Shimano RD-M640 Zee Shadow Plus 10 Speed Rear Derailleur

This thing is awesome. I used it on a rebuild of an old Trek. Running 10 speed rear and a single naked chain ring. Not only does the clutch keep the chain on, but it keeps it SUPER quiet. Very smooth and precise shifting and a pretty light weight part too given the performance. 10/10 would buy again. 100% worth the money.3k mile update:Still holding up strong. Have done zero maintenance except upping the clutch pressure slightly. I will never use another derailleur again.

This was a lot cheaper when I bought it a few years ago. It is just great. Shame how much it costs now. It's almost still worth it. 10 speed Shimano is basically dead but I'm locked in and loving it. Shifts every bit as good as 10 speed 105, and has the clutch. Super low profile too. Almost looks like an 80's derailleur with the tiny cage. Perfect for a suburban commuter or anything else really. I hear it's been discontinued, another terrible decision by the bike industry.

What can I say? This derailleur along with the Z shifter work flawlessly on my mountain bike. If all you need is 10 speeds I highly recommend it

Install was a snap and I had it adjusted in less than 5 minutes. The secret to a quick set up is to click your shifter into 10th gear then mount the deraileur and install the chain. Using the 10th gear limit screw, adjust the deraileur until it pedals perfectly in 10th gear. Then, pull the shifter cable tight with pliers and tighten the shifter cable bolt on the deraileur. After, shift through the gears and use the adjusting nob on the shifter to fine tune it. Done! 5 minutes, perfect shifts.Another nice thing about the derailleur is if you look down from the top of the bike, the derailleur doesn't stick out past chainstay. This makes it much more difficult to damage the derailleur in case of a get-off. Very nice derailleur, smooth and quiet. Seems to be very good quality. I'll know more as I put more miles on it.

I’ve been running an original Sram X7 long cage for a couple years on a 1x10 conversion. My local shop recommended the Zee but it was backordered so I was lucky to find it on Amazon. Best decision I’ve ever made. No more dropped chains and shifts extremely quick and crisp. I was able to change it out and get it adjusted pretty easily after watching a few YouTube videos. Out of box it feels sturdy and well made. I highly recommend

As a few other reviewers have mentioned, this is an excellent product for kids bikes like my 6 year old sons 20” bike.My son really liked the gear indicator on his previous setup, so I wanted to pair it with an indicator shifter, and ended up with the SHIMANO Deore SL-T6000 Shifter.This short cage derailleur is great for kids, way fewer rock strikes and a clutch to reduce the chance of throwing a chain.Wish I would have done this upgrade directly instead of an in between Alivio setup.

This has got to be the best derailleur Shimano has ever made for the money! Wide range (it says 11-36, but I've seen people running 11-42), check, clutch, check, shifts smoother than warm butter, check, easy to install, check, the cable routing in legit, check, and it's sexier than a French supermodel, CHECK! All this for less than $60? You can't even see a decent movie or go to a decent restaurant for that! Hook it to a SLX, Zee, XT, Saint, or XTR and you will high five yourself! Shimano owns DH and Enduro! If God were on a budget and shredded, he'd use this derailleur!

I was new to mountain biking and this was going on my Cannondale catalyst 4 hardtail. For the money, this is one of the best derailleurs you can get, and I can say that with confidence. shifts extremely smooth on flat and on slight inclines, for more harsh inclines it will still shift it just doesn't like it too much. However, behind that and the relatively small range cassette. I have no complaints. if you are looking for something for the trails where there will be a lot of climbing you might want to steer away from this but if you are up for building some serious muscle it is good. Like I said in the title I have run this since 2020 and have had zero problems with it. The durability is also extreme, it can take a real bashing and it has taken several rock hits and come out okay.