Yes. If you look on the back of a truck or trailer axle you will see a set of large "cans". Inside is a rubber diaphragm and a big azz spring. This pushes a lever that applies the brakes. The air pressure on the diaphragm pushes the spring and releases the brakes. The can is a two piece unit with a large band clamp in the middle. To replace it, you must first insert a T-rod that hooks in place. You tighten the nut on the T-rod and it collapses the spring, then you can take the clamp off and split the can. If you don't use the T-rod and loosen the clamp the can will explode apart and can cause death! I still have about 20 T-rods in my tool box from when I used to work on trucks. They come with the replacement brake cans.

Two airlines, a service line that does the brakeing, and a emergency(parking line) that charges and releases the brakes.
If you loose the service line you will only have the stopping power of the tractor, not the trailer. If you lose the emergency line, the trailer brakes automatically set and if adjusted properly and working will stop the vehicle, or if your already stopped it will prevent you from moving.


Oh, and on topic, I have lost a set of wheels from my semi trailer and didn't realize it until my next stop. The whole caboodle, all I had left was the axel and the brake shoes. Light weight that day so it was still a couple of inches above the ground, so no sparks.

A friend of mine has a car carrier buisness...he lost a mercedes on I 10 and didn't know it untill the CHP pulled him ove and tried to charge him with hit and run... Remmber, a 70 mph tire can easily take outa windshield and kill somebody....

Exactly correct and that is what happened to mine. (the red line is the emergency and the blue line is the service) I figured it out when I was having a very hard time stopping.

I just purchased my boat , And last week , when we went out for the test ride , we actually followed the guy out of the marina. About five minutes into the trip the back wheel just decided to take a path of its own. Watching it come off was almost horrifying it went off of the road , hit a bump and flew what looked to be like 50 feet in the air into the oncoming lane of traffic with cars approaching. it bounced one time more and flew back off the road ! We went back to the spot several days after looking for the wheel and tire , and finally on the 3rd try found it . It was amazing how far off of the road it had gone, and landed . Im still in disbelief.
When i called the guy to tell him i wanted to meet for a boat ride , he took it to his shop to have the bearings/seals inspected . It appears that on reassembly one of his guys failed to tighten the lug nuts.
It sheared off every stud on the hub, and actually distorted two of the holes on the wheel ,i think its still useable though.

"I think its still useable" how friggin much is a new wheel compared to if it turns out to not be useable...starts wobbeling because of the egged out holes, and the mating surface is warped, comes off and kills somebody????? they should be the ones replacing the wheel anyways..it was their boat and there mechanic at the time of failure.

Two weeks ago I was coming home (about a 1 1/2 hour drive) I had just driven there the day prior and did not even unload my boat. All four wheels were cool to touch when I got there. The boat sat up all night, came home the next day. About a good hour out we pulled in for ice cream, then I saw the smoke. I pulled the rim off and let the brake hub stay there, about 4 inches off the ground. Drove home at 45 MPH. Just before getting home on a curve I saw my brake drum going across the road. Ran over got it and drove on home. The hub came off over the nut and washer. The bearing were burned up. Just got them replaced.
By the way, I noticed that all of the bearings are now made in CHINA, none in the USA!
By the way, was the wheel on when you left, as in did someone take it off for you?

Glenn

Washer?
 

You said the nut was still there, but what about the big washer that holds the outer bearing? If that was left off at some time, like when you had the axles serviced, I could see the bearing failing and the whole deal coming off as you said.

I too lost a tire and wheel off a three axle trailer and had no clue un-till a couple pulled along side to tell me what happened.

So glad it did not hit anybody.

Lesson learned, don't trust an air gun, always use a torque wrench.

Nut, cotter pin and large washer were all there including the inner race of both bearings.... Just no hub, wheel / tire. And no damage to trailer or anything strange during the 20 miles of driving when it occured...

You can still get USA made Timkens, but chances are you'll probably have to order them. I replaced all the bearings in a tri-axle trailer earlier this year, called the local bearing place told them what I needed and assumed they would be Timkens since they had about 1000 signs all over. They handed me the Made in China specials in a zip lock bag. I needed enough to at least get one side done, but gave the other half of them back and told them to order me some Timkens. So I have China specials on one side and Timkens on the other, probably put a good 1000 miles on the trailer this year. Plan to tear it apart and do a visual when I get a chance to see if there is any significant difference between the two.