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Suntour derailleur missing a spring?
#1
Hi all,

I'm new to this forum. I've just started working on getting an old 12 speed road bike that was given to me back into working order. I don't have much experience with bike repairs so I've been learning as I go.

The rear derailleur on this bike is an old suntour derailleur. I couldn't find any model number anywhere on it, even after spending half an hour with a rag and a can of WD40 getting all the grime off it.

I'm a bit confused by this derailleur, because unlike the shimano derailleurs on the mountain bikes that we have in our household, the uppermost pivot point (where the derailleur bolts onto the hanger) does not seem to have a spring in it. So when the derailleur is on the bike it is free to flop back and forth around this pivot point. The chain and the shifter cables were completely rusted, so I've already taken them off, which makes it a bit hard to see how the derailleur is meant to behave under normal circumstances. I thought that maybe the opposing tension on the chain and the shifter cable would keep the derailleur in the right place without a spring in the pivot point, but until I get a new chain and cables and put it all back together its hard to tell.

So my question is - Is the derailleur broken? Should there actually be a spring in that pivot point which is no longer working? And if that is the case are modern derailleurs compatible with old non-indexed shifters like I have on this bike?

Scott
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#2
Pictures would really help...
In general, modern, indexed rear dérailleurs are compatible with non-indexed shifters. Look at how they are attached, not all bikeas have dérailleur hangers, and not all hangers are threaded (old Simplex stuff comes to my mind), but the hanger can be threaded by a bike shop.
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#3
(01-18-2014, 11:16 PM)sgodwin Wrote:  The rear derailleur on this bike is an old suntour derailleur.
the uppermost pivot point (where the derailleur bolts onto the hanger) does not seem to have a spring in it.
So my question is - Is the derailleur broken? Should there actually be a spring in that pivot point which is no longer working?
Scott
Funny you should ask. I just finished servicing mine. Old non-indexed Suntour rear derailleurs DO NOT have a spring in the uppermost pivot point (where the derailleur bolts onto the hanger).
The spring is in the lower pivot, that area retained by a fastener that looks like the upper one you removed, if a good chain was on the bike it would be obvious to you.
Measure the old chain to check for wear, if it's toast, your rear freewheel (sprokets/gears) is too.
I like KMC chains. KMC X8 series, Z8, Z7, and Z33 will give you a tough chain with a "quick" disassembly link. 8 speed chains & below should work.
You could check the old chain to see if it is especially narrow, but I can't imagine why it would be on a 12 speed.
There is a very good chance that a modern 7 speed freewheel will fit. Some here don't like shimano, but I like one model for the ratios. 6 speed version here.
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#4
This is the derailleur.

The pivot point I'm talking about is the one indicated by the red arrow. The lower pivot (blue arrow) has a spring and seems to be in good working order.

I don't really want to spend a lot of money on this bike. My goal is really just to learn more about how to service bikes in general while getting this one up and running so that I can use it as a commuter.

The chain was completely rusted and seized in a few places, but the rear cassette (shimano) looks pretty good. It actually looks much newer than the rest of the bike, so I think a previous owner must have replaced it at some stage.
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#5
First, clean it up, service the idler (jockey) wheels, give the rest a tiny amount of light oil to aid articulation where needed.
Your lower (blue arrow) fastener might not be original IMO. On mine the fastner is an allen head also. But either way, there is NO spring in the top pivot (red arrow). Trust me.
Measure the chain to check for stretch. If it fails, you should replace it AND the rear gears or the slightly worn rear gears will eat your new chain up. Trust me. There again, if you aren't going to ride much, to the store once & awhile etc.. don't worry about it.
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#6
If the chain is properly sized (and you are not in the small-small combo on a triple) there will be sufficient tension from the pulley spring to pull the derailleur forward to the stop on the frame.
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