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  • spongy brake pedal

    hey guys, im going to try and get help via here because i have a situation with the brakes. i revised my frond brake calipers and put 2 brand new ones in the rear and after that air kept being in the system.

    I replaced the master cylinder
    replaced the hydraulic bomb
    replaced the hydraulic servo with a non leaking unit
    replaced rear calipers
    removed the abs
    removed the valve that reduces pressure to rear brakes when lifted since it was stuck

    bled the system over a dozen times manually and machine wise

    now it just goes down a little, brakes well and after the second pump the brakes work mint. Then after a drive again the small spongy feeling just a tad and then after another press again good brake pressure. i cant figure out whats wrong its terribly frustrating.

  • #2
    Warped discs or runout at the hub, disc pushing on the pads and pushing the pistons back into calliper
    Panthero Coupé quattro 20vt
    Indigo ABY coupé
    Imola B6 S4 Avant

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    • #3
      interesting.

      The spongy for the first press or two brake feeling is something i have had for a while despite a caliper rebuild and new master cylinder.

      I suspect the caliper carriers as the inside face of my front and rear discs always seem to get a ring of corroded/crusty build up for a cm or two on the outer circumference. I put this down to the caliper not squeezing the disc squarely. I'm not suspecting warping or run out as there is no pulsing at the pedal and surely if the pistons were being beaten back by a wobbly disc, you would feel it?

      New caliper slide pins are all very well and good but there is little to be gained from new pins when the hole they slide in and out of isn't the right sizer anymore.

      Can i find new caliper carriers? nah. :-(

      I found myself contemplating getting in touch with a machine shop and seeing if they could machine out the hole and insert a shim back in there to bring it back to size. This must be what recon people did back in the day when you could get refurbished carriers?

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      • #4
        I just got brand new rear calipers as a rebuild didnt suffice. However i think error404 is on to something. Tis always at The rear. I put a screwdriver in between and you van see the screwdriver move in a certain part of both discs when the pedal is pressed. So lets hop this fixes the problem.

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        • #5
          BTDT try new discs and clean the hubs up
          Panthero Coupé quattro 20vt
          Indigo ABY coupé
          Imola B6 S4 Avant

          Comment


          • #6
            I had to laugh today when i went into a Formula 1 auto centre...

            To be fair they did have on car brake disc skimming kit and went in to find out all about it.

            The technician who did it was not very inspiring. Apparently they don't measure run out at all when they do the job and he couldn't tell me what they aim for when done but it is within tolerances. (how the hell do you know that if you don't measure it??!!) He then went on to tell me that if the total thickness after machining is less than the allowed limit then they wont do the job so run out won't be an issue...

            hmmm.

            I explained the spongy pedal getting firmer when pressed a couple of times and he said that skimming or run out (whatever he thought that was) wouldn't fix the fading problem. I explained that sponge and fade were different and then the manager told me it was £100 per pair of discs to do the job.

            I left.

            That's a shame as part of me likes the idea of the process but as a new pair of discs would cost less than that i might as well just get new ones. I have a dial gauge and stand on the way to check the hub face for run out before putting new discs on - no point in having a flat disc on a wobbly surface!

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            • #7
              okay guys a little update, new rear discs and same problem.

              the hydraulic part is completely disconnected ( plugged hole at brake cylinder and return line to servo) and still a spongy pedal, even after removal of the abs still a spongy brake pedal,

              my rear left brake caliper is a brand new caliper but the bleed screw is at the bottom instead of top like on my rear right wheel. i think its a rear caliper of a 200 hp audi 200 quattro. they look exactly the same like my 20v but the nipple is at the bottom. could this be the problem to my brake problem? perhaps air cant seep out because the nipples is at another location. i have literally replaced or fixed everything there could be to replace and still nothing. same as before. brake pedal sinks and after a second pump pedal stays good. i think it is still air so there has to be something im doing wrong with the bleed procedure. the car has been bled over a dozen times vacuum assisted, with pressure and manually.

              update on what i did

              new rear brake calipers
              removed abs
              new rear discs
              new master cylinder
              a replacement hydraulic servo( old one was leaking)
              another hydraulic bomb
              disconnected hydraulic system
              bled 20 times.
              new brake lines ( soft brake lines)
              removed rear valve on rear bridge.

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              • #8
                Originally posted by Jimmaey View Post
                okay guys a little update, new rear discs and same problem.

                the hydraulic part is completely disconnected ( plugged hole at brake cylinder and return line to servo) and still a spongy pedal, even after removal of the abs still a spongy brake pedal,

                my rear left brake caliper is a brand new caliper but the bleed screw is at the bottom instead of top like on my rear right wheel. i think its a rear caliper of a 200 hp audi 200 quattro. they look exactly the same like my 20v but the nipple is at the bottom. could this be the problem to my brake problem? perhaps air cant seep out because the nipples is at another location. i have literally replaced or fixed everything there could be to replace and still nothing. same as before. brake pedal sinks and after a second pump pedal stays good. i think it is still air so there has to be something im doing wrong with the bleed procedure. the car has been bled over a dozen times vacuum assisted, with pressure and manually.

                update on what i did

                new rear brake calipers
                removed abs
                new rear discs
                new master cylinder
                a replacement hydraulic servo( old one was leaking)
                another hydraulic bomb
                disconnected hydraulic system
                bled 20 times.
                new brake lines ( soft brake lines)
                removed rear valve on rear bridge.

                Bleed nipple at the top of the calliper....
                Last edited by jade; 29th August 2016, 11:11.
                RS 2 580HP

                Comment


                • #9
                  Try bleeding caliper off the car with the nipple up.

                  Sent from my LG-H955 using Tapatalk

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                  • #10
                    hey all , we have found the source of the problem. a rip off mechanic who said he would locate the problem in no time ! he literally changed out the entire car while quattro-nick told him to bleed the caliper with the nipple up. after assuring me he did everything he possibly including 4 liters of brake fluid through the system i didnt know what else. a quick trip of quattro-nick to my house and we bled the car accordingly including the caliper upside down and voila ! car works like a charm. thanks everyone diesel-den especially quattro-nick for helping me locate the problem so quick! i never knew how corrupt these garage workshops could be. rediculous !

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                    • #11
                      Glad to here.

                      Sent from my LG-H955 using Tapatalk

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                      • #12
                        great news!

                        I shall be trying this myself...

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                        • #13
                          your welcome buddy!
                          audi coupe quattro b2 2.2 20vt project (573hp-626nm)
                          TWINCHARGED power,zero lag
                          AEM W/M injection

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                          • #14
                            Nipples must always be at the top !









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                            • #15
                              Spongy brakes

                              A trick I learned when I was working was attach a hand operated vacuum pump with a reservoir attached and draw the fluid thru works a treat every time

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