Here is the text from PRC's Tech Sheet: Securing Rear Axle Assembly
Locking down the rear axle of your chassis is a vital step in the assembly process. If this is done incorrectly, the axle will be allowed to move from side to side and thus cause multiple problems. In addition, where and how you secure the rear axle is just as important as locking the axle down entirely. Locking the axle down in various locations can have varying effects on how your chassis performs.
Obviously, there are severals ways to lock the rear axle down, however, we strongly suggest following the below procedure for the most advantageous results.
RIGHT REAR
• We recommend placing one axle collar on each side of the right rear bearing. Be sure to center your axle
in the location in which you desire and then tighten each collar evenly. There should be NO clearance between the bearing and axle collar.
• Aluminum axle collars will often become worn or cracked from use. If your collars have cracked in some way, they will no longer be able to secure the axle in the manner in which they were designed. Be sure to replace any axle collars if they have become cracked or damaged.
LEFT REAR
• We recommend securing the left side of the axle by drilling and tapping the axle. In order to do so, we recommend using one of the set screw holes in the shoulder of the bearing. After drilling the axle, simple run a bolt down through the shoulder of the bearing and into the axle. (Which you no longer have to do since we provide machined set screws and pre-drilled axles)
• By securing the Left Rear in this manner you are ensuring that the axle may not slide from side to side.
In conclusion, taking the proper steps to secure your rear axle can save you a large amount of time and headaches later on. This process will ensure that your axle does not move from side to side and yet, it still allows your chassis to flex and perform in the manner in which is was designed.