What do you actually check on a pre-trip inspection?

I would be curious to what state you got your cdl in and which school? If you don’t mind sharing.

 

Wheel seals are on the inside of the hub around the axle spindle... When they go out the hub oil will all leak out and streak the inside of the tire as it spins. Usually the earliest way to catch such a problem is to see the oil in the brakes or streaking the inside of the inner most tire. You ever heard of a truck or trailer loosing a set of duals??? That is what can happen if a bad wheel seal is not taken care of... All the oil leaks out, the bearings over heat and melt then the hub either eats the spindle nut away or slips over the spindle nut and the entire wheel/drum/hub assembly comes off. The following is a picture of a wheel seal.

 

Pretty hard to catch that leaky seal when you don't crawl under there and look
But yet the OP states he does a very thorough pre trip.. even though he admitts he doesn't look under the truck or trailer

 

I changed out 3 wheel seals on my setup (1 drive, one on the lead, and 1 on the pup) this summer alone... Id hate to know what it feels like to completely loose a wheel end at a gross of 106k+

 

If it’s got oil it’s go time!

 

If it leaks on the tire. That's a pretty bad leak.

Most times they don't get that bad. You can catch it long before the tire.

 

Pretrip check does truck start -yes Is the a big white box in the mirrors-yes. Let’s roll