I would NOT
disassemble the differential unless you find some reason to do so during these procedures. The diff has some bearings that are a pain to deal with as well as several seals you would want to replace if you took it apart. There are also gear lash adjustments that require dial gauges and shims to adjust.
1 – Verify that the Diff lock and 4X4 switches are both in the off position. Put the quad in Neutral, turn the ignition key on and rock the quad back and forth to allow the differential to disengage (if it can). Turn the ignition key off.
2 – Put your quad in park and jack up the front until both front tires are off the ground. Engine should be off.
3 – Spin the right tire (as you sit on the quad) by hand. You should feel a jerkiness to the rotation (about 16 “jerks” per rotation). This is normal and is just the limited-slip diff doing its thing.
4 – Spin the left wheel by hand. It should turn smoothly.
5 – With the key on (motor off), press the 4X4 button. You should hear the 4X4 / diff lock actuator run for a second. If you do hear the actuator run, skip to "Checking the differential’s function" below. You should also see the 4X4 indicator on the display…if not, you probably have a bad indicator switch in the actuator motor or a wiring issue (shorted/broken wire) but this will not keep the 4X4 from engaging (it will, however, keep diff lock from working).
If you do not
hear the actuator motor, either something is jammed, you have a bad actuator, or you have an electrical problem.
First, check your fuses, there is a fuse for the 4X4 function. Since you state that you are getting 4X4 function when you engage the diff lock, I doubt that the fuse is bad. If it is not that, check the 4X4 switch with a continuity tester to verify that, when in 4X4 (not diff lock) position, it shorts the blue/black wire to the blue/green wire and the blue/red wire to the light blue wire in the black connector that comes from the switch assembly. If this is not true, your switch is bad. If it is true, the problem is that the actuator is jammed or one of the three relays is bad or the actuator motor is bad.
To see if the actuator is jammed by a faulty differential, you will need to remove the actuator from the differential so you will need to drain the fluid from the diff. You will also need a set of metric Torx / star drive wrenches (don’t recall the size) that are capable of working with “security Torx” bolt heads. These tools will have a hole drilled in the center of the star so that a pin that protrudes in the same place on the bolt head will not stop the tool from engaging the bolt. I got my set from Harbor Freight. Only one of the bolts has the “security Torx” head and, if you do not have a set of "security" Torx, you can remove the single "security" bolt with a pair of locking pliers and then replace it with a standard socket-head bolt of the same size.
Drain the diff fluid into a clean container so that you can check it for crud and bits of metal. If there are sizable metal bits…it’s a bad sign for your diff.
Refer to the parts view here
for parts identification.
Checking the differential’s function
Verify that the 4X4 switch is OFF (turn the key on for a moment to let it [attempt to] disengage then turn it back off. The actuator is the black plastic thing bolted to the back left side of the diff and is #19 in the parts view. Unplug the two plugs from the actuator. Remove the Torx bolts that hold the actuator motor on and pull the actuator out (carefully pry around the edge with a flat blade screwdriver). You will then see a linear gear (flat bar with gear teeth) #23 on a round shaft #18 near the bottom of the opening the actuator came out of. This linear gear meshes with the round gear on the actuator motor. Verify that there is no junk in the linear gear’s teeth or the actuator motor gear and that there are no damaged or missing teeth in either one. If any rust or corrosion is evident, there is likely a leak in one of the seals (drive shaft or one of the axles) or in the vent tube and moisture has gotten into the diff. If all looks good, attempt to slide the linear gear to the right (note that it should be all the way to the left in 2WD mode). You may need to turn the right wheel a little to get the linear gear to slide. Sliding the linear gear should move the fork connected to it which will, in turn, slide the splined adapter #31 which you should see directly behind the linear gear. Sliding to about half way between left and right will engage 4X4 mode on the diff. All the way to the right engages diff lock.
Slide the gear to the center of the opening to place it in 4X4 mode (again, you might need to turn the right wheel to allow the splines to mesh). You should now only be able to turn the right wheel with some difficulty as it will attempt to turn the front drive shaft. Also, the left wheel will want to turn in the opposite direction that you are turning the right wheel. If this does not happen or you cannot get the sliding gear to slide to the center, you probably have a damaged diff and it’s time to take a flashlight and see if you can see through the actuator opening and detect any damage (missing teeth, chunks of loose metal, something bent, cracked, or broken). If you see damage, it is up to you if you feel it is worth trying to repair it or just replace the whole diff.
If the diff seems to work fine, slide the linear gear back all the way to the left.
Checking the actuator motor function:
In the 2WD mode, the paint mark on the actuator motor gear should line up with the paint mark on the motor housing. If it is not, then you will need two “C” or “D” batteries and some wire to use as a 3V power source so you can run the motor (I will detail this later).
Assuming the gear is aligned correctly, re-attach the two electrical connectors to the actuator, turn on the ignition key, and press the 4X4 button on while watching the actuator gear. The gear should turn some (about a full turn?) counter-clockwise and stop. Press the 4X4 button again to turn it off – the actuator gear should turn clockwise back to its original aligned position.
If one or both of these does not happen, the actuator is bad or it is not getting the proper voltages from the 4X4 relays.
Testing and aligning the actuator motor:
Use two “C” cell or “D” cell batteries in series (plus to minus) to create a 3V power source. I will leave it up to your imagination as to how to keep the batteries in contact while performing the following procedures but I can tell you, a helper is handy. Maybe some electrical tape stretched between the bats?
Locate the electrical connector that has 5 connector pins and is located on the outer perimeter of the actuator motor. Orient this connector so that it is facing you and is on your left. In this position, we will call the top-most pin, pin 1 and the next one down pin 2, and so on. Take a piece of wire from the minus (negative) side of your 3V battery pack and run it to pin 1. Then, take another wire connect from the positive side of the battery pack and touch it to pin 2 of the same connector. The motor should run counter-clockwise. Let the motor run to perform at least one full revolution of the gear to verify it has no hang-ups. Now, reverse the polarity so that the positive side of the battery pack goes to pin 1 and the negative to pin 2…the motor should run in the clockwise direction. Again, let the motor run to perform at least one full revolution of the gear. Once clockwise and counter-clockwise function has been verified, use the battery pack to run the motor until the painted mark on the gear is aligned with the painted mark on the motor housing.
If the motor tests OK but still does not operate correctly when connected to its wires and activated by the 4x4 and Diff Lock switches, then the problem is electrical (one of the relays, the switch, the fuse, or faulty wiring). We have already checked the fuse and switch (at least for 4X4 mode) so that leaves the relays and wiring. Since this can get into some serious tracing, just let me know if you get here and well continue to troubleshoot the relays & wiring.
Re-installing the actuator motor:
Make sure that you have aligned the gear on the actuator motor as detailed above. Verify that the linear gear in the differential is all the way to the left (2WD mode). Verify that the 4X4 switch on the quad is in the OFF position.
Check the O-ring #23 is in place and in good condition. Lubricate the O-ring with some differential oil and slide the actuator motor in place on the differential. Install the bolts into the actuator with the "security" bolt in the lower hole. Torque the bolts to 10 ft.-lbs (13 N-m).
Refill the diff with SAE 80 API GL 4 or GL 5 Hypoid gear lube to the point where the lube is level with the bottom edge of the fill hole. Reconnect the electrical connections.