I just purchased a middle-aged SUV that has “freewheel” hubs on the front axle. What do these private centers do? Is it necessary or just a gimmick? Should I have them on “Locked” or “Free”, and when should I change the setting? Clement
Freewheeling hubs are optional but very useful – with a small but real benefit to performance, fuel economy and some reduced wear.
You should always set it to “Lock” when using 4WD and preferably set it to “Free” when returning to 2WD. Here’s how and why:
When in 2WD mode, the front prop shaft is disconnected from the gearbox. But it is still connected to the front differential, front driveshafts and front wheels. Even though these wheels are no longer running, they still turn while the car is moving… so they rotate their drive shafts, differential, and prop shaft.
That’s a lot of heavy metal to rotate, acting as a “rolling resistance” load that the engine must devote energy to overcome.
What freehubs do is separate the wheels from the drive shafts.
Now the wheels continue to turn, but the driveshafts, differential and prop shaft – separated at both ends – remain stationary. This saves the engine some rev-resistance energy and frees up more power for performance or fuel savings.
It also avoids wear on the front transmission components, which would otherwise engage their gears and bearings without any constructive purpose.
It’s okay, but a waste, to leave free hubs locked all the time. The vehicle will simply operate as if it had conventional axles. In theory, you can also engage 4WD when the front axles are set free, but you’ll be in 2WD mode only and this time the gearbox will spin the front prop shaft, differential and drive shafts to no beneficial effect. The front wheels will not receive power.
What is not acceptable is to leave the hubs in the free setting if you operate the “low range” transfer case. This doubles the torque transmitted by the gearbox, which is acceptable when shared between two axles but can put too much pressure on only one axle to handle. This could damage the rear gear and even cut off the rear driveshafts.
In practice, most of the time you’ll be driving with the axles free and only locking them when using 4WD. If you’re in tough conditions that require frequent changes between 2WD and 4WD, you can leave it in the locked position to save having to stop and adjust the axles on each change and only release it again when you’re back on good roads.