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Replacing the Front Fork

A front fork may be replaced to (1) upgrade the shock absorbers, (2) allow attachment of disc brakes, (3) replace a bent or cracked fork, or (4) to get a prettier color. In general, the pieces of the front fork (for example, an individual shock) aren't replaced individually -- the whole thing is swapped out. If you're taking the fork apart to get at the individual parts, see our section on front shock absorber cleanout. For example, you can stiffen or soften a shock absorber by replacing individual elastomer units.

First, we need to get the old fork off. There are a few things we need to remove first, like handlebars, brakes, and front wheel.

Open the brakes and drop the front wheel off.

Now release the tension on the brake spring by turning the tensioning screw out (counter-clockwise). This makes it easier to put things back together on the new fork.

Now remove the brake mechanism from both sides of the fork. Usually, this is a hex-head bolt that threads into the spindle on which the brake lever pivots. Turn counter-clockwise to remove the bolt, then slide the brake mechanism off the spindle.

Cut any cable ties that secure brake cable and speedometer cable

Now you're ready to drop the fork out of the steering tube. Unscrew the cap at the top (assuming you have a threadless headset). This cap pushes the stem down against the bearings -- it's what keeps the headset tight. The screw goes into a star nut inside the steerer.

Now loosen the stem clamping bolts until the stem is loose on the steerer tube. 

Remove the stem from the headset. Remove any spacing rings that were underneath the stem.

Some headsets may have a second clamp underneath the stem. If you see a second ring with a bolt in it, loosen it and remove it also.

Some forks are a bit more complicated. For example this is a "double crown" fork. You must also remove the top crown from the fork before the fork will slide out the bottom of the steering tube. The bolts on the back of the top crown clamp the crown to the center fork tube (big arrow), and to the stanchion tubes of the front fork (smaller arrows). Loosen these hex bolts.

Put a drop cloth under the fork to catch errant ball bearings.

Now just give the top of the headset tube a good shove, and it should slide out the bottom of the steering tube. But of course, it won't. You may have to tap on the top of the steerer. Use a block of wood to avoid damaging the metal.

As the fork slides down, have an assistant hold the lower bearings, so they stay up inside the frame. Try to extract the bearing complex intact. Hopefully, the bearings will be in a bearing clip. If not, catch and save them.

 Once the fork is extracted, remove the top bearings as well.

Slide the bearing cup off the top of the crown of the old front fork. You'll need it. The bearing cup is the ring that sits against the bearings at the bottom of the steering tube.

Threaded headset note:  For a threaded headset, you'll need to remove the stem from the tube of the front fork. (More detailed instructions for disassembling a threaded headset are found elsewhere.)

Using a headset wrench, uncouple the top of the fork from the steering tube, and slide the fork out the bottom. Again, watch for ball bearings and bearing cups, so you get everything back together properly.

Once the old fork is out of the steering tube, clean and lube the inside of the steering tube. Make sure the surfaces where the bearings sit aren't pitted.
Using a degreasing solution, clean the bearings, cups, and clips. A good technique to get dirty gunk off free-rolling bearings is to roll then between layers of paper towel. The towel will pick up the gunk.

For bearings without retaining clips, grease the bearing ring, then push each hole down onto a bearing on your work towel. This is lots easier than trying to pick up the bearing and stick it into the ring.
Grease the outer and inner bearing cups. Assemble each set of bearings: outer cup, bearing ring with bearings, then inner cup. If you lost a ball bearing (of course you're going to lose a ball bearing!), leave the empty slot in the upper set of bearings -- the lower set bears the weight of the bike.

Slide the bearing cup onto the steerer tube of your new fork. Gently tap it down until it's flush with the crown.

Put the bottom bearings into the bike frame.

Slide the steerer of the fork into the steering tube of the frame. Move the frame horizontal, or put the bottom of the fork onto the floor, so the fork won't fall back out.

Now slide the top bearings, and the cap that sat on top of them, onto the steerer. 

Put any spacers you'll be using onto the steerer, then slide the stem on. But don't tighten the stem yet. We're just measuring.

Mark the top of the stem by scratching the steerer with an awl.

Now cut off the steerer with a pipe-cutter or hacksaw, about 1/4 inch (1/2 cm) down (towards the bike frame) from your scratch. (You need a small space between the stop of the steerer and the top of the stem, so the headset cap can tighten the stem down against the bearings.)

The masking tape does two things here: (1) it keeps the bearings from creeping out as the saw vibrates the steerer, and (2) more importantly, it keeps metal filings from drifting into the bearings.

Now you need to put a star nut into the new steerer. Of course, you didn't remember to buy one. So you'll recycle the star nut from your old fork. Insert a dowel into top of the old steerer, and tap the star nut through until it comes the bottom. (CAUTION: some forks have a tapered tube. If your old steerer has a smaller hole at the bottom than at the top, you can't do this! Buy a new star nut.)

Need a new star nut? Go to the UMB store!

Now slide the star nut into the new steerer. Using your dowel, tap it down until the top of the nut is about 1/2 inch inside the steerer.

Now slide the spacers and stem back on. Don't tighten the stem yet. Move the bike so the fork's dropouts are pressing against the ground. Inspect the bearings to be sure everything is in place.

Put the headset cap on. Tighten the top cap onto the top of the stem until there's no longer any "play" when you push the front wheel against the ground. If you feel resistance or hear rubbing in the headset when you turn the handlebars back and forth, you've tightened things a bit too much. Back off.

Now replace the front wheel. Match the alignment of the wheel with that of the stem, and tighten the stem securely.

Install the brakes, whether disk or rim brakes. Adjust them as outlined in the brake tuneup section. Put the speedometer cable and detector wand into place on the new fork. When everything seems proper, take your new fork for a test ride.

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