FSU FX4

How exactly does the On the fly 4x4 work?

dilloncawthon

how does it work or what does it mean?

it means you can shift into 4hi at any speed up to 55mph i believe.

how it works is a little more complicated.

FSU FX4

I mean i knew u could **** "on the fly" lol i mean like do u still have to put it in N? I gues i meant how do you do it

nashtruck

You can switch from 2wd to 4hi or back while driving, on the fly, no stopping. For 4low you have to be stopped and tranny in neutral (not on the fly)

dilloncawthon

oh ok lol. no you don't have to be in neutral.

D94R

Your front hubs are always engaged. Therefore your front axles, front gears, and front drive shaft are always rotating at speed when driving. Shift on the fly uses an electric motor to engage the transfer case to split power to the front when engaged. The electric motor serves the same purpose as the 'stick' used to when you used to have to manually engage the transfer case (rarity to find something 4x4 with a stick these days).

Since the front drive line is turning at the same rate as the rear driveline you can "shift on the fly" as there is no offset in gear speed in the transfer case to worry about any binding or grinding of gears.

The reason for having to stop (or be 5mph or less) to go to 4 low is because you are using a gear reduction (gear change) in the transfer case to change the output speed to your drive lines. There is a difference between the tranny output speed and the transfer case output speed when going to 4low and trying to shift on the fly into that would cause hell on the gears/case as there is no synchro in the transfer case to match speeds. (Like a manual tranny has synchros to match engine and tranny speed when shifting, you also don't have a clutch in the transfer case to abosrb the "hit" the gear change will create). Thus you must be stopped or very low speed to achieve gear speeds that will be close enough you can engage the gears and not create binding or grinding.

60DRB

...actually, the hubs are not always engaged and the front shafts are not rotating when in 2wd. If all is working correctly, the 4wd solenoid and engine vacuum pressure disengage the front hubs when the engine is running. When you push the 4wd button, the shift motor on the transfer case engages the transfer case gears (what the manual 4wd shift stick does in many trucks) and at the same time the solenoid releases the vacuum that holds the actuators off the front hub splines.

If your front drive shafts are rotating when you are in 2wd, you have a problem with your actuators or 4wd vacuum system.

Also, when shifting to 4-HI on the fly you should not be accellerating. Let off the gas when you shift to 4 HI.

D94R

You are right, I forgot the vacuum actuator on the F150. I was referencing back to my Ranger.... sorry.

FSU FX4

Well thats good to know lol