Bicycle Mechanics - Bizarre rear derailleur...

Hey all.

I've been working on bikes for a couple years, including doing some complete overhaul of a few older bikes, but this one has me stumped.

My sister's former college roommate just settled permanently in this area and had her bike shipped up from home. Rather than having a bike shop put it back together after it shipped, she asked me if I could do it. No problem, I figured, probably just have to put some handlebars on.

Anyway, got the bike, took it out of the box, and the chain was twisted. Broke the chain down, fixed the twist, and noticed that the rear derailleur is weird. It looks pretty cheap and is simply labeled "SIS". The frame has no derailleur hanger on it. Rather, it has a plate that is screwed onto the rear dropouts, and the RD bolts onto the plate about inches below the dropout. I through the wheel on and there is literally no spring tension on the derailleur. It just flops lazily down beneath the bike with the pulleys below it, equally limp. There is not b-screw on the derailleur to adjust.

Anyone dealt with something like this before? I'll try to get some pictures up later....

Thanks for the help,
Nick

SIS is Shimano.

"SIS" implies a Shimano derailleur but this sounds like it's been badly abused. The twisted chain is a good indicator something serious happened to the bike.

Pictures and more info on the bike, number of cogs and any component names you can find would help a lot.

Also, the "hangerless" jobs are the cheapest possible models, normally put on very inexpensive bikes. It may be better to pick up a better but still low-end DR.

Found TY-22 stamped on the back of the derailleur... It sounds like this indicates a Shimano Tourney derailleur. 6 speeds. And I was wrong, there is pretty strong spring tension on the derailleur, it's just that it's pulling it the wrong direction, i.e. down and back instead of up and forward. Hmm... I'll try to get a picture up in a little while.

Yeah, no hanger = el cheapo.

Many of Shimano's (and others') newer derailleurs have a "top-normal" setup that Shimano claims is better. Reviews seem to confirm that it may be slightly better. Tuning is the same, it will just take you a little while to overcome the learned association between cable tension and derailleur position. At least, this was how it worked for me. I still mess it up.

SIS is Shimano Indexing System. Probably comes with a Uniglide freehub. In this case it's probably a low-end bike but many older bikes (mid-70's and older) that were pretty nice had no derailleur hangers.

If I understand your concern, the torsion spring on the cage may provide enough tension to keep everything in place once it is assembled.

Take a look at the cable, if it's a solid wire, rather than a twisted cable, you will go nuts figuring it out, but it will work fine. Some early index systems used a solid wire to provide definite positioning of the rear derailleur, rather than counting on tension between a spring and a cable.

Found TY-22 stamped on the back of the derailleur... It sounds like this indicates a Shimano Tourney derailleur. 6 speeds. And I was wrong, there is pretty strong spring tension on the derailleur, it's just that it's pulling it the wrong direction, i.e. down and back instead of up and forward. Hmm... I'll try to get a picture up in a little while.

The derailer is supposed to pull down and back... Sounds somewhat like the derailer on my bike. I just replaced the chain and spent forever puzzling over the derailer.

I sorta had to rotate the derailer counter clockwise about 270 degrees to get the spring right. Or actually, I left it loose, put the chain on and slipped the spring into the correct position on the derailer.

You should be able to find a replacement derailleur/hanger on literally any junk bike. That's extremely common on low-end bikes. If it's as old as it sounds like it is, almost anything will be an upgrade.

You can still get claw type rear derailers brand new like this one (http://cgi.ebay.com/Shimano-Tourney-RD-TX31-Rear-Derailleurs-TX31-w-Hanger_W0QQitemZ280231358981QQihZ018QQcategoryZ27950QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp 1638Q2em118Q2el1247)

This line from the ad copy cracked me up:
Best of all, Tourney's visual appearance has a high-level impression that in no way is inferior to its upper classes.