I just replaced all 5 V belts on my 87 420sel. The reason I replaced the belts is because the belt closest to the engine of the two belts for the PS pump/water pump was loose compared to the other one. But after I replaced the two belts on the PS pump (with Conti belts) and set the outside belt tension the inside belt is still loose compared to the outside belt. It makes good contact but is not as tight as the other belt. Is this normal?

You're gonna love this job. Try this: loosen the PS pump and swap the two belts. Move the inside belt to the outside location. Re-tighten and see if you have the same problem or if it has moved with the belt. If the problem moved with the belt, one belt is longer than the other. If the problem did not move, you have one of three problems. First possibility is that one pulley is worn. This does actually happen. The belts of course actually ride on the sides and sometimes the sides will wear enough that the belt will ride futher into the pulley. Other possibility is that the pulleys are not properly aligned with each other. More to the point probably the PS pump is a bit cocked compared to the other pulleys. Often there will be wear on the pivot bolt or in the bolt hole and that will throw off the alignment. Son had an alternator with severe wear on the pivot and we could not keep belts on it. Had to replace alternator to fix. Third possibility is that the bearings in the water pump are going and allowing the shaft to "bend" in towards the other two. Once again, the alignment will be off. Hint: mark ONE belt with white-out or something so you can remember which is which. It's easy to get confused. Since you seem to have the belt closest to the engine loose, I'm gonna guess that if the belts are the same, you have a worn pulley-probably at the water pump. I think it was the weakest metal.

Thanks Bob. I'll check out the PS pump aligment. If thats not the problem, then I've got a new water pump thats been sitting in a box in the garage for the last six months. Maybe this will motivate me to finally install it!