My experiences with Shimano m735 XT rear mech, whether the XTR is that much different, I don't know.
first job with old mechs, soak the pivot end of the mech in dismantling oil to free up any corrosion that is in there, hell, may as well check the hole mech in the oil as the dismantling stuff will get to places you can't and chuck out the mud, grit and other abrasive debris wearing away at your pivots.
Simple reason, where there is aluminium,brass alloy and steel and the potential for moisture expect corrosion, dismantling oil can make a bad job better, I use Plus Gas, the best.
Back off the B screw, now depending on exactly what is holding the back plate to the pivot bolt apply a tool to shift it, but to protect from any possibility of anything springy launching out at you, loosely hold a cloth over the operation site as you make that final move and release the clip. Either that or hold down the plate as you remove the clip.
Once the clip is off, various things can happen, the plate can push up then move to the side ( Notice this direction of movement, it helps later)indicating less corrosion, or it can just sit there indicating corroded parts, ( my last job was this, alloy bolt frozen into the back plate). Then the fun begins in freeing up the parts, but once the tension is off the connection it is only corrosion as the plate should lift off. ( My last siezed alloy bolt involved me gripping the plate which is steel with mole grips and wiggling the plate off, no doubt the overnight soaking in dismantling oil aided that operation)
Inside all there is, is a helical spring and a bit of grease. Where the pivot bolt goes is lined with a brass alloy sleeve, a bearing surface I expect more resilient than straight aluminium alloy, the bolt should just drop out, but if not, try lightly pushing the bolt out, no joy there, out with the plus gas and soak area again as with the pivot apart more chance of the oil penetrating, try tapping the bolt lightly with a soft faced hammer, it will give up with a bit of patience, but might have to be pushed out with an implement depending on the corrosion levels.
Remove spring noting it's orientation, digital cameras are wonderful things, then clean out the whole pivot assembly, the brass insert sleeve I clean out with a thin stiff plastic bristle bottle brush type thing, then look down the tube and see if there are any high points left, if there is, further scrubbing with bottle brush thing and a bit of penetrating oil. Once clean I polish the inside by twisting a bit of paper towel and screwing it into the sleeve and rotate. Paper towel is an abrasive, thats why it polishes, but anyway I polish the sleeve.
Now with everything clean and shiny comes reassembly, which is a reverse of the disassembly, but things are smoother due to no corrosion to hamper. I smear everything in anti seizure grease, it lubricates and stops the dreaded. But a thing worth mentioning here is the grease should be heavy enough so water wont displace it and of a type that does not react with water, as water does get into that pivot and spring housing, so called seals and there is one on the pivot, watch out for it, plastic chips easy, although I suspect the one on the pivot is really there as a cushioning and protecting surface between the steel plate and the alloy of the pivot housing.
Locate the spring in it's correct position, it has a projecting bit on either end, one end locates into a drilling inside the aluminium pivot bolt housing and the other locates into a drilling in the steel top plate. From here it is a bit hazy, as for me everything was lined up, a slight twist of my hand and a push and the thing was together bar the retaining clip, but the action is there in what I say, but shove the pivot bolt through as it seems to help in the operation, with the spring projection in their respective holes twist the plate in the reverse direction to which you noticed it move when dissassembling then push and it will click into place. Then simply refit the spring clip that holds it all together Job Done.
But a question from me from what I heard BITD concerning pivot bolts and what they are made from and the situation should the mech receive a hefty clout, enough to cause damage to the frame, too strong a pivot bolt could actually bend the frame as where is the weak point in the assembly, the sacrificial connection? It is for this reason that I have fitted a drilled SRP alloy bolt and through the pivot I have a captive wire to hold all the gubbins together should the pivot bolt snap.
Any thoughts on this ?
