401A Tension Problem - Overfilled Bobbin
 

I filled the bobbins until they bulged a little bit, and while other machines had no problem with them, in the 401 they made me first have a too tight bobbin thread, and then a few minutes later, the top thread was too tight. I remember someone else having this problem, and I may have just figured it out.

Thanks for posting this. I've occasionally had tension problems with my 503 and once on my 401. It seems as if the tension is too tight (or too loose), and I give up on figuring out what is wrong after threading and rethreading and adjusting the top tension. Then, the next day it's fine. I almost think I imagined it. It's probably happened 2 or 3 times on the 503, which is very similar to the 400 series.

I'm not sure that's the problem I had, as you can't overfill the bobbin on the either of them. By that, I mean it can't fill past the outside edge of the bobbin as it stops filling automatically. I finally adjusted the bobbin filler on the 401, because the it had to be filled too often. I have contemplating adjusting it again to reduce the times I have to fill it.

I'll follow this thread to see if you get any answers.

bkay

Bkay depending on the adjustment the bobbins can be over filled as well as under filled. Also, tension issues on any machine can happen from a bobbin that is filled too tightly or too loose.

Cari

So, how can you control loose/tight? Obviously, by not running the thread through the tension guides, you could make it too loose. How else could you affect it?

bkay

By not threading the machine properly for winding a bobbin, winding a bobbin too fast, winding an uneven bobbin, the bobbin tension guide having a worn spring or the spring not being tight enough. On one of my 301s the spring is actually missing from the bobbin tension guide. I hold onto the thread with my fingers to give it tension while winding a bobbin.

Cari

The only time I have had this problem with my 401A I had some how sprung the bobbin holder and had to get a new one. When I got the new one it has always worked perfect. Be sure to thread the needle from the front toward the back or it will tighten up and break every time.