When propshafts on cars or light commercial vehicle driveline systems fail or are damaged, workshops frequently turn to expensive replacement parts supplied by the vehicle manufacturer. The main reason for doing so is often that it is difficult for repair shops to assess the different quality aspects of a propshaft. Driveline specialist GKN Automotive, the world’s leading OE supplier of propshafts, makes life easier for workshops by offering only OE-quality propshafts via its Aftermarket company GKN Driveline Service.
Professional quality assessment saves time and money
To ensure a reliable repair, the first step is to conduct a sound assessment of the quality of any given propshaft. The rotational forces are just one part of the dynamic forces exerted on a propshaft. The transmission and the differential casing on the drive axle are in constant motion while the vehicle is traveling, which means the longitudinal spacing and diffraction angle are changing all the time. This is particularly so for unsprung differentials, which are frequently used on the beam axles of light vans or all-terrain vehicles. The latter may also be exposed to high impact loads, i.e. these types of vehicles are more likely to suffer propshaft damage. The shaft joints and couplings must also be carefully configured for the usage conditions in order to ensure reliable and long-term functionality.
As well as inspecting joints and couplings during replacement, attention must also be paid to the shaft itself. The weights of many propshafts on offer do not meet technical specifications. A weight higher than that of the original brings several disadvantages. Higher weight subjects the bearings fastened to the vehicle underbody, and which guide the propshaft, to excessive loads. Not only can this lead to premature bearing damage, it can also change the vibration characteristics and generate noise.
Thanks to the latest production processes, GKN Automotive not only exactly fulfils the weight requirements, it also ensures exceptionally smooth running characteristics. Over the last ten years, this has resulted in a reduction of 78 percent in the use of balancing weights, which are attached using a high-precision process. The general need for weight reduction in vehicle engineering is also leading to propshafts themselves becoming considerably lighter. Designing weight-optimised shafts to run quietly and reliably places even higher demands on engineering and materials, i.e. in modern vehicles, compliance with the aforementioned quality features is the main prerequisite for being able to carry out a repair in the first place.
Ballspline technology further improves crash safety
Another important aspect that is often overlooked when it comes to propshafts is crash characteristics. For instance, a higher weight resulting from different wall thicknesses on the shaft tubes can alter the stability of the propshaft in such a way that the higher accelerating masses are transferred undamped during a crash. This may compromise the shaft’s compression and pre-set breaking characteristics. The potential consequences are that, in the event of an accident, passengers may be subjected to far higher forces, including, in a worst-case scenario, possible penetration into the vehicle interior. Existing safety measures can be further supported and passive safety enhanced by GKN Automotive’s ballspline technology. A characteristic of the ballspline is a longitudinal ball-bearing arrangement (see cross-section in image 1), which enables long, fast-responding plunge travel for shortening the shaft.