The main clue to whether you may need to replace your fork bearings is a shudder while braking from higher speeds. This may also be caused by the front brake shoes or an ovaled hub, but a distinct shudder is usually due to the fork bearings failing, or at least the securing nuts may be loose. Either way here's how to remove and replace the fork bearings.

The first step is to remove the front brake lever pivot. When the forks are removed the speedo cable and the front brake cable will still be connected to the fork assembly, so they need to be disconnected. Use an 11mm wrench to loosen the cable where it attaches to the front wheel hub arm so that the cable will be slack. There is a small nut on the bottom side of the pivot which should be held with pliers while the screw is unscrewed from above.

The next step is to remove the headset top and disconnect the speedo and front brake cables. Remove the four screws (two either side) from the underside of the headset to allow the top to be removed. The speedo cable will hold the headset top down - don't try and pry it up! Locate the point where the speedo cable enters the fork tube just below the front mudguard, and feed it in as much as possible. This should allow the clearance needed to lift the headset top, reach in, and unscrew the speedometer cable from the speedo unit.

With this removed, the headset top can be flipped backwards with all the other connection intact.

Allow enough slack to remove the front brake lever. It can be unhooked from the cable end. Be sure to save the two small washers that go on the top and bottom of the front brake lever pivot. Note how the cable terminates against the stop within the lever pivot casting as you'll need to replace it in the same way later.

With a little work, the front brake lever cable outer can be pushed through the throttle tube and pulled clear to where it enters the top of the fork tube. Now it is time to remove the headset.

A single pinch bolt attaches the headset to the top of the fork tube. The fork tube has a cut out that the bolt passes through so to the bolt must be removed completely to allow the removal of the headset. Use a 13mm socket and driver to loosen and remove the bolt.

The pinch bolt has a square nut hidden under the headset which will drop out once the bolt is removed. It fits in to a special slot so it can't rotate which makes it much easier to loosen and tighten the pinch bolt. Keep this in a safe place once it drops out.

There is usually enough slack in the control cables and electrical wires to get the headset off the fork tube without any further disconnections. To get the headset off once the pinch bolt is removed, stand with a leg on either side of the front mudguard and turn the headset from left to right while lifting upwards. You'll need to do this quite a few times, but each time the headset will raise just a bit. The mudguard may try to turn so brace it between your legs.

The forks are locked in place by a top locking ring (blue arrow), a plain locking washer (green arrow) and a lower locking ring/race (yellow arrow). There is a special tool that is used to remove these rings but I find that a hammer and large flathead screwdriver do the trick pretty well.

Turn the mudguard all the way to the left, put the slot of the flathead in to one of the grooves in the upper retaining ring, and tap it with a mallet. Please note: that this picture shows me tightening the ring - to loosen it you'd be turning it anti-clockwise. Usually these rings are not very tight, but if they are as sad as the ones I have pictured here, you may want to use some WD40 in the grooves to ease them up. Once the first ring is off the washer can be lifted off. At this point you need to get some help to get the front wheel of the bike about 18" off the ground so that you'll have enough room to get the forks out of the frame.

The bearings above are supposed to be held in place by a race, not loose, but the one here have been destroyed somehow and all the bearings are rusty. Start to loosen the bottom ring and have someone support the forks from below. Once the final ring is removed the entire front wheel, mudguard, and fork tube should now drop out the bottom of the frame.

The lower fork bearings are also in a race. To replace them just slip the old bearings off the fork tube. Inspect the race mounted on the fork tube - this is the area that the bearings make contact with the fork tube - to be sure it is not pitted. If it is, it can be removed with a blowtorch to heat it, and by tapping it from below until it comes off the fork tube.

Also inspect the area where the bearings meet the frame at the top and bottom, and clean them thoroughly. It is unlikely these will be a problem but replacement parts can be bought and fit into the frame. I've never done it myself so I am not sure exactly how to get the old one out as it is a pressed steel fitting.

Fit the new lower bearing and smear it with grease. Refit the fork tube in the frame and temporarily fit one of the top locking rings so the forks don't fall out while you get the front wheel back on the ground.

When the front wheel is back on the ground, remove the temporary locking ring and slide the well greased top bearing in place...

..followed by the retaining ring/top race. With weight on the front wheel, tighten this race as tight as you can by hand and then only about a quarter turn using the flathead and mallet method. It doesn't have to be super tight as the locking washer will stop it from loosening.

Refit the locking washer. There is a tab on the washer that must fit in to a groove in the fork tube....

...and lastly, refit the upper locking ring and tighten it as tight as you can (within reason). This is also a good time to re-wrap any electrical wires that may have become chaffed over the life of the bike.

Once you have set the headset loosely on the fork tube, refit the pinch bolt with the lock washer at the bolt head end, and the square nut in the underside headset slot. Tighten the bolt until there is friction between the fork tube and the headset but each can still move independently of each other. Do your best to make a visual alignment of the front wheel and the headset and fully tighten the pinch bolt. You can come back later and make any fine adjustments after a road test.

Thread the front brake cable back in to position. Be sure that the small "top hat" engages in the stop inside the lever mount casting, and refit the lever itself with the top and bottom washers. Connect the bottom of the brake cable to the hub arm and test it to make sure it the front brake grabs within the range of the lever pull.

Reconnect the speedo drive and position the headset top above the headset bottom. Pull on the speedo cable where it exits the forks under the front mudguard to ease the headset top into position. Refit the four headset top bolts and take the bike for a test drive. If you find the bike weaves, the top lock ring is too tight. If the front brake still causes shuddering under braking then either the locking ring is not tight enough, or the brake shoes are rubbing intermittently due to a warped hub surface.