Unusual rear hub failure

[Chris Bamford]

Unusual to me, anyway. 1924 Speedster, pulling away from a stop sign and GRAUNCH. Car coasted to a stop about eight blocks from home. Almost pushing distance.

The cause was clear after pulling it apart the next day, but it has me wondering... did Ford make some of these hubs in two pieces? That's an awfully clean break otherwise, considering I pushed the car maybe only 40 ft after it failed, hardly enough to 'polish' the mating surfaces against each other.

The failed hub has a Ford script, along with a T and a separate D H stamped in the end. The D H looks like my set of stamps, but I don't remember doing it or if I did, what it might mean. This hub has been on the car since 1992 or might have been replaced during a major overhaul around 2009.

Anyone else seen this kind of failure?

[Scott_Conger]

yup

http://www.mtfca.com/discus/messages/59 ... 1451600361

[TXGOAT2]

I'd guess the circular wear cuts had something to do with it failing.

[BE_ZERO_BE]

Seen it several times before.
It's uncommon but not that rare.
A wheel that wobbles will fatigue that stress point.

[Jerry VanOoteghem]

It happens to 26/27 wire wheel hubs too.

Really, they should be Magnafluxed prior to installation in a wheel, though I admit, I've never had that done. I do however clean the hubs very well and visually inspect for cracks. Better than nothing, but maybe not much better... Also, no guarantee that a hub that passes Magnaflux won't eventually do that anyway.

Interesting break. The large radius between the flange and hub nose is obviously there to reduce stress concentrations and prevent this sort of thing. However, there is no such provision on the backside. In fact, there's a sharp corner adjacent to the pilot diameter that the brake drum locates on. Looking at the angle of the fracture, I'd say that the crack began in that sharp corner on the backside of the flange.

[Allan]

I have seen it before. It can leave you with no transmission brakes, just like a broken axle. I have also come across a couple of welded up hubs!

Allan from down under.

[YellowTRacer]

I think that I can describe it better than I did in 2015. You're rounding a corner fairly fast and the spokes and are saying "this is tough I need to bend a little." The backing plate that they're bolted to is saying "well, okay, I'll try." The hub stem is saying "hey, you're a part of me and I can't bend because I'm attached to this rigid axle and it won't let me". so if the spokes are solidly pressed against the hub backing plate (tight hub bolts) and hub stem, you have a strong unit somewhat not breakable and nothing breaks, it all stays rigid. But if the spoke butts are not really real tight against the hub stem then that weakens the unit a little and it breaks at the weakest point. The wheel and backing plate break from the hub stem. Sound logical?

Ed aka #4

[JohnH]

I had that happen a few years ago. Fortunately it was just as I was turning into my driveway, so was able to winch the car into the garage.

[Dan McEachern]

Just to add to Ed's explianation above. If you think about the forces on the flange, the outer wheel plate, when securely bolted to the face of the wood spokes, effectively carries a radial load against the wheel hub, preventing the hub flange from reversed bending in a turn. If the outer plate can slip on the spoke face, the hub flange carries all the flexing motion. This motion and the resulting reversed bending is actually the cause of the flange fatigue failure. If the cars were only driven in a straight line, this failure mode would most likely never be seen.

[TXGOAT2]

Another reason to run tight, straight, concentric wooden wheels.

[Chris Bamford]

Well, this has been very educational. Thanks to all who replied, and particularly Ed and Dan for your helpful explanations and Scott for that 2015 link (which I clearly saw at the time, as I posted to it a couple times).

Car is back together, wheels are tight, all seems fine. It wasn't a particularly long test drive, given our -16°C weather this afternoon!

[Loftfield]

Yup, happened to me exactly the same way. I had never seen this particular failure before but Forum members assured it does happen. It happened while on the steep part of my driveway (scary!) but parking brakes got the car slowed in time to prevent taking out the sheep paddock fencing, a good reason to keep the parking brakes in good condition. I might consider some AC brakes, but no ugly discs.

[Dan Hatch]

This may be more common than we know. Happened to a friend few years back. He was able to get stopped without damaging anything. We took wheel off on side of road. Went back to his shop where we welded the hub. Got the car back to his shop and then went to my shop to find a new hub in my parts pile.
We found I know one other cracked hub and maybe two in my parts hubs before we found a good one.
So check them all. Got to be safe out there guys. Dan

[JohnH]

Here's mine:

[Alan Long]

I wonder if the replacement Hubs available from the Suppliers are made differently and with better materials these days?
Can’t really complain when a 100 year old part fails as annoying, costly and dangerous as it can be.
Alan In Western Australia

[Scott_Conger]

My experience with the new hubs is that they are gorgeous and well made. The only thing is that because they are steel and not iron, you MUST pre-mitigate the fretting which is GOING to occur between the new hub and the (whether new or original) axle. They can and will very quickly become one with the axle and will resist nearly all efforts to remove in the future.

That material issue notwithstanding, they really are superb (you hafta love CNC).

[Dan McEachern]

Scott- the
Ford rear hubs are steel, not CI. The front hubs are malleable iron. This is a classic fatigue failure that is due to repeated bending cycles. Ford must have recognized this failure mode was possible given the generous radius in the corner of the flange which prevents a stress riser that a sharp transition would create. Bottom line is keep your hub bolts tight.

[Art M]

I have seen hundreds of failures like this in testing for rotary fatigue. Car companies are well aware of this type of failure Prevention includes hardening in this area, geometry, and material type
Normally, hard cornering causes this problem. I cannot comment about spoke influence, I am not old enough to have worked during the wooden wheel Era

Art Mirtes

[Allan]

Dan, the generous radius on the outer side of the hub next to the spokes does indeed make for a less stressed transition between hub and flange. However, there is no radius between the flange and the shoulder which supports the brake drum on the inside of the hub. My guess is the failure begins here.
Another stress riser, which to my knowledge was never addressed, is at the rear main web in the engine block where there is a sharp transition from the web to the surface on which the rear main bolt nuts engage. A number of blocks have been known to fail at this juncture.

Allan from down under.

[Wayne Sheldon]

I think that I can describe it better than I did in 2015. You're rounding a corner fairly fast and the spokes and are saying "this is tough I need to bend a little." The backing plate that they're bolted to is saying "well, okay, I'll try." The hub stem is saying "hey, you're a part of me and I can't bend because I'm attached to this rigid axle and it won't let me". so if the spokes are solidly pressed against the hub backing plate (tight hub bolts) and hub stem, you have a strong unit somewhat not breakable and nothing breaks, it all stays rigid. But if the spoke butts are not really real tight against the hub stem then that weakens the unit a little and it breaks at the weakest point. The wheel and backing plate break from the hub stem. Sound logical?

Ed aka #4

ED, Wasn't it (I know I am going to spell his last name wrong!) Mike Bateatte at Calistoga that broke a hub this way? He was running at speed and rounded the first turn only to have the engine roar and the car began slowing down. He coasted onto the grass behind where the pit area was and a bunch of us went running over to see what was wrong. We found them standing outside the car, still in gear, and sitting there with the right rear hubcap spinning in the center of the wheel!

It was ironic that in four years of the Calistoga races, only two wooden wheels were broken, Mike broke them both, and they were solid new spoke wheels! And one of the two broken wood wheels broke the one critical steel piece! Not the wood!
Someone had a spare hub close by, and the wheel was fixed and back on the track about an hour later.