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Thread: ABS pump

  1. #1
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
    Posts
    626

    ABS pump

    Is anyone familiar with the internals of the ABS pump?
    Mine has just recently pushed the brake fluid back out of the top of the reservoir overnight, so I expected a problem with a non return valve somewhere.
    I dismantled the pump and I can see where the non return valve must be near the pump outlet, but no way could I access it. It seems well hidden in the pump body. Anyone know how to check it?
    I also found that the accumulator is discharged, so a new one coming. Suspected that because the pump runs every time I touch the brake pedal.
    I can't see how that would push fluid back out of the reservoir though.

    Very interesting pump design, with 3 radial plungers running inside a roller bearing doing the pumping.
    Pump condition is excellent at 260k km.

    Help needed please.
    Terry
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.

  2. #2
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    198
    Terry,

    I am not familiar with them, nor is anyone I know unfortunately but I am very interested in what you might find out! My ABS pump loses pressure a lot so every time I start the car it takes some 30 seconds for the bloody thing to stop running. I have replaced the accumulator twice already and I am pretty sure that is not the problem. I also rebuild the entire ABS/TC thingy where all the pipes and up in (not sure about the name right now) so I am left with suspecting the pump and indeed in particular the non return valve only. For me it is still workable but it is clear that the pump is running on it's last legs. I have a spare laying around but I would love to know if these babies can be rebuilt.

    Cheers,
    -P

  3. #3
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
    Posts
    626
    Pump is back together while I wait for the new accumulator. Like you I don't think then accumulator is causing the backflow, unless pressure is needed to keep the valve closed.
    The pump design is very simple, there are 3 radial plungers running inside a roller bearing which is off centre. The fluid is pushed inwards through slots in the spindle carrying the rotor. You can follow the drilling towards the pump outlet by the shape of the casting. I am sure the non return valve is in that area somewhere behind a slotted threaded plug which is where the outlet fitting screws in.
    I can get the threaded plug out but not what is underneath it. At least not without destroying things.
    The pump is designed so that none of the rubber seals have to withstand the 170bar operating pressure.
    I will see what happens with the new accumulator.
    Terry
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.

  4. #4
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    198
    Excellent! keep us posted. I don't feel like taking my spare apart just to check that out, sorry

    I have been tipped about a company rebuilding pumps down here by a mate of mine, I am trying to get in touch with them to see if they rebuild these P38 units as well since new ones are expensive.

    -P

  5. #5
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
    Posts
    626
    Apart from seals, I think the wearing parts would only be the rotor and the 3 plungers. Maybe the roller bearing too perhaps. In Aus. getting the parts would be a problem, maybe not where you are.
    Terry
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.

  6. #6
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
    Posts
    626
    New accumulator fitted, and all seems normal now - no ABS/TC/Brake warnings and the pump doesn't run everytime I touch the brake, EXCEPT the pump has to run for 30 sec on morning startup before it cuts off, and the fluid level goes from low to high mark overnight. Don't know if these things are normal or not.
    Maybe I still have a non return valve problem. Don't have a spare pump to play with and brakes are good so I will live with it and see...
    Terry
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.

  7. #7
    Join Date
    May 2013
    Location
    Canberra
    Posts
    42
    I put a new accumulator in this year, which was required as my pump was working harder before, yet my pump seems ok, including the 30 second running on start. Lastly, my fluid behaves the same as yours but I run mine a little higher, without flooding the fluid out. regards,

    Gary.
    MY00' P38 4.6 HSE

  8. #8
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
    Posts
    626
    Thanks Gary,
    Good to know there is a pattern to it. I think I had the level high when I had fluid everywhere.
    I think we both have a leaking non return valve though. I hope to find out how to fix it eventually.
    Terry
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.

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