I purchased an '88 Trail Boss 250 4x4 today with the front hubs not engaging (tested on jackstands). I did find that the wires leading to the right hub were all worn and actually apart. I added new wire where needed and power was flowing through to the hub when the 4x4 switch was selected. I thought this would solve it but still the hubs were not engageing, either of them. The problem appears to be electrical. Could the wires that were touching each other where the insulation was worn have damaged any electrical components? Is the guage of wire used a factor? Are there any common checks or repairs for the hubs. I am mechanical but have not dealt with this type of 4x4 system in the past. Any comments would be greatly appreciated!!! Thanks!!!

 

the 4x4 engagement system on polaris work like the air condition compressor on your car. by magnitic clutch. they are located in the hubs.which mean the have a coil in there. but i cant see both going out at the same time!! but ya never know!! i would check around that area if you have power to there. wire size would not matter.

 

Do you have an ohm meter? Check for resistance through the magnet. If the magnet is bad, it will either be no resistance (grounded out) or infinite resistance (torn wire or something). It IS strange to have both go out at once, but I guess it can happen. Knew a guy who ran his without a battery, blew every light bulb on the thing & ruined something in the 4-wd. I don't think that happened to you, though, as you have power going through the wires & he didn't. Let us know what finally fixes it.

 

I have dealt with Polaris hubs WAY to much in my time. Have you checked the hub oil? Polaris hub seals are notorious for leaking and running the hubs dry. If this is the case, try filling the hubs with ATF or Polaris's special hub oil. Turn the hub so that the plug is at 3:00 or 9:00 and oil should just start running out at that point. That is when it is full. Now, the 4x4 might not immediately start working right away. The oil has to get worked into the hilliard clutch and other components to get it to work. Are you sure that you are getting power through the coils in the hub. If both aren't working, there could be a gray wire off some place or the switch isn't working. If not, take the hub apart and check it out for yourself!

 

You can easily help to locate the problem by checking for voltage between the two wires going to each hub. If you are getting voltage (~12 volts) at the hubs, then you know the problem is located inside the hubs. If you aren't getting the voltage down there, then trace the wires back up and keep testing to locate the problem. It could be as simple as the switch. Just some suggestions.

 

I'm not familiar the Trail Boss's but if it's anything like my Scrambler, you should have an electrical connection somewhere on the transmission, it may be near the routing of the pipe. If this connection comes loose you will loose your 4X4 ability. Mine came loose on my Scrambler and I lost 4WD. I was relieved when I simply had to plug it back in. Good luck let us know how it turns out.

Matt '99 SCR440 '00 Trailblazer Both with RCR stage 1 kits

 

Here is my take on the operation of the front wheel engagement. I am interpreting this from the service manual. I used to think it was mostly electric but after reading the polaris service manual it is mostly a mechanical engagment. When you hit the switch to ENABLE 4-WD then the coils in the hubs are energized. They are energized as long as the switch is on, and not just when the front wheels are driving. (I thought it was the other way before). when the coils are energized they create a magnetic field and attract an amature plate which pulls it to the coil and and resists it from turning freely. (the front wheels still are not driving yet) The other side of the armature plate has tabs on it which mate with a roller cage assy. This roller cage assy now also resists spinning freely. The roller cage is driven by the front driveshaft. so far all we have done is ENABLE front wheel drive.

The roller cage assy. has 6 rollers in it equally spaced in the rollercage. They are held in place side to side by the cage but can move in and out of the cage. there is a spring wrapped round the rollers and cage to keep them in while the the wheels are NOT being driven. the set up is kind looks like a centrifical clutch set up. (it is in no way a centrifical clutch). On the inside of the cage the 6 rollers ride on the flat spots of what looks like a hex nut. only in stead of threads on the inside it has splines which mate with the splines of the front wheel drive shaft. This splined nut turns with the rear wheels at all times. THe flat spots of the splined nut (called a cam) are used as ramps to push the rollers outward from the roller cage to pinch (clamp) the outer hub to the drive shaft.

Now to engage the front wheels, With the AWD switch OFF the front axles turn with the rear wheels as usual. The splined hex nut (cam) turns the roller cage and the roller cage turns the armature plate. the rollers stay in the cage cause the spring retains them there. everything spins together and the front wheels can spin on there own. Now throw the AWD switch to the ON. The front axles still turn with the rear wheels as usual. the hex nut still turns the roller cage and the roller cage still turns the armature plate...but now that the armature plate has been attracted magnetically to the activated coil, it resists spinng freely (drags). this also causes the roller cage to stop spinning freely. With a drag on the roller cage the hex cam starts to rotate inside the roller cage and pushes the rollers out engaging the wheel hubs to the front drive shaft. under normal conditions the front tires will override the hub clutch (see post below) and pushes the rollers to the low side of the cam. (front wheels not driving) If the rear wheels loose traction (spin faster then the fronts) then the rollers are forced out of the cage by the hex cam clamping the front hubs to the front drive shaft enaging front wheel drive, only untill the front wheels can start to spin faster then the rears again. ( when rear wheels regain traction). THis is my take on the system. Its confusing without pictures.

While testing on jack stands be sure the keyswithch is on, AWD switch is on and the tranny is in drive. Shorting out the hub wires, if they did, wont hurt the coils any but may damage the switch that supplies power to them, or the power supply, from too much current. If you have an ohm meter the coil resistance in each hub should measure 25 - 30 ohms (at least on a 2000 model). The hubs are also controlled by a reverse speed module, that will not allow the hubs to engage if the rpm,s are over 4000. Looking at the diagram here it looks like power to the hubs is supplied by this module. and not from the battery directly. this is also on the 200 model, I assume something like this is on yours too. Hope this helps in your trouble shooting. GJ

 

GJ, larger tires will spin slower then smaller tires.

 

Yes larger tires do spin slower then smaller ones. I missunderstood the book when they explained how the fronts overdrive them. they really didnt. but it was obvious that the fronts had to spin faster some how. I made a bit of an assumption not thinking it through. And your comment got me thinking how do the fronts overdrive the rears to disengauge the hilliard clutch when both have traction. So I did some testing. 1 rotation of a front tire was equal to about 68" travel distance, one rotation of a rear tire was equal to 65"....yep the fronts spin slightly slower to cover the same distance as the rears. still confused as to how the fronts over drive the clutch I did another test. (since my quad was already up on the lift). I engauged the AWD on the quad, put the quad in gear and marked both front and rear tires at top center. I rotated the rear tire 1 full turn and found that with the fronts engauged, they only spun a little over 3/4 of a turn. then I measured the distance of the front tire travel at just over 3/4 turn and that equalled 52".

It was really surprising to know that when the fronts are engauged (locked with the rears) they dont spin the same speed as they do when both tires have traction (fronts not engauged), but are forced to spin even slower. You would never know though cause the fronts are still helping to pull the quad. Obvoiusly due to gear ratios in the whole system. But this also allows the the fronts to overdrive the hilliard clucth when the rears regain traction even though the front tires spin slower then the rears under normal conditons.

When both tires have traction the fronts spin slightly slower then the rears, but when the rear tires loose traction and engauge the front tires they are forced by the ratio's in the system to travel an even slower. Its confusing but remember the rears have lost traction and are spinning fast enough that even with the fronts engauges at much less then 1 to 1 ratio they are still turning fast enough to pull the quad.

Thanks for the note MikeJKD, Im glad you got me thinking about it. It clears up yet another part of the AWD puzzle for me. I hope I explained what I found in a way that makes sence to others also. GJ

 

Whew!
So does that mean we shouldn't change the rear "wheel" diameter, as it would cause an imbalance in the gearing? Having 26" or 27" tires on 12x7 rims all around would not allow your equation to work? If you do change the rear to the same diameter, does that increase your low end or increase your top end?
Al