Mickey2

You might have to take the tension assebly appart then. I could not find a manual showing how to line up the parts correctly for the 360 so I you have to be careful; take pictures of it along the way and make sure they go back together in correct order and in the right way. Tensioners all work in much the same way but they are not exactly the same either. You might even find Pfaff model 360 or close models with a slighly different top tension mechanisms. The tension spring you mention could be slighly off it's mark or it can be broken. It's a standard replacment part, but needs to be the right one for your machine model. It's well withing a DIY repair even if your first tensioner can be a bit cumbersome.

The Singer 400 series is quite sought after and regarded. They very often need a good cleaning and oiling to get their needle punch power back and much the same treatment as suggested for your Pfaff 360; detect all oil points, give it many repeated oil applications, turn knobs and levers, poke the swing arm action manually with your finger tip, run the machine in between, every day for the next week or two (seriously). I know the advice sounds basic but I mean it seriously, the persistant and repeated turns of cleaning and oiling will sort out most problems by far. It's a bargain price for a 403. Congratulations :- )