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Thread: Toyota Prius Accumulator

  1. #1
    Associate Engineer
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    Toyota Prius Accumulator

    Hello everyone,

    I would appreciate some input in replacing a failing brake line accumulator in my 2006 Prius with a used part in good working condition. The accumulator part number ******* is proving hard to obtain but I've located part number ***** from a Lexus RX400h SUV.

    Deciphering NOK's accumulator model code configuration:
    MZ - Accumulator series (MZ not available for sale through **** sole distributor, *****)
    21 - Nominal pressure. Catalog indicates 20.6 MPa is the maximum working pressure.
    135 - Nominal volume (cm^3). Catalog indicates unit volume.

    I know the larger accumulator may require the pump to run longer but less frequently. Aside from that, I don't see any other significant impact on the brake operating system.

    Would an increase to 180 cm^3 be an acceptable alternative?

    Thank you.

  2. #2
    Administrator Kelly Bramble's Avatar
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    The Toyota part number is 4795030010 which also fits the 4Runner and RAV4.

    Why would you not just go to a Toyota dealership and buy the OEM part?

    Toyota Parts Center Online sells them...
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    My 2006 Prius has about 300K miles. Not a lot of value left. The correct part number specific to the Prius is 44500-47141 at a cost of $1200+ for the complete ABS unit. It's replacement is involved and may take me several hours to complete.

    I am willing to bet $50 for a simple fix. And it's easy because it's externally mounted to the ABS unit. Zero down the system, unscrew accumulator, screw in replacement with new o-ring, and bleed system at the wheels.

    Many owners will replace the entire unit when the vehicle has multiple warning lights indicating system failure. I have no lights. The system is working but not optimally due to worn seal/bladder in the accumulator. At least that's what I believe to be the problem. The tell is the pump working 50% of the time the car is on. I first noticed degredation when the pump was running about 25% of the time. I suspect the nitrogen charge has been leaking slowly and decreasing over time. The pump is working overtime to keep the system pressurized. If it's not the accumulator then it's likely a solenoid valve leaking pressure back to the pump. At that point, I'll replace the ABS unit.


  4. #4
    Administrator Kelly Bramble's Avatar
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    Hydraulic accumulators are sized and pressured to the system operational volumetric and pressure requirements. If you install an accumulator that operates at the wrong pressure charge and/or delivers the wrong volumetric amount of fluid.. your brake system it will not work correctly.

    You need technical specifications on the OEM and candidate accumulator to understand compatibility.

    Good luck.

    https://www.engineersedge.com/hydrau..._equations.htm
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
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    The link about hydraulic accumulator sizing is the reason I considered the alternative volume increase from 135 to 180 cm^3.

    It stands to reason that Toyota had a custom size accumulator manufactured to save on cost and minimize the space required when it produced the Prius. Over 1.4M sold. The same size accumulator was also used in the Camry and Lexus SUV.

    If I built a similar custom system that required an accumulator, I would buy what is commercially available. A similar accumulator by *******, the MB series, is also designed for a maximum working pressure of 20.6 MPa but is only sold in 100, 300, and 500 cm^3. If the system's volumetric requirement is 135 cm^3, I would purchase the available size in 300 cm^3 to meet the minimum volume needed.

    Honestly, I think I just answered my own question. I guess I was just looking for confirmation that increasing the volume would not cause an issue before I started my repair.

    Thanks for the help.

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