Jay, the tensioner assembly has an inner and outer sleeve. The outer sleeve is attached to the tensioner pully. The inner sleeve is secured to the tensioner bracket by that BIG nasty bolt in the middle. There is a small amount of space between the inner and outer sleeves that is filled with a rubber compound not unlike that found in control arm bushings. This rubber is vulcanized to both of the sleeves. When you are cranking the tensioner bolt. you are putting a load on this rubber and this is what keeps the tension on the belt via the pulley. This is the part of the tensioner that is most important in keeping tension on. When the rubber separates, time for a new one. The shock is there to absorb harmonic vibrations only.
1987 BMW 325