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Hydraulic to Vaccum servo conversion

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  • #46
    Nice work Horsty
    I tried this on RHD with a D3 servo (same size/fitting) but it doesn't fit, there is not enough room for the master cylinder.
    I am working on a adapter plate to mount the servo directly to the bulkhead. The bulkhead and pedal box need to be modified to allow the larger 60mm bellow to fit through. Even then I don't think it will work with the standard ABY/3B/RS2 intake pipe, reverse intake will be needed I think. I am going to use the 26.9mm master cylinder too
    Panthero Coupé quattro 20vt
    Indigo ABY coupé
    Imola B6 S4 Avant

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    • #47
      seems a lot of work.

      why not just use the factory bomb setup? what makes it worth the effort?

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      • #48
        the original hydraulic brake booster is way to expensive.
        especially when you have to repair it.
        i got rid of the hydraulic stuff.

        advantages:
        - servo pump is cheeper
        - hydraulic steering lines are cheeper
        - more brake power
        - lighter in total
        - you dont have to press the brake pedal so hard anymore
        (you can compare the pedal pressure almost to the gaspedal pressure)
        Audi Coupé Quattro 20V

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        • #49
          i dont suffer any of those issues, even with 6 pots, i dont need more power than that!


          i can imagine the s2 pump not being cheap though. neither is custom machining and sourcing other parts though.

          still not convinced but enough do it so ill take your word for it. interesting stuff and well worked out either way.

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          • #50
            B3 setup is bolt-on Gaz, it's a real easy swap
            Vac servo used are about £50. New £200.
            Single stage PAS pump is more reliable (you can't buy genuine ZF rebuild kits for the S2 pump anymore) plus they are common to loads of cars inc Porsche so there will never be a parts availability problem with them, likewise the vac servo.
            S2 hydro servo is around £900 from memory. Bomb is £250 and has a finite life, they are NLA too afaik. Try and get a decent dual stage S2 PAS pump, almost impossible! Plenty of practical reasons.
            I'm going to upgrade again to the D3 V10 servo for better line pressure from the dual diaphragm booster, and the better pedal feel of a larger MC.
            Panthero Coupé quattro 20vt
            Indigo ABY coupé
            Imola B6 S4 Avant

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            • #51
              This is the design for the push rod i used.

              Audi Coupé Quattro 20V

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              • #52
                Do you have a picture of the assembly installed on your car Horsty?
                Panthero Coupé quattro 20vt
                Indigo ABY coupé
                Imola B6 S4 Avant

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                • #53
                  Originally posted by Error404 View Post
                  Nice work Horsty
                  I tried this on RHD with a D3 servo (same size/fitting) but it doesn't fit, there is not enough room for the master cylinder.
                  I am working on a adapter plate to mount the servo directly to the bulkhead. The bulkhead and pedal box need to be modified to allow the larger 60mm bellow to fit through. Even then I don't think it will work with the standard ABY/3B/RS2 intake pipe, reverse intake will be needed I think. I am going to use the 26.9mm master cylinder too

                  If you mount the booster directly to the bulkhead the complete setup will be about an inch shorter then std so should fit oem intake also on RHD models. It was no problem on LHD except you need to raise the booster a bit from std center to clear tha banjo on the steering rack and you need to reroute the cable loom in the engine bay. Just fitted this setup to my CQ
                  Last edited by Audi_CQ; 24 May 2015, 00:35.

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                  • #54
                    The bellows on the D3 servo is ~60mm. The hole in the B3 bulkhead is ~45mm. It won't fit without modifying the bulkhead and the pedal box. On RHD the D3 servo won't mount directly to the bulkhead either you need to use a spacer or the servo body hits the bulkhead, due to the profile. Trust me I have all the parts here
                    Panthero Coupé quattro 20vt
                    Indigo ABY coupé
                    Imola B6 S4 Avant

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                    • #55
                      OEM B3 pedal box profile:


                      Modified pedal box and bulkhead profile:


                      Spacer plate:


                      Assembly:
                      Panthero Coupé quattro 20vt
                      Indigo ABY coupé
                      Imola B6 S4 Avant

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                      • #56
                        ok alex thanks for that reasons seem more explanitory now. no parts or mega wonga.

                        so what makes the b3 plug and play and not the s2? all the s2 parts fit the b3 pedal box?

                        is there a b3 thread to stop me butting in on this one?

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                        • #57
                          B3/B4 pedal box is the same, so is the bulkhead mounting holes etc. The only thing plug & play on B3/B4 is B3/B4 stuff
                          Panthero Coupé quattro 20vt
                          Indigo ABY coupé
                          Imola B6 S4 Avant

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                          • #58
                            im confused in your other post you say b3 setup is bolt on. is it just a matter of getting the bits or is it custom piston and spacer work too?

                            i need to do some reading i think to understand the setup more. seems quite a few have done it. i hope my brakes still works as it used to do. otherwise ill need to read more carefully.

                            edit

                            so after reading the d3 is too big for stock fitment,

                            alex - is the audi cab one is direct fit? are you using that if not is there a reason why you went to the trouble of adapting the setup for the d3?

                            the rest seems straight forward and i can see why its done now. cant see why audi used the bomb setup though if function is equal.
                            Last edited by GazzaG60; 24 May 2015, 13:50.

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                            • #59
                              Only for left foot braking...!

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                              • #60
                                Originally posted by GazzaG60 View Post
                                im confused in your other post you say b3 setup is bolt on. is it just a matter of getting the bits or is it custom piston and spacer work too?

                                i need to do some reading i think to understand the setup more. seems quite a few have done it. i hope my brakes still works as it used to do. otherwise ill need to read more carefully.

                                edit

                                so after reading the d3 is too big for stock fitment,

                                alex - is the audi cab one is direct fit? are you using that if not is there a reason why you went to the trouble of adapting the setup for the d3?

                                the rest seems straight forward and i can see why its done now. cant see why audi used the bomb setup though if function is equal.
                                B3/B4 servo is bolt-on to B3/B4 chassis. If you want to fit a vac booster on your motor, jsut buy a RHD vac booster and it will bolt on. B4 hydro cars inc ABY coupe need to also use the servo bracket 8A0611945, but you should already have it on the B3, AFAIK it was used on all RHD cars up to 92.

                                D3 does not just bolt on. D3 and other later models use a dual diaphragm booster so you get more line pressure for less pedal effort. you can also fit a larger master cylinder which gives a better pedal feel when you have larger caliper piston area.

                                HTH, drop me a line if you like mate
                                Panthero Coupé quattro 20vt
                                Indigo ABY coupé
                                Imola B6 S4 Avant

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