A SHOCKINGLY GOOD TIME
Shock absorbers are a major safety component of any car, although they do not support the weight of the vehicle they are vital to the suspension system and control suspension movement.
It is a common belief that shocks are there only for improving the vehicle’s ride and handling, they do however also keep the tyres on the road surface. A car’s ability to steer, accelerate and brake are all down to the friction between the tyre and the road surface, shocks help to maintain vertical loads placed upon the tyres by providing resistance to vehicle bounce, roll and sway.
If shocks become worn they can lead to excessive weight transfer from front to rear and side to side, this will reduce the gripping ability to the road surface and consequently handling and braking performance is reduced.
Escort shocks come in two types, either the usual hydraulic (oil) dampers or the increasingly more popular gas dampers.
Hydraulic (oil) Dampers
Hydraulic dampers are based on a twin tube principle. The inner tube, also known as the working chamber or pressure tube, and the outer tube, also known as the compensation tube or reserve chamber.
As the car moves over an uneven road surface the shock is continually working, as it becomes compressed the fluid contained in the inner chamber is displaced by the piston rod and enters the reserve chamber via a back pressure valve, as the rod move upwards the oil is sucked back into the inner chamber. Adjustable shocks allow the back pressure valve to be adjusted to increase or restrict the amount of fluid which is displaced and thus leads to the stiffness or softness of the car’s damping rate. The disadvantage of this type of hydraulic damper is that the pressure change caused by piston movement leads to the fluid foaming and subsequent cavitation when subjected to permanent load, also the twin tube design leads to fluid heat build up which results in a reduction of shock performance and deterioration of the cars handling and ride.
It is commonly assumed that a gas damper uses gas as a replacement to oil, but in reality the damping still occurs via a column of hydraulic fluid. The gas ( nitrogen ) is separated from the fluid chamber by a dividing piston and is at a pressure of approximately 300 psi.
These shocks operate the same way as hydraulic dampers by passing oil through a fixed hole. The gas chamber enables the dividing piston to move towards the gas chamber, thus reducing its size, when the piston rod is returned, the oil chamber enlarges and the compressed gas chamber presses the dividing piston back into its starting position. The high pressure in the gas chamber is transmitted into the fluid column by the dividing piston and prevents any foaming and cavitation as experienced by non gas shocks. As the shock is designed with a single chamber it allows the fluid to come into contact with the outside wall of the tube rather than in an inner chamber which results in better fluid cooling properties.
Gas dampers result in an optimum damping performance under all operating conditions.
Worn shocks can be fatal so it is worth checking them out every 12,000 miles and here’s the test for doing it.
By walking around the car to each corner, bounce the car up and down several times, when released it should bounce twice. If the shocks are good there will be no more than two bounces from them. If, on the other hand, there are then it means the shock is worn and should be replaced.