How To Checking And Test A Damper Units

How To Checking Damper Units

Here you can get Checking and Test a Damper units.

Almost all modern cars have hydraulic telescopic dampers in their suspension systems. Where the front suspension system is a MacPherson strut , the damper is made into the strut or leg that supports the wheel-hub assembly (See How car suspension works ).

To inspect the condition of telescopic dampers, loosen the wheel nuts, jack the car and support the chassis on axle stands in order that the wheels hang free and therefore the dampers are extended. Remove the wheels.

How front dampers are attached

The front dampers could also be attached to their mounting points at each end by a pivot bolt through a bushed eye. Alternatively, each end may have a threaded pin passing through the mounting bracket. Or there could also be an eye fixed and bolt at one end and a threaded pin at the other.

The upper mounting of a MacPherson strut may be a pertaining to a rubber-bonded block, fixed to a plate bolted to the body. The lower end features a ball swivel joint. With coil-spring parallel-wishbone front suspension, the damper is typically inside the coil spring. The spring is located rigidly within the lower wishbone, and passes through the upper wishbone to a mounting on a chassis outrigger.

Checking for damper leaks

The dampers are filled with a special oil, which provides the damping effect. The piston and rod moving up and down inside the strut forces the oil through narrow passages, which slows down the oil transfer. This restricts the up-and-down movement of the car suspension. The liability of a damper is that the gland seal around the a part of its body where the piston rod moves up and down. it’s not unusual for this gland to fail, allowing oil to flee.

Oil leaks leave a dark stain within the road grime that collects on the damper and on its mounting points. If there are any signs of a leak, renew the damper (See Fitting new dampers ). On a car with MacPherson struts, look around the lower parts of the dampers for dark oil stains. a new damper insert are often fitted (See Renewing MacPherson-strut inserts ). Always replace dampers in axle sets (pairs) to make sure uniform suspension damping on each side of the car.

Checking for damage

Inspect each damper casing for signs of damage caused by flying stones or deep rust. Slight dents might not be too serious, but investigate a deep one further, preferably by taking the unit off the car for close examination and testing during a vice (see Bounce test). Look also at the connecting rod. it’s going to be hidden by a rubber dust cover, which may be pulled back. Check the rod for signs of scoring, pitting or rust. If you discover any, replace the unit, or it’ll damage the piston oil seal.

Wipe the damper clean and check the rubber bush at the bottom of the unit. search for signs of injury , perishing, cracks or distortion. Grip the lower body of the unit and check out to maneuver it backwards and forwards, and twist it about its mounting bolt. If the rubber bush is in fitness, there should be no movement. Check the upper-mounting bush within the same way. If the upper mounting may be a pin, check the condition of the rubber discs.

Look also at any upper mounting on the inner front or rear wings. you’ll need a torch or inspection lamp. Weakening of the turret top during which the damper is fitted is common. Reinforcing plates are often welded, but this is often a job for a professional. If you discover any worn or cracked rubbers, replace them.

Replacing rubbers

Remove the unit from the car. An eye-type bush could also be in two halves (one fitted at each end) with a steel sleeve through the center. After coitus interruptus the old bush, lubricate the eye with soap solution and fit one half of the bush with the steel sleeve inserted. Push within the other half as far as possible, then force the bush into place by squeezing from both ends during a vice.

Some eye bushes are in one piece. With the old bush still in place, take a socket with a diameter large enough for the entire bush and place it during a vice on one side of the eye. Place the new bush on the other side and squeeze with the vice to push the old bush into the socket because the new one is forced into the eye. With pin-type fittings, place the rubber discs over the stem of the unit within the same sequence because the old ones. Note where spacers and washers fit.

Checking lever dampers

A few cars have front-mounted lever dampers that also serve as the top link of the suspension. Disconnect the damper arm from the suspension. Move the arm slowly up and down. To test the damper action, first disconnect it from the suspension (See Replacing lever-arm dampers ). Move the damper arm slowly up and right down to feel if there’s firm resistance in both directions. Replace if defective (See Replacing lever-arm dampers ).

How to test a damper

A bounce test may be a quick, rough way to check if the dampers are working properly. roll in the hay at each service, or if the car seems to be wallowing or riding oddly. Dampers can weaken or lose all effect, in order that the car bounces wildly; or they will seize , in order that the suspension moves little or not in the least . A bounce test will reveal serious faults, but only a garage with special test gear can detect a small weakness during a damper. to hold out a bounce test, inflate the tyres to their correct pressure and take away any load from the car. Drive on to level ground and apply the handbrake.

Stand at one corner of the car, put both hands on the body and down sharply – hard enough to form the suspension hit its bump stop. Keeping your hands in situ , let the car rise, then directly down again. Repeat three or fourfold , then at rock bottom of a push let go and watch what happens. The car should rebound once or twice, then settle at or near its normal ride height. If it bounces more, suspect a weak damper. Repeat the test at an equivalent corner, listening for the scraping or creaking noises that confirm a faulty damper; look it over for leaks or other damage.

If you discover it difficult or impossible to push the car down, suspect a seized damper – generally caused by a bent connecting rod inside. Replace a seized damper. Test at each corner of the car. then mentally compare the results for the four dampers. If one corner feels different from the others, the damper there’s probably faulty. If the fault isn’t a leak, remove the damper from the car and clamp it during a vice. Pull it up to its full extent, then compress it fully several times It should resist evenly in both directions. Unevenness could also be thanks to a coffee fluid level, a faulty valve or air inside the unit. Air gives a spongy feel to the movement. to get rid of air, leave the damper for a couple of minutes to let the air rise. Then push the damper right down and depress it a couple of short strokes followed by a couple of slow, full strokes. If, after this, the damper still feels uneven, fit a new one.

How rear dampers are attached

Rear dampers are attached at rock bottom to brackets on the axle casing, or to where the spring is seated. The fixing is usually a bolt or stud through the rubber-bushed eye. At the top, the dampers are attached to a bracket or mounting point within the floor pan or the inner rear wing. Top mounting points are sometimes hidden in turrets within the inner bodywork, and you’ll need to consult a service manual for the location and type.

If the car has pin-type upper mountings, the rubber discs where the pin passes through could also be on either side of the metal bodywork. Check each side of the mounting plate. To check the top side of an upper mounting, you’ll need to remove trim panels within the boot or, during a hatchback, the car interior trim.

Inspecting rear mountings

Rear dampers with pin fittings at the top are usually fixed through the inner wings, either through reinforced areas or through the top of a turret within the bodywork. Turret-mounted dampers are often found on cars with coil-spring rear suspension, when the turret also locates the spring. To check the tops of the mounting, open the boot or hatchback lid and appearance at the rounded outer side of the wheel arch. The mounting point is usually easy to see. Check the threaded end of the pin for damage (which will make removal difficult), for the tightness of its one or two securing nuts and – most important – for the condition of the rubber disc under a nut.

To inspect the underside of the mounting, loosen the wheel nuts, jack up the rear of the car, support the chassis on axle stands, and take away the wheels. Use a torch to examine an upper pin-type mounting beneath a domed turret on the wheel arch. Use a torch or inspection lamp to examine the condition of the rubber disc and therefore the condition of the metal at the top of the turret. At an equivalent time, use the lamp to see the lower a part of the damper and therefore the lower mounting.

How to check a displacer unit

Cars fitted with hydraulic suspension systems make use of fluid under pressure to supply the springing effect. At each wheel, there’s a displacer unit – a piston with a sealed cylinder that takes the place of the spring. Frequently the units on all sides of the car are connected front-to-back by high-pressure piping, to supply the specified suspension characteristics. In other installations, the inter-connections are across the car – nearside rear to offside rear and nearside front to offside front.

Often, the displacer units also act as dampers, otherwise they’re assisted by hydraulic dampers, which should be checked within the same way as dampers on the other car. Because the suspension relies on fluid under high pressure, it’s essential to find any leaks within the system and have them rectified immediately. Otherwise, either one or each side of the car will sink to the rubber bump stops, with a loss of suspension movement. If this happens, it’s usually possible to drive the car very slowly – maximum 30mph – but it should be taken to a garage for repair as soon as possible.

Sometimes re-pressurising the system will restore its proper function, but this work must be done by a garage equipped to undertake it.
Measuring the ride height of the car will reveal a drop by the suspension. The ride height of the car gives an honest indication of the condition of the suspension. the right height is given within the car handbook. Inspect the displacer units and associated pipework during routine servicing, or at the intervals recommended within the car handbook.

On some cars, the front displacers are within the engine compartment. On others, they will be seen only from underneath the car. The rear displacers can usually be seen and reached from underneath. Jack up both ends of the car on one side and support them on axle stands, with the handbrake firmly applied and therefore the other wheels chocked. The work is easier if you remove the wheels to urge a clear view. Follow the lines of the hydraulic pipes. search for leaks at the pipe unions and for signs of damage caused by flying stone or pipes rubbing against any components.


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