You might as well order a tensioner and shock with your belt. I got mine from Phill at fast lane . I have a 1992 300-E . When a friend of mine replaced the belt the first time , we found after that the tensioner was bad and the tension started to slip. We had to reinstall the belt no damage but with a new tensioner

I do not know what model and year you have . I would highly recommend you look up the proceeder for your model and year. Buy the way on my car you have to remove the fan shroud and the Visous fan first to get at the belt and tensioner. IT may be a good time to replace or check the visous coupler on your fan if it has to come out. Why do the job twice.

Bob Geco