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Thread: Brake Fluid Leak at Bottom of ABS

  1. #1
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    Question Brake Fluid Leak at Bottom of ABS

    When checking my garage today I noticed suspicious marks on the concrete floor.
    As the front right of the NSX is free of the typical fluids found in front engine cars (like oil, power steering fluid and the like) the first thing I checked was the ABS brake fluid level.
    It was near the 'low' mark even though I remembered it to be at 'full' mark about a year ago ..

    The brake fluid at the master cylinder was perfectly fine, though.

    Looking under the car, the drops on the floor were exactly below the lower mounting bracket of the ABS unit and the bracket was wet:

    Click image for larger version. 

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    Before trying to disassemble everything I wanted to ask if it might be a familiar issue as it strikes me a little odd as of where the bracket is wet (all up to the mounting bolts) and that it seem to have no effect whatsoever on the master cylinder fluid level.

    PS: The ABS was not exercised recently but could it be an overflow-during-pump-run issue?
    Last edited by Heineken; 30-06-2018 at 09:08 PM. Reason: Typos
    1997 JDM Custom Order AT VIN 1400005 - Stock
    Heineken's Garage

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    Quote Originally Posted by Heineken View Post
    overflow-during-pump-run issue?
    More sort of a "overflow while not using the car or a stuck solenoid or debris around the gasket. Quite common on older cars but certainly not funny.

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    So you're suspecting a not-sufficiently-closing valve probably in team with foamed up brake fluid in the pressure chamber?
    I'm currently pondering what to do about it. The reservoir was topped-up of course and I'll probably clean the area with brake cleaner. Additionally I could replace the brake fluid and exercise the pump and valves manually and hope that it clears things up .. I'm not expecting too much from that ABS anyway as long as it stops leaking on parts and the floor :-)
    1997 JDM Custom Order AT VIN 1400005 - Stock
    Heineken's Garage

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    Yes, that's the way to go. Exercising all solenoids and hoping that you get as much junk out of the system as possible. There's somehow a description somewhere but I can't help you as I went with the newer pump anyway.

    Some people have taken the unit completely apart. Some went with the later pump, much better anyway.

  5. #5
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    Well, looks like another busy weekend

    PS: Finding the descriptions should be no problem, I remember at least one PDF for a rebuild and several videos on how to flush it manually.
    1997 JDM Custom Order AT VIN 1400005 - Stock
    Heineken's Garage

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    the ABS system is completely separate from the rest of the braking system, save for 4 pistons controlled by the solenoids.... that's why the ABS system fluid can be completely drained without affecting the main brake fluid reservoir.....
    Last edited by britlude; 23-06-2018 at 09:23 PM.
    aka Jonathan!!

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    BTW what happened to the German forum?

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    Quote Originally Posted by britlude View Post
    the ABS system si completely separate from the rest of the brakingg system, save for 4 pistons controlled by the solenoids.... that's why the ABS system fluid can be completely drained without affecting the main brake fluid reservoir.....
    That's interesting as I've my newer pump since 10 years now and completely forgot how the old pump works. Problem is that I know of an NSX where the brake pedal is ultra long (not safe!) and the ALB reservoir is empty. I correlated the long pedal to this but now I'm not sure where to start. It's not my car...just trying to help out.

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    Quote Originally Posted by goldnsx View Post
    BTW what happened to the German forum?
    The one I joined was never much of a help to me, to be honest. The things I posted (like how to repair broken plastics, capacitor replacement, Tokyo Motor Show) weren't taken up in any useful way (except from a friend). It's basically a three-to-four man show and some of them are seriously difficult to discuss with ..
    1997 JDM Custom Order AT VIN 1400005 - Stock
    Heineken's Garage

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    If I understood the technical description correctly than the wheel pressure control is realized by two separate fluid systems:
    1. The ABS system
    2. The master cylinder and caliper system

    Both systems are interconnected via a sliding piston, effectively separating both fluids but allows the ABS system to manipulate the master cylinder / caliper pressure

    Click image for larger version. 

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    If high pressure from the accumulator is pushed into chamber C (by opening the inlet valve an closing the outlet valve) the sliding piston is pushed upwards and:
    • disconnects the master cylinder from the caliper
    • enlarges chamber B which causes the caliper pressure to drop
    • reduces chamber A which pushes back the pedal

    The volume pushed back into the master cylinder (via chamber A) matches the volume by which the chamber B was enlarged. As a result, the brake pedal is pushed back to a position that matches the lower pressure of the caliper.

    When the wheel stops locking the inlet valve is closed and the outlet valve opened. Chamber C is then connected to the pressureless reservoir and quickly discharges that way, supported by the master cylinder pressure in chamber A. Once the sliding valve hits bottom, the master cylinder and the caliper are once again connected. Pressure at the caliper can then be increased the usual way (by further depressing the brake pedal).

    Let's hope that description makes sense and not only to me
    Last edited by Heineken; 30-06-2018 at 09:09 PM.
    1997 JDM Custom Order AT VIN 1400005 - Stock
    Heineken's Garage

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