Booster Pump / Accumulator Noise diagnosis (2 Viewers)

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Again leading me to believe that it's the pump itself under the accumulator.
I've had both my motor and accumulator replaced. The issue only happens when cold. I pump the brakes and after about 30 pumps the noise goes away. Also, bleeding the brakes solves the problem for a while.
When I bleed the brakes i get air out of the lines every time.
 
so now are guys separating the pump head from the motor to swap or service? since its not a serviceable piece and guys can only swap a pump head with a used one that will only fail in the near term, what is the point really? i get that you can separate the accumulator from the motor pump and service the 3 parts in that connection. and I understand that this over all is not a cheap fix. i am trying to understand and over simplify this for myself and others as im sure i will be in the same boat in the near future.

i have some experience with large scale hydraulic accumulators and understand the basic principle of the system. i would think if you replace the accumulator, the motor pump, the spring/tube/oring with all new parts whether together or in stages and you still have issues, i would think the next place to look at is the master cylinder assembly. and lets say you "rebuild" the master cylinder and replace the piston. if you still have problems, you are down to air in the system or a trashed master cylinder body? is the MC pressure switch suspect?

just trying to wrap my head around all this before it actually becomes my problem as well
 
I've had both my motor and accumulator replaced. The issue only happens when cold. I pump the brakes and after about 30 pumps the noise goes away. Also, bleeding the brakes solves the problem for a while.
When I bleed the brakes i get air out of the lines every time.
Same here. Bleeding stops it for a few days
 
so now are guys separating the pump head from the motor to swap or service? since its not a serviceable piece and guys can only swap a pump head with a used one that will only fail in the near term, what is the point really? i get that you can separate the accumulator from the motor pump and service the 3 parts in that connection. and I understand that this over all is not a cheap fix. i am trying to understand and over simplify this for myself and others as im sure i will be in the same boat in the near future.

i have some experience with large scale hydraulic accumulators and understand the basic principle of the system. i would think if you replace the accumulator, the motor pump, the spring/tube/oring with all new parts whether together or in stages and you still have issues, i would think the next place to look at is the master cylinder assembly. and lets say you "rebuild" the master cylinder and replace the piston. if you still have problems, you are down to air in the system or a trashed master cylinder body? is the MC pressure switch suspect?

just trying to wrap my head around all this before it actually becomes my problem as well
I rebuilt my master cylinder as well. I guess the point is trying to find what is actually failing instead of throwing a bunch of money at it
 
I rebuilt my master cylinder as well. I guess the point is trying to find what is actually failing instead of throwing a bunch of money at it

yes! that is what i am after as well! the only other weak link i see is the o-ring for the MC pressure switch, getting old brittle. or the walls of the MC cylinder are pocked. were you able to inspect the inside of that? or the valving inside of the MC has failed and leaks internally?
 
yes! that is what i am after as well! the only other weak link i see is the o-ring for the MC pressure switch, getting old brittle. or the walls of the MC cylinder are pocked. were you able to inspect the inside of that? or the valving inside of the MC has failed and leaks internally?

The white plastic o'ring was cracked. Brakes were soft but the rebuild kit fixed it.
 
so now are guys separating the pump head from the motor to swap or service? since its not a serviceable piece and guys can only swap a pump head with a used one that will only fail in the near term, what is the point really? i get that you can separate the accumulator from the motor pump and service the 3 parts in that connection. and I understand that this over all is not a cheap fix. i am trying to understand and over simplify this for myself and others as im sure i will be in the same boat in the near future.

i have some experience with large scale hydraulic accumulators and understand the basic principle of the system. i would think if you replace the accumulator, the motor pump, the spring/tube/oring with all new parts whether together or in stages and you still have issues, i would think the next place to look at is the master cylinder assembly. and lets say you "rebuild" the master cylinder and replace the piston. if you still have problems, you are down to air in the system or a trashed master cylinder body? is the MC pressure switch suspect?

just trying to wrap my head around all this before it actually becomes my problem as well
It's all trial and error. I'm looking to sell my LC pretty soon and thinking about just replacing the entire assembly so the next owner won't have to put up with this. I have a few things left to try and then it's out with the old and in with the new.
I rebuilt my master cylinder as well. I guess the point is trying to find what is actually failing instead of throwing a bunch of money at it
True, I think there's air getting in somewhere. Just can't seem to find where. I was gonna sell my cruiser until this issue came back. The longest I've ever had it last was 1000 miles. And that was after having it bled by Toyota. Even the coldest of days it didn't happen.
Personally, my next step is checking on the assembly itself for a rubber hose to replace. Then moving to each of the wheel cylinders and replacing the rubber hoses at each caliper.
 
It's all trial and error. I'm looking to sell my LC pretty soon and thinking about just replacing the entire assembly so the next owner won't have to put up with this. I have a few things left to try and then it's out with the old and in with the new.

True, I think there's air getting in somewhere. Just can't seem to find where. I was gonna sell my cruiser until this issue came back. The longest I've ever had it last was 1000 miles. And that was after having it bled by Toyota. Even the coldest of days it didn't happen.
Personally, my next step is checking on the assembly itself for a rubber hose to replace. Then moving to each of the wheel cylinders and replacing the rubber hoses at each caliper.
If you replace the whole assembly, I might take the pump if you're selling it. (Or donating it😜)
 
Pick n pull sells the unit for $24.99. just hard to find
 
Did some investigating - possibly found the culprit.

1. There is a master cylinder pressure sensor (I believe only applicable to units with ATRAC - please correct me if I'm wrong) - it is listed as a non-reusable part as indicated by the black diamond. Replace if your vehicle has it; the part number is listed below.

2. There is an actuator hose (circled in red/orange near the bottom) - you need to check and make sure that there is no wear to this hose and also make sure that the hose clamps are not loose. If air is escaping it will not signal the pressure switch to cut off or air from the accumulator can be bleeding from this hose - I recommend replacing the hose and using new hose clamps as the clamps that are on there can become lose over time.

the unit itself is subject to weather changes and different elements as we drive our cruisers. It's very possible that these have worn out - especially for those of us with higher-mileage rigs which is causing problems. As for those who have replaced their whole unit and still have the issue; ensure that all of the air is bled from the system (this explains why bleeding the system temporarily remedies the situation for some). I recommend running through the steps listed above second to bleeding the system.

For bleeding the system I strongly recommend going to Toyota so they can use their Techstream software to bleed the air pockets trapped inside of the abs unit itself.

Of course - if you haven't already replaced the booster pump motor and accumulator, I recommend doing so as this has solved the issue for some (starting with the accumulator)

It's possible that in warmer weather the hose is expanded, thus not allowing air to escape. But with colder temps, the hose shrinks slightly and if it is cracked, that will allow air into/out of the system.

Also, if you read the FSM, it states that if the pump does not shut off after a certain amount of seconds (30-40?) then to bleed and recheck to ensure that the pump stops within its given parameters. It is not until after the pump runs past that threshold that the squealing begins. This explains why bleeding solves the problem only temporarily.

Picture courtesy of MGS88 - he has the FSM posted here: 1998 - 2007 Toyota Land Cruiser Factory Repair Manuals

InkedInkedbrake booster check1_LI.jpg
 
Did some investigating - possibly found the culprit.

1. There is a master cylinder pressure sensor (I believe only applicable to units with ATRAC - please correct me if I'm wrong) - it is listed as a non-reusable part as indicated by the black diamond. Replace if your vehicle has it; the part number is listed below.

2. There is an actuator hose (circled in red/orange near the bottom) - you need to check and make sure that there is no wear to this hose and also make sure that the hose clamps are not loose. If air is escaping it will not signal the pressure switch to cut off or air from the accumulator can be bleeding from this hose - I recommend replacing the hose and using new hose clamps as the clamps that are on there can become lose over time.

the unit itself is subject to weather changes and different elements as we drive our cruisers. It's very possible that these have worn out - especially for those of us with higher-mileage rigs which is causing problems. As for those who have replaced their whole unit and still have the issue; ensure that all of the air is bled from the system (this explains why bleeding the system temporarily remedies the situation for some). I recommend running through the steps listed above second to bleeding the system.

For bleeding the system I strongly recommend going to Toyota so they can use their Techstream software to bleed the air pockets trapped inside of the abs unit itself.

Of course - if you haven't already replaced the booster pump motor and accumulator, I recommend doing so as this has solved the issue for some (starting with the accumulator)

It's possible that in warmer weather the hose is expanded, thus not allowing air to escape. But with colder temps, the hose shrinks slightly and if it is cracked, that will allow air into/out of the system.

Also, if you read the FSM, it states that if the pump does not shut off after a certain amount of seconds (30-40?) then to bleed and recheck to ensure that the pump stops within its given parameters. It is not until after the pump runs past that threshold that the squealing begins. This explains why bleeding solves the problem only temporarily.

Picture courtesy of MGS88 - he has the FSM posted here: 1998 - 2007 Toyota Land Cruiser Factory Repair Manuals

View attachment 2186004
I'll note the first Master cylinder pressure sensor was not listed in FSM as: "not re usable". It was used from July 1999 to Aug 2000.

I be very interested to see the newer (Aug 2000-) 89637-30050 Master cylinder pressure sensor from Toyota parts just out of the box. Anyone have a picture?
 
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I had this issue and posted it here. The only fix is to replace the master cylinder assembly. Its expensive. You might be able to reuse your motor and accumulator but I would rebuild the motor.

 
I had this issue and posted it here. The only fix is to replace the master cylinder assembly. Its expensive. You might be able to reuse your motor and accumulator but I would rebuild the motor.

By chance, did you have the high pressure switch tested with Toyota? I'm trying to educate myself as much as possible; if the switch is the issue, why does it only happen when it's cold? And why does bleeding the system 100% remedy the problem temporarily?
 
Super helpful posts! I found another cross reference part for the Toyota tundra 2003-2005.

Not 100% sure about this
69F03597-5492-4AC9-8588-3BA52E37A511.png
 
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