Checking the shock absorber (Mercedes-Benz S-Class W126)

Note: The models in question can use gas shock absorbers with or without separator pistons. In gas shock absorbers with separator pistons between the gas and oil chambers, the piston rod is located at the top of the shock absorber, while in shock absorbers without separator pistons, it is located at the bottom of the shock absorber.

A knocking noise coming from the rear shock absorbers may be caused by the following reasons:

The upper shock absorber mount cushion is not installed correctly.

The rubber cushion of the lower shock absorber mount has come loose.

If there is significant oil loss, the separator piston may begin to hit the piston rod.

The working piston has become disconnected. Press the rod, release it and then press it again. If a knocking sound is heard when switching from the compression cycle to the rebound cycle, the shock absorber must be replaced.

Hissing sound from rear shock absorbers:

If the balance piston is not well sealed, gas can penetrate into the oil chamber, forming foam there, the presence of which is indicated by hissing sounds when driving. This defect requires replacement of the shock absorber, even if it still functions normally.



Checking shock absorbers removed from the car (front and back):

Remove the shock absorbers.

Carefully inspect the rods for surface damage.

Check the rods for bending. To do this, lay out the shock absorbers on a wooden surface in the order in which they were installed.

Insert the rods one by one. A bent rod will inevitably get stuck in the guide bushing.

Note: The thin film of oil on the piston rod is a factory issue.

Holding the shock absorber in its working position, slightly stretch it and then compress it. A serviceable shock absorber in both cycles gives a smooth, even ride without jamming.

If there are signs of oil leakage, the shock absorber must be replaced.

Checking the oil reserve:

To check the oil reserve, measure the piston rod clearance (a). When oil is lost, this clearance increases for shock absorbers with separating pistons, and decreases for shock absorbers without separating pistons.





During this check the shock absorber temperature should be approximately 20°C.

Note: A thin film of oil on the piston rod is a factory occurrence and is not a sign of an oil leak.

Remove the rod and place it upside down on a flat surface.

Shock absorber with equalizing piston: press the rod so that the stop on the working piston reaches the separating piston. Measure the gap (a) and compare it with the specified value.

Shock absorber without separating piston: compress the shock absorber until a clearly defined resistance is felt, indicating that the piston has entered the cavity with oil. Holding the shock absorber in this position, measure the gap (a) and compare it with the specified value.

The picture shows two rear shock absorbers, the first of which (1) is made by Fichtel&Sachs, has markings of one or two transverse white lines. Shock absorber (2) (produced by Boge) marked with an oblique white line.

Caution: The hissing sound that may be heard when the shock absorber is compressed is not a sign of any malfunction.

Shock absorber	Clearance "a" of piston rod, mm
	new	permissible max value
With separating piston front and rear	0±2	32
Without separator piston front and rear	20±2	0
Fichtel&Sachs	105±2	82
Water	147±2	137

Note: A shock absorber with a separating piston must be replaced if the maximum permissible value of the "a" value is exceeded, and a shock absorber without a separating piston - if the gap "a" value does not reach the maximum permissible value.

Further testing of shock absorbers requires special equipment and can only be performed at a service station.