Most modern 4×4′s are equipped with suspensions better suited to road conditions than off-road work. Modifications are often necessary to increase ground clearance and improve payload. Also, vehicles that excel off-road may need softening up for road use. trouble is not all spring and shock manufacturers make well-researched products and many a disappointed traveler has cursed a salesman. bilstein, koni, Old Man Emu and TJM all make high-quality systems but above all, make sure you purchase them from a competent professional who is able to select an appropriate spring/shock combination. Backyard mechanics with limited knowledge are a liability.
When coil springs are exchanged for higher rated units make your selection carefully. Light-duty units will feel similar to those that the manufacturer has fitted but will ensure longer life of the shock absorbers, especially if they are gas type. Medium rate springs will improve road holding, reduce body roll and improve payload by a small amount. Hard springs will improve road handling, on-road adhesion, reduce body roll and are recommended for vehicles with loaded roof-racks. They they improve heavy payload handling, stability and safety but may feel harsh on road. poorly selected springs often cause instability at speed.
With leaf spring vehicles such as the old Hilux or Land Cruiser pickup, the change is even more impressive. The new springs smooth the on-road ride and at the same time increase the axle articulation due to spring lubrication between the leaves. this improves off-road traction especially over rocks and dune driving.
Spring assisters/Air Springs
Coil spring assisters come in the form of helper coil springs that fit inside the existing coils or rubber blocks squeezed between the coils of a spring to resist its collapse. Firestone make a highly effective inflated to suit load and conditions are another option. Once prone to failures the new models are earning a good reputation.
Problems caused by suspension mods
The most common problem caused when the vehicle’s ride height is increased is over-sensitive steering and most likely to occur with a suspension lift of 50mm or more on a solid front axle. this is caused by a change to the camber angle and must be corrected with replacement bushes. The angle at which the prop-shaft universal joints operate is also increased by a suspension lift, often resulting in accelerated wear or vibrations. Other items to check are the brake hoses. There must be ample length to cope with additional axle travel made possible by the new shock-absorbers. However, mismatching components: taking shocks from one manufacturer and springs from another, is a common cause of premature failure of after-market suspension components. The stretch of the shocks and the height of the springs must be matched properly and not by guesswork.
Gas shock absorbers
Few vehicles have gas shock absorbers fitted as standard equipment and for vehicles expected to work long hours off-road they are essential. In the past, few four-wheel drive manufacturers have paid enough attention to shocks absorbers.
Working 4×4′s need gas shocks. For example, my own Land Rover 110 went through two sets of standard shock absorbers within 30 000 kilometers. Once the second set had worn out, the first being replaced under guarantee, I replaced them with Bilstein shocks. When selling the vehicle after clocking up 130 000 kilometers the shocks were as firm as when I fitted them. Gas shocks often make the ride a little firmer but the real advantage comes when cornering or carrying a load. The difference in my case was a significant improvement in ride even when compared with brand new, standard shock absorbers.
Torsion bar suspension problem
When fitting gas shocks it is essential that the suspension setup is checked and adjusted if necessary. Not centralizing the suspension before fitting gas shocks can cause rapid destruction of the shock absorbers. the reason for this is when a suspension system, particularly independent wishbone types, are set in the ‘central’ position when the vehicle is at rest, the shock absorbers act as bump stops instead of the rubber bumps designed for the job. The internal components are literally hammered to pieces. Secondly, torsion bars set in increase clearance can cause problems when the shock absorbers central or neutral position is altered. in this position the shock absorbers cant work as they should. The resultant poor ride is then blamed on the shocks, when the real culprit is the backyard mechanic who thought he knew better than the vehicle manufacturer about how the torsion bar should be set. Thirdly, do not assume that if your vehicle is brand new that the suspension is correctly set up. Many imported vehicles stay lashed down to the pump-stops in crates for months and when they are delivered the suspension has ‘sagged’ and must be reset. torsion bar suspension is particularly prone to this.
A shock absorber, simply described, is a metal tube filled with oil through which a piston moves. on the piston is a valve which permits oil to pass through a limited rate. The tube is connected to the chassis and through at a limited rate. The tube is connected to the chassis and the piston is connected to the axle. The oil’s limited travel damps the movement of the piston and therefore the axle to which it is attached. This prevents oscillation that the springs would create if left undamped. as the piston moves in the cylinder heat is generated. Heat thins the oil and makes the shock less effective. What is worse, the oil in a hard working shock mixes with the air and bubbles are formed. The mixture of hot air and hot oil is able to pass through the valve easier than pure oil, which means that the shock will lose its effectiveness, to the point where the ride becomes uncomfortable and unpredictable. Gas shocks are different in that they are pumped with a small quantity of inert gas. This gas cannot mix with the oil and so the main reason why shock-absorbers become soft as they get hot is eliminated. Shock-absorbers on a heavy loaded 4×4 on a rough sand track work almost as hard as shocks on a competition rally car. I know of one Range Rover which after being called to rescue the survivors of an accident in Northern Botswana (that was me in 1987), ‘cooked’ a gas shock by racing to get to the accident scene. the shock was blackened by heat and destroyed. I have used three brands of shocks in eight 4x4s that I have owned I can highly recommend Bilstein. They are undoubtedly very robust and are my first choice.
Bushes made from hard rubber are fitted in various locations in suspension systems to soften the vibrations generated by the wheels, engine and transmission. in Off-road vehicles these bushes are stressed more than in a normal road vehicle and as a result wear out and need periodic replacement. Bushes are located in various places, namely leaf spring shackles, steering dampers, control arms locating the axle, radius arms and steering control arms. The effects of worn bushes can be vague steering, a vehicle that steers itself when driving straight, instability, an uncomfortable ride on corrugations, clunks and bangs on rough terrain and clunks when reversing or braking. A worthwhile option when replacing bushes is to fit polyester units. polyester is replacing the rubber in bushes in industry from shipping to heavy machinery and vehicles are reaping the benefits of the research into new age plastics and graphite’s. The advantages of polyester are long life and stiffer suspension which aid stability and safety. A little more vibration is sometimes transmitted to the driver but this is rarely noticeable and they frequently cost less than genuine parts.