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
