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Thread: Brake bleed - not much happening at the rear...

  1. 17th March 2014, 12:13 PM #1
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    DiscoClax
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    Question Brake bleed - not much happening at the rear...

    G'day all, hoping for some help on this one.

    I've replaced the front brakes on my D1 update (non-ABS) with Defender callipers (Ø45mm pistons) and slightly longer flexible hoses. I can bleed the fronts no worries. Absolute doddle. However the rears are being problematic. Firstly tried a manual bleed and couldn't get all of the air out. Hmmm, so I sourced a Gunston EziBleed (pressure-bleed) kit and tried that on Sunday. I can crack the rear nipples and nothing comes out. Only getting some fluid out (very little) if the brake pedal is also depressed. The fluid fair shoots out of the front nipples when I crack them. I've tried both 8 and 20psi, result the same. I've pulled the rear nipples are they are clear and free.

    I've currently got the reservoir off the master cylinder replacing the sealing grommets which I should (hopefully) get tomorrow. I pulled the reservoir off to clean the gunk out of the bottom of it. Um... the fluid flush is a tad overdue...

    As far as I can tell the rear brakes were working OK before the swap, plus when I manually bleed them a slug of fluid comes out each time the pedal is pumped (as you'd expect) although significantly less than the front circuit.

    So what am I missing here? Has the prop valve carked it? Is there something unique in this system I need to be aware of? I've had a look around the forum and the bleeding seems to be straightforward, plus RAVE indicates it should be really simple (manual or pressure), so I suspect something is amiss. I would really appreciate some sage counsel from the experienced before I start ripping it to bits.
    Last edited by DiscoClax; 17th March 2014 at 12:24 PM. Reason: Added info
    DiscoClax
    '94 D1 3dr Aegean Blue - 300ci stroker RV8, 4HP24 & Compushift, usual bar-work, various APT gear, 235/85 M/Ts, 3deg arms, Detroit lockers, $$$$, etc.
    '08 RRS TDV8 Rimini Red - 285/60R18 Falken AT3Ws, Rock slider-steps, APT full under-protection, Mitch Hitch, Tradesman rack, Traxide DBS, Gap IID
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  2. 17th March 2014, 12:30 PM #2
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    Tank
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    Have you checked the rear brake lines along their length for crushed/crimped pipes?
    I have the engine running whenever I bleed the brakes, is all of the old fluid out and you are starting at the rear passenger side caliper ?
    If you can't get fluid to flow easily you may have a blockage in the Caliper/Lines or any inline valves, best of luck, Regards Frank.
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  3. 17th March 2014, 12:54 PM #3
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    Thanks Frank...
    In order... Yes and yes (but I haven't tried bleeding with the engine running for two reasons - 1. I'll gas myself, and 2. A pressure bleed should work anyway.)

    Next step (once reservoir is back on) was going to be pulling the rear flexible line and seeing if the fluid flows freely from there. Then work up or down the system from that. Rear calipers and lines were not touched (apart from replacing the flexible hose section).

    I'm wondering if the relatively low fluid flow out the back is indicating an issue in the rear circuit somewhere?

    Cheers.

    Quote Originally Posted by Tank View Post
    Have you checked the rear brake lines along their length for crushed/crimped pipes?
    I have the engine running whenever I bleed the brakes, is all of the old fluid out and you are starting at the rear passenger side caliper ?
    If you can't get fluid to flow easily you may have a blockage in the Caliper/Lines or any inline valves, best of luck, Regards Frank.
    DiscoClax
    '94 D1 3dr Aegean Blue - 300ci stroker RV8, 4HP24 & Compushift, usual bar-work, various APT gear, 235/85 M/Ts, 3deg arms, Detroit lockers, $$$$, etc.
    '08 RRS TDV8 Rimini Red - 285/60R18 Falken AT3Ws, Rock slider-steps, APT full under-protection, Mitch Hitch, Tradesman rack, Traxide DBS, Gap IID
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  4. 17th March 2014, 04:42 PM #4
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    dont forget the brake biasing valve...

    thats usually the culprit in a no delivery to back brakes. if you had brakes that were locking on then I would be blaming the lines.
    Dave

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  5. 18th March 2014, 09:44 AM #5
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    OK, I'm sourcing a known good used proportioning valve (biasing valve) today and I'll try that out tonight when I reassemble the MC reservoir. Seems like the most likely culprit.
    DiscoClax
    '94 D1 3dr Aegean Blue - 300ci stroker RV8, 4HP24 & Compushift, usual bar-work, various APT gear, 235/85 M/Ts, 3deg arms, Detroit lockers, $$$$, etc.
    '08 RRS TDV8 Rimini Red - 285/60R18 Falken AT3Ws, Rock slider-steps, APT full under-protection, Mitch Hitch, Tradesman rack, Traxide DBS, Gap IID
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  6. 19th March 2014, 11:54 PM #6
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    Before you go replacing everything, refit the MC and fill with fluid. then crack each join in the line until it starts flowing at the rear.

    When I did mine I couldn't get it to bleed, so I left the rear passenger bleed valve open and went up to the front and cracked the connection at the front of the proportioning valve, then the rear of it. I went down to the back and cracked the connection at the top of the flex line where it drops down to the diff after that it started to run out at the caliper.

    A lot of messing around, but I didn't have to undo them very far to get fluid flowing.

    Neale
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  7. 21st March 2014, 11:45 AM #7
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    Closure...

    It was the bias/proportioning valve at fault. I probably pushed some gunk into it during the process and somehow knackered it. Replaced it with a known good used unit and at all bleeds well and the brakes are solid now.

    Thanks
    DiscoClax
    '94 D1 3dr Aegean Blue - 300ci stroker RV8, 4HP24 & Compushift, usual bar-work, various APT gear, 235/85 M/Ts, 3deg arms, Detroit lockers, $$$$, etc.
    '08 RRS TDV8 Rimini Red - 285/60R18 Falken AT3Ws, Rock slider-steps, APT full under-protection, Mitch Hitch, Tradesman rack, Traxide DBS, Gap IID
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