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
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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
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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).
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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.
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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 where the servotronic relay plugs into. I snipped the power and ground connections as well as the blue signal wire. That wire appears to go 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.
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