So while I was finishing up the brake DIY guide
it dawned on me that although I’ve referred to a rear axle alignment gauge, I’ve never gone into much detail on how it works, how to make one or what it looks like… and I’ve never shown a photo of one.
OK... so it's not universal. The rod length will vary from bike to bike and it's of no value on a bike with snail cam adjusters like a DRZ for example... or a shaft drive anything. So I lied... so sue me.
What you need:
All you need to make one is a 35 cent piece of steel 1/8” welding rod... about 36" worth, and a zip-tie. For a total investment of what? 40 cents maybe. You can make this tool tricker and fancier... but I doubt you can make it cheaper.
Get at least 1/8" steel rod for this... smaller diameter or softer materials are too flexy and inaccurate.
Why you need it:
Rear axle alignment, with few exceptions, is usually only as accurate as the axle block and swingarm hash marks… which is to say not very accurate at all.
Rear axle misalignment can cause unstable tracking down a straight road, “odd” handling in corners, accelerated tire wear, brake pad wear and chain and sprocket wear.
How you make it:
Cut the rod to length so it is a few inches longer than the approximate distance from your swingarm pivot shaft center to the rear axle center… in the case of the KTM LC4, about 29-30” is fine.
Grind a point on one end of the rod and bend that end at a 90 degree angle. The length of this bend will vary from brand to brand, model to model, but the idea is to have the major length of rod parallel with the swingarm when measuring.
In the case of the KTM LC4, a handy length is about ¾”.
Now grab a zip tie, put it tight over the long end of the rod and cut the tail off short and to a point. Congrats… you have made a tool.
If you need to, you can make more complicated sets of bends to clear things that are permanently in the way. The drawing is an approximation of a tool for a '79 to present Harley-Davidson with a rubber mount driveline.
How it works:
On a KTM LC4, there are rounded plastic buttons in both ends of the swingarm pivot shaft and one on the fixed end of the rear axle… and then an aluminum axle nut.
It doesn’t matter which side you start on. You place the pointy end in the center of the plastic button on the swingarm pivot shaft...
... and slide the zip-tie so the pointy end of it aligns with the center of the axle… that is the "reference length" for one side.
Now you transfer the tool to the other side and see where the center of the axle is in relationship to the reference length.
Adjust that side of the axle (or both sides, more or less) until both sides measure the same distance by the tool, then using the current alignment as a baseline, readjust your axle for proper chain tension for your particular bike.
That's it... you done.
This is the "whole tool"... complete with blatant promotional background.
Small example of why alignment is a good thing:
It’s hard to believe, but with a 40 cent tool, you can get your axle aligned to an accuracy of less than one millimeter.
Can you screw it up? Sure you can... I did once recently because I wasn't paying attention, and my rear brake pads looked like this with a less than 2mm misalignment:
So there ya go,