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  1. #1
    casual poster
    Join Date
    Jul 2015

    Default HQ loose rear drum brakes whilst bleeding front discs

    in my hq i have the brake system as follows

    wb girlock front calipers
    hq standard rear drums (new shoes / cylinders, shoes adjusted)
    aftermarket prow flow disc/drum proportioning valve with bleeding tool installed whilst bleeding. (all lines are in correct inlets)
    chrome dual diaphragm booster
    hq disc/drum master cylinder (did have the aftermarket chrome one but went back to origional)
    all new brake lines / rear hose

    I bleed the rear brakes first and get them to pressure, no air in lines, can hear them engaging, wheels lock up when engaged. no worries there. i go to bleed the front brakes, here is were the problem is. as soon as pressure starts to build in the fronts i instantly loose the rear brakes. so i move back to the rear brakes and try and bleed them again. very minimal if not no fluid comes out. i have released all pressure and started again numerous times, and still have the same outcome. i have put the original master cylinder back on still no luck, thought it might have been a vacuum issue so have had the car running and still no luck. could it be the wb calipers? any suggestions would be a great help as this is really frustrating


  2. #2
    Do you ever leave?
    Join Date
    Jan 2017
    Nth Qld


    Some masters have the front circuit on the front union some locate it at the rear [reversed ].
    A check valve in master cylinder should only be installed in the drum rear circuit . Located behind the pipe seat .
    HQ Factory proportioning valve on the underbody removed ?? Distribution block and warning switch in engine bay

    Machined drum to size of shoes is called radius grinding ,the only correct way to do it.

    Adjustment of shoes should give slight drag equal both sides . NEVER back off the adjuster. This will give a crap pedal .

    Always lube between linning and backing plate , smear of grease is enough on the rubbing points

    9 inch dual diaphragm booster is for 4x disc .

    bleed master on bench then in car
    bleed longest line run first LHR RHR , LHF RHF

    Clamp hoses one at a time to diagnose problem circuit . Cannot clamp braided style .

  3. #3
    Part of the furniture
    Join Date
    Nov 2018


    Sounds like the proportioning valve may be faulty....or the lines to it mixed up.
    Use the correct PV, which is PBR # 6307.

  4. #4
    Do you ever leave?
    Join Date
    Jan 2017
    Nth Qld


    The crack pressure to the rear drums is different car to car .The usa vehicles generally run higher prop pressures compared to ozzy cars . Running higher pressure on an ozzy car will cause rear wheel lockup earlier under emergency braking low traction conditions .

    Vacuum bleed front and rear brakes then pressure bleed if u like .
    Have the brake light switch removed so the prop piston can shuffle back and forwards if it needs to . It should self centralise once brakes are bled out. The advantage to vacuum is no pressure is used .
    Last edited by swampy; 22-11-2021 at 01:37 AM.

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