I have a 99' Scrambler 400. The "passenger side" front wheel engages into 4wd mode whether the 4wd switch is on or off. The 4wd is not on all the time, only when the rear wheels lose traction. The "driver side" front wheel works as it was designed to. Has anyone else had this problem and if so any ideas why and/or how to fix it?

 

1) Check the hub fluid level. This is a plug in the hub body removable with a hex key or allen wrench.
If it is low, that is your problem right there. Even if full, drain it (or if dry, add some, drive it around, then drain it.)

2) Refill with either Polaris hub oil or Mobil synthetic type F ATF fluid. Fill the hub until oil leaks out the plug hole at the 4 O'clock position (a little less than half way up).

If this doesn't cure the problem, try changing the hub fluid again.
If it still doesn't work right after 2 hub fluid changes, post back here & I can give a few more things to try.
Farmr

 

Thanks Farmr 123,

I have already tried filling and draining the hub a few times. I have been using the Mobil Synthetic ATF for the last year or so without any problems. I drained and checked the fluid again today and it was full and clean. I refilled it and rode around without any improvement. Any additional suggestions would be greatly appreciated.

 

Check the torque on the hub nut. It should be between 110 & 120 inch pounds torque preload on the bearings. (Torque the nut while spinning the wheel with the front of the machine on jackstands). If the bearings are too loose or too tight, that can effect 4wd engagemeng/disengagement.
If that doesn't do any good, my next guess would be that the spring that goes around the rollers is stretched, weak, or broken. To check that out, remove the axle nut, washer, and outer bearing. Next to come out should be a cage with rollers around it(some machines may or may not have another washer in between the bearing & cage). The way the hub works is a magnet engages the rollers, to lock in the demand drive, and when the magnet is turned off, the spring is supposed to pull the rollers down from the cams, disengaging the 4wd. If the spring is weak or broken, it will not want to disengage. The spring is very picky about being over stretched. If you suspect the spring, what I would recommend is to clean the roller cage & rollers up good in solvent, then take it to your dealer, and have them put on the new spring. To do it right, they have a special tool (which prevents overstretching the spring). My dealership doesn't charge labor for such little jobs (5 minutes, tops) as long as it is on the machine you bought from them. Hopefully, your dealer will be as generous.