You are happily humming along over England’s poorly surfaced roads in your Subaru Outback when you hit a section of freshly-laid tarmac. The road noise just about disappears, although you suddenly hear a faint whirring sound that seems to be coming from somewhere towards the rear of the vehicle. It varies with speed, and immediately your thoughts turn to the worse: Differential getting ready to blow itself apart? Gearbox going south?
No, it’s most likely a wheel bearing nearing the end of its life. Such was the situation I found myself in a few weeks ago. My Outback (still to be properly introduced, I know – I hope to have a post about the car available soon) had finished its work conveying us to and from France for a family holiday when, just a week later, an unwelcome hum started to intrude into the cabin anywhere over 30mph. The question at this point was how to determine which of the rear bearings had gone bad.
The car’s MOT history said that just a couple years ago, the nearside bearings, front and rear, had failed the test. So it was likely the offside rear (since I did the offside front when I first got the car), though on this generation of Outbacks, it is difficult to determine that for sure. For whatever reason, the usual 12 & 6 test looking for play in the wheel doesn’t particularly work, unless the bearing is really far gone. You could use a temperature sensor and check the temperatures at the hubs after driving for a while, but this is unreliable and could read incorrectly if, for instance, you have a brake grabbing. Some people put the car up on jack stands, engage drive, and let the wheels spin up to the speed at which you start to hear the sound. That’s just plain reckless. In my case it was as easy as looking at the axle nuts – the nearside rear, as per the MOT records, was indeed much newer and shinier than the offside. Diagnosis confirmed.
Replacing the rear wheel bearing and hub assembly is actually a fairly straightforward job. Begin by removing the brakes. The brake hose is short, but you can conveniently hang the caliper on the anti-roll bar to get it out of the way. The bolts for the caliper bracket are accessed from behind, and Subaru has helpfully notched out the control arm to allow easy access. Once the bracket is off, the disc should pull off, but in the event that it is rusted into place, simply drive a bolt into the two holes on the front of the disc to work it loose.
Next you’ll need to remove the handbrake assembly. These drum-style handbrake setups look complicated, but on the Outback it is not too difficult to work with. Just be sure to take a photo of it before you remove it, and keep all the parts together. Give everything a good shot of brake cleaner, and then begin by removing the two springs at the top. Remove the retainer screws holding the shoes in place next, and you’ll be able to pull everything off easily.
Now you can see where the hub is bolted to the control arm. Again, these four bolts are accessed from behind, and again, Subaru has made it easy to get at them with a long enough extension. I have added arrows to the photo below to show where each of the bolts are as you’re looking from behind. They are not terribly tight, so it shouldn’t take much work to get them off.
You can then start to work the hub and bearing assembly off. This will probably take a bit more work. Begin by pressing the axle shaft out of the bearing. This could be difficult if the shaft has rusted into place, but work at it patiently and it will come out. You might also find that the hub has rusted to the control arm, as it did in my case. Once I had the axle shaft free, I just pounded on it with a rubber mallet until it broke free. After it comes off, use a wire wheel attachment to clean up the mating surfaces, which will help the reinstallation process.
Unless you want to give the next person who replaces the wheel bearing a hard time, apply copper grease to the axle shaft and around the edge of the hub assembly. Then seat the new unit in place, and apply some blue loctite to the bolts before you reinstall them. Thread them in and torque them down to 48ft-lbs. I like to snug the bolts down with my ratchet first, and then torque them in a diagonal fashion to help ensure everything is seated properly.
Finally, reassemble the handbrake. This is a good time to clean everything, scuff up the pads, and readjust the handbrake. Apply some copper grease to the back of the disc where it will mount onto the hub before putting the disc back on, and then reassemble the brakes. At this point you’ll have to mount the wheel and lower the vehicle so that you can torque the axle nut down to 177ft-lbs. Last of all, raise the vehicle again, remove the wheel, and stake the new axle nut.
As you can see, provided nothing is too rusty, or your handbrake hasn’t disintegrated inside the disc, replacing the wheel bearing is a job that can easily be completed in half a day. This is largely owing to to the way Subaru engineered the rear end. Now, the next time you are cruising along and hit that stretch of freshly-laid tarmac, it should be perfectly quiet and serene inside your Outback.