Shimano RD-M640 Zee Shadow Plus 10 Speed Rear Derailleur

It's awesome to get the same build/design quality of the pro-downhill level derailleurs at a non-pro price. This thing is fairly bulletproof in it's build quality, has a great clutch system to keep my chain from dancing, crazy easy to install with a new chain, and shifts smooth. Being it's not original equipment to my rig, my cassette is such that I have to really watch out for straining my transmission (running a 2x chainring). YES, it's an older bike, but just try and catch me on a downhill. It's not what you have, but how you use it!

This derailleur is awesome!Pros: No chain slap! Easy setup! Shifts real nice and crisp like!Cons: It doesn't go to class for me so I can ride more.Hit light downhill trails and dirt jumps with it. No problems yet. Had one small fall that only scratched the derailleur but didn't hurt it mechanically in any way.Note: This isn't exactly a con because you will probably never need to touch the clutch tension adjustment inside the derailleur, but should you decide to mess around with it I want to warn you that Shimano put red locktitie on the 3 small bolts that hold the cover on. This can make removal tricky. If you use a slightly rounded or wrong size hex key you will most likely strip the socket cap screws.

we Great derailer.It works with my 34 tooth cassette and 30 tooth chainring. Select the part number for 36 tooth cassette. The photos shows it fitting and a 20 inch wheel diameter kids bike. The cage clears the fat 20x 2.8” tires.The derailer keeps the chain on the gears over bumps even with clutch off.There is a slight increase in pulley friction drag with the clutch on and in the largest cassette gear. So my kid rides with the clutch off. Still is a large decrease in chain slap over the stock derailer.

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.

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

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.

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.