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Cycling ABS to bleed 1990 cq20v

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  • Cycling ABS to bleed 1990 cq20v

    New rear calipers fitted, system bled and finally a functional handbrake has returned But, as has been discussed many times on the forum before, bleeding seems to be an issue. I used a pressure bleeder and sent 250-300ml through each corner but still have a pedal which only firms up if pressed twice. Once firm though, all is good.

    I know about operating the ABS module to cycle any trapped bubbles past the solenoids and down the brake line towards the caliper but, this seems to require vagcom. I don't have vagcom and even if I did, I don't think it is compatible with the 7a engine.

    How would I go about getting the abs motor to run on my car to simulate the 11 second burst vagcom would create if I could plug it in?

    I may try the classic two man bleed technique next as I've read that pressure bleeders on their own may not move the volume needed to dislodge bubbles, and to be fair - fluid didn't exactly flow out of the nipple when it was undone.


  • #2
    Why not just drive it and hammer the brakes a good few times to operate the ABS...….then do the 2-man method?!

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    • #3
      This is mentioned in my research so far and there is no reason why it won't work. The only thing I'm thinking is that you wouldn't ever know which brake circuit is locking up and the cycling may not bleed the one that needs it?

      Not really sure if that's the case though, if the fluid in it came from one central chamber then I could see it working but I think it has one chamber per circuit...

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      • #4
        I rebuilt everything on my car from scratch and the abs pump had been left empty for over 6 years. I had no issues bleeding. Just take your time and do all four corners again slowly and methodically. Make sure the fluid you are using is new, unopened and un shaken bubble free brake fluid and pour slowly so as not to get any small bubbles in it.
        Nothelle S2 Avant in restoration
        Wr Ur Quattro (also in restoration)

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        • #5
          That's good to gear! ​​​Did you use pressure or vacuum or. 9nenway valve or the good old 2 man technique?

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          • #6
            Originally posted by steve briance View Post
            That's good to gear! ​​​Did you use pressure or vacuum or. 9nenway valve or the good old 2 man technique?
            I started off with air operated vac bleeder but it broke, so I went back to the old fashioned way. I have a brake bleed container with a one way valve. It says you can do it single handed but in my experience its better to have someone pump the brake for you, so you can shut the valve whilst the fluid is actually flowing
            Nothelle S2 Avant in restoration
            Wr Ur Quattro (also in restoration)

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            • #7
              this weekend I will give it another go!

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              • #8
                Originally posted by steve briance View Post
                this weekend I will give it another go!
                Good luck. Another little tip I was told by an old mechanic friend is to remove each bleed nipple and coat threads in copper grease. This stops the air sucking back via the thread when you are bleeding and also prevents them from seizing
                Nothelle S2 Avant in restoration
                Wr Ur Quattro (also in restoration)

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                • #9
                  Don't forget a mechanical issue can cause a soft pedal also, such as tapered pads or disc run-out.
                  Panthero Coupé quattro 20vt
                  Indigo ABY coupé
                  Imola B6 S4 Avant

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                  • #10
                    I like the top tip re grease on threads. I've actually got stainless bleed nipples so they don't seem to seize but, air sucking past the threads still applies.

                    As for tapered pads. I see that and do wonder whether the caliper carriers could contribute to the feel. Whenever you get refurb calipers - they come with new slider pins. This is all well and good but if the hole they slide in is worn it makes no difference and your caliper has some play. I don't seem to be able to find new rear carriers (trw don't do them any more) so found myself wondering if an engineering firm would be able to ream out and sleeve the holes like is done with an engine block?...

                    Will do the easy stuff first and see how it goes with that

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                    • #11
                      It would be easier to ream oversize and machine new guide pins. I can do it but as a one-off it’s not a cheap fix.
                      Panthero Coupé quattro 20vt
                      Indigo ABY coupé
                      Imola B6 S4 Avant

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                      • #12
                        If you think the ABS is an issue, bleed it with the engine running
                        Mike

                        http://www.s2-audi.co.uk

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                        • #13
                          Update.
                          Today I finally got round to bleeding my brakes, 2 man method piece of wood under pedal to limit travel.

                          The master cylinder nipple is strangely not at the highest point but a small bubble came out, the nipple on the end of the pressure limiter underneath is properly awkward to get to but access better through wheel arch. Didn't get a bubble from that, in fact very little fluid which is in keeping with its job I guess.
                          With engine running each corner was done and n/s/r let out 3 very small bubbles. O/s/r let out a stream of bubbles despite having previously used pressure bleed.

                          Fronts had no bubbles.

                          The net result is the pedal doesn't need a push to firm up now but I still wouldn't describe the pedal as feeling firm / solid. I noticed the rear calipers twisting around on its slide pins when helper was pressing the pedal which probably isn't helping.

                          All the others cars I drive regularly are much more modern and have great brakes. My brakes are alright but maybe I'm chasing an end result that is just not possible.

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                          • #14
                            Well, you wouldn't beleive it but I've just bought 2 new TRW rear caliper carriers on ebay for £46! Last ditch effort - if these don't sort it then the pedal is probably as good as it is going to be.

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                            • #15
                              Well done for getting some air out. Maybe bleed again after a few miles.
                              As to pedal feel, it depends what you are used to I think. My wife's Passat has very fierce brakes. You touch the pedal and almost go through the windscreen .
                              My S2 brakes feel much more tame but do work really well if you press on the pedal hard. Maybe just drive it a bit and see how you get on.
                              Nothelle S2 Avant in restoration
                              Wr Ur Quattro (also in restoration)

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