Saggy Chains and Shimano 600 Parts
I recently inherited a 1980-81 Peugeot bike from a family member. The thing is in stellar shape except for one annoying little detail, which is that as soon as I pedal backwards the chain sags alarmingly between the rear cogs and the chain ring. To make it even more obnoxious, about one out of every four times I stop pedaling it feels like to rear cogs/freewheel continue to kick or grab and the chain sags and jerks back and forth. If I put it on a stand and turn the cranks, as soon as I let the rear wheel just spin I can watch my chain jump around and my rear derailleur extend and retract as the drive train alternates between spinning free and grabbing.
So far I've tried adjusting the derailleurs and messing with the chain tension. There's no B-tension screw on Shimano 600 derailleurs, or at least I can't see it, so I removed two links from the chain. It got better, but no so much better that I'm excited to ride the thing while I listen to the chain rattle around.
Is it a chain tension problem? Is the free wheel acting up, or does it sound like the rear derailleur is binding? Any help is greatly appreciated.
Check the derailer pulleys.
Clean the innards of your freewheel. 99.99% of the time that's what causes chain droop when back peddling or coasting. Most of the time taking it off and drooling light oil in between the inner body and outer part that has the chainwheels on it will loosen it up. They are a PITA to take apart and get back together - spring loaded ratchet pawls are the hard part and there may be a jillion tiny loose balls inside.