274 replies to this topic

[Keith Novak]

I'm confident now that the inner races should not touch but in some cases they do and this leads to very early failure. 

 

I built up a new hub and when installed at 140 or 160 ft-lb torque, there was an ever so slight bit of play at any direction.  I used it for one weekend and that play became significantly more pronounced.  When I pulled the hub apart, it was apparent that the ends of the inner races were in fact together.  This was readily apparent by where grease was and where it wasn't.  It had been squeezed from the gap.  Inspecting the inner races showed absolutely no sign of damage.  I haven't cleaned all the grease out yet but this tells me that the races in the hub body have been compressed.  This is exactly what you would expect without preload.  The forces going into the bearings are too sudden and the weakest part, the casting becomes damaged as a result.

 

From a manufacturing point of view, you would not want to make the ends touch.  It would have to be very precise in order to have the required preload and both the cast hub and inner races would need tolerances that would drive the costs too high.  The gap should be close however to help prevent foreign material from entering the bearings via a tortuous path (maze).  I believe that there are manufacturing variances in the machining of the cast hub body that cause the inner races to bottom out, prevent the preload, and cause the hub to fail.  It's not the only failure mode but definitely one of them.

[Bench Racer]

Are there any marks on the inside ends of the inner races where they touched. End chatter if you will. At the OEM state the ends are ground very smooth.

[Keith Novak]

There are no signs of chatter.  The ends are still very smooth.  In this particular case, I think all the clamping force was holding the inner races clamped together, not the bearings clamped between inner and outer races.  What is visible is a faint film showing there was a little bit of grease between the ends of the inner races either from installing them into the hub or sliding the hub onto the greased spindle.  There are now little beads of grease around the outside diameter of the races where the clamping force squeezed the grease from between the two ends and into the cavity of the hub.

 

I may find the other hub to be a bit different.  That one had no play when originally installed but has developed some in the same weekend so it had some preload but not enough.

[RazerX]

If it isn't ruined yet.  I would be 'interesting' to take some material off the end of the inner races and see if that a) removes the slop and then how long it lasts.  If the hub material is flexing or bell mouthing it may continue and become even more pronounced and exacerbate the weakness for better analysis. 

[Parity]

 

 

If it isn't ruined yet.  I would be 'interesting' to take some material off the end of the inner races and see if that a) removes the slop and then how long it lasts.  If the hub material is flexing or bell mouthing it may continue and become even more pronounced and exacerbate the weakness for better analysis. 

 

Being done right now.

[Keith Novak]

A couple practical notes since I seem to be having a good old time with front hub failures.  I've had to get some from autoparts stores on short notice to fix issues:

 

Carquest house brand:  I can't remember who their brand is off the top of my head and it doesn't show on their website. " Premium" bearings.  They have very heavy duty flanges compared to most others but the machining on the inside looked low quality.  They spun great after rebuilding.  One hub had play from the start and the other lasted around 7 sessions before it showed play.

 

Duralast:  Looking at the hub, the flange struck me as very thin looking.  I compared it to an OEM 1994 hub and it looked about the same though.  Nothing really caught my eye about the bearings.  Torqued to 160 there was no play.  They didn't feel super smooth but that's not uncommon with freshly built hubs.  Three sessions and they wobble and make a disturbing howling noise in some corners.  I decided not to see how long they would last like that.

 

OEM Miata with the original coating of filth muck:  After a wirebrushing to get the heavy stuff off, I pulled them apart and questioned whether I should even rebuild them.  The grease was clear and untouched.  I rebuilt the hub with a heavy patina on the outside and they are fantastic.  The innards still look immaculate.  They are extremely smooth and outlasted the Duralast on the other side so it seems to be hub and not tire.  The car will literally roll in a breeze on these hubs. 

 

Clearly, the old Japanese built hubs had better materials and/or machining than the Chinese ones on the market currently

[DrDomm]

Keith, you're referring to junkyard hubs right?  How can you tell that they are "OEM"?

[Keith Novak]

I am referring to junkyard hubs.  Good question on how to tell OEM.  I've seen a good number of hubs now but certainly not enough to write a OEM hub spotters guide.  I was basing my assumption due to the appropriate amount of external filth for the age of the car they came off.  I think the problem is relatively new though so I'm thinking older is better.

[Todd Green]

We recently did a 6 hour at MMP (WERC) and a 99 (on Hoosiers I believe, it was Bruce Pendelton's car) had a hub failure.  I got this from one of the drivers:

 

Brand new hub from Mazdaspeed (according to the car owner). It was
definitely the hub as it came completely off the spindle with nut still intact. (Ours left only the inner race and nut.)

 

FWIW.

[Bench Racer]

Interesting that no failed hubs mentioned from the NASA Nationals this past weekend.

[Todd Green]

I wonder how much rumble strips/curbs has to do with it?  Miller is pretty bad.  Never been to Road Atlanta so I can't compare.  The hubs on our enduro car were purchased probably within 6 months of the hub that failed on my "sprint" car (they were my spares that got comandeered).  I pressed in the studs just the same as the others.  Car has run 6 three hour enduros and a handful of sprint races, and other sessions with no failures or bearing issues.  Of course we try to stay off the curbs for enduros with it and I crash the heck out of them in the sprint car.  Tires were Toyo RR's for the first 6 hour (and early sprints) and BFG R1's for the rest.

 

Also I talked to Mazdaspeed about this and they recommended doing 160+ ft/lbs for torque (at least on their MSP heavy-duty hubs).

[Parity]

Definitely some curb jumping going on at Road Atlanta. I know of at least one driver who replaced front hubs during the event.

[speedengineer]

Interesting that no failed hubs mentioned from the NASA Nationals this past weekend.

If it counts, my front hub failed at ABCC this weekend, just after NASA nats at Road Atlanta last weekend.  I can't help but theorize that some of those curbs had a part to play in the failure. 

 

Fortunately, I felt the compliance/vibration through the steering wheel and pulled off and got towed in.  After I had it up on jack stands, wiggling the wheel I figured it was just a bad wheel bearing.  Went to replace it, pulled off the rotor, and surprise, nearly broken hub.  Glad I stopped when I did!!!

 

This was a Timken hub assembly from Rockauto that I installed last April.  It has perhaps 8ish race weekends on it, running ~2400lbs on SM6 and SM7.  Clearly the sharp corner from the machined flats for the studs caused a stress concentration, which is where it broke.

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[Ron Alan]

If it counts, my front hub failed at ABCC this weekend, just after NASA nats at Road Atlanta last weekend.  I can't help but theorize that some of those curbs had a part to play in the failure. 

 

Fortunately, I felt the compliance/vibration through the steering wheel and pulled off and got towed in.  After I had it up on jack stands, wiggling the wheel I figured it was just a bad wheel bearing.  Went to replace it, pulled off the rotor, and surprise, nearly broken hub.  Glad I stopped when I did!!!

 

This was a Timken hub assembly from Rockauto that I installed last April.  It has perhaps 8ish race weekends on it, running ~2400lbs on SM6 and SM7.  Clearly the sharp corner from the machined flats for the studs caused a stress concentration, which is where it broke.

Ever any contact(even slight)with that corner wheel with anything?

[speedengineer]

Ever any contact(even slight)with that corner wheel with anything?

Nope, that corner hasn't contacted anything.  This was the front left that failed.  It's been to Road Atlanta twice and Road America once, both of which have some fairly harsh curbing.  However, most of that curbing abuses the right side, not the left. 

[CWright]

When you tow, do you tie down the car through or around the wheels?  I've read that there is an anecdotal connection between tieing down the wheels and hub failures.  However, it seems that the most likely cause is steady state cornering loads on the LF coupled with SM6/SM7 grip and the stress concentrator you identified.

 

 

C

[Todd Green]

When you tow, do you tie down the car through or around the wheels?  I've read that there is an anecdotal connection between tieing down the wheels and hub failures.  However, it seems that the most likely cause is steady state cornering loads on the LF coupled with SM6/SM7 grip and the stress concentrator you identified.

I think I mentioned it earlier in the thread, but in my case the car is never towed.  It is stored in a garage at the track.  I can't imagine the forces of towing are anything like what it is cornering around a track.

 

I still can't imagine this being anything other than a change in manufacturing/materials etc. in the hubs.  All of a sudden we have a rash of failures that weren't happening before across a wide range of tires/tracks/etc.?

[CWright]

I think I mentioned it earlier in the thread, but in my case the car is never towed.  It is stored in a garage at the track.  I can't imagine the forces of towing are anything like what it is cornering around a track.

 

I still can't imagine this being anything other than a change in manufacturing/materials etc. in the hubs.  All of a sudden we have a rash of failures that weren't happening before across a wide range of tires/tracks/etc.?

 

I agree, it (towing being the culprit) seems a long shot.  Just thot I'd ask given that speedengineer appears to live in Michigan and raced the car at RA and RATL, long tow's... 

 

But it also seems unlikely that the hubs of all manufacturers have changed unless we can conclude that the hub failures have all come from one factory and they supply multiple bearing suppliers.  Is that possible?

 

C

[Bench Racer]

When looking at the picture from the threaded stud picture one can view an impression from the screw holes in the rotor transfered (90* rotated from the threaded holes in the hub flange)to the hub flange. Also it looks like the knurled portion of the stud extends outward beyond the munting surface of the hub flange. Are there sufficient chamfers on the inside of the rotor so the the rotor was FLAT against the hub mounting surface?

IIRC there were a couple other failure pictures posted with the same square pattern terminating or starting at the hub flange threaded holes.

[Keith Novak]

That square fracture pattern is exactly what you would expect from a 4-lug wheel.  They're inherently weak.  During cornering, every time 2 lugs are horizontal, all the stress goes through a single lug with the maximum stress right at that fracture line you see.  If I had never seen one of these fail and you asked me to draw a picture of how it would fail, it would look just like the picture.  A 5-lug wheel will spread the stress much more evenly but that's probably not a solution we'll see in SM. 

 

Why we're seeing many more of these now is most likely due to cheaper metal, cheaper manufacture, and grippier tires.  That specific hub looks more prone to cracking than many others I've seen.  The machining on the back side for the flat surface where the stud presses into has a corner that looks too sharp and will increase the stresses even more.