This spring I purchased a new 2021 bike with all Shimano SLX components on it. Smooth rolling and clean precise shifting, I did not have any problems until about 400 miles of trails. On one outing in September I remember starting out OK then midway into the ride my chain pops off. This had never happened before. I was surprised but I slipped the chain back on the 1x12 drivetrain and started again. A minute later it happened again. This time I stopped to see what could be wrong. Are the brakes locking up? Is something stuck in my gears? Is my derailleur messed up? I got on the bike and tried to ride back to the trail head. I couldn't do this easily. As soon as I stopped pedaling the chain would jump off the chainring. In order to make it back I had to put a positive pressure pushing forward on the pedals. Gliding or back pedaling would immediately make the chain jump. Back at the car I took off the rear wheel to see what could be amiss. The problem I found was that the free-hub was no longer "free". Trying to spin it by hand would make it barely move. I was obvious something was broken inside to keep it "locked" up.
I took the bike back to the bike shop I had purchased it from. After some investigation I got the news that the rear hub was broken. How could this be I asked? The bike is new! They could not answer but the good news is they replaced the entire rear wheel with same from another bike. This one was spinning just fine.
I took the bike with the new wheel out for a 15 mile ride with no problems. The next weekend I went out again but this time with not a good outcome. Just like the first time, my rear wheel locked up again and the chain popped off. I took the bike back to the bike shop. This time they said there was nothing they could do but raise this as a warranty issue with Shimano and send the two broken hubs back to Shimano for "investigation". I week passed until Shimano notified the bike shop they were sending a new XTR hub as a replacement for the failed SLX hubs. They tacitly admitted there was an "issue" with these SLX hubs. I don't know if the problem is a design, materials or quality control problem. But there is a problem.
I got my rebuilt wheel with a new XTR hub after about a month of waiting and rebuilding. I have been out several times since with no issues. I probably have 30 miles on the new hub and am not expecting it to lockup like the SLX hubs did. So far it is as smooth as butter. Keeping my fingers crossed.
Would appreciate reading other's experiences. If anyone has a similar experience with 2021 SLX hubs please let the community know.
