How does 4wd work?

[CokeZero]

I'm a noob to 4WD. I've only had a newer truck that had hubs in the front that if you turn to the left they are in "auto" lock mode and turned to the right is locked in all the time.

I noticed there isnt any locking hubs on my 97 k1500 silverado so how exactly does it work? Are they always locked in? just when you use the floor shift, youre good?

 

[df2x4]

The front diff is open at all times on these trucks. In really nasty situations you'll only ever be spinning one front wheel. You wouldn't want it locked 90% of the time anyway, steering would be very difficult.

 

[DerekTheGreat]

Thought I read the driver's side axle is always engaged but when you pull the lever it uses that thermal actuator thing to engage the passenger side axle? I don't really know either. And I've always assumed that until wheel slip actually happens or there is a difference in wheel speed between the left and right wheel, both wheels are getting power (spider gears aren't in play). Before I put a posi unit in my Fireturd I could sometimes get both wheels to peel, very briefly and especially on painted garage floors. Would do that if the throttle was quickly stabbed & released but not outright floored, which is why I assume the crap I wrote earlier.

 

[RichLo]

yep, floor shift enguages the transfer case (power going to the front diff) then the thermal actuator enguages the passenger side axle which in turn enguages the front diff to complete the 4wd action.

Not much usually goes wrong with the floor shifting transfer case (push button is a different story) so people usually start with replacing or upgrading that thermal actuator in the front diff.

 

[evilunclegrimace]

The front diffs on these trucks have the drivers side Tire,Axle,left side diff shaft and side gear turning in the direction of travel 100% of the time. This can and does cause the spider gears to turn and cause the Passenger side side gear and inner axle to rotate in the opposite direction of travel. The passenger side Tire, Axle and outer diff shaft also turn the the direction of travel but do not affect the diff in any way UNTIL the actuator causes the left outer shaft coupling to move in toward the center of the diff. At this time the friction from the outer diff shaft causes the inner shaft to turn forward and when their speed matches they couple together


This why sometimes you can feel the front diff engage and is also the reason you hear about someone breaking the front diff when the have been stuck and did not engage the 4WD BEFORE they became stuck.