We frequently replace rear wheel bearings on many 2012-2019 Subaru models. They fail far more frequently other models we repair. Subaru has acknowledged the problem issued a service bulletin that calls for replacing the failed rear hub, but they also say that the brake backing plate may have manufacturing flaws and they recommend replacing it with an updated unit.
We’re not so sure replacing the backing plate is necessary, but we’re not engineers, so we might not be right. We want our customers to understand Subaru’s explanation, what we have observed, and the limits of what we can determine before choosing a repair. We created this page to help you make an informed decision.
| Model | Model years |
|---|---|
| Forester | 2014–2018 |
| Impreza | 2012–2019 |
| Crosstrek | 2013–2019 |
What Subaru says
Subaru bulletin 05-70-19R, revised December 2, 2020, describes a change to the rear brake backing plates. Subaru says uneven mounting surfaces can distort the hub and bearing assembly when its mounting bolts are tightened. Over time, this can lead to a howling noise from the bearing.
For the condition described, Subaru directs technicians to replace the backing plate and hub/bearing assembly together on the affected side. The bulletin says production changes improve the backing plate’s mounting surfaces. It does not provide a numerical flatness or thickness-variation limit that we can use to judge an individual plate.
How the backing plate could affect the bearing
The NSK cutaway below illustrates why this explanation is mechanically possible. In this type of hub bearing, the outer bearing raceways—the tracks the balls roll against—are built into the outer component with the mounting ears. If that component distorts, the raceway geometry can change too. The illustration explains the construction so you can see how mounting the hub assembly might twist and affect bearing clearance. Unfortunately, there’s no way for us to know how much distortion would occur with a given backing plate thickness variation.
What we measured
We measured the thickness at four locations on one in-service backing plate and then did the same on a new plate. The table records those readings in inches. This is a sample of just one used plate on one car, so it may not be representative of every affected vehicle.
While the measured thickness variation looks to be twice as bad on the new production plate, that may be because the plate is actually two plates sandwiched together, and since they had never been bolted together / compressed, there may have been a gap that created the one thick spot.
| Measurement | In-service plate | New plate |
|---|---|---|
| 1 | 0.38415″ | 0.38750″ |
| 2 | 0.38040″ | 0.38015″ |
| 3 | 0.38155″ | 0.37995″ |
| 4 | 0.38240″ | 0.37995″ |
| Maximum minus minimum | 0.00375″ | 0.00755″ |
What the measurements can tell us
These measurements describe the loose parts, not their shape under bolt load. They do not prove that the original plate caused the bearing problem, or that a new plate would improve bearing life. Subaru hasn’t issued a service specification, and we don’t have the engineering knowledge to know how much is too much. To me, a bit under 0.004″ doesn’t seem like it would be enough to cause a problem, but I don’t know that. Will the just under 0.008″ on the thickness variation on the new plate get better once it’s installed? I don’t know that either.
Your repair options
Subaru’s prescribed repair is to replace both the bearing assembly and backing plate. We will explain that repair and its added cost, and let you decide whether to include the backing plate when we replace your bearing. If requested, we will measure the backing plate on your car during bearing replacement and share the results before you decide. We do not have a specification that makes this a pass/fail test, and the measurements cannot predict how long a replacement bearing will last.
We Stock Bearings and Backing Plates
Whether you decide to do a bearing only or to replace both the bearing and the backing plate, we have you covered. If you’d rather that we measure your plate before making a decision, you won’t need to wait an extra day or two to order the part from Subaru. Or, if we discover your backing plate is falling apart from rust, we’ll have the needed parts on hand.
