Rear Axle interlock?

You would literally grenade your differentials. Because what happens with that kinetic energy when only one wheel connects in a spin out?

 

That's called full lockers. Most trucks that see any sort of offroad use have lockers on both drive axles, as well as the inter-axle lock. Milk trucks, oilfield trucks, logging trucks, and the list goes on.

 

4 way lockers is what its called. You'll have an inter axle lock and a differential lock for each axle. IMO every truck should have at least 1 differential lock in addition to the interaxle just because you never know when you might need it.

 

Many road tractors do not have axle lockers. They're typically air-actuated via switches in the cab (next to the inter-axle lock switch, typically), and should NEVER be used on dry pavement or above about 15-20 mph, if you want your rear-ends to stay together.

 

Depending on what axle you have you may be able to have a Detroit Locker installed in one diff.

 

I ordered my 2014 389 with a locker in the rear axle only, rarely use it. You can add a rear locker to an Eaton rear end by notching out your housing to accept the solenoid that actuates it, and adding an air switch to feed it. You have to replace the whole third member as well ( IIRC the ring and pinion are the same as open diffs) also the axle shafts on the actuator side of the differential is different as well (right shaft on rear, left on front) I did both on a 2003 379 when I regeared it.

 

I did the rear cause I throw a lot of "iron" in the winter, and I rarely put it on the front axle. The cost would be like replacing a whole third member plus an axle shaft plus the labor to notch housing and run an air switch.