pressure, if this fails..the system cant maintain pressure and subsequently causes the pump to overwork and fail. replacing the pump in this scenario will just be a bandaid...as the new pump will still fail after a while.


47026-60090 GENUINE OEM TOYOTA PISTON, MASTER CYLINDER 4702660090 | eBay the piston assy looks like this

 

[thoff25]

Your best bet is to buy one of those code readers from amazon, I got one for $30 it’s def worth it. OBD2 scanner

 

[FBELTRAN24]

Sounds like a brake line is either broken, worn, or bad. Maybe this is why you had zero fluid in the reservoir, and no brakes. Happened to me too recently. Check your lines before replacing the brake master cylinder. Itll save you

With you being in the snow/rust belt, it sounds like a busted/rusted out brake line to me.

Did you look for where the brake fluid leaked out?

If you do have a busted/rusted out brake line it would do exactly what you have describe, the booster pump would run continuously and no brake pedal, this is especially true for a busted brake line going to the rear.

I would check all along the metal brake lines for the leak before I would do anything to the brake/ master cylinder/ABS pump/booster!!

 

[werminghausen]

your pump was squeaky clean, so your failure must have been something else in the assy. the piston assy is connected directly to the brake pedal...and has an oring which traps pressure, if this fails..the system cant maintain pressure and subsequently causes the pump to overwork and fail. replacing the pump in this scenario will just be a bandaid...as the new pump will still fail after a while.


47026-60090 GENUINE OEM TOYOTA PISTON, MASTER CYLINDER 4702660090 | eBay the piston assy looks like this

Hi earthrealm

My braking power is not the greatest and I had the same issue (no good braking power) before the incident /brake failure.

Could your note be a hint.

With 'piston' you meant master brake cylinder piston- correct?
This piston in the T4R might just work as any other master brake cylinder? ... I guess.

Sure, if the piston seal of the master brake cyl. is not tight any longer then the brake pedal would drop to the bottom and not find a stop....

I don't know if this problem occurs in my brake.

Again my brakes have been much better in the past and I should find the reason for the weak brakes.
Could be
-air in the fluid? (But I just bled the brakes)
-brake pads bad? (Replaced pads 3 years ago- ceramic pads....)
-calipers bad? (I had rebuilt the calipers also 3 years ago.... the pistons were partially stuck in the calipers)
-master brake cylinder?


Any further hints?

Best, Martin