I ordered a set of used 450R shocks from a seller on Ebay. They came off a 2008 TRX450R. They didn’t look too abused, so I went ahead and installed them on my 400EX without rebuilding them.
I read about swapping 450R shocks on a 400EX in several articles on the Internet. They all said you have to grind the shocks, but none really described how to do it. After holding the shocks in place, I could see that it would be much better to grind a little off the upper shock mount than the actual shock body itself.
After grinding the mount, the top of the shock body still hit where the nut is welded in for the body mount. (Inside the shock mount tab) If you really don’t want to grind on your shocks, you could cut off the bolt and tack weld the body mount right to the top of the shock tab, but I chose to grind the shock. It was just a tiny shave off the surface to make it fit. If you put the top of the shock in the mounting tab and wiggle it around, trying to line up the bolt hole, you will scratch the surface of the shock enough to figure out where to grind.
With the stock front compression settings at he first notch, the front of the frame measured 12 1/2 inches from the ground. After swapping in the 450R shocks, the same spot measures 13 inches. The a-arms are at the bottom of their travel with no rider. the compression on the 450R schocks is all the way at the top (no extra compression)
The 400ex shock is at the top of this picture. You can see the 450r shock is a little bit longer. When you take off the stock shocks, the a-arms drop a little. When you put the 450r’s in, they use up all the space.
Here is the upper mount after grinding away enough material so the shock fit without hitting the inner part. The bolt hole still wouldn’t line up. The top of the shock needs to be ground just a tiny bit.
In this picture you can see the small spot that needed to be ground off. You could also try grinding the nut inside of the shock mount, but since it was such a small amount, I chose to do it this way.
This is the final product. With the 450R shocks mounted, the front end sits half an inch higher than stock. The suspension feels much firmer on compression and the rebound is smooth. Gone is the bounce of the stock 400 shocks. After riding around the yard, the front end feels way more stable, and it doesn’t lean as much turning. The real test will be in the sandy whoops at the river bed later this week.