My 4 wheel drive is not working correctly. When I switch to 4 wheel drive it doesn't go in. When I switch to 4 lock it goes into 4 lock. If I switch from 4 lock to 4 wheel it works. I remove the servo and it works perfectly. The linear gear moves freely in the differential. There are no worn teeth on either gear.
I am methodical about changing my differential oil. I change it way more often than is needed but I get into a lot mud so I thought it would best.

I am at a loss. Everything looks like it should be working perfectly. The only thing I can think of is that the servo is weak

[2015 Z Force 800 53/Trail EPS]

My 4 wheel drive is not working correctly. When I switch to 4 wheel drive it doesn't go in. When I switch to 4 lock it goes into 4 lock. If I switch from 4 lock to 4 wheel it works. I remove the servo and it works perfectly. The linear gear moves freely in the differential. There are no worn teeth on either gear.
I am methodical about changing my differential oil. I change it way more often than is needed but I get into a lot mud so I thought it would best.

I am at a loss. Everything looks like it should be working perfectly. The only thing I can think of is that the servo is weak

So mechanically all looks good and the slider works smooth and nice. So when you push the button to go into 4wd, it doesn't. First let me ask...do you hear anything? Ok, next, you flip the safety over and hit the locker button and it locks. Then when you "un-click" the locker it unlocks and stays in 4wd. Is that about right? My opinion...your "high-quality", Chinese dash switch has gone south. And it won't be the first one
 

Did you get this issue figured out? Mine won't switch to 4x4 at all. I can get the diff lock to work but no sound trying to put in 4x4