Shimano XT derailleur seized

[DeRailled7]

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…

 

[Montana St Alum]

Nice troubleshooting.

 

[irie]

Helpful post, will remember this.

 

[kombos]

Just did mine. Thanks for this post.

 

[DeRailled7]

Happy you’re finding this post useful.
Another question i had about my XT derailleur was how much tension should there be on the pulley’s arm with the clutch on. That is how much tension to keep the chain tight and the shifting working smoothly. Turns out to be 4.4-5.4 Nm on my M8100. The following two pictures show you how to set it.
hope that helps.

 

[mrmonkey09]

I know I'm a few years late, but this was the most helpful thread when I ran into a similar issue. I wanted to add a few notes for anyone in the future:

1. Getting the plate axle out was much harder than I'd expected. I used penetrating oil a few times and eventually had to press it out with a bearing press. Worked perfectly, so I'd recommend trying that. I used sandpaper to sand the rust out and it worked perfectly.
2. If you remove the clutch switch pin (Not sure the official name), just know there is a notch you need to slide it back into that's at the very base. It's hard to notice but key to get it back in.

 

[Bear-uk]

I know I'm a few years late, but this was the most helpful thread when I ran into a similar issue. I wanted to add a few notes for anyone in the future:

1. Getting the plate axle out was much I'd expected. I used penetrating oil a few times and eventually had to press it out with a bearing press. Worked perfectly, so I'd recommend trying that. I used sandpaper to sand the rust out and it worked perfectly.
2. If you remove the clutch switch pin (Not sure the official name), just know there is a notch you need to slide it back into that's at the very base. It's hard to notice but key to get it back in.

I also used the above post to sort my deraulier out a couple of weeks ago

 

[cream]

Also got here late, but had to comment. Happy to see posts like this. I repair things all the time rather than replace and I also use XT derailleurs on my bikes. Nice mech piece and the price is quite decent. Reliable too.

Sadly, I must confess I replace them when they have significant performance issues rather than repair. But to honor this post, I will service them in the future

 

[steve_sordy]

I had exactly the same problem, the same findings and the same fix, except that I didn't pliu the hole with sealant.

But only once have I ever had this problem and I've been using Shimano mechs for a long time. However, I tend to break the mechs and need to replace them, so maybe I had a good spell and had had that particular mech for long enough for it to rust out.

I agree that it is a design flaw. But I doubt that leaving a hole was a deliberate act of sabotage by Shimano designed to inctrease sales. Not fixing it however, once it had been drawn to their attention is a deliberate act.

 

[FINJP]

Maybe i have same issue, 4k driven cube with same link. My chain started to jump with small gok and , i though it is worn gok, so replaced two small ones. Hundred km fine and same fuk. Now new gears and chain, but same shit with small gear. Chain seems to wobble so must be the tension as well

 

[Ndanger]

Maybe i have same issue, 4k driven cube with same link. My chain started to jump with small gok and , i though it is worn gok, so replaced two small ones. Hundred km fine and same fuk. Now new gears and chain, but same shit with small gear. Chain seems to wobble so must be the tension as well

Out of curiosity, have you checked the alignment of the derailleur, I find that it is easy to hit a rock and bend the hangar. When I have problems with the drivetrain that the obvious fixes don't work it ends up being the bent hangar.

 

[DeRailled7]

Maybe i have same issue, 4k driven cube with same link. My chain started to jump with small gok and , i though it is worn gok, so replaced two small ones. Hundred km fine and same fuk. Now new gears and chain, but same shit with small gear. Chain seems to wobble so must be the tension as well

Like Ndanger said maybe your derailleur is bent. Your LBS can check and realign it. One other thing to check if you find your chain ‘loose’ is check the adjustment of the B screw. That screw adjust the position of the derailleur. There’s a line marker on the reverse side of the derailleur plate. It will cause sagging if not adjusted properly. I had that problem almost every time i bought a new bike.