B6 Steering Upgrade: Adding a B7 S4 Rack with Servotronic.

[Kevin C]

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 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.

[Kevin C]

Location of Servotronic Relay (borrowed picture) 80485866_4f4bf415ed_o.jpg

[Matt Devo]

wait, you actually want servotronic? Lots of B7 owners pull the relay to disable it

[Kevin C]

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.

[Spike00513]

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.

[Biged243]

It’s 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. Didn’t 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 that’s another reason why I didn’t even bother with the retro fit for the relay.

[Kevin C]

It’s 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. Didn’t 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 that’s another reason why I didn’t 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.

[hilld]

I like all this talk about racks. Kevin can give demos with the relay in or with it out to the doubters.

[Gin+]

Excellent info. I think servotronic is a cool feature on the b7.

[Kevin C]

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

[Biged243]

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.

[Spike00513]

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.

[Kevin C]

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

[oaybar007]

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.

[fR3ZNO]

Interesting retrofit. Good job compiling the info into one thread, will be interested in hearing how you like it after all said and done.

[Biged243]

I installed it without retrofitting the servo. It’s 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, it’s 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.

[Kevin C]

I installed it without retrofitting the servo. It’s 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, it’s 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.

[Biged243]

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.

[TheOnlyJClark]

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?

[Kevin C]

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).

[TheOnlyJClark]

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.

[Kevin C]

My bad :)

[Kevin C]

A quick update, the rack and the wiring harness are in. I tested it without the servotronic and it is drivable, although a little heavy at low speeds.

Servotronic gets hooked up this week. I will post the results. So far so good. I like the S4 rack.

[Kevin C]

Signal wire for speed sense. I verified that I had the right wire by probing with my scope and spinning the wheel. On my 2003 its the blue / white wire in the green connector.

The servotronic works as designed. I agree that its a bit over boosted at low speeds. (EDIT) Once driving above 20 - 30 mph it feels perfect. Fine tuning will come later.

servotronic_spped signal.jpg

[Matt Devo]

A quick update, the rack and the wiring harness are in. I tested it without the servotronic and it is drivable, although a little heavy at low speeds.

Servotronic gets hooked up this week. I will post the results. So far so good. I like the S4 rack.

is the B7 S4 rack w/o servotronic heavier than the stock B6 A4 rack?

Signal wire for speed sense. I verified that I had the right wire by probing with my scope and spinning the wheel. On my 2003 its the blue / white wire in the green connector.

The servotronic work as designed. I agree that its a bit over boosted at low speeds. Once driving it feel perfect. Fine tuning will come later.

I thought it wasn't boosted at all over ~10mph or such. Or maybe that's just the RS4 version?

[Kevin C]

is the B7 S4 rack w/o servotronic heavier than the stock B6 A4 rack?


I thought it wasn't boosted at all over ~10mph or such. Or maybe that's just the RS4 version?

Very much so... I got used to it but it felt like manual steering at low speeds (in a lighter car, manageable though).

Above 15- 20 mph the boost drops off and it feels good. Pulling into a parking lot at low speeds it's almost too easy, it feels a bit weird. There may be some hysteresis, if your going from 40 mph to 15 it seems to hold off and keep the assist low.

I only went for a short drive last night to make sure it worked. I have the S4 relay, I may try the RS4 or mod what I have. The main thing was to just get it working and figure the rest out later.

[Nollywood]

My car has servotronic steering, and it feels very different to my old B6.

[Kevin C]

My car has servotronic steering, and it feels very different to my old B6.

I agree, totally different feel although I'm getting used to it. It feels perfect on the highway, the assist could be dropped a smidge around town.

[Kevin C]

Update: Switching over to summer tires resulted in an entirely different feel. I'm pretty sure the boost is partly tuned to match how much low speed turning resistance the tires offer. Snows have a lot more siping and blocks, the summer tires have almost none. The low speed steering tightened up quite a bit with the summer tires, I'm sure all season tires would be somwhere in between.

Short story I left the servotronic as is.

[bommbbaa]

Hello

[bommbbaa]

Hello.
My name is Danijel.
i am looking for harnes,wires and relay for servotronic mod.
If somebody can help me i will pay and will be verry helpfull.
Audi A4,B6,2004,1.9tdi quattro
Thank you

[codemode]

Hello.
My name is Danijel.
i am looking for harnes,wires and relay for servotronic mod.
If somebody can help me i will pay and will be verry helpfull.
Audi A4,B6,2004,1.9tdi quattro
Thank you

I plan on swapping my steering rack as well, since mine is leaky.
What do you want to know exactly?

[bommbbaa]

Hi.
Thanks for reply.
Now i got the rack and harnes with relay.
I dont know exactly how to wire everything?
One conector is on the relay,i dont know about the yelow one and other wires.
Thanks for help

[Kevin C]

The wire in my photo isn't really yellow, its just bad lighting.

From the servotronic relay:

Black Wire: Switched power (ignition switch).

Brown Wire: Ground

Brown / Blue : To servotronic solenoid on the rack (brown connector)

White / Red : To Servotronic solenoid on the rack (brown connector)

White / Blue: To ABS unit for speed sensing - wire looks a bit yellowish and you cant see the blue stripe in the photo (connects to the blue / white wire in green shell, see photo)

[bommbbaa]

Thanks for reply.
Great,when i put everything together i will let you know.
Have a nice day

[bommbbaa]

Hello.
You helped me with servotronic instalation Audi B6.
I am in progress now,please tell me for black wire-ignition switch.
On whitch fuse can i wire?
Horn or fuel pump....?
Thanks

[shoemaker617]

as far as i remember servotronic steering racks were designed for the cars with heavier motors up front. The real upgrade would be getting a b7 2.0t rack which is a bosch style rack(the gearing has been optimized for better handling). I tried this before, and the bottom line(for me), waste of time and money. Way to much work to put a used an abused part in your car(make sure your pull the boots back an check the gear for rust, they will leak! went through 3 of them)when you can get the same result with a brand new part for like 600$ with a core return



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[Kevin C]

as far as i remember servotronic steering racks were designed for the cars with heavier motor up front. The real upgrade would be getting a b7 2.0t rack which is a bosch style rack. I tried this before, and the bottom line(for me). Way to much work to put a used an abused part in your car(make sure your pull the boots back an check the gear for rust, they will leak! went through 3 of them, when you can get the same result with a brand new part for like 600$ with a core return


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Not true, the servotronic system is standard on B7 A4 with the 2.0T engine, that was donor vehicle I got the harness from. 4 cyl with servotronic. The B7 2.0T rack is the slower ratio. Also the feedback is controlled by the relay, not the the rack. Right now I have a S4 relay and I like it. Its also possible to try the A4 2.0t relay or the RS4 version. If you want the faster steering ratio you need the S4 / RS4 rack, otherwise there is no good reason to do this.

I have had the same used S4 rack for 2 years. EDIT: 12/08/2024 - 6 years on the salvage yard rack and still going strong. I sourced a used low mileage unit from an area that doesn't use road salt. As with any used part taking your time and getting a good one matters.

Also, on the B7 A4 forum the S4 rack is considered an upgrade.

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

The RS4/S4 racks have a different ratio. I instantly felt the difference in steering feel. You feel it more with the FBSW as it is a smaller diameter then stock and with the factory A4 rack it was sloppy and you needed to over correct the wheel to compensate with the FBSW. When I swapped to the RS4 rack it was a night and day difference ,you just point the wheel in the direction you want to go as well 2 1/2 turns lock to lock.

[Kevin C]

Hello.
You helped me with servotronic instalation Audi B6.
I am in progress now,please tell me for black wire-ignition switch.
On whitch fuse can i wire?
Horn or fuel pump....?
Thanks

I just used a meter and found a 30 amp switched circuit on the fuse panel and used a fuse tap with a 3 amp fuse in it for the servotronic.

[shoemaker617]

Not true, the servotronic system is standard on B7 A4 with the 2.0T engine, that was doner vehicle I got the harness from. 4 cyl with servotronic. The B7 2.0T rack is the slower ratio. Also the feedback is controlled by the relay, not the the rack. Right now I have a S4 relay and I like it. Its also possible to try the A4 2.0t relay or the RS4 version. If you want the faster steering ratio you need the S4 / RS4 rack, otherwise there is no good reason to do this.

I have had the same used S4 rack for 2 years. I sourced a used low mileage unit from an area that doesn't use road salt. As with any used part taking your time and getting a good one matters.

im speaking as a everyday driver...so your saying you wont get the same result by just upgrading the tierod ends?

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