This kit replaces the forward differential mount bushings - known as the pinion mount bushings. The OEM units are soft rubber and break down fairly quickly with that wear accelerated the harder they are used. The worn bushings allow more movement of the rear differential under changing loads.This can intially be felt behind the wheel as slower and sloppier responsiveness, and as the OEM bushings near the end of their life or fair it can be accompanied by noise, vibration and secondary movements under changing loads - especially as you get on the gas and come back off of it.SuperPro's differential mount upgrades maintain OEM levels of noise, vibrations and harshness isolation in the cabin so your car maintains the new factory levels of comfort. At the same time performance is significantly improved with the differential more accurately located under a wider range of conditions and the service life dramatically improved with our materials maintaining peak performance throughout their life rather than slowly softening and degrading like natural rubber