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Shimano Zee M640 Rear Derailleur

Average User Rating: (Excellent) Vital Rating: (Excellent)
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Tested: Shimano Zee Derailleur - Become a Trail Ninja

Rating: Vital Review

by Nick Zuzelski

In the craze of clutched rear derailleur technology coming out these days, Shimano's newest offering is targeted to fit the market of gravity riders looking for performance while keeping some hard earned money in their pocket. Enter Zee.


Zee RD-M640 Highlights

  • 10-Speed Only
  • Short Cage
  • Weight: 250 grams
  • MSRP: $109.99

The Zee rear derailleur features Shimano's Shadow Plus technology. Translation: The rear derailleur is strategically mounted and tucked in with a low profile design, decreasing the vulnerability of hits or impacts, and thanks to an innovative clutch, you aren't going to hear much chainslap noise while blitzing through rocks and braking bumps. The clutch is fully serviceable and adjustable so you can keep things maintained and running smoothly after some use and abuse throughout the season.

New to the whole clutched derailleur technology? Shimano has integrated a one-way clutch mechanism into the derailleur knuckle. This provides significantly increased resistance when the chain pulls on the cage, preventing excessive chain slack, which was previously the cause of the dreaded chain slap and poor retention.


All of Shimano's clutched derailleurs have an "on" and "off" mode, activated by a small gold switch. The only time we saw a need to put the switch in "off" mode was during wheel removal and chain installation to allow the derailleur to swing forward with less force.

Shimano offers two models of the Zee - A "DH spec" that fits up to a 28 tooth cassette, and a "Freeride spec" that fits up to a 36 tooth cassette. This is accomplished using a different sized b-link that can be purchased independently for converting your rear derailleur between modes.

On The Trail

We have been running both the DH spec on a downhill bike and the Freeride spec on a 1x10 trail bike. Both setups are holding up following some muddy, rocky abuse.

One area we have really enjoyed has been the benefits seen on the trail bike. The option to have both a clutched rear derailleur AND a short cage able to handle a wide range 11-36 cassette? Yes please.

Combined with the Zee shifter, shifting performance is crisp, precise and snappy quick. The derailleur has been a set-and-forget endeavor and has been free of any ghost shifting and skipping after a proper flogging on the trails for a few months.

One of the reasons we are seeing such great long term durability and continued performance in this derailleur can be greatly contributed to the extremely low profile of the Shadow Technology. The main derailleur body is much less exposed and seems to hide from rocks, stumps, and shuttling abuse that destroys more conventional designs.


Zee's clutch has virtually eliminated chain slap. Since installation, our test bikes have been silent slayers. No more ugly excessive tape or old tubes/tires/who knows what needed to keep your frame quiet and unscathed. Win. But wait… this has developed an unforeseen yet small downside - we have routinely scared the $#% out of hikers and slower descenders when running in Zee stealth mode. Sometimes it is nice to have a little noise to let people know that you're coming up behind them. I think we'll survive though.

If you have yet to throw your leg over a bike with a clutched rear derailleur, you better believe the hype - this new breakthrough is making bikes so quiet and dialed that you will never want to be without a clutched setup again. It's that good.

While the clutch is fully serviceable and adjustable, we haven't had the need to adjust any factory settings. They're working great, but it is nice to know that some adjustability is available if needed.

What's The Bottom Line?

Given the impressive features, performance, and durability we've experienced, it's hard to call the Shimano Zee rear derailleur a compromise. Coming in at half the cost of the Saint equivalent, this is a very good choice for budget-minded riders looking for solid shifting performance with Shimano's proven Shadow Plus technology.

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Silent and Deadly

The Good:

low cost, works great, reliable

The Bad:

none so far

Overall Review:

I got the zee clutch after reading on some forums that you can run it with 9 speed sram shifters. I wanted to go with a 1x setup but didn't want to upgrade my entire drive train and shifters just yet. I mounted a small spacer I picked up from home depot to the derailleur to get the correct pull and the shifting has been flawless.

The clutch simply works. I use it in conjunction with a narrow/wide chainring and haven't had a chain drop since. Not one in 8 months so I ended up removing my chain guide where it sits lonely in a box gathering dust. And the silence is wonderful. I hate noisy bikes.

If you're on the fence about getting a clutch derailleur just do it. Like a dropper post, it's hard to go back once you do.

Zee right derailleur?

The Good:

Low cost, clutch, black, strong. Great warranty service.

The Bad:

Clutch is finicky and fragile. Replacement parts? Good luck.

Overall Review:

I traded a warrantied XTR shadow+ derailleur, new in box, for the ZEE, because it was cheap. I chose the ZEE specifically because it has a steel backplate in place of the aluminum one which lives on the XTR. This aluminum backplate turned out have a significant weak spot, which I broke. I figured that due to this key difference, the ZEE would have a fighting chance.

I mounted up the ZEE on my G-Spot, with a 11-36 cassette and an MRP Mini Guide. Things were great, the clutch was effective, the chain was silent. After four months, the clutch started weakening in strength, and effectiveness. I popped off the clutch case expecting to find a similar tiny little wrench to what the XTR has, instead finding no tool at all. I grabbed a pair of narrow pliers and adjusted the set screw tighter by about a quarter of a turn. I returned the case cover and applied the clutch, and it wasn't much tighter. I rode for a few more weeks, then popped the cover off again and the clutch strap fell off in my hand. What was one piece, became two.

I called Shimano tech support, and learned that those fancy little clutches have literally no replacement parts available. They were very kind, and sent me a shiny new ZEE derailleur, which I will do my best to keep in one piece.

The lessons I learned were:

- Never apply the clutch with the cover off, the mechanism relies on the inner moldings of the case providing support from the outside.

- If you don't know the torque spec for the set screw on the clutch strap, and have a crow footed torque wrench with MINIMAL Newton- Meter values, then don't go trying to adjust it. What is that torque spec? Nobody seems to know.

- If you run a short cage derailleur without a clutch, an 11-36 cassette, and a chain long enough to reach the 36, the chain will catch in the rear wheel very often. I discovered this undesired side effect on a set of 30ft. tables, when my rear wheel locked up. I came skidding to a stop and looked down to see that my chain was being eaten by my frame. This occurred during my two week wait for the warranty replacement unit. I figured that because I had a chain guide on the front, I could just ride without the clutch and it would be noisy at worst, I was wrong. It happened at least four times during the day of shuttling.


Product Shimano Zee M640 Rear Derailleur
Riding Type Dirt Jump / Slopestyle, Downhill, Enduro / All-Mountain, Freeride / Bike Park, Trail
Speeds 10-Speed
Clutch Yes
Cage Length Short
Weight 0 lb 9.7 oz (275 g)
Miscellaneous Wide ratio spec for Freeride: 11-32 or 36 tooth
Close ratio spec for DH: 11-28 tooth
Low-profile design
Direct Mount option
Shimano SHADOW RD+ spring
Price $109.99
More Info

Shimano Website

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