My new NC, 2008 PRHT with 43k miles, has a subtle hum in the front when turning (or veering) to the left. I'm figuring wheel bearing as they are a known issue with these cars. But today I jacked the front end up and there is NO play in the right wheel, when spinning it by hand there is brake pad drag noise, but little else.
I tried the front left wheel to see if there was any difference, a bit less noise, but just a bit...more like the pad noise stands out more since there is less constant noise during the rotation. The main difference seems to be that I can spin the right wheel hard and get three rotations before it stops, while the left one will spin four times.
Is that enough of a difference to 'prove' the wheel bearing is going bad? I tried a mechanics stethoscope but got nothing.
If I do replace it, I'll likely get the RX-8 ones and do both sides at the same time.
Swap them side to side? ;)
Noisy wheel bearings rarely have play and never have noticeably different rotational drag. The brakes are more likely to be the cause of the difference left to right.
It's PROBABLY the left bearing. But there is a small chance that it is the right. Fortunately if you swap the left bearing and it is still making the noise, you have a good used one right there to replace the other side with.
If it's only subtly noisy, it's hard to tell when spinning the wheel by hand with the brakes on there. You could try pulling off the pads and rotors, then spinning the hubs by hand; might show which one has a bit of drag.
Claff
HalfDork
11/30/22 11:37 p.m.
I've replaced three wheel bearings on my tracked NC, one front and both rears. One rear made horrible noises for a long time but never had any play so I wasn't really sure it was the wheel bearing. Then it self-destructed during the '19 Pro Solo Finale. When the other rear started making similar noises, I replaced it right away.
I'm a cheapskate so I replaced these with used knuckles from Redline Auto Parts and that made things easy to swap out.
No advice, but passing interest: is the RX-bearing swap just bearings, or does it also require hub?
In reply to Keith Tanner :
Any idea when those will be in stock?
russde said:
In reply to Keith Tanner :
Any idea when those will be in stock?
Try looking at your local Mazda dealer also. The PN is F189-33-04X.
No Affiliation but I have had good luck with parts from TASCA https://www.tascaparts.com/oem-parts/mazda-hub-and-bearing-f1893304x
In reply to miatafan :
Even better, if you do 2 HPDE or autox events a year, sign up for Mazda's Team Support program. Unbeatable prices on stock parts.
TASCA just drop-ships, I think. If their supplier is out, they're out. We carry our own inventory so we sometimes have stuff when the warehouses don't - but if we run out and they're out, we can't get more.
Always swap tires around before condemning a wheel bearing.
In reply to Keith Tanner :
I went ahead and signed up...I'll hopefully be able to auto-x it this month.
That part number comes up as "Following SKUs are no longer orderable :F189-33-04X Please remove to proceed". So I may just order the stock ones if it turns out I do, in fact, have a bad one.
Ranger50: Good thought, I'll try that this afternoon if I get time
Ranger50 said:
Always swap tires around before condemning a wheel bearing.
I will admit to having been burned by this 
Bearings have a little different tone than tire noise. More nasal, if that makes any sense. They also tend to be very load specific (like shuttting up completely when you change the load a certain way) whereas tire noise tends to be rather insensitive to loading.
Tire noise also changes based on the road surface, so a E36 M3ty road is a good diagnostic tool.
