Rear axle and wheel bearings

November 20, 2011 at 6:49 pm
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Beam axles are found on many different types of car, from sports models to sedate family saloons. But the general designs are basically simple and servicing them is not as difficult as it would outwardly seem.

A beam (or live) rear axle is a rigid metal casing usually made as a one or three-piece pressing. It extends between the rear wheels of a frontengined, rear-wheel-drive car. The axle assembly houses the differential and crown and pinion gear in the central, bulbous section and the half-shafts and bearings in its two arms. Its function is to transmit the drive from the propeller shaft to the road wheels.

This type of axle is rigid along its entire length and cannot provide independent suspension for the road wheels. But it is flexibly mounted to the car chassis or body by the springs of the car’s suspension system. An up or down movement of the road wheel at one end of the axle causes a reciprocal movement at the other end. The axle is therefore said to be ‘live’.

The main difference between live axle types is the way the outer ends of the halfshafts are supported at the wheel hubs as all halfshafts fit to differential gear on sliding splines at their inner ends. The differences influence the way in which the various forces and loads, to which an axle is subjected, affect the component parts. But generally very close design similarities make it difficult to tell exactly which type of axle is fitted to your car until you begin to dismantle it from the wheel hub. It is therefore necessary, to know something of the different types that you are likely to encounter.

There are three types of live rear axle, semi-floating, three-quarter-floating and fully-floating.

Semi-floating axle

The most common live rear axle found on modern cars is the semi-floating type. This employs a bearing on the inside of both ends of the axle casing in which each half-shaft, with its wheel hub attached, rotates. The halfshaft and bearing must, therefore, support the load from the weight of the car, the side thrust due to cornering and the torque force transmitted by the drive. Should the portion of the shaft between the bearing and the hub break, the road wheel will be free to fall off.

Three-quarter-floating axle

Three-quarter-floating axles, have a bearing on the outside ends of the axle casing. The bearing is fitted in the hub and not over the halfshaft.Consequently the halfshaft is not subjected to the weight load of the car and a failure would not allow the wheel to fall off. The bearing, however, is prone to heavy wear.

Fully-floating axle

Fully-floating axle systems are rarely found on modern cars, being used mainly on heavy transport vehicles. The hub is mounted on the axle casing in a way similar to the three-quarter-floating type, but two bearings are used in each hub instead of one. The halfshafts support none of the vehicle’s weight load.

Servicing semi-floating axles

The axle halfshaft and its bearing are the components that need to be removed for inspection or replacement.

There are two basic types. The most common is the type whose hub flange and halfshaft are made as a one-piece unit.

Removing and replacing integral types

If both halfshafts are to be removed for inspection, the axle will have to be drained of oil to prevent any leakage on to the brake assemblies when the shafts are pulled from the axle casing.

Use a spanner to loosen and remove the hexagon or square headed axle drain plug. This is found on the lower part of the differential housing. Catch the oil in a tray or container that has capacity of at least 1.5 litres.

Jack up one road wheel by placing the jack under the axle casing where the suspension springs are connected to it. Support the axle at its raised position, preferably with an axle-stand. Repeat the procedure at the other wheel.

Apply the handbrake and remove the wheel-stud nuts and take off the road wheels. Release the handbrake and disconnect each of the handbrake cables from its actuating arm on the back of the brake plate or disc.

The wheel hub will then be visible. On integral types, this appears as a flange containing the mounting studs for the road wheel. Look for bolt-heads behind this flange; there are usually four. These secure the bearing retainer plate to a corresponding flange or mating surface on the end of the axle casing and hold the bearing in position. Remove these with a spanner.

On some axles the bearing retainer nuts cannot be seen and are only accessible through a hole in the hub flange. Look through the hole and turn the hub until a nut comes into line. Use a box-spanner to remove the nut. Turn the flange through 90° to find the next nut and so on.

In some cases an entirely different method is used to hold the bearing in place. This variation employs a large internal circlip fitted in a groove inside the end of the axle casing. Use a pair of circlip pliers to remove it.

The halfshaft will now be free to come out of the axle casing, along with its bearing. The bearing is a press fit both on the shaft and in the axle casing. Some force may therefore be required to extract the shaft. A special tool called a slide hammer is used to remove the halfshaft. This is bolted on to the road wheel studs and its operation jars the shaft and bearing from the housing. If you do not have a slide hammer, you can use an improvised method. Bolt the road wheel back in position on the hub. Place a piece of wood on the back of the wheel to protect it and strike the wood with a hammer. Spin the wheel to a point diagonally opposite the first blow and repeat. Do this until the shaft comes free.

Before the shaft is completely withdrawn, note the position of any shims, O rings, oil-seals, gaskets or spacers that may come away with the shaft. You will need to renew all such components before fitting the replacement.

The bearing may be held to the shaft by a very tight press fit or held in place by a retaining ring. Checking bearing tolerances and the trueness of the shaft is virtually impossible without special equipment. Only a garage is likely to have this so take the shaft with its bearings along to your local agent. They will check the components and if any are worn, fit replacements. Do not attempt to remove or replace parts yourself. An attempt to remove a bearing held on to the shaft by chiselling off the retaining ring will probably result in a ruined shaft. Replacing a bearing involves heating the components to a high temperature, then pressing them together with a force of several tons per square inch. A garage will do this for you. If a replacement shaft is needed then it is usually supplied with oil-seal, retainer plate and bearing ready fitted.

The new or repaired halfshaft should be a tight push fit into the axle casing. The bearing should be filled with hypoid oil first and then tapped gently into its housing with a wooden drift. Make sure the splined inner end locates in the differential gear. Reassembly is the reverse of the dismantling procedure, but remember to tighten all bolts to the manufacturer’s recommended torque.

Removing and replacing two-piece types

An uncommon variation of the conventional semi-floating assembly is one whose shaft can be unbolted from the hub flange. This does not affect the dismantling procedure as described above. But it may mean that replacement halfshafts without the built-in flange are marginally cheaper to buy than the one-piece type.

Servicing three-quarter-floating axles

There are two basic types of three-quarter-floating axle. The common arrangement has a two-piece hub which houses the bearing, the ‘wheel’ end of the hub forming an integral part of the halfshaft. This is the split-hub type.

Though increasingly rare on modern cars, some three-quarter floating axles have hubs which must be split from the halfshaft before the shaft itself or the bearing can be removed. This is the one-piece-hub type.

As with semi-floating axles, the components requiring attention on three-quarter-floating types are the halfshaft and bearing. The split-hub types will be dealt with first.

Removing and replacing split-hub types

To remove a split-hub type, raise the car, support the rear axle and drain off the oil, as described above. Remove the road wheel and brake drum or disc caliper. The outer flange face of the half-shaft will then be seen. There is usually only one small screw which holds this to the other part of the hub, as the wheel studs pass through the entire assembly to hold it securely together when the road wheel is in place. Use a screwdriver to remove the screw. The outer flange with its halfshaft can then be pulled out by hand. If the hub is fitted with a splined extension for knock-offtype wire wheels, undo the four nuts that hold it to the outer flange face first. Remove the extension to gain access to the retaining screw.

The hub and bearing retaining nut will then be visible. There may be a tab washer behind the nut. This is used to stop the nut from shaking loose, so bend the tabs away from the flats of the nut before attempting to undo it. There may also be a lock washer behind the nut; pull this over the threads with your fingers.

A slide hammer will be needed to extract the hub with its bearing from the journal on the outside end of the axle casing. The bearing itself can be removed from the hub on a bench or worktop. Support the hub, inside face down, around its edge. With a hammer and light drift strike the bearing downwards through the hole in the top of the hub. Notice the position of the oil-seal behind the bearing and particularly which way its lip faces. Look too for any spacing shims or gaskets which may be fitted and which will need to be renewed on reassembly. Prise the oil seal out with a screwdriver and tap a new one into the hub with a light drift. Ensure that the oil seal enters the hub squarely or it may break. Try to use a tubular drift of the same diameter as the oil-seal to avoid this.

Before drifting the new bearing into the hub fill it with fresh hypoid oil and ensure that it runs smoothly. Test for smooth running by holding the inner ring firmly and turning the outer ring at the same time.

Reassembly is a straightforward reversal of the dismantling technique but before replacing the shaft check it for obvious wear and damage. If none is apparent but you have cause to suspect a fault, take it to a garage to be checked.

Removing and replacing one-piece-hub types

A slightly different procedure is required to dismantle a three-quarter-floating axle with a one-piece hub.

Chock the front wheels of the car to stop it rolling forwards while you wrestle with the large nuts that secure the rear-wheel hubs. Loosen, but do not remove, the rear wheel nuts. A domed cap should be visible protruding through the centre of the wheel. This is the dust cap covering a large castellated nut. Lever off the cap with a screwdriver. Use pliers to pull out the split-pin from the castellated nut and slacken, but do not remove, the nut.

Jack up the car as described above, remove the road wheel and then undo the castellated nut completely. Drain the oil and remove the brake drum or disc caliper as previously outlined. You will now need a special puller, either bought or hired, to free the hub from the shaft. Position the arms of the puller behind the hub or screw them into the holes provided depending on the type, and screw the threaded bar inwards so that it makes contact with the end of the shaft. Keep screwing the bar in until the hub pulls away from the shaft.

The bearing housing will be seen behind the hub once this has been removed. The housing is bolted to the axle case flange, usually by four bolts. Tab washers may be used to secure the bolts so bend these out of the way before undoing the bolts. Where drum brakes are fitted the same bolts may be used to hold the brake back-plate in position, but this will usually stay in place even when the bolts have been taken out, due to the kind of mounting.

The bearing housing will now be free of its mounting. In this kind of assembly the bearing itself is of two-piece construction and usually the taper roller type. It comprises an inner ring, an outer ring and many individual rollers which fit between them. As the housing is pulled away from the axle the outer ring of the bearing will come away with it, leaving the inner ring in place on the shaft. The rollers will then drop out of the bearing. Be careful not to lose any of the pieces. A sheet of white paper spread out on the ground in the work area will help show up any rollers that do fall out.

Another puller with reversible legs will then be needed in order to pull the outer ring from the bearing housing and then to pull the inner ring from the axle shaft. The inner ring is a tight fit on the shaft, but to ensure that it is retained securely, a small key inserted in a groove in the shaft, in front of the bearing, may also be found. This can be removed by tapping it gently with a hammer. Now pull the axle shaft from the casing, complete with ring, by hand.

Place the axle shaft in a vice, cushioning the vice jaws with strips of wood to prevent damaging the shaft. Use the puller with reversible legs to remove the ring from the shaft.

The outer ring is then pulled out of the bearing housing.

Once all the bearing components have been separated, wash them in petrol and reassemble them ready for testing. Hold the inner ring in one hand and rotate the outer ring with the other. Feel for any roughness in operation and look for pitting of the surfaces. Buy a new bearing if any damage is found. Drift a new inner ring to the axle shaft with a piece of soft tubular metal, making sure that the smaller diameter of the tapered type faces outwards towards the hub end of the shaft.

With the bearing housing on a bench or suitable surface, prise out the oil seal with a screwdriver blade. Tap a new oil seal in place, followed by the outer ring. Try to use a drift with a diameter the same as the components to minimize the risk of damaging them as they are knocked into place.

Reassembly is a reversal of the dismantling procedure but ensure that all nuts and bolts are tightened to the recommended torque. These figures should be shown in your manual.

The differential unit

The differential unit and crown and pinion gear can in most cases be removed and overhauled with the axle in place on the car. This job is dealt with in another article.

Removing live rear axles

The rear axle itself will have to be removed from the car only infrequently—for example, a major service, or in the event of serious damage to the axle casing itself. In the latter case virtually all that can be done is to transfer the other components to the replacement unit.

Live rear axles are attached to car bodies in a wide variety of ways. Almost any combination of the following sus-pension system components may be used to suspend the axle. You will have to consult a manual or examine your car to determine which system is employed and then remove the appropriate components as shown here. You will also need to know exactly how your axle is removed once it has been freed. For example, it may be taken out through a wheel arch, pulled out from one side only or simply lowered from below. This will affect which components have to be removed and the removal sequence.

Whatever the axle removal procedure you will first have to take off the braking system components including the hydraulic pipes and handbrake linkages from both the axle and the wheel hubs. The halfshafts and hubs must be dismantled as described above.

Raise the car and support it with chocks or axle stands just forward of the rear body suspension mounts. These points afford the safest and most secure support.

If the car’s exhaust pipe runs below the axle it will have to be removed.

Position a jack under the differential housing and raise it until the weight of the axle is just supported by the jack. Doing this will prevent the axle from dropping during the removal procedure. It is important not to raise the jack too high or the suspension springs will start to compress making it difficult to remove any mounting bolts later. You can now start to remove the necessary suspension parts. The following components may be encountered: semi-elliptic leaf springs, coil springs, lever or telescopic dampers, stabilizer bar, Panhard rod and radius arms.

Semi-elliptic leaf springs

The axle may be fixed to semi-elliptic springs either over or under the leaves( figs. 23/1 and 23/2). But in both cases it is held by U bolts. Some axles must be removed with the springs still attached, in which case the spring mounts themselves must be unbolted. But generally the procedure is very similar. If the axle has to be separated from the springs, simply unbolt the nuts and lever the U bolt from its mounting plate. Notice the order of any washers, spacers or rubber cushions that may be released.

Telescopic and lever dampers

Telescopic and lever dampers act on the axle casing or the suspension spring. They are connected at their lower end directly, or by a short linkage to the axle or spring usually by a single bolt through a locating bracket. If the damper acts on the axle itself, remove the bolt from the bracket to free it first. Where the damper connects to the spring it can be removed in the same way but check first that it is necessary. Some lever arm connection points are a taper fit under the bracket connecting nut. These often jam tight together making removal difficult. The joint may be separated by tapping the lever lightly with a hammer or applying penetrating oil.

Radius arms

One or two radius arms are used at each end of the axle to control the movement of the rear axle. These are usually tubular, pressed or solid steel attached at one end to the underbody and at the other to the axle. The axle mounting point incorporates a fixed bracket into which the bushed end of the radius arm fits. The design permits an up and down movement of the arm so the single through bolt in the axle bracket may have a lock nut. Use two spanners to undo these, then push the arm upwards or downwards to free it from its bracket.

Stabilizer bar (anti-roll bar)

A stabilizer bar is fitted to prevent the car body rolling uncontrollably from side to side. It takes the form of a long continuous U shaped steel bar or rod. The bar is fixed to the axle at both sides of the differential housing by rubberized clamps or insulators as they are sometimes called. The upper U arms of the bar are similarly fixed to the underside of the body.

The clamps on the axle must be unbolted. This is a straightforward operation but take note of the position of the clamp cups and rubber blocks for reassembly. If possible leave the body mounting points in place. Push the bar upwards away from the axle.

Panhard rod

A Panhard rod is sometimes fitted in addition to an anti-roll bar to prevent lateral movement of the axle. It locates transversely across the car from a mounting on the underside of the body to a bracket on the axle. Removing it from the axle involves undoing the nut which holds a single bolt through the bracket. The body mounting point may also have to be removed in a similar manner.

Coil springs

Coil springs may or may not have to be taken off in order to free the axle, as this depends on the suspension layout. If the car is fitted with coil springs sandwiched between the body and the trailing arms, the springs may not have to be removed. But the rear end of the trailing arm must be disconnected from the axle. The shock absorbers can often be left in place. J Each trailing arm is fixed by brackets at one or two points on the axle.It is usually secured by one bolt passing through each bracket. Separate the arm and axle by undoing the bolt.

Coil springs are sometimes located in cups directly mounted on the axle casing itself. With this con-figuration the springs must be released before the axle can 2 fe\ \.– “” y II j I x / be removed. Most springs will come out after the lower damper mountings have been undone. When both springs are to be removed complete the operation on only one side at a time, do not release both dampers at once.

Lower the jack under the differential to allow the axle to swing down as far as possible on the side you are working on. The coil spring will then be under minimal pressure between the body and axle cups. Grip the spring by hand and compress it slightly by pushing downwards. Pull the spring to one side and it should come out of the cups quite easily.

Coil springs which enclose a telescopic damper are sometimes encountered. The only difference in removal procedure from the above types is that the upper damper mountings must be released as well as the lower ones to free the axle. A single nut securing the damper to the body will usually be found protruding through the tops of the rear wheel arches, accessible from inside the boot. Undo the nut and the axle can be lowered after the other components have been removed.

Bump stops

Bump stops are rubber blocks mounted either on the underside of the body or on the axle. Their function is to cushion the blow from contact between axle and body when a severe road bump causes the suspension to travel its full limit.

If the bump stops are fitted to the body they will not affect axle removal. But some stops are bracket mounted on the axle itself, and may interfere with or make axle removal difficult if they are not taken off first. To do this simply unbolt the bracket from the axle casing. There may be two or four bolts holding it in place. Remove these and pull the bump stops away. A gentle tap with a hammer may be necessary to free them. Check with your manual to find out whether one or both stops have to be removed.

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