BMW – How To Properly Install Driveshaft Flex Disc (Giubo)
The flex-disc (also known as universal joint or giubo or guibo) is a flexible rubber disc that connects the transmission output flange to the drive-shaft input flange. The flex-disc absorbs drive-train vibration and backlash. All of the engine’s torque must be transmitted through the flex-disc before it can run through the drive-shaft, differentials axles and finally to the wheels. The flex-disc lives a tough life and due to this it does eventually fail and require replacement. Common symptoms include a drive-line vibration, that may increase in intensity under acceleration and/or drive-line thumping. In inspection, there should be no cracks or bulging of the flex-disc. Any cracking or bulging indicates a failing flex-disc and replacement should be planned.
When replacing and installing a drive-shaft coupler flex-disc, there are specific guidelines to follow. We often find that DIY-ers as well as technicians, install the flex-disc improperly and this results in a premature failure of the new flex-disc (remember all that engine torque being fed through the flex-disc). In general, there are two main types of flex-discs. We’ll call them the flat-type and the doughnut-type.
Finally, when replacing any flex-disc, and especially one that has been run to the point of destruction, you should replace the driveshaft centering guide bushing. This is a small bushing that is pressed into the “nose” of the driveshaft. The bushing fits snugly over the end of the transmission’s output shaft and centers the driveshft (the flex disc just transmits the torque). If the guide bushing is worn the shaft may still vibrate after installing a new flex-disc.
The flat-type flex disc must be oriented so that the molded-in arrows on the outer circumference of the disc are pointing toward the transmission flange “fingers” and the drive-shaft flange “fingers”. If installed in any other orientation, the flex-disc will quickly self-destruct.
The doughnut-type flex disc will typically have a thin metal band around the circumference of the disc. The disc is installed (no reference points as with the flat-type) and the band is cut and removed after all of the bolts are installed and the nuts are tightened.