How to fit spring assisters

November 20, 2011 at 6:49 pm
filed under Car Care, Uncategorized
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If you decide to load your car up heavily at the back, either with luggage or extra passengers, there will be a great deal of weight on the rear suspension. Attaching a trailer or caravan will increase this even further and may well impose a strain on the rear springs far in excess of what they were designed to take. This will result in low clearance at the back—your exhaust or differential may then run the risk of being scraped. Handling will also be affected by the uneven weight distribution, making the car dangerous to drive.

Fitting suspension aids, or spring assisters, will overcome these difficulties. They effectively uprate a car’s suspension system under load and restore its balance. At the same time, by taking the strain, they minimize the danger of your original spring components failing. Providing the assi-ters fitted are of high quality, your car’s ride and handling under normal loading conditions should not be unduly affected.

Choosing assisters

Spring assisters fall into four main categories: hollow rubber or rubber and coil springs; air cushion springs; coil spring damper units; and airadjustable damper units. Because of wide variations in suspension design, the choice of what to fit is likely to be restricted to one or two types.Lcyland front-whcel-drive cars, for example, have unconventional Hydrolastic and Hydragas suspension units mounted above independent trailing arms.They can be fitted only with the rubber, or rubber and coil type, of assister. Fortunately, suspension aids usually come in complete kits, designed around a specific car, so there should be no mistake providing that you quote the make, model and year of your vehicle to the dealer.

If you do have to choose between two different types of spring assister, you should bear in mind that the cheaper ones will not be as efficient as the more expensive, complex designs. A simple rubber spring may have good load-bearing characteristics, but it will not give such a smooth ride unladen as a progressively-sprung damper unit. In the spring-damper market, where several manufacturers offer a similar product, it is generally accepted that the more expensive ones give a better ride and last longer. If you intend to make use of your spring assisters only once or twice a year, it may well be worth spending a bit more to ensure a comfortable ride for the rest of the time.


Fitting suspension aids is a relatively straightforward job, and you will not require any special tools. The kit of your choice should contain all the necessary parts and a set of instructions referring specifically to your particular car. Always start by checking the kit to see that it is complete, and identifying each part in turn. In every case when fitting assisters, the car must be jacked up and supported— either on body jacking points, chassis box sections, or subframe members—so that the back axle hangs freely from the suspension. For this, use either axle stands or wood blocks with a base area of at least 30 x 30 cm (12 x 12in.). Never leave the car supported on a jack, which may fall over or collapse; or bricks, which might crumble. In order to make the rear suspension more accessible, you should also remove the back wheels.

If you want to fit the air cushion, hollow rubber or rubber/coil type of assister, measure the distance between the centre of one of the rear wheels, and the top of its wheel arch, while the car is still on the ground. This will help you to check later that the assisters are correctly fitted. Before beginning any further work, read the kit instructions and get some idea of where the spring assisters are going to be located. Remember that the principle of all spring assisters is to provide extra resistance between a car’s unsprung weight (body, chassis, engine and so on) and its sprung weight (including axles, wheels, trailing arms and so on).

Fitting coil spring damper units

The coil spring damper is an expensive but efficient assister which replaces a car’s original shock absorbers. There are units available for most cars with conventional dampers and some others as well and they have the advantage of doing two jobs at the same time. The coil spring part provides the extra assistance while the damper acts in the normal way, controlling the car’s pitching motion.

Identify your original shock absorber and note what type of fixings it has to the axle and car body—they will be of either the ‘pin’ or ‘eye’ variety.The pin fixing consists of a threaded bolt which goes through a locating hole, with rubber grommcts and washers either side. It is secured by means of a locknut. The eye fixing has the threaded bolt running through a rubber bush at rightangles to the damper and is secured in the same way. The car illustrated has two pintype fixings but others may have two eyes or a combination of both types. The procedure for dismantling them is the same in both cases.

Start by finding out where the damper is connected to the body inside the car. It will be in the boot or, in the case of a hatchback or estate car, in the passenger compartment, but you may have to undo a bit of trim in order to see it. Undo the locknut and note the position of the grommets and washer, as the new ones supplied in the kit must go back in the same place. Move back under the car and undo the bolt securing the bottom of the damper in the same way. Grip either end of the damper firmly, in both hands, and press the two halves together. The damper can now be removed.

Some cars with trailing arm suspension, such as the Citroen 2CV, have their dampers mounted horizontally. The method of removal is, however, exactly the same.

To fit the new unit, begin by putting new washers and grommets or bushes on the end pin or eye fixings. The kit instructions will show you the exact order of assembly. Next, compress the unit and insert the pins on either end into their locating holes on the bodywork and the suspension. If there is an eye fixing on one end, make sure its locating pin goes through the rubber bush properly.

Any further washers and grommets must now be placed on the pins, and the locknuts screwed on. They must not, at this stage, be tightened up.

Repeat the above operations for the other side of the car.

With both units in place, it is now necessary to check that the brake pipes and exhaust do not foul them. This is something which the kit manufacturers do their best to avoid and if they cannot, they usually give detailed instructions on how to overcome the problem. Sometimes, however, difficulties can arise, especially if your car has nonstandard pipe fittings. If the brake pipes are too close, try to reroute them by bending or altering the position of their support brackets. You should not attempt to bend the pipes themselves. Do the same for the exhaust pipe whose mounting will probably be easier to modify.

When you are sure that the new springs can move freely, refit the roadwheels and lower the car to the ground. With the weight of the car on the wheels, tighten all the nuts and bolts on both units. Bounce the car several times and make sure that the springs are still free of obstruction.

Fitting hollow rubber springs

The hollow rubber spring assister is a simple device which is both easy to fit and relatively cheap. In this case, the ‘wasp-waisted’ design of the spring provides a progressive resistance under load, by fitting between the rear axle and car bodywork. The exact method of fitting varies according to individual cars but the kit instructions will refer speci-fically to your vehicle. Check the kit instructions carefully before starting any work.

Cars with live rear axle suspension

On cars with live rear axle suspension, start by jacking up the car, supporting it safely, and removing the wheels. The first part of the kit to fit will be a metal plate (known as the reaction plate). This must be attached to the chassis or car bodywork, above the point on the axle where the spring will go. When the spring is compressed it will strike the plate, which in turn takes the strain. On some cars, there will be a small rubber bump stop already fitted above the axle to stop the suspension fouling the bodywork under bumpy conditions. This should be unscrewed or unbolted first.

The next step is to drill a hole through the box section above the axle. The reaction plate can now be fitted by bolting it on through the hole. The rubber spring itself must now be secured to its mounting bracket. This will involve inserting a bolt through the spring and out of the other end. Stick the bolt to a screwdriver with a bit of plasticine and it can then be easily guided through the holes. Check with the instructions that all the washers provided are in the correct order, and then tighten the locknut on the bracket until the spring is firmly held, but not distorted.

Place the bracket and spring assembly on to the axle, underneath the reaction plate. Fit the two U bolts provided underneath the axle and through the locating holes in the bracket, screwing down the nuts loosely. If there are brake pipes running along the axle, try first to divert them slightly be undoing the nearest securing clip. If this cannot be done without damaging the pipes, then the aluminium bracket must be cut to accommodate them, according to the manufacturer’s instructions.

With the spring now loosely fitted in position, you must carefully jack up the hub until it is at its normal height. You can tell this by measuring from the centre of the hub to the wheel arch and comparing it with the measurement taken when the car was on the ground. The car’s suspension will be compressed to its normal unladen position, and at this point there should be a small gap (never greater than 5 cm or 2in.) between the rubber spring assistcr and the reaction plate. If there is no gap, and the rubber spring is compressed, lower the hub and remove the spring/bracket assembly. The bracket must be cut down with a hacksaw, along the V section marked. Reposition it and check the clearance again.

When the correct clearance has been obtained, make sure that the contact faces of the spring and the reaction plate are parallel, and tighten the locknuts on the U bolts.

The ends of the U bolts may now be too long, so use a hacksaw to cut them back to just above the locknuts.

Repeat the above operations for the other side of the car and then run a final check to ensure that nothing will foul the springs when they are compressed under load. The wheels can now be fitted, and the car lowered to the ground.

For a few cars, the springs are attached to the bodywork, and the reaction plate to the axle. Different brackets will be provided in the kits, but fitting procedure is basically the same.

Cars with trailing arm rear suspension

Cars with trailing arm rear suspension, such as the Leyland front-wheel-drive range, usually have the spring assisters fitted to the bodywork in place of the original bump stop. A wedge-shaped bracket will be supplied, and after this has been bolted to the spring according to the instructions in the kit, the whole unit can be bolted on to the bodywork. The reaction plate is then strapped on to the trailing arm. Make sure that the plate and the spring are parallel, and that everything is tightly fixed. Repeat the operation for the other side of the car, then refit the wheels and lower the car to the ground. Check that the springs are not compressed with the car unladen. If they are, and the car has Hydro-lastic or Hydragas suspension, then the displacers will probably need pumping up. This should be done immediately at your local dealer. Remember also to make sure that nothing interferes with the free movement of the springs.

Fitting rubber coil springs

The rubber/ coil spring is a development of the hollow rubber spring assister, which combines ease of fitting with more efficient springing.

Start by completing all the preliminaries of jacking and supporting the car and so on. In some cases, the kit instructions specify that the bump stop must be removed or cut down. Do this only when the manufacturers say so. The coil spring is then strapped to the car axle or trailing arm by means of two large Jubilee clips. If there are any brake pipes running along the axle, then the curved bracket on the end of the coil spring must be slid underneath them before the clips are tightened. Now jack up the hub until the suspension is compressed to its normal level (see ‘Fitting hollow rubber springs’ above). Check that the spring assister is not compressed. If it is, then clearance may be obtained by sawing off part of the rubber stop at the top of the spring. This can be made a lor easier by dabbing some washing-up liquid on the saw blade first.

Ideally, with the car standing on its springs unladen, the spring assister should just be touching the car body, chassis or bump stop, but a slight gap is acceptable. Cars with Hydrolastic and Hydragas suspension may, in addition, need a pump-up to restore their correct ride height.

Fit the other spring in the same way, then refit the wheels and lower the car to the ground. Check that both springs are level and firmly in place. As with all spring assisters, check also that nothing will interfere with their free movement.

Fitting air-cushion springs

There is only one type of air-cushion spring on the British market: the Autoballans. It consists of a hollow ball, made of strong pvc, which is inserted between either side of the rear axle and the bodywork. Fitted with a Schrader needle air valve, it is filled- with air under pressure to provide a simple and relatively cheap form of spring assistance.

Cars with leaf-spring suspension

On cars with leaf-spring suspension, having prepared the car as outlined above, take the Autoballans itself, and start by unhooking the metal outer spring clip from its lug. Now pull it through the inner rubber strap hook and unhook the rubber strap.

The next step is to insert the Autoballans between the leaf spring and the body or chassis, at a point about 15 cm (6in.) from the rear spring fixing.Make sure that the Autoballans, with the heat protector pad attached, is positioned with the pad nearest to the exhause pipe, as shown. If it is nearer than 2 cm, then the pipe will have to be moved farther away (see ‘Fitting coil spring damper’). Next, wrap the rubber strap around the leaf spring and hook it together, holding the Autoballans in place. Follow this by hooking the outer spring around the strap and back on its lug. The extra plastic strap must now be secured around the leaf spring and up against the Autoballans, to hold it in position. Now carefully jack up the hub until the suspension reaches its normal height and check that the Autoballans is not compressed. If it is, then it has been fitted too far back along the leaf spring. At the same time, make sure that there are no sharp protrusions likely to interfere with the ball when it is compressed under load, and that it remains the specified 2 cm from the exhaust pipe. Repeat the above steps for the other side of the car.

The air-hoses must now be fitted. This is done by fixing the valves in holes which you will have to drill in boot cross-members, then connecting these to the rubber hoses from the balls by means of plastic tubing. Start by drilling a 6 mm hole through either side of the boot floor, as close as possible to the springs. Take care not to damage the springs, the petrol tank or any other nearby components. Smooth off the rough edges of the holes with a file to avoid damaging the hoses. Now feed the rubber hoses from the two Autoballans through the holes until they protrude about 5 mm (|in.) and then cut them. Make sure that the hoses will not be pinched or cut in this position when the suspension is compressed.

Next, find two convenient bodywork support brackets at either side of the boot and drill an 8 mm hole in each. Feed the clear plastic tubes, with valves attached, through the holes and then screw the valves tight. Pull the rubber hoses through the bodywork a further 25 mm (lin.) and push the plastic tubes into them, to a depth of about 10 mm (fin.). Finally, push the rubber hoses, which will now have increased in diameter with the plastic tube inside, back through the holes in the boot until they are a tight fit. The roadwheels can now be fitted and the car lowered to the ground. Check that the springs are still in position and not fouled in any way. They can now be inflated to the correct pressure by means of the valves in the boot.This is normally 0.4-0.8 bar (6-12psi) depending on the load to be carried.

Cars with coil spring suspension

The Autoballans can also be fitted to cars with coil spring suspension providing the coils are of a large enough diameter to accept the balls, and there are no obstructions, such as struts, running down the middle of them.

Having supported the back of the car and removed the road wheels, warm one Autoballans in hot water to soften it. Next compress it with your foot until it is flat and pinch the rubber hose to prevent air reentering. Insert it between two coils, halfway up the spring, and use a piece of cardboard to wedge it in place. Repeat this for the other side of the car, and then remove the wedges.

The rubber hoses and air valves can now be connected in the same way as those on leaf spring suspension cars, as described above. Carry out the same checks for fouling, refit the wheels and lower the car. In this case, however, it is important to inflate the Autoballans to a pressure of 2 bar (30psi) for the first couple of days of use. This enables the springs to seat properly and to ‘run in’. Having completed this period, deflate theAutoballans to the manufacturer’s recommended pressure—normally 0.85-1.6 bar (12-23psi) with the car unloaded.

Air adjustable dampers

Airadjustable damper units are similar to the coil-spring dampers already described. In this case, however, the spring assistance is obtained by means of a pressurized air-chamber rather than a simple coil spring. By filling the chamber to various pressures, ride height can be adjusted to suit different loads. The dampers are fitted in the same way as coil spring units, but the two air pipes running from them must then be connected to a common valve box. With an air-line connected to the valve, the dampers can be inflated to the correct pressure.

An advanced development of this idea, which comes in kit form, enables the air pressure, and therefore the ride height, to be adjusted from inside the car. This is done by means of an electric air pump, controlled by a switch mounted under the dashboard. This pumps air to the dampers at the desired pressure. A similar device has also been designed to complement the Autoballans. It connects conveniently to the two valves exposed in the car boot.Unfortunately, although these systems are efficient, they are also complicated and expensive.

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