Chain comes off the rear small sprocket on back peddling?

[elmore leonard]

The chain comes off my rear small sprocket on back peddling. The bike rides good other wise.
I have noticed other riders on the side of the road with the same problem. Without a wheel wrench it is quite hard to free up and put back onto the gear cluster. What causes this malfunction?

[Painkiller]

(04-05-2015, 08:34 PM)elmore leonard Wrote:  The chain comes off my rear small sprocket on back peddling. The bike rides good other wise.
I have noticed other riders on the side of the road with the same problem. Without a wheel wrench it is quite hard to free up and put back onto the gear cluster. What causes this malfunction?

most common culprit is rear derailleur out of alignment

[nfmisso]

followed by RD H limit not adjusted correctly.

[elmore leonard]

(04-05-2015, 08:50 PM)painkiller Wrote:  

(04-05-2015, 08:34 PM)elmore leonard Wrote:  The chain comes off my rear small sprocket on back peddling. The bike rides good other wise.
I have noticed other riders on the side of the road with the same problem. Without a wheel wrench it is quite hard to free up and put back onto the gear cluster. What causes this malfunction?

most common culprit is rear derailleur out of alignment

Thanks for the replies. The chain is bunching up just before the rear gear cluster when back peddling. The bike is very nice and I have ridden it for a couple of years. I'll post a pic. The derailleurs are old Suntour and they may have be mismatched previously. I think I will change both of them out to something newer.

[nfmisso]

I'll take the Suntour derailleurs.  Those are better than the new stuff.  May need a bit of refurb though.

The upper and middle pictures show some issues with chain length AND/OR a tired spring in the RD.

[elmore leonard]

(04-06-2015, 02:41 PM)nfmisso Wrote:  I'll take the Suntour derailleurs.  Those are better than the new stuff.  May need a bit of refurb though.

The upper and middle pictures show some issues with chain length AND/OR a tired spring in the RD.

when I'm in the smallest rear sprocket the derailleur hits the frame of the lower drop out arm.
Which spring is the RD? Can you buy replacement springs at a good bike shop?

[nfmisso]

It is the spring inside the rear derailleur (RD).  Bike shops rarely stock parts for old RDs, unless it is a very specialized vintage store.  After taking the RD apart, the problem spring can be identified and a suitable replacement found (industrial supply sources - not bikes) or fabricated (not that difficult if you have the tools and patience).

[elmore leonard]

(04-06-2015, 03:52 PM)nfmisso Wrote:  It is the spring inside the rear derailleur (RD).  Bike shops rarely stock parts for old RDs, unless it is a very specialized vintage store.  After taking the RD apart, the problem spring can be identified and a suitable replacement found (industrial supply sources - not bikes) or fabricated (not that difficult if you have the tools and patience).

thanks Nigel.