A few weeks ago I was riding my 8 week old Bronson, which has brand new 2017 XTR M9020 brakes, and one of the carbon lever blades snapped like a twig. I'm still not quite sure why it snapped -- I had just attempted a steep techie climb, which I did not make, and slid back down the hill a bit so perhaps I snagged the lever blade on a rock. I was quite upset that the "Trail" variant of an XTR product could break so easily. Upon investigation, it occurred to me that the blade is "Carbon", but not "Carbon Fiber". Thanks alot Shimano -- carbon without the "fiber" is really just some fancy plastic. So, I wanted to replace the blade with a tougher one and I noticed much chatter and confusion on this topic in various discussion threads and comment threads. Ergo, I thought I'd write my story. First, The M988 aluminum blade is a dead-solid match for the M9020 carbon so I chose the M988 for toughness. Like many bike repair tasks, this job is easy once you know how to do it. Here are some keys:
For reference: http://si.shimano.com/pdfs/ev/EV-BL-M9020-3781A.pdf
1. See pic of useful tools, both to remove old blade and to attach new one: curved seal-puller (to remove fixing bolt cap), 2mm hex (for lever axle fixing bolt), punch (must be less than lever axle hole diameter), a second straight seal puller or second punch to aid in lever axle alignment during installation, slip-joint pliers, rubber mallet for tapping the lever axle (pin) back into place.
2. To remove the busted blade you MUST REMOVE the little fixing bolt that holds the lever axle (pin) in place. The bolt is accessed via a small 2+mm hole located on the base of the blade on the bar-side. First use the curved seal-puller to pull the plastic bolt cap, then just use the 2mm hex key to remove the bolt. DON'T LOSE THE BOLT OR CAP -- your replacement blade does no include these parts.
3. Use punch to tap the lever axle up and out from the bottom. The broken blade should now easily pull away from the base lever assembly.
4. You'll notice that each blade unit has two coil springs already fitted into the assembly: one spring fits snuggly to the assembly and is the spring the helps the blade return to position after pulling towards the bars; the other spring has a longer extension arm extending maybe 5 to 7mm away from the assembly and helps return the blade when pushed away from the bars, i.e., tensions the slack so it does not rattle during riding. This "long spring" is important to get positioned properly when installing the new blade -- make sure this spring catches towards the inboard side of the receiving cup (while not contacting the cam guide surface).
5. To install the new blade, first catch the "long spring" extension on the inner part of the receiving cup. You'll feel some spring tension when you then position the holes of the blade unit with the holes in the base assembly. I then used my straight ring-puller, pushed down from above, to keep the two main parts roughly aligned. I then pushed my punch (with a diameter slightly smaller than the holes) up from the bottom for a very accurate alignment of all parts (this of course pushes the ring puller up and out of the holes). This is not a trivial action since the punch might want to catch on some of the aligned parts as you work it through the hole. At this point you can test the lever pull action as a sanity test. Then the trickiest step: re-inserting the axle/pin. To do this, push the lever axle (pin) down (pushing the alignment punch down) and work it through the hole. You might need the pliers or rubber mallet to help nudge the pin down through the hole. I also applied a small amount of Slick Honey to the pin to help it slip through.
6. Check the install and basic lever pull action against your "good" side lever. They should feel the same. Be sure to also check the feel if you lightly push the blade away from the bar -- that long spring should help the blade snap back to its resting position.
7. Finally, screw the fixing bolt back in place and push the cap in place.
Sorry, no YouTube vid -- after finally getting two new aluminum levers in place, and getting back on my bike after a two week down-time, I did not want to remove one to go back through the process and risk breaking some small part. Hope this helps!
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