Shimano Deore RD-M6100-SGS rear derailleur: setup and repair

How to confirm you have an RD-M6100-SGS

The RD-M6100-SGS is a 12-speed Shadow RD+ derailleur, which means it has a clutch (Shimano calls it a stabilizer) and a switch lever with ON and OFF positions. It bolts straight to a standard derailleur hanger.

On the M6100 the clutch sits under a plate unit cover held on with screws. The RD-M9100 and RD-M8100 derailleurs use a plate unit rubber cap you can remove by hand instead, so if your derailleur has a screwed-on cover, that fits with it being an M6100.

The matching SL-M6100 shifter comes in two versions: a standard one with its own band clamp, and an I-SPEC EV version (SL-M6100-I) that mounts to a Shimano brake lever. The CN-M6100 chain has gray pin link plates and brown roller link plates and is joined with a QUICK-LINK.

The switch lever matters for everything below. Set it to OFF when you install or adjust the derailleur, and to ON for riding. With it ON, the chain slaps less and is more likely to stay on.

RD-M6100-SGS specifications

Torque figures

On carbon handlebars, Shimano says to check the shifter clamp torque with the bar or bike maker.

Install the RD-M6100-SGS

Before you start: check the hanger is straight with a hanger alignment tool such as Shimano TL-RD11. No amount of adjusting will make a derailleur on a bent hanger shift well.

1. Set the switch lever to OFF.

2. Start the B-axle into the hanger by hand and make sure it goes in straight, not at an angle.

3. As you tighten, hold the derailleur so the stopper plate sits against the B-tension stop on the hanger with no gap.

4. Tighten the B-axle to 10–12 N·m with a torque wrench.

   From DM-MARD001, installation of the rear derailleur

5. Check now and then that no gap has opened between the stopper plate and the B-tension stop. A gap there makes shifting worse over time.

Set the high limit screw

1. Shift the chain onto the smallest (10T) sprocket.

2. Look at the derailleur from behind the bike. Turn the high limit screw until the center of the guide pulley lines up with the outer face of the smallest sprocket.

   From DM-MARD001, stroke adjustment (top)

Size and join the chain

Before you start: on a full suspension bike, a chain that is too short can overload and damage the drivetrain when the suspension compresses. Size it with the suspension fully extended, then check it at the point where the chainstay is longest.

1. Wrap the chain around the largest chainring and the largest (51T) sprocket, without running it through the derailleur.

2. Bring the two ends together at the back of the cassette. Where they meet is your starting point.

3. Add links on top of that. Hardtail: 4 to 5 links plus the QUICK-LINK. Full suspension: 5 to 6 links plus the QUICK-LINK.

   From DM-MARD001, checking the chain length

4. On full suspension, put the bike in the largest chainring and largest sprocket and compress the suspension to the point where the chainstay is longest. The chain must not go tight.

5. Cut the chain with a TL-CN29 or TL-CN35 chain cutter. Seat the chain properly in the cutter and push the pin all the way out. Never cut through a link that was previously joined by a QUICK-LINK; it damages the cutter.

   From DM-MACN001, cutting the chain

6. Thread the chain through the derailleur cage. It must pass on the derailleur body side of the chain retaining pin or plate in the cage. Routing it on the wrong side can damage the chain or the derailleur.

7. Fit a new SM-CN910-12 QUICK-LINK: put one half into each inner link end, with the arrow pointing the way the chain moves when you pedal, seen from the front of the link. Pull the link together until both sides are fully seated (Shimano lists the TL-CN10 tool), and check both sides.

   From DM-MACN001, connecting the chain

To remove a QUICK-LINK, slide both sides to release it. Shimano says to use its own tool for removal, and never to reuse a QUICK-LINK once removed. Fit a new one whenever you replace the chain. See also how to set chain length.

Replace the shift cable

Before you start: stop the rear wheel from turning while you clamp the cable and crimp the end cap.

At the SL-M6100 shifter:

1. Loosen the cable fixing bolt on the derailleur.

2. Press the release lever 11 or more times to put the shifter in its starting position.

3. Unscrew the inner hole cap on the shifter, pull out the old cable and feed in the new one.

4. Screw the inner hole cap back in only until it stops. Forcing it can strip the thread.

   From DM-MBSL002, replacing the inner cable

At the derailleur:

1. Back the B-screw out until the stopper plate touches the bracket body with no gap.

2. Size the outer casing. Put a sealed outer cap on temporarily, line it up with the bottom of the derailleur's casing holder and leave enough slack. On full suspension, measure at the point in the travel where the cable run is longest. Leave enough at the front for the bars to turn fully.

3. Cut the casing with a cable cutter such as TL-CT12, round the cut end back to a true circle, fit the sealed outer cap and route the inner cable. If the derailleur moves a lot on your bike, use the aluminum sealed outer cap supplied.

4. At the frame's casing stop, fit the sealed outer cap with tongue and the rubber shield. You can skip this with full-length casing. Do not bend the tongue.

5. Check the shifter is still in its starting position, clamp the inner cable in the groove under the cable fixing bolt and tighten it.

6. Take out the initial stretch: hold the derailleur so it cannot move and work the shifter several times. Then loosen the bolt, pull the cable taut in the groove and tighten the cable fixing bolt to 6–7 N·m.

   From DM-MARD001, securing the inner cable

7. Cut the cable so about 20 mm sticks out, crimp on an inner end cap and check it cannot touch the spokes.

Grease the inner cable and the sliding parts of the casing with SIS SP41 grease, and use OT-SP41 casing. A polymer-coated cable can look fuzzy as it wears; inside the casing this is only cosmetic.

Set the low limit screw

1. Use the shifter to move the derailleur in toward the largest sprocket.

2. Turn the low limit screw until the center of the guide pulley lines up with the center of the largest sprocket.

   From DM-MARD001, stroke adjustment (low)

Set the B-tension screw

1. Shift to the smallest chainring and the largest sprocket while turning the crank. If the cage hits the sprocket during the shift, tighten the B-screw until it clears.

2. The RD-M6100-SGS with the 10-51T cassette uses setting (A). Turn the B-screw until the line on the inner side of the outer plate lines up with the tip of the highest tooth on the 51T sprocket.

   From DM-MARD001, adjusting the end adjust bolt

3. Shift through all the gears and check it shifts smoothly.

4. Redo this whenever you change the cassette to one with different tooth counts. On some frames the B-screw is also what keeps the derailleur from hitting the chainstay.

For the general method across brands, see how to adjust a rear derailleur.

Adjust the indexing (SIS adjustment)

1. Set the switch lever to OFF.

2. Shift to a sprocket 5 to 7 steps down from the largest one. On a double, use the big chainring.

3. If the chain already rubs the next larger sprocket, turn the barrel adjuster clockwise until it goes quiet.

4. While pedaling, turn the barrel adjuster counterclockwise until the chain just starts to rub the next larger sprocket.

5. Turn the barrel adjuster 5 clicks clockwise. That is the correct setting.

   From DM-MARD001, SIS adjustment

6. Shift through all 12 gears while pedaling and listen for noise in every gear.

7. Set the switch lever back to ON and test ride. Shifting should be smooth, consistent and quiet.

Replace the pulleys

Replace the pulleys when they have enough play to make noise. The replacement set is Y3FY98010, and the pulley screws are Y5V598140.

1. Remove the pulley screws and take out the guide (upper) and tension (lower) pulleys.

2. Fit the new pulleys. If they have arrows on them, the arrows must point the way the pulleys turn when you pedal forward. Some pulleys have no direction.

3. Tighten the pulley screws to 2.5–5 N·m.

   From DM-MARD001, replacing the pulleys

Adjust the clutch friction

If the clutch feels weaker or stiffer than it used to, you can reset it.

1. Set the switch lever to ON.

2. Remove the screws and lift off the plate unit cover.

3. Turn the friction adjustment screw to increase or decrease the friction. Turn it gently: never put 0.25 N·m or more on this screw.

4. Check the friction with a torque wrench and hexalobular bit in the outer plate. The reading to turn the cage should be 4.4–5.4 N·m.

   From DM-MARD001, adjusting friction

5. Refit the plate unit cover and tighten its screws to 1–1.5 N·m. Make sure the cover is on before you ride.

Remove and fit the CS-M6100 cassette

Before you start: if you tighten the lock ring with a sprocket out of line, the splines can shear and the wrench can suddenly slip and hurt you.

1. To remove, hold the cassette with a TL-SR24 sprocket remover on a sprocket outboard of the middle (holding it on an inner sprocket is unstable), unscrew the lock ring with the Shimano lock ring tool and slide the cassette off.

2. To fit, slide on every sprocket except the 10T, largest first. Line up each wide spline with the wide groove on the freehub body, marked side facing out.

3. The two sprocket spacers are different thicknesses. Do not swap them.

4. Fit the 10T so its wide part lines up with the wide part of the 12T. The alignment marks on the 10T, 12T and 14T should line up.

5. Thread in the lock ring and tighten it to 30–50 N·m.

   From DM-MACS001, installation of the cassette sprocket

Parts and consumables

Tools

• 2 mm, 3 mm, 4 mm and 5 mm hex wrenches
• Cross head screwdriver [#2] and hexalobular [#27] driver
• Torque wrench (the values on this page run from 1 N·m to 50 N·m)
• TL-CT12 cable cutter
• TL-RD11 hanger alignment tool
• TL-CN29 or TL-CN35 chain cutter, TL-CN10 QUICK-LINK tool
• TL-LR10 or TL-LR15 lock ring tool, TL-SR24 sprocket remover, adjustable wrench

Troubleshooting by symptom

Shifting is poor and indexing will not fix it

Check the hanger with TL-RD11, clean and grease the cable, and check the casing is not too long or too short. Then redo the indexing.

Shifting has got worse over time

Look for a gap between the stopper plate and the B-tension stop. Refit the derailleur as in the install steps.

Cage hits the 51T sprocket when shifting

Tighten the B-screw, then set it properly as in B-tension.

Chain rubs the next larger sprocket

Turn the barrel adjuster clockwise. See indexing.

Noise from the cage

Check the pulleys for play. Replace them if they are loose and noisy, as in pulley replacement.

Chain slaps or drops on rough ground

Make sure the switch lever is ON. If it is and the clutch feels weak, adjust the friction.

Chain skips or a link looks bent

Inspect the chain for bent or cracked plates. Clean it with a neutral detergent, never an acid or alkaline rust remover, and lubricate it.

Related: Adjust a rear derailleur, Set chain length, Shimano XT M8100 brakes, Shimano CUES, SRAM GX Eagle