Not selectable, but I've had very good luck with Detroit Trutracs (Torsen geared type, no clutches to wear). They are completely invisible on the road and they engage smoothly when needed, without any driver input.
Not the best for a rockcrawler (will not actuate with a wheel in the air unless you tap the brakes), but for what I do, I'm very pleased with how they work. This winter I am yet to engage the front axle in my XJ.
1969 M715 6x6
1963 J300 Swivel frame
Last edited by Mikel : 01-25-2020 at 08:09 PM.