The Honda XR400R's rear suspension consists of a single shock absorber with a spring surrounding it. When you purchase an off-road motorcycle, it will typically come with the suspension set at "zero" or whatever the former owner preferred. Each rider has his own set of preferences for the rear suspension's settings. The Honda XR400R has two main settings for the rear suspension: preload and damping. Preload is basically the amount of pressure on the spring without a load and damping is the stiffness of the shock upon compression or rebound.
Remove the XR400R's seat by loosening and removing the two bolts near the rear-bottom of the seat and sliding the seat backward.
Use and Allen key to loosen and remove the two hex-head bolts from the right side plastic cover. Pull the side cover off of the XR400R.
Use a ratchet and socket to loosen the exhaust clamp holding the muffler to the exhaust system, then loosen and remove the top and bottom retaining bolts from the muffler. The top bolt is located above the muffler canister, and the bottom bolt is located near the end of the muffler pipe. Pull the muffler from the XR400R.
Loosen the air cleaner clamp. Pull the air cleaner's plastic tube from the carburetor.
Disconnect the wiring harnesses beneath where the seat used to be by pressing the locking button on each harness and pulling each one toward the rear. Remove the rubber strap holding the wires to the metal bar and pull to disconnect the clip holding the harnesses to the subframe's upper bar.
Loosen and remove the two lower subframe bolts. Loosen and remove the upper subframe bolt from under where the seat used to be and pull the subframe toward the rear of the XR400R to remove it. The subframe is the smaller, metal frame on the rear of the motorcycle.
Place a motorcycle jack under the center of the bike and raise it off the ground.
Place the pin spanner wrench on the locking nut -- the splined nut on the top of the shock absorber -- and loosen the nut. Adjust the preload by turning the adjuster nut -- the nut directly below the locking nut -- using channel-lock pliers. Tightening the nut increases the preload and loosening the nut lowers the preload.
Measure the length of the spring. The spring must be between 8.08 and 8.56 inches from top to bottom. Loosen or tighten the nut if the spring is not within these specifications.
Trace the shock to its lowest point and locate the small adjuster screw on the chain-side of the shock mount. Turning the screw clockwise hardens the rebound damping and turning it counterclockwise softens the rebound damping.
Locate the shock compression damper, the small cylinder on the chain-side of the shock. Turn the screw at the top to adjust the shock compression damping. Turning the screw counterclockwise softens the compression damping and turning it clockwise hardens the compression damping.
Place the subframe back on the XR400R and torque the upper bolt to 20 foot-pounds and the lower bolts to 31 foot-pounds.
Reconnect all harnesses that were disconnected in Step 5, making certain to connect only matching color wires together. Wrap the rubber strap around the wires to secure them to the frame and insert the clip back into the hole in the subframe.
Push the air cleaner tube back onto the carburetor and tighten the clamp.
Place the muffler back onto the bike and tighten the muffler clamp to 14 foot-pounds and the top and bottom muffler bolts to 24 foot-pounds each.
Place the side cover back on the bike and tighten the two hex-head bolts. Place the seat back on the XR400R and tighten the two bolts.
Lower the motorcycle jack.
