November 21, 2011 at 8:32 pm
filed under Car Care, Uncategorized
Tagged body work, brakes, car care, Electrics, filters, gearbox, lubrication, oil, steering
If your car exhibits patterns of uneven wear on the front tyres, sags at one or both sides when stationary, or displays a tendency to wander across the road when driven at speed, there is an obvious defect in one or more of the front suspension or steering components. Similarly, any knocking or rumbling noises emanating from the frontend of a car are a signal that a visual examination and a series of physical checks should be carried out at the earliest opportunity. Failure to do this may result in a component breaking at a potentially dar rous moment, rendering your car uncontrollable or the least, immobilizing it. Even if the above symptoms are not apparent, it is worthwhile to make regular check on all of the relevant components to ensure that they remain in a satisfactory and serviceable condition.
This article is the first of a three-part series that covers various aspects of servicing a car’s frontend components and includes the front suspension as well as the tyres, wheels and wheel bearings. The next article deals with the steering system and the third is concerned with the various components in the hydraulic braking system.
Numerous front suspension designs have been employed by car manufacturers but the basic types share many similar features. Once you have established this, you should ignore the sections which are not applicable and refer only to those that are relevant to your car.
At weekly intervals it is important to check that the pres-sures of your car’s tyres are correct and appropriate figures can be found in your owner’s handbook or by reference to your local dealer or tyre specialist. The most reliable method of checking tyre pressures is to use a small pressure gauge of the type that can be purchased from most accessory shops. The job should always be carried out with the tyres cold to avoid false readings caused by expansion of the air in the tyre due to heat. If necessary, you should deflate or innate the tyres until the correct reading is reached. At the same time as checking the pressures, you should also examine the condition of the tyre walls and the tread. If you find any cracks or cuts on a tyre, you should discard it and obtain a new one as the overall structural integrity of a tyre can be jeopardized by such defects. Tyre wear is automatic in motoring but it should occur evenly across all points of the tread. Uneven wear is wasteful and indicates that there is a defect in the suspension or steering systems. Any fault must be located before fitting a new tyre or this, too, will wear unevenly. If the degree of uneven wear is minimal, it maybe possible to cure the fault and continue using the tyre. If you are obliged to purchase a new tyre and wish to fit it yourself rather than leave the operation to a local garage or tyre specialist, the technique is covered in a later article.
In many cases a wheel defect will be quite apparent to the driver of the car because of the vibration that is transmitted to his hands via the steering wheel when the car is in motion. It is unlikely that a wheel will sustain damage unless the car has been involved in an accident or has been carelessly driven over a kerb. However, you should make a visual inspection of the condition of the front wheels, in particular round the area of the rims and, if you notice any dents or cracks, you should discard the damaged wheel and replace it with a new one that can be purchased from your local dealer. Alternatively, you may be able to obtain a suitable second-hand wheel from a local breaker’s yard.
Next, you should check the run-out of the front wheels. Run-out is a measurement of the extent of movement from the vertical plane that is evident when a wheel is rotated. Although an accurate measurement of run-out demands the use of special dial gauges, it is possible for the DIY mechanic to obtain a reasonable guide to the truth of his car’s wheels by using a small pointer placed close to the wheel rim. The pointer should be positioned on a jack or axle stand so that it reaches half-way up the wheel rim. You should then gently spin the wheel round by hand so that you can estimate the amount of run-out by close visual inspection of the variation of the distance between the pointer and the wheel. If necessary, rotate the wheel a few degrees at a time and measure the gap with a feeler blade. If you can detect any more than a slight amount of runout, the maximum acceptable figure is 0.102 mm (0.04ins), it is likely that the wheel is defective. However, similar results could be caused by a faulty wheel bearing so you should carry out a further test before discarding the wheel and fitting a new component.
A final check should be made to the balance of the wheels. This is a job that is best entrusted to your local garage or tyre fitting specialist which will have the necessary equipment to measure the static or dynamic balance of the wheels and, if necessary, will then be able to fit the appropriate balance weights to correct the setting.
There are two basic types of wheel bearing, the tapered and the straight. The type that is employed on the front of a car is normally dependent on whether the front wheels are driven or non-driven. Driven wheels are usually fitted with straight bearings whereas non-driven wheels are, in most applications, equipped with tapered bearings. Straight bearings must be renewed if they are worn or defective but taper bearings can be adjusted to compensate for wear. If this does not produce an improvement, they too must be replaced with a set of new components.
To check for wheel bearing wear, first disconnect the battery, jack the front of the car off the ground and position it on axle stands. Grasp the road wheel at the top and bottom and attempt to rock it backwards and forwards. If you can detect any play, it indicates that the relevant bearing may either be incorrectly adjusted or worn and consequently it must be adjusted or replaced. An additional test is to rotate the wheel by hand while listening for any grinding noises or roughness. During this test, ensure that you do not mistake the inherent differential noise, in the case of front-wheel drive (FWD) cars, for bearing noise and, in the case of cars fitted with front disc brakes, do not misinterpret any interference between the disc and the brake pads as bearing noise.
King pins are subjected to considerable forces when a car is in motion and thus a degree of wear is inevitable during the vehicle’s life. Consequently, the condition of the king pins must be checked regularly to ensure that the amount of wear has not reached a critical and, in some cases, potentially dangerous extent.
The method of checking for king pin wear is similar to that described above for checking for wheel bearing wear but the aid of an assistant is required.
With the battery disconnected and the car securely positioned on axle stands, your assistant should grasp each road wheel in turn, at the top and bottom and attempt to rock it. You should lie beneath the car as he docs so and inspect the king pin housing very closely in order to deter-mine the exact origin and amount of any movement that is apparent; the king pin housing is situated immediately behind the hub assembly.
If you do detect wear in the king pins, the bushes and in some cases, the king pins themselves are probably in need of servicing or replacement.
If your car is fitted with telescopic dampers, the first check must be carried out with the car positioned on a flat area of ground with the handbrake securely engaged. Press down as hard as you can on one of the front corners and then release it. The car body should bounce on its springs but return to its original position after no more than one and a half bounces. A prolonged period of bouncing indicates that the damper is defective. Repeat this test for the other front damper and note the results. If both dampers appear satisfactory, you should carry out the next scries of checks. If either one of the dampers fails the above test they should be replaced as a pair.
In order that further checks can be made, disconnect the battery and place the frontend of the car on axle stands. With the car positioned in this manner the front wheels will hang down and fully extend the dampers. This will allow you to make a more thorough inspection of each unit. First, examine the central rod in the damper, looking for any signs of fluid leakage or distortion. If possible, grasp the rod with your hand and attempt to rock it in order to test for internal wear. Next, pay close attention to the upper and lower damper mountings and check for any rusting or cracking that can weaken the car’s structure and permit the mountings to flex. Grasp the body of the damper and push and pull it to check for any looseness at either of the mountings. Check also that the mounting rubbers are in satisfactory condition. If they are cracked, contaminated by oil, frayed, or have become spongy they must be replaced. Finally, look closely for rust or damage on the main casing of the damper, as this, too, indicates that leakage has occurred in the past, and that it should be replaced.
If any of these tests reveal faults in either of the front dampers you should replace both of them. This is essential if you are to avoid an imbalance in the degree of damping.
The MacPherson strut suspension design employs a tele-scopic damper, one end of which runs in a tube that is attached to the stub axle. The other end of the damper rod is located inside a coil spring and attached to the car’s inner wing panel. You may find it impossible to reach the rod by hand in order to check it. However, you should carry out the rebound test and visually inspect the condition of the unit, looking for any signs of the defects that are described above. Check also for rust where the strut is bolted to the wing.
If your car is fitted with lever arm front dampers, the first check should be fitted to assess the number of bounces after each front corner is depressed and released as described in the preceding section. You should then examine each damper unit visually from underneath the car, having supported the frontend on axle stands and disconnected the battery connections.
The first symptom of a defect that you should look for is leaking fluid. Lever arm dampers operate on the principle of hydraulic fluid displacement and any leaks will have an adverse effect on the performance of the damper. Check also for any looseness or signs of wear on the lever arm connections. Grasp the lever firmly by hand and test for any movement. Finally, check that the operating links to the lever and the lever itself are not distorted.
If you are prepared to remove the damper units from the car you can carry out more thorough checks on the workbench, such as determining the rate of lever movement but this is often unnecessary as most faults will be revealed if you carry out the checks detailed above thoroughly.
The majority of modern cars are fitted with coil springs in the front suspension although some cars, such as the Fiat 126, employ a transversely-mounted front leaf spring and others, such as BL Morris Marina, use torsion bars. Several other BL models are fitted with an Hydrolastic or Hydrogas suspension system whereas some versions of the BL Mini are equipped with a very simple design of rubber spring sandwich between a lower wishbone and single upper link.
A damaged or excessively worn spring will have a marked effect on a car’s handling and, if only one of the springs is defective, the car will list to that side. In addition, excessive strain may be applied to the damper at that side and the suspension may become compressed fully until it strikes its bump stop when the car is driven over a bumpy stretch of road, giving the occupants of the car a very uncomfortable ride and risking damage to the car.
To check the condition of the springs, you must measure the car’s ride height at each side. Before you can do this, however, you must be aware of the manufacturer’s speci-fication for your car. This information may be contained in the owner’s handbook but you may have to consult your local dealer. Check the setting with the car positioned on a level area of ground and with no extra weight in the passenger compartment or the boot. Ride height is usually measured from the ground at the centre of the wheel to the highest point on a specified wheel arch but the actual reference points may vary so check this carefully with your local dealer who will advise you.
If you find that the measurement at one, or both sides is incorrect, you must replace both springs to maintain the car’s balance; it is not feasible for the DIY mechanic to attempt to repair these components.
Anti-roll bars are sometimes referred to as stabilizers and are fitted to many cars as a solution to the problem of the car’s body rolling or leaning over when the vehicle negotiates corners. The anti-roll bar basically stiffens the front suspension in order to alleviate the amount of roll.
Because of their exposed location at the front of the chassis, some types of anti-roll bar are prone to accidental damage. This will usually result in some degree of distortion of the bar and, if this is the case, fitting a new one is the only cure as a damaged one cannot be repaired.
The most important check to make to an anti-roll bar is at the mounting rubbers. These normally last a long time but they do suffer wear and require periodic renewal. If they are badly worn, you will probably hear a knocking or rattling noise when driving over rough surfaces. Check the rubbers at the front mounting points looking for any cracks or deterioration. To renew the rubbers you should disconnect the battery and position the car on axle stands. Use a socket on a suitable extension to remove the fixing bolts and then lift the brackets away. If necessary, use a sturdy screwdriver or similar implement to lever the bar downwards until the rubbers can be lifted out.
The new rubbers, which can be purchased from your local dealer, should be fitted into the appropriate places and the brackets re-fitted. If you find it difficult to realign the bar because of its natural springiness, you should enlist the aid of an assistant to manoeuvre it into position while you refit the bolts correctly.
In the case of anti-roll bars that are fitted with internal eye bushes, pressing out the old bushes can, in some cases be more difficult. It may be possible to press them out by hand or with a suitable drift although if this is not the case, you should use the two socket method which is described below in the section below headed Renewing a suspension arm. The new bush can be pressed home carefully in the jaws of an ordinary bench vice.
To remove an anti-roll bar completely, you must first detach the bushed fixings as described above and then remove the main mounting nuts. These are usually casellated nuts with a split pin fixing so you should use a suitable pair of pliers to straighten the legs of the split pin and then carefully pull it out of the hole. The castellated nut can then be undone and lifted away. Remove the nut from the other side and then use a soft-faced hammer to tap the ends of the bar from the fixing points. To fit the replacement bar, simply insert the ends into the appropriate housings and re-fit the nuts and split pins. If you find it difficult to insert the bar correctly, enlist the aid of an assistant to partially tension the bar while you guide the ends home. Your assistant should hold the bar firmly in place until the nuts are fully tightened and the split pins are re-fitted.
Cars fitted with wishbonetype front suspension have the springs mounted between suspension arms or wishbones whereas those other cars that are equipped with Mac-Pherson struts at the front generally have a single arm fixing the lower end of the suspension assembly to the chassis or the inner wing panel. These components are ignored by many DIY mechanics during general checks on the front suspension as they are often long-lasting and trouble-free components. However, as with other suspension components, they can suffer from wear or sustain damage and thus their condition should be checked carefully so that any necessary repair work can be identified.
The tests described above for checking the condition of wheel bearings or king pins will usually expose faults in the suspension arms as well. If, during a test, you detect any movement of the road wheel that is not explained by a wheel bearing or king pin defect, then it is possible that a suspension arm is at fault. Close visual inspection is, however, a vital aid in the location of a defect of this kind. You should look very carefully for any signs of distortion or wear and renew any part that is suspect.
This operation is relatively straight-forward on cars that are fitted with the MacPherson strut type of suspension. Begin by disconnecting the battery, then jack up the front of the car and position it securely on axle stands. Remove the relevant road wheel and then use a suitable wire brush to clean away any deposits of road dirt from the suspension arm. The major fixing points are usually held by castellated nuts fitted with a split pin so use a pair of long-nosed pliers to close up the ends of the pin and then pull it from its hole. The castellated nuts must then be removed and the joints separated with the correct type of ball joint splitter. Next, you should undo the smaller through-bolt that attaches the arm to the mounting bracket on the chassis or inner wing and use a suitable drift to drive out the bolt.
You should draw annotated diagrams of the arrangement of any thrust washers or rubber spacers as you dismantle the assembly so that, by referring to these diagrams during re-assembly, you can ensure that all of the parts are re-fitted correctly. Failure to do so may result in damage.
On some cars it is necessary to renew the arm as a complete unit but, on other models, the arm may be serviced if it is not distorted or damaged in any way. You should consult your local dealer who will be able to tell you whether a manufacturer’s service kit is available for the suspension arm fitted to your car. If a kit is not available, you must renew the complete arm. If a kit is available, it will include new bushes, nuts, ball joints and circlips (where fitted) and split pins. On some suspension arm designs, the main ball joint can be removed and renewed. These types can be identified by the presence of a retaining circlip on the joint. To remove this second type of ball joint you must remove the circlip, using either a small screwdriver or a pair of circlip pliers, and then press the joint out by hand. Fitting the new joint is a simple reversal of this operation. To renew suspension arm bushes, you must use a large bench vice in order to exert firm, even pressure on the assembly. Place the suspension arm in the vice with a socket on each side of the bush. One socket should be of a larger diameter than the bush and should bear against the bush housing, while the other should be of a similar size to the bush so that it can press against it. As the vice is gradually tightened, the smaller socket will force the bush out of the housing and into the larger socket and the new bush can be fitted by carefully reversing the above procedure.
When you have completed the servicing procedure, refit the arm to the car by reversing the removal order and ensure that you replace any other parts with the new units supplied in the service kit.
Renewing a suspension arm on a non-MacPherson strut suspension car is a more complicated operation and usually requires the removal of the coil spring. This operation must be approached with care as a compressed coil spring stores a large amount of energy which must be released gradually by the use of the correct tools. Once the spring has been removed, it is a relatively straightforward matter to remove the mounting bolts that fix the relevant suspension arm and lift it away. It may be possible to service the suspension arm if it is not damaged or distorted so you should contact your local dealer and determine whether service kits are available. If they are not, you must replace the complete arm. Fitting the parts from the service kit involves renewing the bushes in the manner described above. The arm can then be re-fitted to the car by reversing the removal operation.
If you follow the checks described above and carry out the appropriate repairs once a defect is detected, you can maintain your car’s front suspension in the best possible condition. Parts two and three of this scries cover aspects of the steering and front braking systems.
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