Posted 31 August, 2021 at 11:00
Dictionary of popular suspension errors: Part 1
Is it necessary to pump 2-pipe dampers before installation? Does the air suspension bellow tear when lifting vehicles with the engine running? What helps against the notorious “morning sickness”? A lot of half-knowledge is circulating around the topics shock absorbers, air suspension etc., which has long since been part of the “Dictionary of popular suspension errors”. This book is still purely fictional, but in the opinion of the BILSTEIN Academy, the first entries could be as follows.
Sometimes the information is spread that it is absolutely necessary to “pump” 2-pipe dampers before installation in order to vent them. This is a misconception! The fact is: 2-pipe shock absorbers are installed in vertical position or up to a maximum of 45° inclination, but stored horizontally at the dealership. However, this “change of position” has no relevance for the installation and the so-called “pumping” is unnecessary. If there is still not enough oil in the inner tube/working tube after installation, this is not a problem at all. 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 a simple tip: Simply remove the shock absorber from the packaging and install it. The same applies to the so-called “morning sickness” with 2-pipe shock absorbers. 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.
The subject of air suspension is also a story full of misunderstandings. 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 Popiol reassures: “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 is therefore not loaded by overpressure. 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.