Blower Wheel Mystery

Last week I was on the interstate with the AC on when over from the passenger floorboard
I noticed a gurgling/fluttering sound. Sounded like bubbling water really so turned off the AC and pulled in at the next gas station. Quick inspection of feeling the HVAC housing and vent [lack of] airflow made it obvious that the fan wasn't right.

Upon taking the motor out that evening, found the wheel (squirrel cage) no longer connected. The wheel bouncing around and contacting the spinning shaft plus the house apparently sounds like water to my ears.

Somehow the center of wheel broke out or melted out. Hard to say since I had the back window open and door vents cracked for the dog so I don't know when it stopped blowing out the vents. Too much noise and other airflow. Meaning, I don't know if all the melting happened after the failure or before.

HVAC housing was perfectly clean still from the rebuild. No sharp pieces of plastic, just melted bits. Fan motor was replaced during the rebuild so it's not super old. Squirrel cage was the original.
I do have the blower relay mod.

I just can't figure out what caused this. The outer vanes of the canes show light scuffs on a couple of them but I suspect those came when it was rattling around. No chips or anything. Inside the housing was all smooth as well.

Ran to the jy this morning and grabbed a few wheels (2 different styles). Cleaned one up and reinstalled everything. Fan sounds as smooth as it did originally and blows hard.

The concern is that I didn't 'fix' anything. And I wouldn't have reused the wheel if it had shown any visible issues.

Photos to follow

Another important piece is that the shaft didn't spin in the slotted hole. That part was still on the shaft. The retaining washer-thing, also on the shaft did have melted bits squished up through it.
Just seems like if the shaft getting hot was the cause then it would have melted out the flat spot and spun inside the wheel.

Anyways, probably a fluke but annoyed the cause isn't obvious. To me at least.

It looks like the melting was after the fact from the friction of the motor axle turning inside the broken cage and the force of gravity causing the cage to slump, and the plastic to flow toward the bottom.

If there was no debris found inside, I'd say it was a stress fracture of the cage that caused it to fail originally, and a new one will fix it.

That's strange!  I can't imagine what would have caused the plastic to have gotten that hot in that area to do that.  Like you, I'd have thought the heat would have been where the shaft meets the squirrel cage.

Is it possible that the shaft got so hot from the motor that it heated up that plastic, but that the hub was capable of withstanding the heat and the plastic farther out wasn't?  

Thanks guys. Hopefully it was just a bad cage and won't happen again

It's possible Gary - I could see that area just past the reinforced area getting hot enough (even if the shaft sleeve was hotter) to where the resistance of the vanes cause it to stretch out and eventually tear free.

Fortunately as far as replacing things go, this is an easy one but still hope it doesn't do it again anytime soon as it will undoubtedly happen on a 90 degree day

The melting/wear damage likely only happened after it broke apart. That plastic would be far more brittle now than it was 40 years ago...and it probably started to crack, and eventually the center broke out. The starting torque is really hard on them (not just Bullnose fans...any fans) and every time the fan started, the crack probably moved a 1/16" or 1/8" every time, until it eventually snapped. My 2 cents;).

Agreed. I wonder if there's a different fan blade still in production that'll fit. Seems to be similar to what my 1995 Ranger uses?

AFAIK my fan (stock motor and blade) is still good (although the noise to flow ratio leaves a bit to be desired IMHO), but since I daily mine, I do have my concerns since I do use my A/C a lot (and the heater/defrost in the winter, obviously).