Primary down side: poor rebound
It's an easy job if you have the following tools:
impact wrentch
14mm allen socket - got mine at an industrial tool supply store
dremel tool, or bench grinder
tie-down straps
Here’s what I did:
1. I compressed my fork legs with a tie-down strap
2. Loosened the valve body with the impact wrench, but didn’t remove it
3. Removed the tie-down strap to release the forks, and turned them upside-down.
4. Removed valve body
5. Ground off the “stacked” part of the nut so it could be removed.
6. Removed 2 shims, and reassembled. Loctite might be a good idea on the shim nut.
7. Don’t use the impact to tighten it up. I just used a torque wrench and I think 35 ft-lbs was all I could get it to.
I have lots of trail miles on it since, so here are my thoughts.
On smooth easy trails, the difference isn't very noticeable. However, it is a significant improvement over the stock forks on difficult trails as long as you have the correct spring rate. I ride rough / rocky single track in North Idaho and found the bike to deflect quite a bit less. The high speed compression is better, but now the rebound is more than you will want.
Overall, the KDX forks still are terrible. Removing two shims makes them suck a lot less, but they’re still terrible when you push the bike hard on difficult terrain. Having them reworked with racetech components is the best thing that can be done for them, but that’s $450 or so. I plan to switch to KX forks in the future.