Today we focus on the sealed wheel-bearings, which are often found on the half-shafts of rear-wheel-drive vehicles or in the front hubs of front-wheel-drive cars. These come sealed as a unit, which cannot be dismantled. They are tough in the sense that they last a long time, but it can also be a tough job to replace them when they do wear out.

Today we focus on the sealed wheel-bearings, which are often found on the half-shafts of rear-wheel-drive vehicles or in the front hubs of front-wheel-drive cars. These come sealed as a unit, which cannot be dismantled. They are tough in the sense that they last a long time, but it can also be a tough job to replace them when they do wear out.

Sealed bearings will signal their distress by making a noise, but make sure you correctly identify this.

Get your mechanic to listen to the noise. Then get a second opinion. Finally jack up a rear wheel and get someone to spin the wheel while you use a long screwdriver as a stethoscope with its handle against your ear and its tip on the axle housing. There will be noises emanating from the gears inside the differential, but the growl of a worn bearing should be unmistakable.

If your diagnosis is firm, raise the corner of the vehicle where the tired bearing is and remove the wheel and brake drum. Unscrew and remove the nuts that attach the bearing- retaining plate to the flange on the axle tube.

A large hole is provided in the half-shaft flange, where the drum attaches, to allow access to these nuts with a tube spanner or a socket and extension. Rotate the axle to align this hole with each nut in turn. If you are lucky, the half-shaft can now be pulled out by hand.

Alternatively turn the brake drum around and install it loosely on the half-shaft flange by means of the wheel nuts or bolts. Then use the drum as a slide-type puller. This should persuade the half-shaft to emerge from the axle tube. Just remember not to hammer the brake drum and not to lose any of the end-float adjusting shims.

If these methods fail a professional workshop will use a slide hammer to yank the stubborn half-shaft out of the axle tube.

The half-shaft, when it comes out of the axle tube, will bring with it the sealed bearing and a retaining collar.

The axle tube oil seal will be left in place in the axle tube. The oil seal should be renewed as a matter of course. Prise out the old seal, using a seal extractor, a long screwdriver or even the splined end of the half-shaft. Tap a new seal squarely into the axle tube, using a drift made from a length of pipe with a diameter slightly smaller than the outer diameter of the seal. Make sure that the lip of the seal faces inward to prevent the diff oil escaping, and lubricate the lip of the seal with grease.

Take the half-shaft, complete with retaining plate, to an engineering shop to be pressed off using a hydraulic press.

The new bearing comes with a new retaining collar and they will again be pressed on by the engineering shop and the half-shaft can then be refitted to the axle tube. Any roughness where the seal contacts the shaft must be cleaned off using emery paper.

Installation of the half-shaft is the reverse of the removal procedure.