Booster Pump / Accumulator Noise diagnosis (2 Viewers)

[grundsethp]

I followed the troubleshooting guide posted in my post to diagnose the problem. The pressure switch that goes bad is inside the ecu(black box on the side of the module. It is not the master cylinder pressure sensor.

Look at the PH pressure switch troubleshooting page:
Use an ohm meter to check the resistance across the pins shown. The pressure switch controls the pump. When the pressure is low, it will be 1kohm. When the pressure is high, it will be 0ohm.

When the switch does not work, it will stay 1kohm. That tell the ecu to keep pumping. Then it starts make the screeching sound. If it pumps for more than 5 min, the warning lights and buzzer turns on. For some reason, when it gets cold, the sensor sticks since it spends hours at high pressure when cold. I have seen some improvement if you pump the brakes a few times after you turn off the truck and remove the key. That reduces the pressure and changes the switch to 0ohms.

If you change the brake fluid, you have warmed up the unit. After

 

[grundsethp]

Not sure how to edit the previous post. Made a mistake in my last sentence. It should be 1kohm.

The pressure switch changes in resistance if it works correctly.
1kohms = low pressure
0kohms = high pressure

 

[Landcruiser949]

Not sure how to edit the previous post. Made a mistake in my last sentence. It should be 1kohm.

The pressure switch changes in resistance if it works correctly.
1kohms = low pressure
0kohms = high pressure

Interesting. So replacing the unit is the only way to go eh? Is there a DIY solution or someone I can send the unit off to for rebuild? I'm willing to push my luck opening the system if I'm going to buy a new one anyway.

 

[grundsethp]

I do not know of any DIY solution. You could open the ecu and trace the circuit to the pressure switch if you open the black ecu box on the side of the master cylinder. If the solder joint looks bad you could try to reflow it.

 

[bdruff]

I followed the troubleshooting guide posted in my post to diagnose the problem. The pressure switch that goes bad is inside the ecu(black box on the side of the module. It is not the master cylinder pressure sensor.

Look at the PH pressure switch troubleshooting page:
Use an ohm meter to check the resistance across the pins shown. The pressure switch controls the pump. When the pressure is low, it will be 1kohm. When the pressure is high, it will be 0ohm.

When the switch does not work, it will stay 1kohm. That tell the ecu to keep pumping. Then it starts make the screeching sound. If it pumps for more than 5 min, the warning lights and buzzer turns on. For some reason, when it gets cold, the sensor sticks since it spends hours at high pressure when cold. I have seen some improvement if you pump the brakes a few times after you turn off the truck and remove the key. That reduces the pressure and changes the switch to 0ohms.

If you change the brake fluid, you have warmed up the unit. After

View attachment 2187642

The last sentence in the FSM says t replace the hydraulic brake booster assembly. But you’re saying the problem is in the black box on the side of the master cylinder? If it is the pressure switch, wouldn’t the FSM say to replace the box, or whole MC assembly if it isn’t sold separately?

Am I missing something?

 

[Landcruiser949]

The last sentence in the FSM says t replace the hydraulic brake booster assembly. But you’re saying the problem is in the black box on the side of the master cylinder? If it is the pressure switch, wouldn’t the FSM say to replace the box, or whole MC assembly if it isn’t sold separately?

Am I missing something?

Sadly, techs in general are taught to replace things instead of making repairs. It makes sense that the FSM would say to just replace the entire unit. There very well could be a DIY solution

 

[Eyedaho]

Does anybody have a picture of the actual pump, or can someone explain what type of a pump it is? I know people are replacing/rebuilding the motor and accumulator, but I'm not seeing any rebuild parts for the pump itself. Is it a rotary pump? Is it all metal like an oil pump, and that's why it's not being rebuilt? Sorry if I'm being thick or missed a bunch of posts explaining this, but I just can't picture what's between the motor and accumulator.

 

[Landcruiser949]

Does anybody have a picture of the actual pump, or can someone explain what type of a pump it is? I know people are replacing/rebuilding the motor and accumulator, but I'm not seeing any rebuild parts for the pump itself. Is it a rotary pump? Is it all metal like an oil pump, and that's why it's not being rebuilt? Sorry if I'm being thick or missed a bunch of posts explaining this, but I just can't picture what's between the motor and accumulator.

I posted a picture of the breakdown a few pages back. It explains everything.

 

[Eyedaho]

I posted a picture of the breakdown a few pages back. It explains everything.

I'm hoping that someone has a photograph of the inner workings of the pump itself, or a brief explanation of the actual pump mechanism.

 

[bdruff]

Sadly, techs in general are taught to replace things instead of making repairs. It makes sense that the FSM would say to just replace the entire unit. There very well could be a DIY solution

The brake booster is sold as a unit but the black box is not part of the unit. If it said the whole master cylinder assembly, including the booster, that would make more sense. The booster assembly is sold as a unit and then they also list the whole thing including the master cylinder assembly and brake booster assembly as a part number. The FSM just said t replace the brake booster.

 

[kruisinkid]

a page ago i think it was said it is a sealed pump head. most likely resembling a water pump. does not seem serviceable in any way. someone would have to run one through a band saw, but im sure its just an impeller on a shaft. i would think its the least likely part to fail in the system.

 

[bdruff]

Does anybody have a picture of the actual pump, or can someone explain what type of a pump it is? I know people are replacing/rebuilding the motor and accumulator, but I'm not seeing any rebuild parts for the pump itself. Is it a rotary pump? Is it all metal like an oil pump, and that's why it's not being rebuilt? Sorry if I'm being thick or missed a bunch of posts explaining this, but I just can't picture what's between the motor and accumulator.

The pump sits under the accumulator. The motor also bolts to the pump.

 

[kruisinkid]

a table i made last week: (for a 12/99 build LC)

master cylinder piston rebuild kit	449360330	67.03
accumulator	4795060010	340.91
motor pump	4796060010	1311.72
accumulator pipe	4795530010	1.91
accumulator spring	9050116160	1.91
accumulator o ring	9030113014	3.42
pressure sensor spacer	9056116009	1.48
pressure sensor o ring	9030115014	2.85
brake booster firewall gasket	4478560010	6.21
brake MC valve body sub assmbly	4702560012	1202.93
accumulator/motor pump sub assmbly	4707060010	765.82
entire MC/accum/pump assembly	4705060012	2178.27

 

[Eyedaho]

a page ago i think it was said it is a sealed pump head. most likely resembling a water pump. does not seem serviceable in any way. someone would have to run one through a band saw, but im sure its just an impeller on a shaft. i would think its the least likely part to fail in the system.

That's exactly what I was wondering. Thank you for the explanation!

 

[grundsethp]

Here is a system diagram for the system

 

[grundsethp]

Brake master cylinder diagram

 

[bdruff]

I followed the troubleshooting guide posted in my post to diagnose the problem. The pressure switch that goes bad is inside the ecu(black box on the side of the module. It is not the master cylinder pressure sensor.

Look at the PH pressure switch troubleshooting page:
Use an ohm meter to check the resistance across the pins shown. The pressure switch controls the pump. When the pressure is low, it will be 1kohm. When the pressure is high, it will be 0ohm.

When the switch does not work, it will stay 1kohm. That tell the ecu to keep pumping. Then it starts make the screeching sound. If it pumps for more than 5 min, the warning lights and buzzer turns on. For some reason, when it gets cold, the sensor sticks since it spends hours at high pressure when cold. I have seen some improvement if you pump the brakes a few times after you turn off the truck and remove the key. That reduces the pressure and changes the switch to 0ohms.

If you change the brake fluid, you have warmed up the unit. After

View attachment 2187642

I bought a booster and accumulator. Put it in tonight and still problems. I've been reading a ton and o think this is the problem. The high/low pressure switchs not working.

Strangely, the new unit does not shut off. Pressure is very high.

Kinda bummed here.

 

[Landcruiser949]

I bought a booster and accumulator. Put it in tonight and still problems. I've been reading a ton and o think this is the problem. The high/low pressure switchs not working.

Strangely, the new unit does not shut off. Pressure is very high.

Kinda bummed here.

Did you have Toyota bleed the system with techstream? You have a brand spakin new unit? That sucks man.

 

[bdruff]

Did you have Toyota bleed the system with techstream? You have a brand spakin new unit? That sucks man.

Used from eBay. Bleeding didn't help this time. The motor wouldn't shut off and there is crazy pressure. Reading lots of other threads...it sounds like it's the pressure switches in the black box on the side of the master cylinder.

 

[Landcruiser949]

Used from eBay. Bleeding didn't help this time. The motor wouldn't shut off and there is crazy pressure. Reading lots of other threads...it sounds like it's the pressure switches in the black box on the side of the master cylinder.

Used? Not remanned? How many miles were on the donor?