In our October 2007 issue, we had just finished installing a set of wide A-arms on our Project YFZ450. To complement the width of the front end, we also received a rear axle from Leager Racing. Many people wonder: "Since the front of the quad is already wider after you do an A-arm install, will adding a wider axle really make that big of a difference?" Well, yes it does.
By keeping all four corners of the machine close to an equal width, there is less possibility of tipping over at high speeds, letting you corner faster. Also, if the rear end is narrower, the quad can be more prone to sliding. Aside from making your quad wider, aftermarket axles also offer more strength than their OEM counterparts. The metals used in the more expensive aftermarket units make them stronger to prevent bending and breaking under extreme use. This doesn't mean they won't break, just that it is less likely to happen.
The unit that we have chosen to install is adjustable from 0 through +3 inches. This makes it compatible for someone who wants to use it as a stock replacement or for cross-country or motocross racing. Read on to see how easily this modification can be done to your quad.
Note that use of an air impact gun makes parts of this install easier and more efficient.
Skill Level - Intermediate [2/5]
Tools Required - Allen wrenches, flat-blade screwdrivers, large crescent wrench, impact wrench and sockets.
Time - About an hour, depending on how dirty or rusted the parts are.
Summary - A good handling mod that can easily be done in a few hours.
1. The first thing you want to do is clear out a work area and loosen the rear wheel lug nuts. Now raise the rear end off the ground with an ATV stand or hydraulic lift. After this has been done, remove both rear wheels. |  | 
2. The next step is to remove the rear wheel hubs. Take out the cotter pins and use an air impact gun to remove the axle nuts. These nuts are installed very tight and usually take more force than can be applied with a regular socket or wrench. |
3. Now remove the axle locknut. On some models, you may want to do this before taking off the wheels and with the machine on the ground. With our YFZ, there are two Allen head setscrews opposite of each other to keep the nut from backing off. Back those almost all of the way out and then use an axle nut wrench or large crescent wrench to remove the nut. Have someone holding down the rear brake pedal while doing this to keep the axle from moving. | 
4. Remove the two bolts that secure the rear brake caliper to the caliper mount or brake stay. Don't remove the brake line. Just put the caliper off to the side and you'll be fine. | 
5. Next, remove the rear sprocket from the sprocket hub. Again, on some models the sprocket hub may slide off of the axle, eliminating this step of the procedure. Many axles feature a sprocket hub that's nonremovable and that's why we've chosen to show this. |
6. With the rear brake caliper now out of the way, you should be able to slide the brake rotor hub off of the axle. Depending on how old your quad is, it may have a little corrosion built up in the splines of the axle and will require a little effort to get off. |  | 
7. We are now at the point where you can slide the axle through the bearing carrier. If at any point when you are sliding the axle out it seems to get stuck, just take a rubber mallet or a dead-blow hammer to give it that little extra oomph and it should slide right out. |
8. From this view, you can see the significant difference in the length of the new axle compared to the old. | 
9. On the axle for this machine, you must remove a retaining clip in order to slide the sprocket hub off of the old axle. This can be done by using a couple of large flat-blade screwdrivers to lift and work the clip off. Just be careful not to stab yourself. Once that is done, slide the sprocket hub off and clean it so you can install it on the new axle. | 
10. You first need to reinstall the sprocket hub. Smear a small amount of grease on the splines of the axle where the hub goes. This will ensure ease of removal in the future. Slide the hub onto the new axle and install the retaining clip. |