A car sitting lower than normal at the front is a danger sign that should not be ignored. It indicates a fault in the front suspension which, if left untreated, is likely to lead to a much more dangerous condition. As the suspension fails, a rough ride will develop. This in turn will lead to uncontrollable steering with possibly fatal results. Because the front wheels are used for steering the car, they need a much more complicated suspension system than the rear wheels. The suspension systems at the front must allow the wheels not only to move up and down, but also to swing at various angles to the car frame.
Testing Car Height
The height at which a car sits on the road varies according to its make and model. The car manual will list the manufacturer's ride height specifications; alternatively, your authorized dealer will have the information. To test this height accurately, you should first drive the car, completely un-laden and with a minimum amount of fuel in the tank on to a completely flat surface. Then take the measurements from the ground to each of the four points specified on the car. If any of the measurements is below the recommended minimum, suspension faults are indicated.
Types of Suspension System
A large proportion of cars on the road today use a spring suspension system fitted to the front wheels. There are two basic types of spring: coil springs and leaf springs. This, the first of three articles, deals exclusively with coil spring systems. Variations in the coil spring system, leaf spring systems and other mechanical and non-mechanical systems are described in the following two articles.
Coil Spring Systems
Coil springs in suspension systems are larger versions of the type of spring we all know and there are two common systems that use them—the simple MacPherson strut system and the more complicated double wishbone system. There is another double wishbone system that uses leaf springs. This is dealt with in the second article.
A typical McPherson Strut suspension system. Most other strut/coil spring systems differ only slightly.
A typical double wishbone coil spring front suspension system.
MacPherson Strut System
A typical MacPherson strut system has one assembly fitted to each wheel to give them independent movement. Each unit consists of a vertical strut (the damper) surrounded by a coil spring. The strut and the coil spring are both held between the same two collars. The upper collar is connected via a flexible rubber mounting to a metal frame, which is bolted to the car wing valance. The top of the rubber mounting passes through both the metal frame and a hole in the wing valance to form a characteristic convex shape inside the engine compartment. The top of the damper passes through the upper cup, rubber mounting and wing valance. This protruding end of the damper is threaded and held on the metal frame by a retaining nut. The lower end of the damper forms an integral unit with the lower collar and this in turn is connected to the stub axle.
Faulty MacPherson Strut Springs
The coil spring in the MacPherson strut system prevents the telescopic damper from both rapid movement and complete closure. Any weakness in this spring allows the damper to close while the car is at rest, so that the front of the car sits lower than the specified height. Weakness here would allow violent road shocks to be transmitted to the chassis resulting in a rough ride. There is usually little difference between the various MacPherson strut type systems and the following information will apply with only slight variations to all cars fitted with this type of suspension system.
Removing MacPherson Strut Springs
To remove MacPherson strut coil springs—or any other coil spring - you will need special coil spring compressors. It may be possible to hire these if you do not wish to buy. Alternatively, there is a second method utilizing the weight of a fairly large friend on the wing and purpose-made clips which can be bought at any good accessory store. You will need an assistant to help you with some of the work anyway. Before you start, clean the worst of the road dirt from the springs and shock absorber mountings to prevent it being trapped in the compressed springs.
It is unlikely that only one side will suffer from worn or damaged springs, so expect to replace both units. First slacken the wheel nuts on both front wheels, then jack up the car and support it on axle stands. Next, remove both wheels and thoroughly brush the mountings. If you are using a spring compressor, skip the next paragraph. If you use the spring clip method, do not raise the car from the road at this stage. With a friend sitting on one wing to compress the spring, bind two or three adjacent coils together with the special clips. Repeat on the other wheel. Now put the front of the car up on the axle stands and remove the wheels.
With the car on the axle stands, open the bonnet and locate the suspension mountings on either side of the engine compartment. The flexible mounting protrudes through a hole in the wing valance and the threaded tip of the damper with its retaining nut can be seen. Measure the length of thread which extends beyond the nut, then remove the nut and its cranked retainer. You can now remove the bolts securing the top of the suspension unit to the side valance. Next push the piston rod down through the hole and move it to one side to lodge against the underside of the valance. Now, from underneath the car, again compress the piston and remove the top mounting assembly, the dished washer and the upper seat from the top of the spring. Finally, lift the spring from its bottom seat and draw it over the top of the damper piston and out of the car. On some cars it is easier to dismantle the strut "hub end first".
Re-fitting MacPherson Strut Springs
Unless the damage is severe, it is rarely possible to check these springs by eye, even when you have removed them. But worn or weakened springs are the usual cause of the car being low at the front and the only remedy is to fit new springs. When buying replacement springs, make sure they are both the same rating as each other and as the old springs. The new springs must be compressed before you attempt to fit them and to the same compression rate as the old springs. This is best done by clipping the same number of adjacent coils together. The clips must be applied in the same position on the new springs as on the old springs.
To fit the new springs, first slide the spring over the piston of the dampers and make sure that you locate it in place on its lower mounting seat. Next, pull up the piston and locate the upper spring seat on the flats cut into the piston rod. Then put the dished washer, convex side up, on the piston rod and fit the top mounting assembly. Make sure that the steering is in the straight-ahead position, then fit the cranked retainer at 90 degrees to the wheel. Coat the threaded extension of the piston rod with Loctite and loosely fit the nut.
Finally, refit the mounting bracket and tighten the damper piston nut. To do this, first locate the bracket and put the retaining nuts through the holes into the engine compartment. From above the car, apply the nuts to these retaining bolts and tighten them to the specified torque (consult your manual or dealer for this). Remove the spring compressing clips with great care, re-fit the road wheels and lower the car. Finally, slacken off the piston retaining nut. Have your assistant hold the spring to prevent it turning and re-tighten the nut to the specified torque, checking by measuring the length of piston thread protruding through the nut, which should match the measurement taken on removal.
Double Wishbone Coil-Spring System
There are two types of double wishbone system. The type discussed here uses a coil spring. The second type (fitted only on older cars) uses leaf springs and is discussed in part 2. The single, outer end of each wishbone (so called from its shape) is connected via a swivel joint to the stub axle. The swivel joint can be one of two types: the older king pin type and the more modern ball joint. The upper wishbone is never the same size as the lower one. It is usually shorter, to allow the wheels to tilt as they move up and down during normal use. The double, inner end of the top wishbone is directly mounted on the chassis with screwed or rubber bushes. There are several methods of securing the lower wishbone to the chassis. It can be directly mounted via screwed or rubber bushes or splined to the damper unit which is bolted to the chassis. With both lower wishbone mounting systems, the damper is connected to the lower arm. It then passes up, through the upper wishbone, to connect with the chassis. This damper unit, usually telescopic, is surrounded by a coil spring. As the wheel moves up and down, the wishbones pivot on their connections and the telescopic damper reduces the amount of movement reaching the chassis. The coil spring absorbs the road shocks.
Faulty Double Wishbone Coil Springs
The double wishbone coil spring suspension system is much more complicated to dismantle and repair than the MacPherson strut system. To remove the double wishbone coil springs, on some cars it is necessary to take out the front axle as a complete unit. On the majority of cars, for example the Fiat 124 described below, this is not necessary. If you are in doubt as to what type of syspension system is used on your car, it is better to remove the axle before starting, rather than find out that you have to do so half way through the job.
Spring Removal Axle In Car
The method of removing the double wishbone coil springs with the front axle still in the car varies slightly from car to car, but this description for the Fiat 124
can be adapted for other cars. First slacken the wheel nuts on the front two wheels, then jack up the front of the car and place it on axle stands. You will next have to undo the nuts holding the top damper shank. To do this open the bonnet and reach the nuts through an access hole in the wheel arch. While undoing these nuts, you will have to prevent the damper shank revolving. Take a suitable open-end spanner that will hold the shank still, then undo the retaining nuts. Next, release the nut and take out the bolt holding the bottom of the damper to the lower swivel arm. You can now remove the damper by lifting it up out of the gap in the lower wishbone arm.
The spring is easier to remove if it is taken out complete with the wishbone. To do this, first use two clamps to compress the spring carefully as described on page 562. Next, you will have to disconnect the flexible brake pipe unions from the main lines. Excessive fluid loss can be prevented by first unscrewing the reservoir cap, stretching a piece of polythene across the reservoir, then replacing the cap. After disconnecting the unions, plug the main lines; this also will help to prevent fluid loss and keep out dirt. For the next stage, you will need a special tool - the Fiat service tool puller (No A47044). You may be able to borrow or hire this from a Fiat garage. If not, you will have to buy one.
Unbolt the stabilizer (anti-roll) bar from the control arm and use the puller to split the tie rod from the steering arm. Next, you will have to remove the wishbone assembly from the wheel arch. To do this first unbolt the upper wishbone arm from the body, then unbolt the lower arm from the cross-member, and finally lift out the whole assembly. While doing this, take careful note of the position of all the bolts and of the length of thread beyond each bolt. This will enable you to re-assemble the parts correctly, without upsetting the steering/suspension geometry. You can now remove the springs from the wishbone. First, slowly release the spring clamps. Then when the pressure has been fully released, prise apart the wishbones and remove the coil spring along with its seating. Make sure that you buy the correct new spring for your cor's make and model, then re-assemble the components by reversing the above procedure.
Replacing Springs, Axle Removed From Car
Replacing the springs on cars with double wishbone coil spring suspension systems can only rarely be done with the front axle still in the car. In the majority of cases, you will have to remove the front axle before working on the suspension. Front axle removal is a complicated job and the method varies for each make and model of car. This is fully described in a later chapter. When you have removed the front axle assembly and are in a position to work on it away from the car, it is possible to remove the front coil spring in a similar manner to that described earlier in the article.
Also see: Suspension Repair Part 2
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