Advanced Steering and Wheel Alignment Service

Advanced Steering and Wheel Alignment Service

AUTOMOTIVE SERVICE TECHNOLOGY

Transverse mounting are usually not so good as those obtained by lengthwise mounting.

Spring Bushings Spring eyes are generally bushed with a bronze bearing, though rubber bushings are sometimes used and nylon is popular for some small cars. Bushings may be press fitted or screwed into the eyes, depending on the design. The object of the bushing is to permit renewing a wearing surface at low cost. Spring bolts or pins, which may be either threaded or smooth, pass through these bushings for attaching the spring to the hangers provided on the frame. (See Figs. 19.22 and 19.23.)

The bushing and the spring bolt or pin therefore form the bearing surfaces which support the load on the spring. Much more bearing surface is available with threaded than smooth surfaces. Because. There is considerable movement between bearing surfaces when the spring vibrates, it is necessary to provide means for lubrication. Usually the bolt or pin is drilled through the centre for half of its length, with a side hole at its middle so that a lubricant can be forced through a lubricant fitting, onto the bearing surfaces. Sometimes a groove is made in the centre of the bolt or pin to hold lubricant there (see Fig. 19.23). Synthetic-rubber washers are often fitted between the bushings and hangers to prevent loss of the lubricant. Spring bolts are subjected to hard service and considerable wear takes place if proper lubrication is not provided.

Nylon- and rubber-bushed assemblies do not require lubrication. Rubber bushings are usually made From moulded rubber enclosed within an inner and outer steel shell. The outer shell is a press fit into the spring eye and the inner shell is rigidly held in the hanger by tightening the spring bolt, serrations (saw teeth) being provided on the ends to the inner shell to bite into the hanger. In this manner, all movement between the spring and bolt is taken up by the rubber so that no lubrication is required. Rubber washers are inserted between the ends of the outer bushing shell and the hanger to prevent all metal-to-metal contact between the spring and the hanger (Fig. 19.24)

A spring bolt or pin must be tightly secured against rotation in the spring hanger so that all relative motion will be between it and the bushing. One method of doing this is to use a bolt knurled under the head so that it bites and does not turn when pressed into the metal of the hanger. In another method a seat is provided in the hanger for the bolt head so that it cannot turn. A pin can be secured against rotation by a key or a clamp bolt that fits into a groove provided in the pin.

SUSPENSION SYSTEMS

Spring Shackles

The spring shackle, a swinging support which permits the leaf spring to vary in length as it is compressed, is mounted between the spring and the hanger by bolts or pins. Since movement occurs at both ends of the shackle, two bushings are used; that is, one is provided at the hanger in addition to the one in the spring eye. The general practice is to use one shackle on front springs, either at the front or rear support. For vehicles having a Hotchkiss drive, the rear springs are always pinned to the hanger at their front support and shackled at their rear support. Rear springs on vehicles using the torque-tube or torque-arm drive are shackled at both supports. The distance between the spring hangers

should allow the shackles to be nearly vertical when the spring carries its normal load. Many types of shackles are in use. Links of one form or another are often used, one on each side of the spring eye. The pins shown in

Automotive SERVICE TECHNOLOGY

Fig. 19.23 are threaded into the bushings. The ends of the pins are tapered to fit snugly into the shackle links, which are held together by a draw bolt to lock the pins in position. Individual links, without any connection between them, can be used with shackle bolts locked in the links. Shackle links may be combined into a single- unit construction by means of a centre cross bar or by making it a single piece and the shackle bolts are locked in the link by knurled bolts. For this type of shackle, some play must be allowed between the shackle link and the spring eye and hanger so that free movement can occur between them. When assembling, the shackle bolts are drawn up as tightly as possible, then backed off about one-half turn to prevent binding. The nuts are held on the shackle bolts by cotter pins. A heavy-duty assembly is shown in

Fig. 19.25.

Another type of shackle, in which one of the bushings is fitted into the shackle, is called the “Y”. The plain shackle pins are locked in position by small clamp bolts. This solid Y- shaped shackle can be made very rigid and is a good design for heavy-duty vehicles. The U-shackle, in which the shackle bolts and shackle are combined into a single unit by a U-shaped forging with threaded ends (Fig. 19.22), is used on spring mountings on a large number of passenger cars. Upper and lower threaded bushings are used to hold the U-shackle ends. These hardened steel bushings are tightly threaded into the frame hanger and into the spring eye, and loosely threaded over each end of the U-shackle. Free movement is then allowed between the steel bushings and the shackle ends. The outer threads on the bushing are very coarse, while those which screw over the bolt are finer. The outer threads are threaded in the opposite direction to the inner threads so that the shackle end is drawn into the bushing as the bushing is turned into the hanger or spring eye. These shackles may be inserted either through the inner or outer end of the hanger. Lubricant is introduced to the steel bushings through lubricant fittings and holes in the shackle ends. Bumper coil springs are sometimes incorporated in the shackle to eliminate shocks. Such shackles are usually used on front springs and are called kick shackles. They help to reduce the transmission of road shocks to the frame and to the steering wheel, thereby helping to avoid front wheel shimmy. Blocks of rubber, confined in boxlike housings on the frame, can be used instead of bolts and shackles on the springs. The ends of the main leaf are then flat and fit between the blocks of rubber. This installation does not require lubrication since there are no metal bearing surfaces. Leaf Spring Lubrication Some manufacturers and designers of springs do not advocate leaf-spring lubrication because reducing friction between the leaves destroys the capacity Of the spring to absorb the energy of shocks without excessive rebound. However, it is generally necessary to keep the leaf surfaces lubricated to prevent undue wear and squeaks and to keep a spring flexible. The leaf surfaces should be lubricated by spraying them with oil or by forcing grease, usually a graphite grease, between the leaves. Many vehicles have spring covers to retain the lubricant, and some have fittings to replenish the lubricant. These covers keep the spring surfaces lubricated and also protect the spring from water, dirt, snow, and other foreign matter. Spring leaves should be sprayed with oil or lubricated with grease at least seasonally (twice a year). Some leaf springs have thin rubber inserts placed between the leaves so that there is no metal-to-metal contact. No lubrication is then needed between the leaves as the rubber gives when there is a tendency for one leaf to slide on another. Other leaf springs have self-lubricating bronze inserts. Spring bolts and shackle bolts, when not rubber mounted, and the spring seat on torque tube drives are usually fitted with pressure grease fittings. These should be lubricated every 1,000 miles with semi-fluid chassis lubricant.

Coil Springs

Coil springs (Fig. 19.26) are widely used for passenger cars, particularly with independent heel suspension. They are made of alloy steel rods coiled to the desired size. The load rating of a coil spring depends on the diameter and length of the rod used to make the spring. Greater flexibility is obtained by using a long rod with a small diameter. The effective length of coil springs can be made much longer than leaf springs since the active spring material is coiled

SUSPENSION SYSTEMS

into a small space. Therefore, it is easier to obtain the desirable spring flexibility and frequency for a particular vehicle. (The word “kit” appearing in Fig. 19.26 refers to groups of replacement parts sold in sets.) Since the coil spring is all one piece there is no friction as there is between the leaves of a leaf spring. Since there is no friction to oppose deflection of the coil springs, the deflection of the spring absorbs the energy of a road shock by the resistance of the internal strain force of the spring material only. Because coil springs are so flexible, good shock absorbers must be used with them to prevent excessive rebound. The coil spring can be used for springing only and cannot transmit any side thrust nor take any torque reaction. Therefore, it must be used with suitable torque-rod structure, which will take these thrusts and hold the axle in alignment

(Fig. 19.27). Coil-spring mountings are very simple. The hanger and spring seat are shaped to fit the coil ends and hold the spring in place and cups which fit snugly on each coil end are often used for mounting~ With independent suspension, the upper cup is usually formed within the frame and lower cup fastened to independent arm supports. Rubberized fabric spacers are placed into the cup to insulate the springs.

Rubber Bumpers

Rubber bumpers are mounted either on the spring or its supporting member to prevent metal-to-metal contact when the spring is compressed. With independent suspension, the suspension arms sometimes butt against rubber bumpers. Rubber bumpers are usually block or cone shaped (Figs. 19.28) and are mounted by bonding them to a metal strip that is fastened to the supporting member (usually the frame) or spring; or by means of a rubber button, moulded on the base of the bumper, that fastens into a hole in the frame. The resistance of the rubber increases with the deflection of the spring and helps to absorb sudden blows. Rubber has many desirable properties that make it useful as a shock absorbing medium, hence the “rubber spring”, in the B.M.C. suspension (Fig. 19.29). The main function of a shock absorber is to regulate the spring rebound so that the spring returns to rest slowly, thus preventing sudden jolts and bounces being transmitted to the vehicle body and its occupants and cargo. Shock absorbers which only check the spring rebound are termed single-acting.

FIG. 19.27 Rear-axle coil-spring system — independent

Coil-spring mountings are very simple. The hanger and spring seat are shaped to fit the coil ends and hold the spring in place and cups which fit snugly on each coil end are often used for mounting. With independent suspension, the upper cup is usually formed within the frame and lower cup fastened to independent arm supports. Rubberized fabric spacers are placed into the cup to insulate the springs.

Rubber Bumpers

Rubber bumpers are mounted either on the spring or its supporting member to prevent metal-to-metal contact when the spring is compressed. With independent suspension, the suspension arms sometimes butt against rubber bumpers. Rubber bumpers are usually block or cone shaped (Figs. 19.28) and are mounted by bonding them to a metal strip that is fastened to the supporting member (usually the frame) or spring; or by means of a rubber button, moulded on the base of the bumper. that fastens into a hole in the frame The resistance of the rubber increases with the deflection of the spring and helps to absorb sudden blows. Rubber has many desirable properties that make it useful as a shock absorbing medium, hence the “rubber spring” in the B.M.C. suspension (Fig. 19.29). The main function of a shock absorber is to regulate the spring rebound so that the spring returns to rest slowly, thus preventing sudden jolts and bounces being transmitted to the vehicle body and its occupants and cargo. Shock absorbers which only check the spring rebound are termed single-acting.

AUTOMOTIVE SERVICE TECHNOLOGY

A shock absorber may also dampen the compression of the spring by absorbing part of the energy as the spring is depressed. Shock absorbers which check compression in addition to rebound are termed double-acting. Most shock absorbers used at the present time are tubular double-acting because they permit the use of more flexible springs (Figs. 19.30 and 19.31), and in the case of coil suspension, can be conveniently mounted inside the spring. The operating principles are shown in more detail (Fig. 19.32). Shock Absorbers and Stability Originally, shock absorbers or “dampers” were fitted to cars as an accessory or a luxury item. Now they are a very important part of the whole suspension system. Steering, braking and road-holding qualities are dependent on specially designed shock absorbers, fitted as original equipment and properly maintained. In many independent front suspensions the shock absorbers are built in as part of the “upper control-arm” assembly instead of the tubular types, but in all cases maintenance is restricted to tightening all fastenings and inspecting and replacing rubber bushes or mountings. As most units are sealed and welded and not repairable in the workshop, faulty ones are replaced with new or exchange sets. A few makes are adjustable for stiffness or road and load conditions by a small control valve.

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