Steve,
I had that problem recently and in my case it was because the spring had come off on one side. I posted a detailed repair w/pics -- if you have the same issue.
http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,viewtopic/t,369161/sid,1fd6320f3800433ce9ff5fd91a730f1e/
Byas