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  1. #1
    Andy Graham
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    Saab(s)
    '88 vert, '88 Aero
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    Brakes won't bleed

    Tried to fix a low pedal in the vert and have only succeeded in making it worse.

    I bled in the order specified in Bentley (LR, RF, RR, LF). The first pair of the split system (LR/RF) bled fine but the second pair (RR/LF) refused to cooperate. Both calipers emitted nothing but a bubbly mess. There was a little bit of fluid oozing from both bleed screws so I replaced them both. Strangely enough, that seemed to work -- the bubbles went away and the pedal was nice and firm. But as soon as I started driving the pedal lost pressure.

    So, started again -- LR/RF again bled fine and RR/LF again were both full of bubbles. Pedal is worse than when I started -- pretty much goes to the floor.

    OK -- where to from here? Will a failing master cylinder cause bubbles in any part of the system? And will a failing master cylinder affect one half of the system (specifically RR/LF) and not the other? Or should I suspect a caliper or line? (there is no apparent leak).

    (By the way I have posted this on SC, Saabnet and SW -- what a tart!)

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  2. #2
    Mike
    Moderator Shazam's Avatar
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    30 Jul 2010
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    Rochester, New York, USA
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    Saab(s)
    1973 96
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    I had a similar problem a couple years back (but with all four brakes, and a constantly mushy brake pedal, and air bubbles when bleeding), I eventually gave up and took it to my local mechanic. Turns out that there was a small leak (rusted through) in the lines that was enough to keep letting air in, but not big enough for me to see a difference in the brake fluid level. The fluid was dripping on the car itself, so I never noticed any drips underneath the car.

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  3. #3
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    14 Aug 2010
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    Medford, MA
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    683
    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    It sounds to me like a line, or maybe something in a connection (nut or flare not seating maybe). Could also be the connection between the fluid reservoir and the master cylinder itself (I'd say this on another car, but I've never heard of this failing on a c900 enough to suck air into the system). When master cylinders go, in my experience, they need a few pumps and then start to act normal, and when you're sitting at a stop sign the pedal might sink to the floor.

    (By the way I have posted this on SC, Saabnet and SW -- what a tart!)
    When I have a baffling problem, I, too, am a promiscuous poster. I tend to do those three fora as well.

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  4. #4
    Andy Graham
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    08 Aug 2010
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    Oz
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    Saab(s)
    '88 vert, '88 Aero
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    I'm now sure it's the master cylinder sucking air so will either rebuild or replace.

    Reasons it's the MC:

    As expected, the affected system (RR/LF) is fed by the line nearest the pedal end of the MC.
    When pumping the brakes while bleeding I observed bubbles in the MC reservoir.
    The repetitive pumping of trying to bleed the brakes has made the problem worse, ie weakened the MC seal further.
    I tried bleeding using the pressure method (clutch bleeding setup of bike pump and inner) and bubbles at caliper eventually disappeared. Of course, the pedal soon went soft again after a few pumps.

    I'm inclined to rebuild as it's much cheaper and suspect it's simply a sealing problem, but will reserve judgment until I look at the MC.

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  5. #5
    Griffin Davies
    Rebellious Agitator Grif900's Avatar
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    09 Mar 2011
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    Olde Cape Cod
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    Saab(s)
    88 SPG
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    I think the master cylinder is gone.

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  6. #6
    Andy Graham
    modérateur
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    08 Aug 2010
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    Oz
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    Saab(s)
    '88 vert, '88 Aero
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    Hey grif how you doin, still driving that Grove? (Or was it a Liebherr?)

    Yeah MC was always most likely but I don't like throwing parts at a problem -- prefer to think it through and weigh up the evidence. Having a spare car gives me that luxury I guess.

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    Last edited by SpecialTool; 06 July 2011 at 09:38.

 

 

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