I replaced both belts. This is a tricky repair to adjust even though it is relatively simple to install the belts themselves. Here is what I learned the hard way: both belts will seem too loose when you replace them. If you have the front of the machine elevated (as you must) the motor, which is on a spring loaded track, will move towards the back of the machine and tighten both belts. When you make the adjustment on the pump belt (the lower one) as described in the instruction sheet, it will be too tight. The reason being that the motor has drifted towards the rear with the elevation of the machine. If the pump belt is too tight, it prevents the drive belt from engaging enough to turn the spin cycle. Also the machine needs to be level or slightly downhill towards the front of the machine for the same reason. This is a really well-built yet simple machine (which is why it is still working after 24 years) but the belt adjustment is dependent on the slackness of the pump belt allowing the drive belt to tighten enough to function.