The 1987 through 1999 BMW 3 Series convertibles utilize a fabric tension strap to pull the top back when you are putting the top down. These tension straps can wear out, effectively losing all of the tension, over time. So how do you know when it is time to replace your tension straps?
When opening your convertible top you should not have to push the rear window section down by hand. Although you cannot see them without removing the top or headliner, there is a pair of nylon tension straps that pull tighten together when open the top, which allows the rear window bow to retract enough so the window and rear of the convertible top clear the top lid without you have to do anything by hand.
These tension straps will lose their elasticity over time or the front or rear loops may break. A good time to install new tension straps is when your are replacing your BMW convertible top.
Although it may be possible to reuse your existing tension straps, we highly recommend you purchase new straps when replacing a convertible top for the BMW 3 Series. Used tension straps are subject to stretching over time and will wear out faster than your new convertible top.
Replacement straps are relatively inexpensive and can only be accessed by removing the headliner and top so it can be a good idea to get new ones.