Problems with rear derailleur
 

Picked up my first road bike, a 2000 Specialized Allez Sport A1. Bike appears to be in mint condition, however, I can't seem to get it to shift correctly. Here are the symptoms and what has been tried to fix it:

- When trying to index the rear derailleur I can get it to shift nice and smooth from the smallest ring to the biggest ring without issue. However, trying to shift back is where I run into a problem. After 1 click it's clear that the chain is not going to go down to the next smaller ring. Easing off the tension allows the chain to move, but it's not smooth and very often will skip 2 rings. Also, once I let out enough tension to get the chain all the way back down to the smallest ring, it lacks enough tension to go back up.

- It's a 17 year old bike so I assumed that there was some friction built up in the cables and housings. So I replaced them all, but with the exact same results.

- Finally caved and took it to a professional bike mechanic. He ran into the same problem I was running into. The hanger was bent but has been realigned (problem persists). Chain has plenty of life left in it. We also put a wheel on it from a used bike in the shop with the exact same component group and 9 speed cassette (problem persists). Checked frame alignment (spot on - no issue there). Shifters appear to be in perfect working order. Visually, the cassette looks to be in perfect working order. All signs point to a bike with very low miles on it.

At this point I'm not sure what to try next. The mechanic suggested getting a new derailleur even though the one on there appears to be in good shape. Next he suggested a new cassette and chain to see if that is the problem for some reason (even though chain is in great shape and cassette 'appears' to be in good shape as well).

I don't have any problems with these suggestions but want to make sure I'm not going to blow more money on this thing unnecessarily. Is there anything else I should be trying before replacing those parts? Is it possible that the old barrel adjusters on the downtube are causing friction? They aren't particularly smooth when trying to turn them.

A couple of things to try.

1 - Adjustment: You might try adjusting the B-Screw on the derailleur to get the shifter guide pulley as close to the cassette as possible without touching it in any gear.

2 - Maintenance: I assume you've checked your chain for excess stretch.

3 - Parts: Have you tried compressionless cable housing?

The symptoms you are describing seem to indicate friction somewhere in the system. Did you replace ALL of the shift housing runs, including under the bar tape and the last run going into the derailleur? I would suggest solvent cleaning and relubricating the derailleur. Check the shifting action by pulling on an exposed run of shift wire and see if there is still sluggish response moving to the small cogs; if so there is still excess friction somewhere. A remote possibility is a weak return spring, but unless it is heavily corroded that is unlikely, or the shifter is not paying out cable correctly; the wire pull test should diagnose this.
Also, if the hanger was bent it is possible that the derailleur has gotten damaged as well.

I forgot to mention that the B-screw was adjusted. Mechanic confirmed that I had done it correctly. Mechanic also measured (or whatever you would call it) the chain and said it had plenty of life left. I don't know what compressionless cable housing is yet (I'll look into it). However, machanic said they use same cables and housing in the shop that I put on the bike myself.

Eventually derailleurs wear out. There are a bunch of pinned connections that are exposed to the same grit that chains are. When these connections get worn, the derailleur gets sloppy. You can tell if you grab the parallelogram and twist, you can feel slop in one that is burned out, a new one will be tight.

You can check the friction in your housings by grabbing the cable and pulling it first from the RD end, and then from the shifter end. No friction = easy pulling.

All the cables and housing was replaced from the shifter down to the derailleur. Mechanic confirmed it all looked good. We took the derailleur off the bike to inspect it further, seems to be in tiptop condition from a visual standpoint. I think a thorough cleaning is in order before ordering a new one. I'll take it off the bike and clean it and re-lube it. Will also do the same to the shifter to be thorough.

Mechanic said the return spring looks good and feels plenty strong. Also, said derailleur appears undamaged but admitted that it can be hard to tell just by looking at it.

Can you elaborate on what the wire pull test is?

I'm a newb so I don't have a particularly keen eye for some of this stuff. However, the mechanic did give me the impression that the cassette and derailleur appeared to have very few miles on them. He manipulated the derailleur by hand both on the bike and off.

Cables move beautifully through the housing. Although, I did not test them through the whole system. Maybe that will reveal something, but I'm not hopeful. You'd think a bike mechanic would find something that obvious in about 5 minutes.

When in the small rear cog, pull the exposed run of shift wire like a bowstring and see how the shifting functions; this will take the shifter out of the picture and hopefully narrow down the source of the problem.

Thanks!

Does the bike have a removable d-hanger? I've had similar problems when the hanger was loose.

If the housings seem good, everything is tight, and no amount of adjustment seems to make it shift well, then it is reasonable to start replacing parts. If the derailleur checked out, then it could be the shifter. Is it sti? There are lots of little parts in those that can wear.

LUBE THE SHIFTER....... Sounds like the grease has gotten old and thick. Can you MANUALLY shift the rear Der. by pulling the cable, then releasing it?hen the SHIFTER is sticking.

If lubing the shifter doesn't fix the issue, i'd suspect that the upper roller on the derailleur is heavily worn, and has way too much side-play in it's bearing/bushing.... You mentioned a bent der. hanger, and THAT can cause excessive wear in the upper roller!

Should there be any play in those rollers at all? The lower roller can me moved side to side an almost imperceptible amount. However, the upper roller can has about a 1/8th inch of play side to side.