It's going to be at leas a couple of weeks or more to get parts and the time off work to get mine fixed, I'm still debating with myself if I'm just going to replace the entire assembly or the motor/pump/accumulator portion which I can get for a little more than $700.

I also saw you can get the master cylinder without the motor/pump/accumulator portion for around $1180 which would save about $200 over the entire assembly if Marten just needs that part.

47025-60081 Genuine Toyota Brake Master Cylinder Sub-Assembly)

Even a little cheaper here.

Toyota 2003-2005 Toyota 4Runner Brake Master Cylinder 47025-60081 | Toyota Parts

Thanks Au and Sam for your efforts

I am running out of time. Sick of my inability to analyze the situation properly I already ordered the new hydro booster unit. It's the full unit, to get this unit out of the failure equation.
I should have the unit soon and I'll let you know what difference it makes.

Martin

Hi Au,

Rock hard pedal meaning you had no brake booster at all.
You have a leak on the pressure side
In lack of a technical diagram of the unit it is unknown where the leakage might be located
1)hydraulic 3-cylinder pump/check valve being part of the pump so that pressurized fluid cannot flow backward,
2) accumulator super low on gas (cannot store much energy meaning any leakage is amplified by a weak accumulator) ,
3) downstream a potential leak on the pressure side toward the master cylinder.

Unfortunately I don't have any better information.,

Can you do these quick tests and see how well your system responds once pressurized?

test1:
Key in ignition position
press the brake pedal 3 times as a start.... after how many brake actions
does the motor come on. After 1, 2 or 3 pushes?
For instance after every second push you'll hear the motor. So you push 2 times...brake motor.... push 2 times...brake motor.

(my T4R has the 1-2 pattern. Every second pedal action the motor comes on)


test2
Key in ignition position
Push the brake pedal more often... say 10 times.
Does that trigger the low pressure alarm (all 4 dash lights plus alarm sound)?

(I can trigger the alarm after 6-8 pedal actions)

These tests don't tell you how leaky your pressure side is because these leaks are relatively slow - you said it takes overnight for all pressure to leak out.

But it can tell you probably about the basic condition of the brake health.

I am sure you will get rid of your symptoms with a new unit.
Martin

I just ordered the complete assembly for mine as well, not taking a chance with not replacing it all, don't have the time for my vehicle to be down if just replacing some parts of it doesn't solve the issue.

I was going to order from Ourisman since it was less initially ...BUT after shipping and them charging taxes was added as well it was $100 more than ordering it from ToyotaPartsDeal, who was less on shipping and didn't charge me $96 in taxes!!


I should have it somewhere between May 2 and May 7, then I need to find the time to install it.

Martin,

I tried both already...BUT I'm have trouble even hearing the electric motor running, I have been noticing over the last year or so the motor kicking in more often, running longer than it should and it was nosier than is was in the past, I'm pretty sure the brushes are worn out and barely making contact and running must more slowly than it used too, hence why it takes 3 to 4 minutes to build up the pressure to stop the alarm and get the lights to go off.

All that said, it is 20 years old so I think I got more life out of it than I would of from any other manufacturer!

Good decision.

My approach: Why do it the right way when I can do it my way.

You went as far as you could so a good decision. If you are not too burned out by this, I would like to see your failure analysis. Maybe tear the block down and look at internal seals.