Shimano XT rear derailleur - broken cam unit

[Off_da_brakes]

I fitted a new Shimano XT clutch rear derailleur to my trail bike two years ago when I built it up from new. I went for 1x10 setup using a 42 expander and a 32t n/w chainring. A year or so in and I started dropping the chain quite regularly. I replaced the chain, cassette, expander as well as the chain ring (which was quite worn given a poor chain line, which was corrected with the new chainring). Soon after this I'd occasionally still drop my chain. I shortened the chain to what was possible with the bike "fully compressed" in the lowest gear and all the air released from the rear shock. And frustratingly I'd still drop my chain (yes, the clutch was always engaged).

 

Did a little google research and found that the clutch unit on XT and XTR clutch derailleurs could be adjusted by simply removing the plastic clutch cover on the derailleur and tightening the adjuster screw. The recommendation was to tighten in quarter turn increments given the derailleur's sensitivity to these adjustments. I was not aware of this prior to reading reading one of the articles.

 

I removed clutch cover hoping that the adjustment would sort out my chain dropping issues. To my surprise the "cam unit" was broken (at this stage I did not know this part is called a cam unit)! This is the first time the clutch cover was removed and neither had I ever caught the derailleur against a rock etc. My first thought was oh fook, I need a new derailleur. Then thought of asking if any fellow hubbers had a trashed derailleur from which I could salvage the "cam unit". Then did a little more research only to discover that the cam unit (now discovered its name) commonly fails/breaks and can easily be replaced. I found the replacement unit on bike-components.de at the exorbitant price of EUR1.64. I ordered 4 units (along with a new campy chorus group set for my new road bike build...). Hopefully all arrives in the next week or two. Hopefully dropped chains will be a thing of the past as I honestly do not know how long I've been riding with a broken clutch unit. The derailleur still functions normally, just without the clutch. A pic of where the unit sits in the derailleur (sorry, pic's a little out of focus), the broken cam unit cage as well as the replacement part taken from the bike-components.de website.

 

Hope my experience helps anybody else in trying to ID one possible reason for a dropped chain when using an XT clutch derailleur.

 

Edit: changed bikediscount.de to bike-components.de

Edited January 12, 2017 by Off_da_brakes

[the nerd]

Yep! Most LBS's will try sell you a new mech.. my LBS ordered one from Shimano and all was well again!

[myveonix]

Coolheat? May the gods be with you

[the nerd]

Coolheat? May the gods be with you

Yep within the same week. I know. I was myself shocked.

[worriesnot]

Had the same issue almost a year ago.

LBS had the part by laying around and fixed it during a major service. Think they charged R50 or something stupidly cheap to replace the part. 

[Bomberman]

Nice read, never knew something like this could happen.

[dave303e]

Can you post a link to the part please?

[cfcjim]

http://lmgtfy.com/?q=shimano+cam+unit+for+RD-M820+bike-components.de

 

 

[shaper]

Learn something new every day, thanks for the post.

[nox1111]

same here - had to replace mine after a couple of days, bought a spare,

Edited January 13, 2017 by nox1111

[Sparki 1]

thanks for the post

[Spoke101]

There is a simple way to tell without removing the clutch cover. Just occasionally turn the clutch function off and then on again, if there is no/very little resistance when re-engaging the clutch then it either needs a service with a very expensive type of dry grease. Otherwise just give the derailleur cage a pull and check the resistance.

[typhoon]

 

Hope my experience helps anybody else in trying to ID one possible reason for a dropped chain when using an XT clutch derailleur.

 

Edit: changed bikediscount.de to bike-components.de

 

I had the same thing with my XT derailleur. Was told that Shimano don't bring in "parts" for their derailleurs.

I went around the local bike shops asking if they possibly had an old derailleur that was broken but the clutch was still good. 

Eventually found one, they pulled the clutch bits out for me and sent me on my way.

Even though I don't use the clutch on my 1x10 setup, it was the principle that it was broken that I wanted it fixed.

[PhilipV]

I have a rather fresh, but broken type 2 derailleur that I'm keeping in my box of weird stuff for the day that I need to rebuild a derailleur clutch.

Side note. Shimano clutches don't really like oval chain rings

[Pusher]

Yep! Most LBS's will try sell you a new mech.. my LBS ordered one from Shimano and all was well again!

I need a new one as well and I haven't gotten around to looking for one yet. Do you mind advising who your LBS is?

[Suidwes Boytjie]

Dammit... My XT clutch cam unit failed as well. Took it in and part was ordered to be fixed. Part arrived and put in and still my clutch engagement didn't function properly (was phoned by the mechanic himself to inform me, who also told me that this is a common issue with XT Clutch derailleurs) ended up with new derailleur.