Originally Posted by
gyozadude
If the problem arose before removing the spring, then that would indicate the spring had already failed and it is still inserted in there and not doing its job. So you need to go re-examine it and see if it's in the right holes, or if it's cracked. The RD has an unmistakable orientation. If you put back the spring and the pulley arm isn't tight to the main body and does not require strong fingers to pull down, then the spring is not working for you and that's still your problem. The chain is a secondary issue.
I'm not saying that the chain might not have caused the issue, because cross chaining with too short of a chain can bust up RDs and snap the spring. So you may need to fix multiple issues: a) you cross chaining, b) lengthen the chain, c) RD pulley arm spring.
The mounting bolt spring, which you are talking about, works 100% and is not broken. The cage pivot spring however, I believe is either broken or missing a vital screw. I may just take the thing in to my bike shop to both compare with the 105RDs they've got and for any advice they can provide. I am sure hands on diagnostics is a lot easier than over the line.
@Fietsbob, I appreciate that you are helping make this a lively thread and thank you for that.. but if you aren't going to help actually diagnose and or repair/replace what the problem is then please go tell somebody else to go out and buy a new derailleur. kthx