The BILSTEIN Academy is seeking to clarify technical misunderstandings

Is it necessary to pump twin-tube dampers before installation? Does the air suspension bellow tear when lifting vehicles with the engine running? What helps against the notorious “morning sickness?”
BILSTEIN says a lot of half-knowledge is circulating around the topics of shock absorbers, air suspension and so on, which has long since been part of the “Dictionary of popular suspension errors.”
This ‘book’ is still purely hypothetical, but in the opinion of the BILSTEIN Academy, if it were real the first entries could be as follows.

Pumping twin-tube dampers
BILSTEIN says sometimes information is spread that it is absolutely necessary to “pump” twin-tube dampers before installation in order to vent them but that this is a misconception.
It states the fact is that twin-tube shock absorbers are installed in a vertical position or up to a maximum of 45° inclination but stored horizontally at the dealership.
However, it says this “change of position” has no relevance for the installation and the so-called “pumping” is unnecessary. It states that if there is still not enough oil in the inner tube/working tube after installation, this is not a problem at all, as when the shock absorber starts “working” later, it sucks in the required oil itself.
That’s why Rainer Popiol, head of the BILSTEIN Academy, offers the following simple tip: simply remove the shock absorber from the packaging and install it.

Morning sickness
The same applies to the so-called “morning sickness” with twin-tube shock absorbers.
BILSTEIN explains that this phenomenon is based on the fact that the shock absorber oil cools down overnight, thereby reducing its volume. As a result, it contracts, so that in the end there may be too little oil in the inner tube.
The movement of the piston rod / working piston, however, quickly sucks in supply through the bottom valve and compensates for the deficit. If the oil warms up, the volume also increases again quickly.

Air suspension
The subject of air suspension is also a story full of misunderstandings, says BILSTEIN, which explains that one popular theory is that when vehicles are lifted with the engine running, the air suspension bellows are pressurised until they burst; at least if the workshop mode has not been activated. But Rainer says this is not the case.
“Many workshops or inspectors anticipate a problem here that does not exist in this form at all. It is correct that in the case described, air is rather let out and the bellows are therefore not loaded by overpressure,” Rainer said.
“Strangely enough, the opposite problem occurs in reality: there is a risk that the vehicle is deflated onto an unpressurised or at least partially deflated air spring. In this case, the component can indeed be irreparably damaged.
“The BILSTEIN tip: if the vehicle has a jacking mode, use it on the lift. If this is not available or was forgotten during lifting, the air spring should be filled with a suitable diagnostic device before lowering.”

For more information, visit www.bilstein.com

Photo: Copyright BILSTEIN 2021.