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Thread: B8.5 SQ5 Master Cylinder replacement

  1. #1
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    B8.5 SQ5 Master Cylinder replacement

    Hey guys, haven't been around much lately, haven't even been driving the SQ5 as it's been sitting in the garage on the lift. Now that I miss it, and want to take it up north on a snowboarding trip, I'm working through the brake issues I've been having.

    I think this problem began when I replaced a rear clogged bleeder screw a while back and introduced air, or maybe it was when I replaced the front pads/rotors. The pedal was initially firm and if you did anything more than moderate braking, the pedal would fall to the floor, feel like your skidding on gravel and ABS engaged.

    Knee jerk reaction is air in the system so I bled the brakes probably five times and ran the ABS output tests. I did this several times also and bled the brakes again.

    Fast forward to today (which is months later that the car has been sitting in the garage - sigh), I replaced the master cylinder this past weekend after talking to some people and doing further research. There's no engine RPM drop, which would be indicative of a vacuum leak, so I'm pretty sure the MC is shot. I did this without removing the bulkhead, which is what is called for in the repair manual. Because of this, I didn't bench bleed it and plan to bleed it on the car through the nearest caliper, which is the undertaking for this afternoon.

    What comes next? Is the output tests/ABS cycling required? Or do I roll right into bleeding? I've seen posts all over the place of when to invoke the ABS output test.

    Many thanks!

  2. #2
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    Quote Originally Posted by shaggymatt View Post
    Hey guys, haven't been around much lately, haven't even been driving the SQ5 as it's been sitting in the garage on the lift. Now that I miss it, and want to take it up north on a snowboarding trip, I'm working through the brake issues I've been having.

    I think this problem began when I replaced a rear clogged bleeder screw a while back and introduced air, or maybe it was when I replaced the front pads/rotors. The pedal was initially firm and if you did anything more than moderate braking, the pedal would fall to the floor, feel like your skidding on gravel and ABS engaged.

    Knee jerk reaction is air in the system so I bled the brakes probably five times and ran the ABS output tests. I did this several times also and bled the brakes again.

    Fast forward to today (which is months later that the car has been sitting in the garage - sigh), I replaced the master cylinder this past weekend after talking to some people and doing further research. There's no engine RPM drop, which would be indicative of a vacuum leak, so I'm pretty sure the MC is shot. I did this without removing the bulkhead, which is what is called for in the repair manual. Because of this, I didn't bench bleed it and plan to bleed it on the car through the nearest caliper, which is the undertaking for this afternoon.

    What comes next? Is the output tests/ABS cycling required? Or do I roll right into bleeding? I've seen posts all over the place of when to invoke the ABS output test.

    Many thanks!
    NVM, found the order.

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