SUSPENSION MODIFICATIONS!

by **Rislar** Sat Jan 16, 2010 10:31 am

SUSPENSION MODIFICATIONS

Most modern 4x4s 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 traveller has cursed a salesman. Bilstein, 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.

Heavy-duty springs

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 the gas type. Medium rate springs will improve road holding, reduce body roll and improve payload by a small amount. Hard springs will improve off-road handling, on-road adhesion, reduce body roll and are recommended for vehicles with loaded roof-racks. They improve heavy payload handling, stability and safety but may feel harsh on-road. Poorly selected springs often cause instability at speed.

Professional safari operators fit these systems to Land Rover Defenders with good results. The ride is quite a bit better than the standard springs and the axle travel, when combined with gas shocks, is improved.

With leaf spring vehicles such as the old Hilux or Land Cruiser pickup, the change is even more impressive. The new springs smoothe the on-road ride and at the same time vastly increases the axle articulation due to spring lubrication between the leaves. This improves off-road traction especially over rocks and dune driving. Stick to well known, respected brands such as Bilstein, OME and Dobinsons.

Spring assisters

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 restrict its collapse.

Firestone make a highly effective inflatable air spring system, springs that are 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

While heavy-duty springs increase ride height, the angle at which the prop-shaft universal joints operate is increased, 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 the most 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, not by guesswork.

Gas shock absorbers

Few vehicles have gas shock absorbers fitted as standard equipment and for a vehicle expected to work long hours off-road they are essential. In the past, few four-wheel drive vehicle manufacturers pay enough attention to shock absorbers.

Working 4x4s need gas shocks. For example, my own Land Rover 110 went through two sets of standard shock absorbers within 30 000 kilometres. 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 kilometres 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 problems

Gas shock absorbers are, in my opinion, the first accessory that should be considered for a working 4x4. The improvement in handling and safety are, in many cases, extraordinary. When I hear reports of bad handling when carrying a load, or skittish behaviour on gravel, even with a new vehicle, the answer is so often simple: Fit a set of good quality gas shocks. Not only do they improve the ride, they last two to three times longer than standard shocks.
When fitting gas shocks it is essential that the suspension setup is checked and adjusted if necessary. Not centralising the suspension before fitting gas shocks can cause rapid destruction of the shock absorbers. The reason for this is that when a suspension system, particularly independent wishbone types, are not set in the ‘central’ position when the vehicle is at rest, the shock absorbers act as bumpstops instead of the rubber bumps designed for the job. The internal components are literally hammered to pieces. Secondly, torsion bars set to increase clearance can create problems when the shock absorbers central or neutral position is altered. In this position the shock absorbers can’t work as they should. The resultant poor ride is then blamed on the shock 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 bump-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.

Why gas?

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 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 air and bubbles are formed. The mixture of hot air and hot oil passes through the valve with ease which eventually causes the shock to soften until the ride is uncomfortable and unpredictable. I have used three brands of gas shocks in the seven 4x4s that I have owned I can highly recommend Bilstein. They are undoubtedly very robust and are my first choice.

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 heavily loaded 4x4 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.

Polyester Bushes
Polyester bushes reduce the rate of wear and permit easier articularion of springs.

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 axles, radius arms and steering control arms.

The effects of worn bushes can be vague steering, a vehicle that steers itself when driving straight, instability, 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 rubber in bushes in industry from shipping to heavy machinery and vehicles are reaping the benefits of the research into new age plastics and graphites. The advantages of polyester are long life and a stiffer suspension which aids 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.