DeRailled7
Active member
The other day i noticed my chain was sagging, it was not tensioned by the derailleur anymore. The derailleur is a Shimano XT, my bike is a Trek Rail 7 with about 3400km on it. Engaging/ disengaging the clutch didn’t make any difference. My first thought then was that the clutch needed to be serviced. Servicing the clutch is easy enough. Once i removed the clutch cover i couldn’t see anything wrong with it. It was still clean and appeared to function properly. I still proceeded to clean it and grease it. That of course didn’t fix the problem.
A bit more investigation pointed to the plate axel (see diagram). The plate axel is the pivot over which the clutch is installed on one side and onto which the plate assembly is attached on the other side. The plate assembly is the ‘swing arm’ that holds the pulleys. The plate axel should be free to rotate, it was completely seized!
Removing (unscrewing) the plate assembly required some effort but once removed i discovered the problem, rust! The plate tension spring was very rusted, the chamber where it sits was full of rust and very fine sand dust. The pictures below shows how it looked after i did some cleaning, forgot to take pictures right after opening it.
Needless to say the plate axel was completely seized. After dripping rust penetrating oil, letting it sit for a while, applying more oil, i was able to turn the axel and finally remove it. I then sanded the rust off using very fine grain sandpaper. Once everything was cleaned i sprayed the spring with a rust inhibitor, greased the plate axel and reassembled the derailleur. It is now working as new.
The big question is how did water and sand dust get into the plate tension spring compartment in the first place. Turns out there is a good size hole on the plate assembly that will allow this to happen. On the diagram one can see there is a hook at the end of the spring that needs to pass through a hole on the plate to create tension.
It is through that hole that water and sand can get into the compartment. Water can easily get in simply when washing or riding in wet conditions. This summer was very dry and the trails very dusty, so no surprise sand dust found it’s way inside too.
My solution so far has been to plug the hole with silicone caulking, the same used around bathtubs. Might not be a permanent solution but should help control this problem. I’m also going to do more preventative maintenance, i.e. take the derailleur apart more often.
i suspect many of you have had to replace a ‘broken’ derailleur, that’s a common solution pushed by our LBS, just replace it. Derailleurs are fairly simple and unless they are bent can be easily serviced. If you’re a conspirationist you might think Shimano has left that hole unprotected so that their derailleur break more often. Possible, possible…
A bit more investigation pointed to the plate axel (see diagram). The plate axel is the pivot over which the clutch is installed on one side and onto which the plate assembly is attached on the other side. The plate assembly is the ‘swing arm’ that holds the pulleys. The plate axel should be free to rotate, it was completely seized!
Removing (unscrewing) the plate assembly required some effort but once removed i discovered the problem, rust! The plate tension spring was very rusted, the chamber where it sits was full of rust and very fine sand dust. The pictures below shows how it looked after i did some cleaning, forgot to take pictures right after opening it.
Needless to say the plate axel was completely seized. After dripping rust penetrating oil, letting it sit for a while, applying more oil, i was able to turn the axel and finally remove it. I then sanded the rust off using very fine grain sandpaper. Once everything was cleaned i sprayed the spring with a rust inhibitor, greased the plate axel and reassembled the derailleur. It is now working as new.
The big question is how did water and sand dust get into the plate tension spring compartment in the first place. Turns out there is a good size hole on the plate assembly that will allow this to happen. On the diagram one can see there is a hook at the end of the spring that needs to pass through a hole on the plate to create tension.
It is through that hole that water and sand can get into the compartment. Water can easily get in simply when washing or riding in wet conditions. This summer was very dry and the trails very dusty, so no surprise sand dust found it’s way inside too.
My solution so far has been to plug the hole with silicone caulking, the same used around bathtubs. Might not be a permanent solution but should help control this problem. I’m also going to do more preventative maintenance, i.e. take the derailleur apart more often.
i suspect many of you have had to replace a ‘broken’ derailleur, that’s a common solution pushed by our LBS, just replace it. Derailleurs are fairly simple and unless they are bent can be easily serviced. If you’re a conspirationist you might think Shimano has left that hole unprotected so that their derailleur break more often. Possible, possible…
