What's the best way to tell if your rear derailleur is worn out?

It seems okay when I wiggle the cogs on it. This is an old bike but doesn't have much more movement than the new bike I have does. The shifting isn't that good. The chain is still in good shape and the cassett isn't very old. The adjustment on the rear derailleur is hard to dial in. It seems that it either doesn't shift up or it doesn't shift down properly. What I mean is that if I adjust it so it shifts up good then it doesn't shift down good and visa versa.

It will hesistate one way or the other.

Should I just take it to the lbs and have them check it out?

besides pulleys that wear out and need to be replaced from time to time, RDs can hold up for years if not crashed. Over time, they do wear in 6 places - the 4 pivots of the pantograph, and the upper and lower bodies. Over time this makes them sloppier, and pivot wear reduces their cable response a bit.

My old workhorse RD developed play in the upper body on the mtg bolt, and since I'm of the school where nothing is dead until it's well and truly dead I jammed a few turns of dental floss in there and it's OK again. That was 2 years ago, and I'm sure I'm on borrowed time, but then I can jump straight from 9s to 12s or 13s or whatever they're up to by then.

I've ridden bikes from the 70s with original derailers that still work. If it still shifts the way it should, then it isn't worn out.

I would definitely suspect the cables of causing shifting issues before I suspected the derailer. How old are the cables and housing on that old bike? Excessive friction in the cables will lead to very odd shifting problems.

I suspect it is the pivots but it doesn't seem any looser than the newer bike I have. I don't know how to tell if it is or not.


It doesn't shift right. The cables and housings are around 2 years old by now. I suppose I could change them anyway just to see since I would change them if I got a new RD. I think I will try this first and see how it works.

I would like to know it is the RD since they aren't cheap and this bike is 20 some years old now. I don't want to spend a bunch of money on it if I can help it

Thanks for the replies.

What kind of bike? Grip shifters, and to a lesser extent brifters, often wear out/fail more quickly than RDs.

It's an old MTB... a GT but the shifters are fairly new, about 2 years old. I hope they aren't worn out already. They are twist shifters.

I did notice that the rear shifter cable has a kink in it by the head tube. I am going to replace all the shifter cables and see what happens.

That is probably your problem.

Dropout alignment is a commonly overlooked issue that's definitely a biggie.

1. Stand your bike up vertically against something and shift into a gear combination that causes the derailleur cage to point straight down.
2. Look at your derailleur from the back of the bike. The derailleur arm should point straight down. If it looks like it's pointing toward the rear wheel - that's your problem.
3. I'll align up to 7-speeds by eyeball. 9-speeds are a lot more picky about perfect alignment and definitely require using a gauge.

I found another problem. The RD is twisted. The front of it is twisted in toward the wheel and the back is outward. I hope you can understand what I mean when I say this. I stuch an adjustable wrench on the rd and twisted it so it is straight now. It shifts great and makes hardly any noise now. I am still going to change the housing that is kinked. I found this when trying what Retro Grouch said to do. Once the bike is upside down it is very easy to notice this. I guess my 20+ year old RD is not worn out yet. How long do these things last? I have now idea how many miles this bike has on it, but the derailleurs are about the only parts that are still original that have moving parts.

Thanks everyone for the input.