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  1. #1
    Senior Member Four Rings Kevin C's Avatar
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    B6 Steering Upgrade: Adding a B7 S4 Rack with Servotronic.

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    Since I'm doing control arms and will need to get an alignment it seemed like a good time to upgrade the steering rack and get a faster steering ratio. The S4 rack upgrade has been covered a few times as has adding Servotronic. I know it's been done, but it seems like a couple of the details on the wiring harness were missing, this is my attempt to get all the needed info into one post.

    Parts Needed:

    B7 S4 Steering rack. The one I picked up is PN 8E1422072F (2007 S4). I picked it up used on Ebay for $138 shipped with 81,000 miles VIN # AUGL78E77A000545 Interchange # 551-59886, 6SPD,AWD,Tilt.

    It was listed as fitting:

    AUDI S4 06-08 Power Rack and Pinion
    AUDI RS4 07 Power Rack and Pinion
    AUDI S4 05 Power Rack and Pinion; Conv, from VIN 903001
    AUDI S4 09 Power Rack and Pinion; (Conv)
    AUDI RS4 08 Power Rack and Pinion; Sdn, thru VIN 904000
    AUDI S4 05 Power Rack and Pinion; exc. Conv; from VIN 400001

    The B7 A4 rack is PN 8E1422072E

    20181226_180249.jpg

    The RS4 rack is also listed as PN 8E1422072C, that appears have been used in earlier B7 S4's and RS4's. The rack I picked up is also listed as being used in the RS4 and the S4, PN 8E1422072F. Short story is it looks like the S4 and RS4 use the same rack and the newer version seems to be 8E1422072F. The C and the F versions use the same housing, the rack gear itself may have changed, but they are called out for the same applications. They also convolve to the same interchange number and compatible PN (8E1422053J).

    Listing for the S4 and RS4 from Wolfauto:
    8E1422072F.JPG
    8E1422072C.JPG

    Wiring:

    I found this thread that has some info including the super useful wiring diagram. What I realized was that there is one last connecter that no one seems to show. In the past its been pieced together by ordering a housing and terminals, but I had never seen the factory install.

    https://www.audizine.com/forum/showt...ve-servotronic

    Wiring Diagram:

    Wiring.JPG

    On Ebay I had ordered an S4 Servotronic relay and all the wiring bits that I could find but I never found an assembly with the socket that the Servotronic relay plugs into.

    Rack to Servotronic Harness: PN 8E1 971 323
    20181230_074045.jpg

    Harness that goes through the firewall: PN 8E1 971 109CB or 8E1 972 120C The CB version appears to have the Home Link wiring in the same grommet.
    20181230_074221.jpg

    That's where the other posts all seem to stop.

    I found a 2007 B7 in the yard and got a look at its wiring harness.

    8E1 972 120C (or 8E1 971 109CB), Show is where it ends up being routed to, it's the tan connector with two wires. It goes from harness 8E1 971 323, through the firewall and ends up in a connector rack just in front of the drivers door (by your left foot).

    20181229_134335.jpg

    I pulled the rack out and traced the connector. Having an Exacto knife really helped, I was able to quickly cut the jacket back and extract the wiring harness.

    20181229_140007.jpg

    With a bit of cutting I was able to get this out. This is the harness section that goes from the kick panel to the panel under the dash the the servotronic relay plugs into. I snipped the power and ground connections as well as the blue signal wire. That wire appears to up to the instrument cluster and supplies the vehicles speed signal. It was way too buried to pull out.

    On Ebay I picked up an S4 Servotronic module PN 8E0 907 307A (638) that one is from a 2004-2005, the B7 A4 uses PN 8E0 907 307D (640) the 2007 RS4 is PN 8E0 907 307C (642). Later S4's use 8E0 907 307G. It's my understanding that the steering boost level is customized to the application and that changing the relay controls the steering effort.

    20181230_074642.jpg

    The far end of that harness ends up under the dash. The blue wires needs to be connected to the ABS speed output and of course you need to connect up power and ground. More details to follow.
    Attached Images
    Last edited by Kevin C; 12-30-2018 at 02:04 PM.
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  2. #2
    Senior Member Four Rings Kevin C's Avatar
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    Location of Servotronic Relay (borrowed picture) 80485866_4f4bf415ed_o.jpg
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  3. #3
    Veteran Member Four Rings
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    wait, you actually want servotronic? Lots of B7 owners pull the relay to disable it
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  4. #4
    Senior Member Four Rings Kevin C's Avatar
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    Quote Originally Posted by Matt Devo View Post
    wait, you actually want servotronic? Lots of B7 owners pull the relay to disable it
    I know. I have read the "yes I pulled it and the world was great" and " I pulled it and put it back posts". I'm starting with it installed. I will try the car both ways. I'm also looking at what the RS4 module does. Optionally I can modify the response of the system to mimic a disconnected relay at anything above parking lot speeds. The relay takes a speed input and turns it into a PWM signal to control the level of assist, if I don't find one I like its not that hard to design a better version.

    I also found variable stiffness motor mounts on the same 2.0t... It seems that they have a solenoid that opens idle to reduce vibration and stiffens the response once you get on the throttle. Seemed kind of interesting.
    Last edited by Kevin C; 12-30-2018 at 01:46 PM.
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  5. #5
    Veteran Member Four Rings Spike00513's Avatar
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    Quote Originally Posted by Kevin C View Post
    I know. I have read the "yes I pulled it and the world was great" and " I pulled it and put it back posts". I'm starting with it installed. I will try the car both ways. I'm also looking at what the RS4 module does. Optionally I can modify the response of the system to mimic a disconnected relay at anything above parking lot speeds. The relay takes a speed input and turns it into a PWM signal to control the level of assist, if I don't find one I like its not that hard to design a better version.

    I also found variable stiffness motor mounts on the same 2.0t... It seems that they have a solenoid that opens idle to reduce vibration and stiffens the response once you get on the throttle. Seemed kind of interesting.
    So you're gonna try retrofitting those too?
    I have Febi B5 S4 mounts and am not sure if I killed them with misfire vibration, which I later fixed (the misfires). I think the mounts are like $30/ea.
    Either way, there seems to be some idle vibration (inline 4 engine is probably inherently unbalanced too, compared to a V8...that doesn't help), and idk how stiff the response is on throttle.

    I know the idea behind rear diff carrier inserts is that they're supposed to help lock in place the drivetrain a bit; not sure if that would yield a good improvement here.

  6. #6
    Veteran Member Four Rings Biged243's Avatar
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    Itís a hydraulic mount that will end up leaking. Not worth it. Stick with oem or jhm mounts. I have the rs4 rack in my car. Didnít even bother wiring the 640 relay in. There are different gears for the b7 a4, s4 and rs4. The rs4 is more if I recall, a screw like gearing. I like my rack much better than the stock and when I had my b7 I did the 640 mod and loved it. So thatís another reason why I didnít even bother with the retro fit for the relay.
    What ever makes sense go with the opposite and you got it

  7. #7
    Senior Member Four Rings Kevin C's Avatar
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    Quote Originally Posted by Biged243 View Post
    Itís a hydraulic mount that will end up leaking. Not worth it. Stick with oem or jhm mounts. I have the rs4 rack in my car. Didnít even bother wiring the 640 relay in. There are different gears for the b7 a4, s4 and rs4. The rs4 is more if I recall, a screw like gearing. I like my rack much better than the stock and when I had my b7 I did the 640 mod and loved it. So thatís another reason why I didnít even bother with the retro fit for the relay.
    You do know that the factory mounts on my B6 are hydraulic? This is just a variable version of what I already have. Not sure what I'm going to do with them, more of a curiosity.

    As far as racks go, so far I have not found any part number evidence that the ratio is different between the S4 and the RS4. I'm still not convinced either way, so far evidence indicates they are the same, I'm trying to prove that wrong. The A4 uses a straight cut rack and pinion, the S4 and the RS4 use an angle cut gear, both are still rack and pinion gears. The effective radius of the pinion gear determines the ratio, not the tooth angle. I did notice that the 8E1422072F rack seemed to have a different tooth profile than the 8E1422072C rack.

    To reduce the ratio (faster steering) the effective radius of the pinion gear needs to increase. To make the happen you either need move the pinion further away from the rack gear ( to allow for the increase in diameter) or cut the pattern deeper into the rack. Basically a faster rack needs to have the pinion increase in diameter or the steering arms on the uprights need to be shortened. (EDIT) : you can also change the effective ratio by changing the profile of the gear teeth. The idea is to engage more towards the tip or the root, changing the effective diameter of the pinion gear. This is how manufacturers make variable ratio rack and pinion steering gear.
    Last edited by Kevin C; 12-31-2018 at 11:35 AM.
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  8. #8
    Veteran Member Four Rings hilld's Avatar
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    I like all this talk about racks. Kevin can give demos with the relay in or with it out to the doubters.

  9. #9
    Senior Member Three Rings Gin+'s Avatar
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    Excellent info. I think servotronic is a cool feature on the b7.
    They're not scared of you. They're scared of what you represent to 'em.

  10. #10
    Senior Member Four Rings Kevin C's Avatar
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    It turns out that for Audi, BMW and Jag some users have developed modifications to fine tune the response. The Jag link shows an add on control that gets you the best of both worlds. One Audi guy inserted a resistor in the servo line, that keeps the feature but mutes its effect a bit. Lots of options.

    https://www.jaguarforums.com/forum/x...ontrol-147084/

    https://www.bimmerforums.com/forum/s...t-Curve-Coding
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  11. #11
    Veteran Member Four Rings Biged243's Avatar
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    https://www.audizine.com/forum/showt...-it-an-upgrade

    There is more info floating in the b7 section but this one covers most of it. There are pics somewhere that shows the gearing differences.
    What ever makes sense go with the opposite and you got it

  12. #12
    Veteran Member Four Rings Spike00513's Avatar
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    What about electric? I think this guy put an electric one into his B6 track car, that he got from a Nissan or something at a junkyard.


  13. #13
    Senior Member Four Rings Kevin C's Avatar
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    Quote Originally Posted by Biged243 View Post
    https://www.audizine.com/forum/showt...-it-an-upgrade

    There is more info floating in the b7 section but this one covers most of it. There are pics somewhere that shows the gearing differences.
    Big ED,

    Thanks for the link. I had spent a bunch of time looking at various posts and I still have yet to find one that shows the B7 S4 and RS4 as having different ratio steering racks.

    https://www.audizine.com/forum/showt...ack-an-upgrade



    Picture of my rack:


    My rack from another angle:

    RS4 Rack:


    I did notice that what looks like corrosion in some of the pictures of used racks is actually grease that's turned dark. Despite the rack having power steering fluid in the center, the rack gear it self is lubed with grease. From some online sleuthing it looks like PN G-052-168-A1 (replaces AOF-063-000-04, G-052-192-A1, G-052-197-A1, A0F-063-000-04).

    The rack gears look the same to me and the PN are listed as interchangeable.

    20190120_105547.jpg20190120_105504.jpgmodded2.jpg
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  14. #14
    Veteran Member Three Rings oaybar007's Avatar
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    This is VERY interesting. My rack is ok but I did debate ordering a rebuilt RS4 rack and having it installed when I had control arms and suspension work going on. I forget who but one of us here had installed it on his avant and had much praise for it. It would be great to get some more immediate steering. I was basically overwhelmed with all the information.

  15. #15
    Veteran Member Four Rings fR3ZNO's Avatar
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    Interesting retrofit. Good job compiling the info into one thread, will be interested in hearing how you like it after all said and done.
    "If one does not fail at times, then one has not challenged himself." - Ferdinand Porsche

  16. #16
    Veteran Member Four Rings Biged243's Avatar
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    I installed it without retrofitting the servo. Itís quicker and more precise. I love the heavier steering ever since I did the 640 mod when I had my b7. So, I figured I will just leave it off. Kevin, itís been a long time since I did the research but reading one of the post it states that the difference between the two is the servo relay. The rs4 has I believe a 642 relay. I thought I had read somewhere that the pinion gear was slightly different. Sorry to have some misinformation in previous post.
    What ever makes sense go with the opposite and you got it

  17. #17
    Senior Member Four Rings Kevin C's Avatar
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    Quote Originally Posted by Biged243 View Post
    I installed it without retrofitting the servo. Itís quicker and more precise. I love the heavier steering ever since I did the 640 mod when I had my b7. So, I figured I will just leave it off. Kevin, itís been a long time since I did the research but reading one of the post it states that the difference between the two is the servo relay. The rs4 has I believe a 642 relay. I thought I had read somewhere that the pinion gear was slightly different. Sorry to have some misinformation in previous post.
    Ed, thanks for the update and comment on the steering ratio, there is a quite a bit of conflicting info.... For the short term I picked up the S4 relay. The used RS4 units are a bit spendy. Once I prove out that I have everything working I will look at a custom version and or test the RS4 version, first step is get it working. A cutout switch is also an option. A fresh set of inner tie rods show up on Wednesday. I still have four calipers to rebuild... I got a bit side tracked on a shop improvement project ($300 of extra insulation to keep the place a bit warmer). Back to the car stuff this Friday.
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  18. #18
    Veteran Member Four Rings Biged243's Avatar
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    What like a vari volt in place of the servtronic relay? They have talked about doing it before. There is a valve in the rack that the relay controls and that valve controls the flow rate by how open it is. No relay equals almost closed valve.
    What ever makes sense go with the opposite and you got it

  19. #19
    Established Member Two Rings
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    Does anyone know the part number for the actual Servotronic solenoid? I am replacing the rack in my B6 with a B7 one that has a servotronic port but no solenoid in it. Know where to get one?

  20. #20
    Senior Member Four Rings Kevin C's Avatar
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    Quote Originally Posted by TheOnlyJClark View Post
    Does anyone know the part number for the actual Servotronic solenoid? I am replacing the rack in my B6 with a B7 one that has a servotronic port but no solenoid in it. Know where to get one?
    I listed three versions with part numbers in the first post. Edit ... Four part numbers. I got my parts on Ebay (also mentioned in the first post).
    Last edited by Kevin C; 01-24-2019 at 07:59 AM.
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.

  21. #21
    Established Member Two Rings
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    Quote Originally Posted by Kevin C View Post
    I listed three versions with part numbers in the first post. Edit ... Four part numbers. I got my parts on Ebay (also mentioned in the first post).
    I was asking for the part number for the solenoid valve only. I have a B7 rack with the servotronics port but no solenoid to connect the electrical to. And for anyone else looking for it it's Part # 8E1 998 317 A You can find them on 2005-2012 A4s and S4s I believe.

  22. #22
    Senior Member Four Rings Kevin C's Avatar
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    My bad :)
    03 A4 Quattro, 1.8T, 02X six speed conversion/ GJW (4.11 final drive). RS4 RSB, H&R FSB.



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