The XTR rear derailleur (1) is fairly simple to service. With the derailleur removed from the frame, first remove the two pulley wheels (2/3); the upper ‘G’ pulley (2/4) and the narrow lower (3/5). The ‘G’ pulley has a moveable centre which allows the introduction of grease into the bearings. The aluminium seals appear quite effective at keeping grit out, so I usually just push the centre until there’s sufficient space to press some grease in, then reverse the pulley and do the same from the other side. Depending on the condition, I may clean the bearings out with a degreaser, which in turn is cleared out with Isopropyl Alcohol and compressed air, before applying fresh grease.
If you’re just topping up the grease, clean the pulley thoroughly so that the body is free of any dirt before you open the bearing. Only a small amount of grease is required; too much will create its own excess friction inside the bearing. I use Pedro’s Syn Grease for all my bicycle bearings.
As you can see from the picture (5) the sealed bearing on the narrow pulley differs slightly, making it possible to remove the bearing seal for servicing.
NB. Take great care when removing the seal from a sealed bearing. If the seal is bent or the edges are damaged you may have difficulty re-fitting or prevent the seals from working effectively when in use. I use a very small jeweller’s screwdriver to prise the bearing seals out and press them back in with a clean cotton bud.
The bearing from the narrow pulley can easily have the old grease completely removed with degreaser. Try not to rotate the bearings too much when the grease has been removed. Same as with the G pulley; clean the pulley body before you open the bearing and go easy on the fresh grease.
Remove the barrel adjuster mechanism from the derailleur body by unscrewing it, clean and put to one side.
The H and L parameter screws can also be removed (6/7), along with the plastic seat which they thread through.
The cage plate of the XTR is also removable, allowing access to the cage spring assembly. Picture (8) shows the Philips-head screwdriver fitting on the top of the cage stop. To remove, push the cage anti-clockwise from the body until you can get your screwdriver in. This can be done with one hand, but make sure you have enough grip to keep the cage still. When the cage stop has been removed, slowly allow the spring to relax, pulling the cage clockwise and past the point that the cage stop previously dictated until it points ‘forward’ (9).
With the spring relaxed, loosen the cage retaining bolt with a 5mm Allen key (10). Remember that the cage is still under a small amount of pressure from the spring, so try to keep a hold of both the cage and the body. The bolt is mounted in the cage and will only protrude 2-3mm when unscrewed.
Now for a bit that has perplexed me slightly. On the M950 there are two holes in the cage for mounting the spring into (11). If you look straight on at the cage as if it were fitted to the frame, there is a hole at 12 o’clock and a hole at 1 o’clock. I bought my M950 used and when I first opened it up didn’t pay attention to which of these holes the spring was mounted into originally (well done, I know!). Anyway, I’ve come to ascertain that there is more spring tension when the spring is seated in the 12 o’clock hole and, perhaps as my derailleur is a few year’s old, it seems to work better in the higher tension setting. I’ve done some searching and checked the Shimano site but haven’t been able to get any definitive information, so I’m entirely open to further information/confirmation and will update this guide accordingly.
So back to it; remember to take note of the position of the spring when you open the cage bolt assembly! Remove the cage from the body, the plastic ring seal and finally the spring. You’ll notice that the tips of the spring are not the same; the tip that sits in the body is longer than the tip that sits in the cage.
The frame mounting bolt can be removed by first prising the retaining clip. To get the clip off, place the flat face of a screwdriver against the threads of the bolt and lever the clip slowly out (12). You could but something in here to protect the threads (I'll use a small piece of inner tube when I refit), but caution should be protection enough. The stopper plate is under a fair amount of pressure from the spring, so be prepared for it to spin clockwise once the retaining clip is removed (13) (it may not happen immediately!). With the stopper plate out of the way, the spring can be removed (14).
The mounting bolt can now be pushed through from the inside and the rubber ‘o’ ring carefully prised from the outside of the derailleur body with a fine point. There is also a smaller ‘o’ ring on the bolt itself (17).
You should now have a completely dismantled derailleur (15/18). The jockeys should already have been cleaned and re-greased by this point. All of the other small parts and the derailleur body can be washed with degreaser, the latter also being rinsed under a hot tap. To make sure everything is rinsed well clean of degreaser, I'll use Isopropyl Alcohol and then dry it all thoroughly. Compressed air, or just blowing, will get any water out of the derailleur pivots/body and folded tissue paper will clear out the spring chambers.
Never having had the experience of dismantling a new derailleur, I’ve had to use a certain amount of guesswork as to where fresh grease should be applied. My grease of choice for this job is Pedro’s Syn.
I’ll give both springs enough grease to have them completely coated in a thin layer, with an extra dab on each spring tip. Whilst there is some need on the springs for lubrication to reduce friction, it appears to me that the greater need is to stop corrosion from the almost inevitable ingress of water, particularly in the main body spring where there is no seal between the cage plate, stopper or derailleur body.
I run a small rim of grease under the outer ‘O’ ring and also inside the barrel of the body that the bolt will run through. This should be enough to lubricate the small ‘O’ ring seal when the bolt is replaced. With regular cleaning in mind, I’ll just run an extra line of grease around the rim of the body-spring chamber and wipe away any visible excess when the stopper is refitted, which leads me nicely to the task of refitting it…
If you refer back to picture (13), this is the position of the stopper in its ‘rested’ state. Our job here is to turn it anti-clockwise until the stopper has cleared the corresponding ridge on the body and been depressed far enough to refit the retaining ‘U’ clip. The first time I did this it went on first time, no problem. The second time I must have spent ten minutes trying to do the same thing. With the body adjust screw fully extended away from the stopper to give you a little extra leverage, the trick is to keep pressure on the outer edge of the bolt so that it is kept fully inserted, then, in a quick, ‘snap’ movement, twist the stopper past the ridge and push it in to place against the body. At this point, keep a good compression on the assembly or the stopper may spring up again. Have the ‘U’ clip to hand so you can push it into its seat in the bolt, then use a pair of stub-nose pliers to press it all the way in. I have a small piece of inner tube handy to place over the thread of the bolt and protect it from the teeth of the pliers.
If you’re finding it a struggle to get the stopper back into place by hand, a pair of pliers can be used. The ‘twist-push’ movement is the same; you’re just taking some of the pressure off of your fingers. Be aware that the pliers can easily slip and take the necessary precautions to protect the derailleur body and also your digits.
For the rest of the derailleur, reassembly is the reverse of disassembly. In addition to the grease on the spring, I’ll also run some around the rim of the chamber on the cage spring, before replacing the plastic seal, and then a thin film around the outside of the seal. The bolt and spacer in the cage spring can also have a light coat of grease, although you may also choose to apply a medium (Loctite 243) thread lock to the tip of this bolt.
It's also worth applying some grease to the H and L limit adjustment screws to help ward off corrosion. Don't forget that your H and L screws are now completely out of adjustment.
When both springs/assemblies are refitted, use a cloth or tissue with some Isopropyl Alcohol on to wipe away any excess grease from the derailleur body.
Lubing the pivots on any derailleur is really a matter of environment. During dry spells I don't put any additional lube on the pivots, spring or spring mounts as it'll attract more dirt than it would otherwise. If it's wet, or I'm expecting water where I ride, then I'll apply a little Finish Line Dry Teflon lube to the pivots, spring and spring-ends. After leaving the lube for 10 minutes or so to soak in and dry, I'll wipe any spill/excess off of the body with alcohol.