Wheel bearing, how I break them, and why

[SirHustlerEsq]

I'm not much of a teacher nor a how-to writer, but I put this on another forum ad thought I'd share. Now that I'm on "real" suspension, 225's on 9's, and driving like a man I'm really wrecking wheel bearings. I'm packing them all with AMSoil 2000 race grease now and for the first time, bearings are lasting more than 2-days. I check the bearings every 3 -5 days and repack if the grease if it's anything other than white.

So, I had some pack knockback again yesterday when I drove around to weigh my car. I bet all that extreme brake heat is what killed the bearing so I had a look.
Yep, the old Redline grease I tried died under the heat

The AMSoil bearing grease started out white, but it was turning gray which tells me it overheated. However I should note that it was not black, viscosity was not reduced, and it did not stink. The Redline greased bearing reeked of burnt grease.
So I decided to rebuild a few bearings

I got my hands on 2-cheap Mazda bearings from a buddy with a Woldpack account. Then I found this...what is this rough black shit in the race? I could feel the "gunk" on the race and took it off with a scouring pad. I'm not impressed for $95 each on an OEM Mazda part. Again, this bearing is new and straight out of the box.

Notice the heat-treatment stripe, I'll discuss that later.
Now we're going to monitor heat


I usually use Timken or ebay China bearings. At this point, according to the notes I keep on the car, it looks like there is no durability difference between Timken or China bearings. I've started buying whatever is cheapest on ebay with a real picture that shows the heat-treating stripe and a rubber seal on the back. The metal seal-type fail quickly by letting brake dust in, the bearings without the heat-treatment stripe do not last one day.

[MadMerv]

Something is dreadfully wrong, which leads to lots of questions......

When did this start happening? What was the last thing you did prior?
Which bearings are failing, outer , inner, or both?
Which wheel(s), fronts only, left, right? How about the rears?
What part(s) is failing?
How tight are you going with the lock nut?

Suggestions:
1. Take off those huge wheels and see if the problem goes away. Wheels with lots of offset put a tremendous load on the outer bearings.
2. Contact Karl Zimmerman at Applied Racing Technologies. He's in Austin, and he is the bearing guru. He is very technical, meticulous, and will tell you anything you want to know.

[SirHustlerEsq]

Something is dreadfully wrong, which leads to lots of questions......

When did this start happening? What was the last thing you did prior?
Which bearings are failing, outer , inner, or both?
Which wheel(s), fronts only, left, right? How about the rears?
What part(s) is failing?
How tight are you going with the lock nut?

Suggestions:
1. Take off those huge wheels and see if the problem goes away. Wheels with lots of offset put a tremendous load on the outer bearings.
2. Contact Karl Zimmerman at Applied Racing Technologies. He's in Austin, and he is the bearing guru. He is very technical, meticulous, and will tell you anything you want to know.

Both fronts die.
The rears were recently replaced for the first time in the car's life.
Sometimes the bearings get chewed up, sometimes the inner race cracks
It looks like the outboard race keeps deteriorating, even though the grease is clean.
I max the torque wrench at 150lb, run a session, tighten, then add torque until knock-back stops.
When I repack them every few track days they last much longer.
The ART bearings died a strange death, little black squares all over the outer race.
Suggestions:
1. not a chance
2. Karl did a great job of taking my $200 then telling me there was nothing he could do after I killed one of his bearings after 4-hours of seat time (on the left, running CCW at Hallett). The right bearing still lives. He told me there was a problem with the heat-treatment but was not willing to replace it.

Again, I thin it's brake heat that's killing them.

[Titus]

Have you come across other high HP track Miatas having similar problems?

Have you thought about directing that brake duct directly at the bearing?

[SirHustlerEsq]

Have you come across other high HP track Miatas having similar problems?

Have you thought about directing that brake duct directly at the bearing?

Yes

Look at the last pic. There is a lip around the duct-shroud that sort-of seals it to the rotor hat. I have bigger rotors on the way with aluminum hats that may change the game a bit...but I'm not sure if the aluminum will transfer more heat from the rotor ring or cool better from the air pumped into it. The 11.75" rotor will lower brake temps dramatically.

My car is no "high HP, it's only been making 232whp since Hallett this year, lol. Yes, the car ran a 1:27.1 at Hallett (I hate John) at 232whp...that's pretty ganxter.

[Titus]

Yes

Look at the last pic.

That last pic is what made me think of it... I was thinking more extreme... The pic looks like the air hits the hub and rotor first, so would be heated before getting to the bearing. Perhaps you could put a little wing in the duct opening that forces some of the fresh air DIRECTLY at the inner bearing.

[MadMerv]

I max the torque wrench at 150lb, run a session, tighten, then add torque until knock-back stops.

You torque the nut to 150lb/ft????????????? That can't be right! It needs to be loose enough for the bearings to do their job(wheels will turn). Am I missing something here?

Don't you think it would make sense to try some stock wheeels/tires and see if the problem goes away? Also, If you think it's brake heat, and you are using the brakes hard enough to destroy the bearings, you need to re-think your driving technique....

Looking at the last picture, I wonder what kind of hub nut that is. Shouldn't it have a cotter key going thru it and have the humps to keep it in place. It also looks to be recessed more that normal.

[SirHustlerEsq]

120-150lb is the spec, it's not an old-world American Iron bearing, and Karl from ART suggested this logic.

I can't run stock wheels, they won't fit over the brakes.

The only place where I'm overheating the pad is ECR, it's fine everywhere else. I always thought that people who spent too much time on the pedal overheated the caliper, but my caliper temps are sub 350*f. What you call bad driving may be the reality of 120mph with an 11" rotor.

[lostlorin]

After you apply the 150 lbs of torque do you rotate the the hub and wheel assy to make sure it is rotating freely, but without side play? Are you packing the bearings correctly or just smearing grease on the outside? Are you checking hub temps?

[SirHustlerEsq]

After you apply the 150 lbs of torque do you rotate the the hub and wheel assy to make sure it is rotating freely, but without side play? Are you packing the bearings correctly or just smearing grease on the outside? Are you checking hub temps?

Yes, I make sure it spins freely; sometimes you can have zero axial or radial play, but still have knock-back when loaded up. I can typically torque to 150lb, track it, torque it, track it...then add torque until the knock-back stops.

Yes, I'm packing them correctly, hence the pictures of me disassebling the bearings and cleaning the outer races. I have no hub temps yet. I will after the next track day.