Share Pics of People Hauling or Towing Something Wrong

[RandyT]

No time for a photo, but today at the merge point of two freeways I saw a CHP officer, flashing lights on, parked behind and protecting a small junk trailer. As we got closer it was obvious the hub and wheel had come off the trailer leaving just the stub axle. Somebody forgot the cotter pin?

Seemed to me the only way to get the pickup and trailer to a safe place would be to just order the pickup to drag the trailer as-is to the shoulder beyond the merge, because getting a wrecker in there and hooked up with a dolly would disrupt traffic and likely cause crashes.

If it happens on the left side the wheel bearing can seize causing it to weld to the nut which unscrews the nut and shears off the cotter pin and the whole assembly comes off.

 

[California]

More likely they didn't notice (or care) when the wheel bearing started overheating, and eventually lost everything.

Wouldn't that seize and break the axle at one of the bearings? I'm pretty sure I saw the entire axle intact clear to its threaded outer end.

If it happens on the left side the wheel bearing can seize causing it to weld to the nut which unscrews the nut and shears off the cotter pin and the whole assembly comes off.

Bingo! I think that explains what I saw.

 

[duramaxsky]

I could see that, hit the tree with the rear bumper and have slightly more car to crumple and your forehead doesn't hit the steering wheel or the windshield, you just get pressed hard into the seat back
though your head may rapidly depart your torso in a rearward direction

The choice is whiplash or impact with the steering wheel. Neither is good.

 

[Renze]

If it happens on the left side the wheel bearing can seize causing it to weld to the nut which unscrews the nut and shears off the cotter pin and the whole assembly comes off.

How can the bearing inner race weld to the nut and not to the shaft, which is already a pressfit ?

 

[WinterDeere]

How can the bearing inner race weld to the nut and not to the shaft, which is already a pressfit ?

Good question, but I've also seen sleeve bearings weld themselves to the retaining washer at their face, without welding to the shaft. Same scenario, in principle.

I can imagine three contributing factors:

1. Thermal mass: Axle has better ability to carry heat away and dissipate it, remaining cooler than nut.
2. Lubrication: Perhaps grease or gear oil flows better thru the cylindrical capillary between axle stub and inner race of bearing, than between nut and the same.
3. Speed: Rim speed increases with radius, and outer rim of inner race at nut might be 20% to 30% larger than radius of inner portion of inner race at axle stub. Speed is linearly proportional to radius, but heat generated is square of speed, so difference in localized heating can be 1.7x higher for a 30% larger radius.

Likely all three of these factors played varying small parts. Remember, a bearing that has been press fit at room temperature will often not remain a press fit when heated, it could have several ten-thousandths of an inch play, at the scale of a small trailer axle bearing. Anyone who's ever played the game of heating a bearing and sliding it off by hand knows that trick.

 

[RandyT]

How can the bearing inner race weld to the nut and not to the shaft, which is already a pressfit ?

Good question, but I've also seen sleeve bearings weld themselves to the retaining washer at their face, without welding to the shaft. Same scenario, in principle.

I can imagine three contributing factors:

1. Thermal mass: Axle has better ability to carry heat away and dissipate it, remaining cooler than nut.
2. Lubrication: Perhaps grease or gear oil flows better thru the cylindrical capillary between axle stub and inner race of bearing, than between nut and the same.
3. Speed: Rim speed increases with radius, and outer rim of inner race at nut might be 20% to 30% larger than radius of inner portion of inner race at axle stub. Speed is linearly proportional to radius, but heat generated is square of speed, so difference in localized heating can be 1.7x higher for a 30% larger radius.

Likely all three of these factors played varying small parts. Remember, a bearing that has been press fit at room temperature will often not remain a press fit when heated, it could have several ten-thousandths of an inch play, at the scale of a small trailer axle bearing. Anyone who's ever played the game of heating a bearing and sliding it off by hand knows that trick.

Something has to happen to cause the nut to shear off the split pin and then unscrew the hub retaining nut on the left side of the trailer.. Where on the right side the effects would tighten the nut and in most cases the hub will slide over the nut and leave the inner bearing and seal on the axle spindle but in some cases the inner bearing and seal will go with the hub on the left side spindle

Take a look sometimes when you come across a trailer on the side of the road with a missing wheel due to bearing failure. On the shoulder side of the trailer the nut will still be on the spindle but on the lane side most times the nut will have unscrewed and go with the flying wheel.

It may not be from the bearing welding to the nut, could be the lopsided wheel hub rubs the nut hard enough to rotate the nut to shear the split pin. But I have seen the outer wheel bearing stuck to the retaining nut to the point that it requires a hammer and punch to separate the two.

 

[Renze]

It may not be from the bearing welding to the nut, could be the lopsided wheel hub rubs the nut hard enough to rotate the nut to shear the split pin. But I have seen the outer wheel bearing stuck to the retaining nut to the point that it requires a hammer and punch to separate the two.

Red hot nuts and inner races dont weld together untill you stop so they can cool down and fuse. Then it takes a lot of determination to shear a castle nut cotter pin, with that much resistance when you take off.
I have split wheel hubs and even transmission casings when bearings jammed, but never sheared a cotter pin. To be honest, with the tire radius, wheel load, 0.5 tire to road friction, 30mm castle nut inner diameter, cotter pin diameter i am used to, i doubt a jammed tire can generate enough torque to shear the cotter pin. The math of an average hub just makes it very implausible, to be honest.

Either way, when youre able to separate the nut and the inner race with a punch and a hammer, thats not enough force to shear a cotter pin.

 

[RandyT]

Red hot nuts and inner races dont weld together untill you stop so they can cool down and fuse. Then it takes a lot of determination to shear a castle nut cotter pin, with that much resistance when you take off.
I have split wheel hubs and even transmission casings when bearings jammed, but never sheared a cotter pin. To be honest, with the tire radius, wheel load, 0.5 tire to road friction, 30mm castle nut inner diameter, cotter pin diameter i am used to, i doubt a jammed tire can generate enough torque to shear the cotter pin. The math of an average hub just makes it very implausible, to be honest.

Either way, when youre able to separate the nut and the inner race with a punch and a hammer, thats not enough force to shear a cotter pin.

Whatever. Something is causing the pin to shear off and the retaining nut to unscrew on the left side of trailer axles.

 

[lilranch2001]

It’s magic!

 

[BigBlue1]

You don't have to lose the axle nut to have the hub come off. If the outer bearing disintegrates (lack of grease... burns up and comes apart) then the hub no longer has retention.