Shimano RD-L525 Light Action Rear Derailleur
 

I 've got an old Centurion LeMans RS with a Shimano RD-L525 rear derailleur that doesn't shift properly. I bought the bike new back in the late 80's and have replaced it but would like to see if anyone has any suggestions. I removed and cleaned the derailleur, same problem exists. Shifting is OK when the cable pulls the derailleur to move into a lower gear (larger sprocket on inside of wheel) but the derailleur does not return when I try to shift into a higher gear (smaller sprockets towards outside of wheel). The spring is not broken but seems to not have enough tension or strength ?

It's possible the derailleur pivots are gummed up. Have you given it a good cleaning and lubing? Also, it's possible that the shifter cable is sticking. When you shift to a smaller cog, derailleur pivot tension pulls the cable. If the cable is sticking, it will counter the action of the derailleur pivot spring.

+1 Fresh cables and housings, even though those bits are probably not the problem. Fresh cable and housing will cost all of $3 or $4. And a cable problem could be your issue.

Sounds like the spring on the derailleur is shot, since you cleaned it already. The Light Action was a good, but low end derailleur. You can find a replacement, or use something better, like a 105 or 600 from that era.

Does the derailleur snap back if you disconnect the cable? Work it by hand, with the cable disconnected from the derailleur. Push the derailleur inward, then let it snap back. If it quickly returns to the high gear position, then your cable is the problem. Watch your fingers.

If you end up installing a replacement derailleur, I would change the cable and housing anyway. So the small investment in cable will not be a waste.

Thanks for the responses, I suspect both of you are correct and the cable is sticking. Thanks for the help pointing out what I should have checked myself.

I happen to like the Light Action RD quite a bit, and have several on bikes I've retrofitted with index shifting. The problem with them was breaking where they were skeletonized for the internal spring, or at least that's what T-Mar told me years ago. I've never had one fail, myself.

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I never thought of it as low end, but solidly mid-range. Its numerical designation puts it right in the middle of the hierarchy, along with what later became Shimano 105 and Deore LX. However, the "L" tosses in some weirdness in Shimano's otherwise clear road/mountain designations.

To me, the finish was not up to what I would consider the mid grade stuff. More steel, less alloy.

I thought it had a nice finish, but I do agree about it having more steel than necessary: a recent weight comparison I didrevealed it to be heavier than comparable offerings from Suntour and Huret, from the same vintage. Also heavier than Deore XT stuff.