S5 Wheel Bearing Replacement DIY: Comprehensive Instructions (other B8 cars similar)

[Europa S5]

As our cars creep up in mileage, and we put heavy-ass wheels on them, wheel bearings are going to start to fail. I’m at 77K miles now, and this bearing has been groaning/humming for at least the last nine months (see video on YouTube to hear how chewed up it was when I rotated it by hand). If your car has a noticeable rotational noise, one that increases with road speed but is independent of gearbox or engine speed, there’s a good chance it’s a dying wheel bearing. Mine got loud enough toward the end that it started to get annoying to listen to when driving. Time to go! I finally got around to fixing it today.

Below is a comprehensive instruction set for you if you’re tempted to DIY. If you have the tools, it’s pretty easy - it took me two hours from wheels up to wheels down, not counting travel time to the shop for a hydraulic press. You will need quite a few tools, including some non-standard drivers, so take note of what’s required (I’ve highlighted these below), but overall, it's not THAT challenging. The two main challenges are: the bolts will take a bit of force to remove while simultaneously trying to NOT strip-out the heads on the triple-square; and, the press fit of the hub into the bearing collar is a *tight* fit and absolutely requires a hydraulic press. This whole instruction set is for a 2008 S5 V8, but this procedure is going to be pretty similar across the B8 lineup, so these instructions will generally apply to A4/S4/Q5s as well (some bolts may be different).


Parts Needed (pics below)
1. Wheel bearing replacement kit. Most OER/aftermarket kits include the following:
- One wheel bearing and housing (OEM P/N: 4H0498625D)
- Four housing bolts (Torx T60), which must be replaced once removed (OEM P/N: WHT000237A)
- One center axle bolt (19mm hex), which also must be replaced once removed (OEM P/N: 8E0407643A)

There are lots of kits available, but I got one just like this: aftermarket wheel bearing kit.

2. Six 10mm triple-square/XZN differential flange/axle bolts that must be replaced once removed (OEM P/N N90441103). While these aren't torque-to-yield bolts, they are marked as "replace" in the service manual, so order new ones. They're cheap; $1.25 per bolt via GenuineAudiParts.com. These are NOT generally included in wheel bearing kits.


Tools Needed
- Torque wrench
- Impact wrench, air ratchet, and air compressor (NOT essential, but helpful if you're doing this by yourself)
- Ratchets, short and long extensions, adapters, and wobbly extensions - probably will need 1/4", 3/8", and 1/2"
- Breaker bar and long cheater bar (you'll be putting a ton of torque on the axle bolt)
- Mallet (to knock the wheel bearing and hub out of the spindle)
- Wire brush (to clean the spindle, axle splines, hub splines, driveshaft flange, and differential output flange)
- Paracord or rope (to hang the caliper from the upper control arms as you work)
- Paint pen or marker (to mark the bolts being torqued)
- 10mm socket or wrench (for the plastic axle shield)
- 17mm socket (for the wheel bolts)
- 19mm socket (for the brake caliper carrier bracket bolts)
- 19mm hex driver/socket (for the large outboard axle bolt.**Note that this is a large, uncommon size**)
- T27 Torx (for the brake rotor keeper screw)
- T30 Torx (for the brake heat shield)
- T60 Torx (for the wheel bearing housing/hub bolts. **Note that this is a large, uncommon size**)
- M10/10mm triple-square (for the differential output flange bolts)
- M12/12mm triple-square (also for the wheel bearing housing/hub bolts.**Note that this is a large, uncommon size**)
- Hydraulic press (to press the splined hub out of the old bearing and into the new one)

Torque Specs
Center axle/hub bolt (19mm female hex): 200Nm/147ft-lb +180 degrees [replace with new]
Bearing housing and hub assembly (four Torx T60): 80Nm/60ft-lb., plus 90 degrees [replace with new]
Axle to differential output flange (six triple-square 10mm): 70Nm/52ft-lb in a star-pattern [replace with new]
Brake caliper carrier bracket (two 19mm bolts): 92lb-ft.
Wheel bolts: 89lb-ft.


Steps:

1. Remove the wheel center caps and break the center axle/hub bolt loose. With the wheel resting on the ground under full weight, loosen the center axle/hub bolt using using the 19mm hex driver/socket. Loosen, but don't remove it yet.

2. Jack the car up and secure it properly, and remove the wheels. You need only jack the front of the car up for the front wheel bearings, and only remove the wheels for which you're doing bearings (you don't have to remove both sides).

3. Remove the plastic axle/driveshaft guide that's secured to the body of the car using the 10mm socket or wrench. It's a plastic nut, so take it easy on this guy.

4. Remove the brake calipers directly at the carrier bracket using the 19mm socket. The bolts are accessed from the inboard side/backside of the spindle. Before fully removing the bolts, feed the rope or paracord through the carrier bracket and tie it to the upper control arms - you don't want the caliper falling off with force and dangling from the brake lines. Once the caliper is removed, tie the caliper high and out of the way.

5. Remove the brake rotor retaining screw using the T27 Torx. If the rotor is frozen to the hub, use the mallet to bang it off. Be ready for the rotor to fall off suddenly, so put something under it to cushion the blow (instead of your feet). The wheel hub now sits exposed.

6. Remove the brake dust shield using the T30 Torx.

For the following two steps, you can change the order based on whether you have an assistant or not. If you DO have an assistant, do these steps before steps 4-5 and have your assistant stand on the brakes as you loosen the bolts on the rotating bits in 7-8. If you're doing it by yourself, follow the additional recommendations in the steps below.

7. Remove the large axle bolt using the 19mm hex driver/socket. This works best with the impact wrench, since you will likely just spin the whole axle using hand tools, and an impact wrench can blast the bolt off faster than the axle will spin. If the axle IS spinning, insert a 3/8" extension into one of the wheel bolt holes and use it to stop the rotation against the threads of one of the bearing housing bolts that are exposed in the spindle assembly. You'll replace this large axle bolt during reassembly.

8. Remove the six bolts that secure the axle to the differential output flange using the 10mm triple-square driver/socket and long extensions. Take special care to seat the driver into the bolt head securely and straight - triple-square is a total pain in the ass and can strip-out easily if you don't seat the driver dead-on straight. Clean the bolt heads out first if you have to.

The bolts can be accessed using two extensions; rotate the whole assembly to bring the bolts to where you can access them. As above, you can use a 3/8" extension to stop the hub and axle assembly from rotating as you put force on the bolts. Note that not only do you need to ensure that the driver is properly seated, you'll also have to really torque them to get them out. Take care as you do this.

9. Remove the axle. This will take a bit of finessing and contortion, but it'll come out at this point. Don't puncture the rubber boots.

10. Remove the wheel bearing housing and hub assembly using either the 12MM triple-square OR the Torx T60 driver to remove the four bolts on the inboard/backside of the spindle. There was a revision somewhere in the build date and the old bolts are triple-square; new bolts are Torx. If it's the triple-square, take care in the same way that you did with the bolts in Step 8, above. Torx is a lot more forgiving. This will also take some force.

11. Remove the hub and bearing carrier assembly. You may need to tap it out using the mallet. Put something under it to cushion the blow.

12. Press the hub out of the bearing bore. The hub itself has the inner splined shaft that inserts into the bore of the bearing. If you have a press, you'll probably know what you're doing. If you don't, bring it to a machine shop, auto shop, muffler shop, etc... someone who knows what to do.

13. Press the hub into the new bearing housing.

14. Clean the mating surfaces. Use wire brushes to clean the spindle bore, the differential output flange, the axle flange, and then carefully clean the splines on the axle and in the hub (also use a rag). When cleaning the spindle bore, be careful not to damage the wheel speed sensor - it's the little black plastic tab on the forward side of the bore. When cleaning the axle splines, plug the openings to the CV joint so you don't contaminate the inside with debris. It's important to clear the mating surfaces, particularly where you need to be sure the bolts are able to seat - and torque down - properly.

15. Mark the axle flange to keep track of tightening in a star pattern. Use the paint pen or marker to mark 1-6 next to the holes. 1-3-5-2-4-6, clockwise.

Reassembly time!

15. Reinstall the bearing housing and hub assembly with the new bearing into the spindle and secure it using the Torx T60 bolts. These are torque-to-yield bolts, so you'll be replacing them (they're shipped with the many available aftermarket/OER bearing kits). Torque these to 80Nm/60ft-lb., plus 90 degrees. Mark the bolts and the spindle with a paint pen to keep track of the 90-degree turn.

16. Reinstall the axle. Once you get it into place, install the center axle bolt so it's snug, but don't torque it yet.

17. Reinstall the six axle flange bolts torquing them to 70Nm/52ft-lb in a star-pattern. This is where the 1-6 markings come in handy. Torque the bolt #1, rotate the axle 180 degrees and torque #2, then rotate back to #3, etc.

18. Reinstall the brake dust shield. Probably no more than 10ft-lb. or so.

19. Reinstall the brake rotor. Torque the keeper screw to like 5 lb-ft. It's really just to hold the rotor from falling off when the caliper is removed.

20. Reinstall the brake caliper assembly. Torque the bolts to 92lb-ft.

21. Tighten the center axle bolt to 200Nm/147ft-lb +180 degrees. Use a breaker bar and a cheater bar to get this much torque down. I pulled the handle from one of my floor jacks and used that and it was *still* hard to get it to the proper torque. Two options to hold the hub stationary for this: either have someone stand on the brakes as you torque it down, or reinstall the wheel and tighten it with the wheel on the ground. I used the brakes, but I didn't have an assistant, so I jammed a piece of 2x2" between the brake pedal and the metal part of the seat bracket and moved the seat forward until the brake pedal was depressed firmly.

Done.

In pictures:

Schematic of the spindle, hub, and axle assemblies, with torque specs. This helps you visualize both what you will be doing, as well as the configuration of the parts.
(I) The bearing is pressed into the housing to form an assembly (#11) at the factory;
(II) the single-piece hub (#10) is pressed into the bearing’s bore;
(III) the mated bearing and hub assembly (red oval at lower right) is mounted to the outboard face of the spindle (#6), and secured with bolts (#23) from the inboard side of the spindle; and finally
(IV) the axle (#21) is installed and the center bolt (#9) secures the axle to the hub.




Wheel bearing kit including new bolts:




New bearing with original hub pressed-in:




Non-standard drive bits required:




Wire brushing the axle flange with the axle in a vice:




Spindle with brakes and hub removed, after wire brushing:




Differential output flange, looking through the spindle bore.




Backside/inboard of the spindle with all components removed. Wheel speed sensor is not shown in this pic:




Inboard side of the spindle with bearing housing reinstalled, and bolts tightened to 80Nm/60ft-lb., but before the final 90 degrees. Note the paint markings to keep track.




… and after 90-degree torquing. Note also the black tab at 10 o’clock - that’s the wheel speed sensor. Don’t break it.




Axle reattached to the diff output flange. Note the numbered markings to help keep track of the star pattern when re-torquing:




My cellulose assistant - a 2x2”, jammed against the metal part of the seat bracket to hold the pedal down while I torque the center bolt on the hub:




Cheater bar used to get the monster torque on the center bolt. That’s the whole handle from the floor jack:

[Jeff V.]

It's good to see such a well done how-to on here. Thanks!

[JoshDub]

Very well done. Thank you for posting the torque specs clustered and in an easy to find spot.

[TTRStud]

Outstanding work/review. You're an asset to the forums! Thanks!

[Europa S5]

It's good to see such a well done how-to on here. Thanks!

Very well done. Thank you for posting the torque specs clustered and in an easy to find spot.

Outstanding work/review. You're an asset to the forums! Thanks!

Thanks guys, and you're welcome. Glad you agree on the torque specs. One of the most frustrating, time-consuming things I encounter is chasing-down torque specs. Even service manuals can be spotty and inconsistent with those.

[zokissima]

Excellent writeup, and I know the entire B8 platform will benefit from your diligence. Thank you for sharing and taking the time.

[A4 Centaur]

Thanks again for such a good write up!

[tbar23]

I started this project last night. Does anyone know if it can be done without unbolting the axle from the center of the car? That process seems to be a huge PITA and is only required to get to the four wheel bearing XZN bolts. If the suspension is pre-loaded to get the axle back up closer to horizontal, does that provide enough access?

[Europa S5]

Does anyone know if it can be done without unbolting the axle from the center of the car?

It *may* be possible to do the wheel bearing job without unbolting the axle it from the differential flange. To try this way, remove the upper pinch bolt on the knuckle upright and disconnect it from the upper control arms, and then you'll have some movement in the knuckle that may allow you to pull the splined end of the axle from the spindle/hub... but I doubt it will be successful. I really don't think there will be enough articulation in the knuckle, nor will the CV joints compress far enough to be able to make up the difference. Another technique could be to remove both lower control arms/ball joints from the bottom of the knuckle, which would give you much more articulation (but removing ball joints is a much bigger pain, IMO, than simply disconnecting the axle from the flange). In all cases, of course, the axle must be removed from the outboard side.

[tbar23]

Thanks. I ended up having success doing what you wrote - disconnected upper control arms after removing pinch bolt. I also removed the lower tie rod ball joint. That allowed plenty of knuckle articulation.

[Europa S5]

That's great to hear!

[dls11b8]

Great write up! I referenced this heavily when doing a bearing on my B8 S4. One note, I did not have to remove the driveshaft completely. There was enough articulation in the CV's to move it out of the spline so I could pop the bearing out of the spindle, without unbolting any of the ball joints.. I used a 5/16" punch to reach past the CV and tap the bearing out of the housing.

My only hiccup was pressing the old bearing off. The bearing was shot enough for the inner race to disconnect, and I had to work it off manually.

[tbar23]

My inner race also disconnected from the rest of the bearing. Was a PITA to remove the inner race from the rest of the hub.

So you were able to get the bearing out without disconnecting any of the suspension bits or unbolting the driveshaft. Interesting and good to know. It didn't look like my driveshaft would have enough play to pull that off. If I do another one, I'll have to keep that in mind.

Thanks!

[dls11b8]

I didn't think I'd have enough to clear either, but with me pushing the driveshaft towards the trans, I was able to make about 1/32" of clearance between the hub and the spline. Just enough to cock the spline out of alignment with the hub so I could sneak the punch in to tap it out. I figured as long as it disengages from the hub, its not in danger of damage from anything, so I'll work around it.

[Europa S5]

Oh, excellent - interesting hear that you can leave the axle attached to the differential flange; could reduce overall complexity of the job in a helpful way. Did you knock the bearing straight out of the outer housing *without* removing it from the spindle? That would have been impossible on mine, as it was difficult to get the bearing apart even under the force of a press. If you did leave the outer housing on the spindle, how did you get the axle back in with only 1/32 of clearance on the end of the axle shaft?

Were all of the fasteners the same size as the ones I had listed (and, what year is your S4)? I know there have been revisions across the platform.

Thanks for the comment on the post; SO glad it can be helpful to us with the B8 MLP cars.

[dls11b8]

Oh, excellent - interesting hear that you can leave the axle attached to the differential flange; could reduce overall complexity of the job in a helpful way. Did you knock the bearing straight out of the outer housing *without* removing it from the spindle? That would have been impossible on mine, as it was difficult to get the bearing apart even under the force of a press. If you did leave the outer housing on the spindle, how did you get the axle back in with only 1/32 of clearance on the end of the axle shaft?

Were all of the fasteners the same size as the ones I had listed (and, what year is your S4)? I know there have been revisions across the platform.

Thanks for the comment on the post; SO glad it can be helpful to us with the B8 MLP cars.

Yes, all fasteners were the same size as yours. The same arbitrary, uncommon, hard to find sizes. Lol

I was able to tap the bearing out of the spindle housing. It was in there tight, and took some time, but it came, 1/64" at a time.

I used a press to detach the hub from the inner race, and to install the hub on the new bearing.

When I put it back in, I used a rubber mallet to gently coerce it into the spindle, then when it was close, I put the bolts in and got them started and drew them in until the axle just touched the spline of the hub. Lined it up, pulled the axle into it a little to engage the spline, screwed the axle bolt hand snug, the tightened the bearing bolts.

It sounds convoluted and complicated when I type it out, but it looked a lot less of a PITA than un bolting the axle flange lol.


Sent from my iPhone using Audizine mobile app

[tbar23]

Definitely less of a PITA than unbolting the axle flange. I have to say, though, unbolting the upper control arms was quite easy and allowed for plenty of room to work.

[SSSSS5]

Thank you ALL for this thread! I replaced all 4 wheel bearings this past weekend on my 2013 B8.5 S5. 111,500 miles. One bearing was a little noisy, but service records indicated no sign of any wheel bearings ever being replaced. So I decided to do some preventative maintenance and do all 4. I would like to add a few things I wish I knew before pulling the job off. Also, I do not claim to be a high quality mechanic. I am simply just a DIYer who got the job done to a non-professional level I consider good and quality, while avoiding the shop.

Pre-job steps=

Go to your local AutoZone (or similar) and rent the following tools. You get 100% of the money back when you return them within 90 days.
27033 - Slide hammer
27032 - Slide hammer head (this head is too large for our 5x112 hubs, but I made it work with some spare bolts)
27271 - 5-7" ton gear pullers
27232 - Large Bearing splitter
27205 - Wheel bearing press kit

Soak up the bolts with a good penetrating oil. Everybody has their preference. Mine is good ole PB Blaster.

Fronts=
Call me crazy but they were a piece of cake. As stated above, removing the axles is not necessary! I did fronts and rears with the axles in place.

-I loosened the axle nut, pulled the caliper, zip tied it up to the spring, removed rotor and dust shield, then attached a (rental) slide hammer to the hub and pulled the hub out. As noted above, the slide hammer head I rented did not line up with the 5x112 bolt pattern. I put one lug on attaching the solo hole, and a smaller bolt on each of the top holes. These bolts will get beat up, so toss them when you're done. Better yet, find a tool that fits!
This a photo of the tool on a rear hub, but I think it fits here.


-The inner race from the bearing stuck on. I also rented a bearing splitter tool, and large gear pullers. I tightened up the splitters behind the collar of the race, and tightened the gear pullers down. Just make sure you have something sturdy the pullers can push against. I used some old nut on a flat metal plate.


-Next I sneaked behind the spindle with the 12mm triple square and loosened all 4 bearing bolts with ease. Just move the axle out of your way with each bolt in order to get the head of the wrench in.

You'll probably need a cheater bar. The lower right wheel bearing bolt was a bit pesky. I had to pry the two lower control arms apart so my socket could fit in place.

Also a home mechanic tip = You can use sway bars as great leverage on things! I didn't have enough space in the wheel well to get the cheater bar on the wrench, so you can see below, I wedged my cheater bar under the sway bar, and over my socket wrench to get enough leverage to loosen the bolt. If you do this, USE EXTREME CAUTION TO NOT STRIP OUT THE TRIPLE SQUARE! It is very easy to do, and I was very careful with this.


-Once you have removed all 4 bolts from the rear, throw the slide hammer on the outer face of the bearing. Attach it with two of the bolts you just took out, but thread them unto the bearing from the outside face. Each side cam came out in 1-5 slides.

-Clean up the spindle! I used a small wire brush, and an old t-shirt. There's a lot of gunk up around that wheel speed sensor.

REASSEMBLY TIME

- With a rented wheel bearing press kit, configure something like the photo below. The bearings should only fit one way onto the hub. I used an adjustable wrench to hold the bottom, and a 30 mm socket to tighten from up top. Impact gun makes this fast. Just be sure to keep everything aligned so you don't cock the bearing on the hub.
[IMG][/IMG]
- You now have a loaded hub and bearing to put on your car. Throw it on, use the torque specs listed on the first post, reassemble the rest, and you're done.



Rears=
The rears are a process. I found the most promising way was also the longest...removing the entire spindle. You can get the top two wheel bearing bolts out just as easy as the fronts, but there's such little room to remove the bottom two. I spent an hour or so trying to find the right combination of wrenches to get to them without a total disassembly, but I just didn't think I could make it happen. I'm sure its not impossible, but I would have sat there and wasted the whole day getting pissed off at it.

This is my half assed diagram that shows what bolts you need to remove to get the spindle out.



- Firstly, same as above getting the hub off. Do this while spindle is still on the car. Don't forget to unclip your wheel speed sensor! Tuck it out of the way.

- Next I removed the 18mm camber bolt on top, then the 21mm strut bolt below, then the dogbone mount bolt. Its the one on the forward side of the hub (left on driver's side, right on passenger's side).

- Next is spring compression. In my experience these springs aren't under a ton of load, so not too dangerous. I used these spring compressors and they worked great, relative to other types. Its heavy and hard to maneuver in place, but once it is, its a piece of cake.




- Ok so spring is compressed and you have the long ass bolt left. Try to wiggle the spring out at this point. If you can, yo wont have to worry about it falling when you remove the hub. Get a wrench on each side of the long bold, and loosen. Mine seemed to go easily. Slide the bolt out, and pry the hub off. The long aluminum spacer will fall out too so don't be alarmed.

- You now have full access to the back of the hub. Remove the wheel bearing bolts. My rear wheel bearings fell right off with no fuss. Install your new loaded hub and wheel bearing, and torque them down. A bench would have been nice at this point ( I need my own garage).

Once that's good, it's REASSEMBLY TIME. Everything seemed to go smoothly in reverse. Just be easy with some of these bolts. You are threading into an aluminum hub. Cross threading is easy, so be sure you aren't doing it!

-I will probably get some flack for this, but I don't have torque specs for the spindle bolts. I am sure they are out there, but I did not find them. They all were very snug after I tightened. I am confident they are tight enough, with just as many threads showing as before I disassembled.

Again, I am no certified mechanic so don't flame me. I'm just posting my experience, hoping it helps some of you DIYers in the future.

Cheers

[Spm58]

Looking to do my front wheel bearings hopefully next weekend and just wondering if anybody has done them without the press, to get the bearing on the hub? Thanks

[SSSSS5]

I didn't use a press (post #18). Was no issue at all using hand tools.

[Spm58]

I saw that the other day when I looked at it but completely forgot haha. I said screw it and got a new hub too, make it even easier

[mjr034]

Having trouble finding a pre-pressed kit online, anyone have any luck?

[SSSSS5]

Having trouble finding a pre-pressed kit online, anyone have any luck?

I had no luck when I did mine. Honestly dont let the press part scare you. With the loaner tool I did a hub in a matter of minutes.

[Arese]

Thanks. I ended up having success doing what you wrote - disconnected upper control arms after removing pinch bolt. I also removed the lower tie rod ball joint. That allowed plenty of knuckle articulation.

Definitely less of a PITA than unbolting the axle flange. I have to say, though, unbolting the upper control arms was quite easy and allowed for plenty of room to work.

It *may* be possible to do the wheel bearing job without unbolting the axle it from the differential flange. To try this way, remove the upper pinch bolt on the knuckle upright and disconnect it from the upper control arms, and then you'll have some movement in the knuckle that may allow you to pull the splined end of the axle from the spindle/hub... but I doubt it will be successful. I really don't think there will be enough articulation in the knuckle, nor will the CV joints compress far enough to be able to make up the difference. Another technique could be to remove both lower control arms/ball joints from the bottom of the knuckle, which would give you much more articulation (but removing ball joints is a much bigger pain, IMO, than simply disconnecting the axle from the flange). In all cases, of course, the axle must be removed from the outboard side.

Great write up! I referenced this heavily when doing a bearing on my B8 S4. One note, I did not have to remove the driveshaft completely. There was enough articulation in the CV's to move it out of the spline so I could pop the bearing out of the spindle, without unbolting any of the ball joints.. I used a 5/16" punch to reach past the CV and tap the bearing out of the housing.

My only hiccup was pressing the old bearing off. The bearing was shot enough for the inner race to disconnect, and I had to work it off manually.

Hi everyone, I dug up this great thread as I'm also trying to replace my rear wheel bearings.
I removed the 2 top triple squares bolts but right now I don't have enough space to access the 2 lower bolts so I'm trying to figure out the less PITA way to unbolt them

In the messages quoted above someone said that they disconnected upper control arms after removing pinch bolt and the lower tie rod ball joint which gave them enough knuckle articulation to unbolt the 2 lower bolts.

Could someone tell me which bolt they were referring to on this schematic?



Also @dls11b8 says that he managed to do it without unbolting any ball joints but I don't understand what he saying when he says there was enough articulation int he CV to move it out of the spline

[bladerunner2049]

Excellent write up and this is such a common repair on these vehicles. I'm not sure how many years it applied to but there was a TSB out for the A5, S5, RS5 wheel bearings. The A5 is the first car I've owned where everything was ceased up from the wheel to the rotor to the hub. Pro tip, ensure you only use a dead blow hammer when removing these items. It's super common for people to overlook this when doing break jobs and if a dead blow isn't used, the impact can cause damage to the bearing. I ended up getting a kit a letting my local shop install them because the brake job was such a pain.

[ELaw]

Fantastic writeup... thanks!

Fpr anyone doing this, I just did the right front on my '12 A4 quattro with ~130K miles, many on salted roads in the winter. So the bearing housing was well and goodly stuck in the steering knuckle. I thought I'd be smart and backed the mounting bolts out a bit and used an air hammer on the heads to drive the housing out... it didn't budge. Then I tried pounding on the wheel flange (which I was replacing anyway) and no luck with that method either. The flange started to come out of the bearing, but zero motion between the housing and the knuckle.

What ended up working was heat. I don't have any kind of torch with oxygen, but I have a "turbo torch" that when used with MAPP gas puts out a good amount of heat. I made sure to pull the axle out of the wheel flange as much as possible so heat wouldn't travel to it, and heated the steering knuckle on the side opposite the ABS sensor only... I didn't want the heat to damage the sensor. I got it warm but not ridiculously hot, tried the air hammer on the bolt heads again and the housing started moving. 2 more iterations of that and the thing fell out.