M1009CUCV said:
locking hubs on m35a2.in the unlock position does the differential still turn and drive shaft .in the unlock position under truck not running you should be able to turn driveshaft freely.not sure what member meant by sprag always turning parts .if that is the case locking hubs are worthless aren't they
It depends. If you have an airshift front axle and the locking hubs are disengaged, then no, nothing turns. It is just like a conventional 4WD vehicle with locking hubs and a selectable transfer case. With the the hubs unlocked and front axle de-selected, the front axle shafts, differential and drive shaft do not turn. Fuel economy, steering and tire wear are improved.
A "sprag" is the earlier from of front axle engagement. It is an overrunning clutch which automatically engages when rotational speed difference between the front and rear axle driveshafts exceed a predetermined slip rate. Simply put, when the sprag senses that one driveshaft is turning faster than the other, it automatically locks in the front axle with no effort or input from the truck operator.
As explained above, locking hubs WILL work on a sprag shift truck. With the hubs disengaged and the truck in motion, the sprag will engage and the front driveshaft, differential and front axle shafts will turn, so you will not gain any advantage in fuel economy because all that heavy metal is still spinning. However, since the wheels themselves are now free spinning, driveability and tire wear are improved.
Is it worth the cost to install a set of locking hubs on a sprag truck? Again, it depends. The cost of a set of locking hubs is about what you would pay for 2-3 pairs of new 9:00-20 tires. IF you do a real lot of driving, the lockouts MAY pay for themselves in tire replacement expense. The ideal setup would be an airshift front axle and locking hubs, which would improve driveability, tire wear and fuel economy. If you have a sprag truck and want to install locking hubs, you may also want to consider either converting to an airshift T-case, or get a REB kit from Memphis Equipment and convert the sprag to a manual front axle engagement. It all depends on how much you can afford to spend and what you hope to gain from the modification.
Overson vs Selectro? Costs are pretty much the same but, as stated above, the Selectro hubs are lower profile and easier on the eye; the Overson hubs are definitely more rugged and more waterproof; but I have yet to see a posting from anyone who has broken a Selectro hub!