Description Reviews The MINI Cooper Belt Tensioner Shock keeps the tensioner from bouncing around on your belt and gives it a smooth operation. This part is a high failure part and until now, you had to replace the whole unit. It might still be a good idea to replace everything if it is original to get a new pulley with fresh bearing, but if it is rather new, a new shock is a great option! If you do not have the proper tension, your belt could slip or wear unevenly. It is very common on the Gen 1 MCS models for the small shock to lose its oil over time or for the bushings on the shock to come out. If any of this happens, the belt tensioner loses its grip on the belt, which can result in belt slippage. This belt tensioner shock is almost the same as the OEM one, but is an aftermarket unit. Hopefully it will be proven to last as long as the original but it helps save the customer money!