Leaf springs are likely to wear because they have several moving parts. They should be inspected at intervals specified by the car manufacturer, or at major service intervals - usually every 12,000 miles (20,000 km).
Before you jack the car up, put it on level ground, make sure that the tyres are at their normal pressures and that the car is at its normal 'kerb weight' without passengers, and with a full fuel tank.
Crouch down a little distance behind the car and see how it sits on the road.
It should appear level from side to side. If one side appears lower than the other, there may be a weak or damaged spring on that side.
Prolonged use of the car with only the driver on board may cause a slight sag in the springs on that side of the vehicle. If the sag is significant, the springs may need to be replaced.
Move to each side of the car and examine the attitude of the swinging link spring shackles, which may be at the front or rear end of the springs. The links should generally be vertical when the vehicle is at its kerb weight.
Any significant deflection to front or rear indicates a weakened spring.
Compare the deflection of the shackles on both sides of the car; they should be approximately the same.
If, from this check, the rear spring or springs appear to be weak, make a further inspection to find the reason. It may be due to damage, or to a general settling down of the springs through age.
Cleaning leaf springs
The standard leaf spring is made from several thin strips of sprung steel of different lengths and held together by clamps.
It is subject to wear as the leaves rub against each other during suspension movement. To overcome this, a tapered-profile single leaf spring is fitted on some vehicles.
Dirt particles between separate leaves accentuate wear and rust. The springs should be kept fairly clean in order to extend their useful life.
The intervals at which this is done will be given in your car handbook.
Modern leaf springs do not need lubricating with oil — which may damage any anti-friction material between leaves. Spray them instead with a silicone-based lubricant.
With most modern cars, leaf springs are found mainly in the rear suspension. Raise the end of the car to clean them.
Remove the hub caps and trims from the wheels, and loosen the wheel nuts. Jack up one side of the car so that the wheel is clear of the ground, and support the car on an axle stand under a chassis member (not under the axle).
Do the same at the other side of the car, so that it is supported under the chassis on both sides, with the wheels clear of the ground.
Chock the front wheels and remove both rear wheels.
The weight of the vehicle is now off the springs, which allows the leaves to separate slightly, making it easier to clean them.
If the spring leaves are really caked with dirt and grease, cleaning them is a messy job.
Look to see if one spring is flatter than the other, in which case the car will probably have a pronounced tilt to one side. This will indicate that you should also check the ride height (See Cleaning and checking leaf springs)
Examine the edges of the spring leaves, look for cracks. Fractures found in the spring leaves cannot be repaired by welding. The leaf or the complete spring must be replaced as soon as possible by a garage. Look at the lower surfaces of the leaves, where the ends of the shorter leaves bear against those above. The tips of the shorter leaf may dip into the surface of the leaf above it, and make a slight depression. The leaves then bind as they move against each other. A slight depression is acceptable, but the spring should be replaced if the depression exceeds a in. (3 mm).
Check the condition of the shackle pins that pass through the rubber bushes. Make sure that they are not bent or badly corroded, in which case they may be very difficult to remove and should be replaced at a garage.
Make sure the nuts on the U-bolts which hold the springs to the axle are tight. If they are loose, the axle will move in relation to the springs. That will cause steering and tyre wear problems. It will also cause the brakes to judder on application.
The spring centre-bolt head or the dowel pin that locates the spring on its mounting pad may also shear.
The axle is then free to move backwards, and may break away from the springs.
A multi-leaf spring has two or more U-shaped clips towards the outer ends. They hold the main leaves in alignment with each other, and may be held in place by rivets or bolts.
Check the condition and security of each clip. If you find one loose or broken, have it replaced immediately.
Otherwise the spring loading will not be evenly distributed during the full suspension travel over uneven ground. This could cause the master leaf to break under stress.