In Whistler I had bumped my Shimano XTR rear derailleur on a boulder whilst rolling backwards, thus bending off the little tab on the B-axle (top pivot bolt) backplate that keeps the spring tension when the derailleur is unmounted. Thankfully, Shimano sells the B-axle assembly as a set, so I had Jarrel bring one in for me. I switched out to my spare RD-M971-GS so I could still ride my Ellsworth. Last week the part came in, so I brought in the old derailleur to the shop and installed the new backplate.
Replacing the plate is a little trickier than one would expect. There is a lot of spring tension, both rotationally and axially, that has to be taken into consideration. What worked for me was installing a 5mm hex key in a vise and mounting the derailleur on it via the B-axle. I temporarily held the backplate onto the B-axle with a 10mm rear hub axle cone, and tightened it down until the stop tab was almost in contact with the upper forging. Removing the B-tension screw, I put a small adjustable wrench on the screw tab and turned the plate into tension and aligned the tab with the end of the track in the upper forging. At this point I tightened the axle cone, thus driving the backplate fully onto the B-axle. Holding the plate down with a small flat screwdriver in the c-clip groove, I removed the axle cone and installed the c-clip. All done. The process would probably be easier with another hand or two, but would be virtually impossible without the vise or some other means to hold a hex key as a mounting base for the work. I used the hub cone because it was difficult to both turn the plate into tension and push it down at the same time.
$18 part saves a $180 derailleur!
0 Responses to “Reborn”