Results 1 to 4 of 4

Thread: brake fluid pressure pump bleeding

  1. #1
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    880
    Total Downloaded
    0

    brake fluid pressure pump bleeding

    For the last few years I have replaced the accumulator on top of my pump a total of 2 times. Once to get the old one of that was clearly not having it anymore, a second time because I suspected the replacement unit to be faulty. Since the second time did not change anything I have become to suspect the pump itself (the non return valve to be exact). Since that is not serviceable (see a few posts back) I have taken a unit from a wrecker I have kicking around. Since I needed to install longer brake lines in the front for my lift I also replaced the pump and followed the bleeding procedure as described here: ABS Brake Bleeding Procedure Range Rover 4.0/4.6

    However, what happens now is that when I press the brake pedal, the pump immediately kicks in and the fluid level in the reservoir varies during braking and pumping. I suspect either the accumulator on this thing to have given out since it was out of operation for a few years or there to be air in the system somehow. I'm going to try and replace the accumulator this afternoon but I was wondering if anyone has any experience with replacing the entire unit and bleeding? Perhaps I am doing something wrong?

    Any advice would be highly appreciated.

    Cheers!
    -P

  2. #2
    Join Date
    Nov 2008
    Location
    Bruthen, Eastern Vic.
    Posts
    836
    Total Downloaded
    0
    When I replaced the accumulator a while back I just opened the bleed screws on the abs body while operating the pedal a few times, seems ok still.
    I still have the fluid level rising and falling because of that non return valve problem.
    I intend to have another go at the non return valve as soon as I can, I am not yet convinced it can't be removed and fiddled with, but I have to get past a broken ankle first.
    Terry
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.
    2010 Guzzi 750

  3. #3
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    880
    Total Downloaded
    0
    The last week I spent countless hours on the brake system and I am getting a bit confused

    I took the pump from the wrecker and put it in the car, tried to bleed the system as described in my first post but the pump would now kick in every second pedal press. Leaving the ignition on (and a power supply on the battery to keep a stable voltage) the pump would kick in about every 10 minutes to repressurize the system. Also, the brake fluid would be dumped into the reservoir when the brake was operated and even overflowed at several times.

    Suspecting air to still be trapped somewhere in the system I used a device that holds about a us gallon of brake fluid and a pump. This device connects through a hose and adapter directly to the brake fluid reservoir. The pressure is kept at around 2bar. This aids in bleeding the system since you can never accidentally run out of fluid. Using this system and the manual for bleeding the brake system I ran almost the entire gallon of brake fluid through the system to make sure any air would really be out. Although the procedure still requires someone to press the brake pedal and turn the ignition (pump) on and off this makes life a bit easier

    This procedure did not help anything to be honest, except ease my mind that there really is no air in there! (I hope). Next suspect would be the accumulator, since the pump (and accumulator) had been sitting around for a long time in the yard I thought about replacing it with a new unit I have kicking around. Daunted by having to bleed the entire bloody system again I decided to give this some more thought. My previous pump had it's accumulator replaced two years ago and within a year my brake system lost it's pressure fairly often so I ordered yet another accumulator and replaced it. This changed nothing however.

    I decided to test the pump itself since we have suspected the nrv a while ago. Fixing a makeshift adapter from the 10x1 thread to standard 1/4" thread found on most hydraulics I fitted a manometer to the output of the pump directly, removing the ETC unit completly, except for the oil reservoir and input. Since the pressure switch is on the pump itself there is not too much risk of blowing things up I thought After switching on the ignition the pump had difficulty starting up, I suspect air since the pump was lifted up and was no longer below the reservoir. It took a few tries to get the oil to be picked up and the pump to actually start building up pressure but eventually it stopped at 160! bar (that was admittedly a bit scary).

    It has been two days since I did that and apart from the pressure dropping down to 150 in say a couple of hours it has remained there for the past few days. If the nrv in the pump would be bad, I would not expect this to happen but the pressure to bleed back into the reservoir. I can't say anything about the accumulator at this point since there is nowhere for the oil to go so who knows if it works as it should. What I am beginning to suspect is that the pressure is send into the ETC body and bleeds of in there somewhere. I did rebuild it last year since it had the plastic washers in there and I replaced it with the steels version from rangeroversolutions. It seems that either I did something wrong (though the brakes did work very well in the beginning, something has gone wrong in the mean time or the problem exists elsewhere.

    After all this I am not sure where to go from here but it seems that the simplest solution is to take it all out, replace the ETC with the one from the wrecker, replace the accumulator on this pump just to be safe and put it all back together again. Rinse and repeat, bleed, and see what this does. Perhaps the nrv in the ETC is serviceable or something else is adjustable at this point but I kinda doubt it. If I get any more results I'll let you guys know

    Cheers,
    -P

  4. #4
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    880
    Total Downloaded
    0
    Sorry for the delays guys but! I finally got around to getting the car through the MOT. I'll concentrate on the brake issues here in this thread.

    So, as mentioned previously I installed a manometer directly to the output of the pump and let it build up pressure. It came all the way up to 160bar and dropped to 150 in about an hour. After that it has been sitting around for a week without any change. Ever so carefully I de-pressurized this setup and took the pump from my wrecker and placed it on the bench for ease of access. I installed the manometer on this unit as well and powered it with a separate power supply (old compaq server unit that can provide 82A continuous). Since the pressure switch was not connected I manually built the pressure up to 80bar and stopped there since undoing the manometer to let that much pressure escape does scare me a bit...

    This test setup was also left for a week (by necessity) and the pressure never dropped so much as a bar. This has led me to believe that the nrv's on the pumps are just fine. The only thing I can conclude is that the problem must exist inside the ETC unit. Somehow the unit is designed such that the pressurized oil can escape back into other parts of the system and with no where else to go, back into the reservoir.

    Since I had to speed things up to get my car through the MOT I have not yet gone through the hassle of getting the one out of the wrecker and replacing it. It is on my wish list for this year, somewhere. Hopefully when it is a bit warmer

    All in all the current setup runs quite well. At first the pump would kick in every other pressing of the brakes but when testing if the ETC and ABS would still work (I always test them on gravel or such) the system must have bled itself a bit more or something but since then the pump kicks in after every 5th time, which is good! In the morning all the pressure is lost from the pump however and the pressure needs to build back up for at least 30 seconds.

    For those of you who were wondering; yes I did replace the accumulator on top of the pump.

    My conclusion so far is that:

    when the pump kicks in after every press of the pedal there is either air in the system or the accumulator is broken. The reason for this is that there is no reserve pressure other then what is in the tiny hose and a single brake action will deplete the pressure quite quickly. When the accumulator does it's job there is spare pressure capacity in that sphere and the pump only needs to run every 4 or 5 times, it also needs to run a bit longer.

    When the pumps runs for very long in the morning, the accumulator is probably not at fault, and the NRV in the pump is likely not at fault either but the problem is probably in the ETC unit.

    Finally, a simple solution to a defective NRV in the pump would be to mount an external unit just behind the pump although I would think that the pressure from the accumulator would still bleed back into the reservoir you would have the required pressure to brake safely.

    Cheers,
    -P

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!