I was reading the manual for my 2014 International sleeper this week. It mentioned using the inter-axle differential lock when backing under a trailer. That's a new one for me. Most of the times I have used it, I have used it when I was 90 degree backing up to a door over a surface that's got so much camber some of the wheels don't touch the pavement.

 

Instead of stopping to get it fixed, I was stupid and tried to make it home with one hell of a drive train vibration. I ended up dropping my rear driveshaft enroute. Using the interaxle lock saved me one hell of a tow bill! I could drive full normal speed, only problem was listening to that annoying beep all the way home.

Mackman: I had an early 90's Mack many years ago. Behind the interaxle lock switch was a spare wire harness that looked just like the one's on the interaxle, fifth wheel slide, and those switches. Unplug the plug from the interaxle switch, re-plug the spare one, and no more beep when activated.

 

I ran into a guy that broke a differential and he locked in the front axle and drove the truck several hundred miles to be repaired. He told me that since the rear differential was broken, it would pull against the front one. I talked to him on the radio, so you can take it with a grain of salt, but it seemed believable. I realize there are different types of interlocks, but I'm assuming this was some kind of front and rear together lock???

 

After reading Thompson Pass Trucker's description of how the Diff Lock and the Inter Lock works, I'm guessing the guy I mentioned used the Diff Lock only? I was told that all the power passed through the front diff and drove the truck off the rear unless locked in some configuration, which is why you would remove the front diff for a single axle usage except that the rear diff on a tandem is not exactly like the single axle diff, let's say on a Fed Ex truck with single. I'm guessing they use some sort of limited slip, otherwise those guys chaining up both sides were just wasting their time.......you could theoretically remove the drive shaft to the rear diff and lock the front diff and drive the truck in an emergency it seems. As to the opening post, I used to shift my 2001 Freightliner in and out of lock at highway speeds on snow all the time. I say highway speed, I never exceeded 45 mph because I was concerned about building heat in the differential for extended usage.