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"Is that my wheel bearing" - easy diagnosis


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Subaru wheel bearings often don't have traditional symptoms, or at least I've never seen one have "play" by grabbing the wheel. I've seen them have play once off the vehicle though, but that doesn't do you any good trying to diagnose insitu.  I've seen enough threads asking how to confirm and having trouble verifying wheel bearings that I snapped a couple bad cell phone pic's while diagnosing one this morning in the dark.

I use a temperature gun which I mention often on forums and so far it's been 100% successful.

1. Drive the vehicle. Get it up to operating temps.  Take temps immediately after driving.

2. Aim the red dot from an infrared temperature gun as close to the bearing/hub as you can. Use the axle stub, exposed on steel wheels, or pop the center cap on aluminum wheels. Or shoot through the slots in the wheels at the rotor close to the hub/bearing and get an "average" of like 5 or so readings - noting the highs and lows. Rotor temps vary wildly depending how far from the center you are - energy dissipation and heat transfer and what not - so that's the reason for a few readings.

3. Compare that reading to the reading on the other hub bearings.

4. If there's a large difference - usually 20-50 degrees in my experience, the side reading higher is a failed bearing. It's always been obvious so far for me, the highest temp on the "bad" side notably higher than anything on the other side. Other way around for the "lows".

***This of course assumes brakes have already been ruled out - not dragging, seized, etc.

This particular vehicle had sound that wasn't noted until after snow tires were installed so it was a uncertain as to whether it was tires or wheel bearing making the growl. The noise wasn't particularly loud and I don't have stellar hearing so I wasn't even sure if it was front or back or both.

It was dark so pardon the pictures but this explains it fairly simply and looks like i've confirmed another wheel bearing.
First pic shows the passengers side at 96 degrees. Drivers side at 127 (highest).
Both rears were 74 degrees.
Looks like we have a bad drivers side bearing. This vehicle has all new brake pads, caliper boots, caliper pad clips, etc.


And that's about the difference, from my bad memory, of previous temps too. About 30 degrees and around the same thing - 120's and 130's for the failed bearing side.

***Probably one of the "funnest" tools to own, can take it inside and play with it! You'll want to take temps of all sorts of
things...campfires, food, kids, windows, doors, computers...



Edited by idosubaru
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This is the USRM - Ultimate Subaru Repair Manual for repair methodology and write ups- not for diagnosis.  If everyone posts questions in the USRM it'll clog up the usefulness of it.  Could you start a new thread in the new generation forum and erase this one and I'll do the same with this post?  



Yours is also a brake issue. In addition to caliper pistons hanging, pads can also wear and heat up due to sticking caliper slides, rusty/corroded pad clips that hang the pads, and failing brake hoses - they collapse internally and fluid can move "to" the caliper due to hydraulic forces, but don't allow fluid to move "back" away from the caliper and release the pad. Other manufacturers this is more common, this isn't a typical failure mode for Subaru's.

Edited by grossgary
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