1:1 Ford LT 9000 Twin Screw ?

[mavrick0]

Both axles always drive. But if you get into a situation that you loose traction the front axle will put all the power to wheel with less traction and send almost nothing to the rear axle. When you use the interlock it locks both axles together so power is equally transferred to both drives. Without a diff lock you then will get the wheel(s) with the less traction spinning on both axles.

[ihbuilder]

It's called a power divider lock ( at lest on all my IH's I have is what it's called ) . The FWD rear has a differential on the input side where the drive shaft attaches to . When you switch the PDL on, it locks that diff to ensure positive drive to both FWD and RR axle . Now bear in mind you still have a diff in each axle so only 1 wheel per axle would turn in a slick condition unless you have 4 wheel lockers (or sumsuch as I never had this lux in my old trucks )also . Note ( as per instruction on sun visor )The PDL not to be used or engaged at highway speeds . It's a great feature to have when getting off road onto a dirt incline , snow or just operating off road .