Main Drive Belt, 6PK1555, OEM - E36, E34, E39, Z3, M50, S52

The main drive belt runs the water pump, power steering pump, and alternator on the M50, M52, S50, S52, and some M52TU and M54 engines. It's very important not to neglect your drive belts as a failure will leave you stranded. They're easy to inspect during normal maintenance such as an oil change or refilling your washer tank. If there are cracks running across the ribs, sections missing, the edges are frayed, or the threads are visible on the belt surface, the belt should be replaced immediately.

If you can, inspect and test the pulleys before ordering your belt(s) - tensioner, idler, water pump, and power steering. Also test the belt tensioner at the same time. Or plan to order new pulleys and tensioner with your belt(s). These pulleys are made of plastic and shatter with age, causing potentially expansive/expensive damage to your engine, radiator, etc. They usually last longer than the belt but now is the best time to replace them. Since they are bolted on, not pressed, they are easy to replace.