The front suspension on your mountain bike ensures that the front wheel will always stay in contact with the ground. By moving up and down when impacted, the fork effectively shortens and elongates to accommodate the stress and uneven ground of the trail. Over time, suspension forks can wear out and cease to function properly, making every ride a bumpy one. If your old suspension for is not working correctly, don't go to the bike shop to have it replaced. Learn how to perform this procedure yourself at home.
Loosen the front wheel axle by releasing the quick-release lever. Pull the wheel out from the dropouts on the fork and set it aside. Locate the front-brake caliper mounting bolt on the back of the fork and loosen it, using a 5-mm hex wrench. Remove the front-brake caliper from the fork and allow it to hang from the handlebars.
Loosen the two stem adjustment bolts on the side of the stem using a 5-mm hex wrench. Check that they are loose by turning the handlebars back and forth. They should turn, but the fork should not. Loosen the stem-cap bolt on top of the stem using the same 5-mm wrench, and set the stem cap aside. Pull the stem off of the steerer tube of the fork and let it hang. You may now slide the old fork out of the head tube to remove it from the frame.
Set the old fork's steerer tube upside down in the centre opening of a crown race remover. Close the crown race remover blades at the bottom of the remover around the bearing race at the bottom of the steerer tube, then twist the handle at the top of the crown race remover clockwise to pull the bearing race off of the fork. Use a crown race setter, a large cylindrical tool with a point at one end, and hammer to set the bearing race in place on the new suspension fork.
Screw a star nut onto the end of a star-nut setter, a small cylindrical tool with threading at one end, with the wings of the nut facing upward. Set the star nut against the opening of the steerer tube of the new fork, then hit the end of the star nut setter with a hammer to install the star nut into the steerer tube. Twist the star nut setter counterclockwise to remove it from the nut and steerer tube.
Slide the steerer tube of the new fork up into the head tube of the bike's frame. Make certain that both the top and bottom head tube bearings, the small metal balls contained in round containers, are correctly in place, one bearing on top, and one on bottom. Slide the stem onto the new steerer tube and attach the stem cap by tightening the stem-cap bolt with a 5-mm wrench. Line the handlebars up with the fork and use the same 5-mm wrench to tighten the stem-adjustment bolts.
Slide the front-brake caliper mount through the front-brake caliper mounting hole at the top of the new fork. Attach the front-brake caliper mounting bolt removed earlier to the rear of the new fork and tighten it using a 5-mm hex wrench. Slide the front wheel into the dropouts of the new fork and tighten the quick-release lever to hold it in place.
Take your bike out for a test ride to be certain that your new fork was installed successfully and safely. The suspension of the fork should feel smooth and crisp compared to your old fork.