SRAM GX Eagle 12-speed derailleur: install, chain gap, limit screws and cable

How to confirm you have a GX Eagle mechanical derailleur

The serial number on GX, X0 and XX mechanical mountain bike derailleurs is laser etched on the back of the inner cage. The derailleur bolts to a derailleur hanger with a 5 mm B-bolt, and it has a B-adjust screw and two limit screws. It shifts by cable using SRAM's X-Actuation pull.

If your derailleur has no limit screws, bolts straight through the frame with an 8 mm bolt and has a Setup Key marked A and B, it is an Eagle Transmission derailleur, not this one. See the Eagle Transmission page. Transmission (T-Type) chains, cassettes and derailleurs are a separate system.

There are two versions of the GX Eagle derailleur:

• RD-GX-1-B1: largest cog 50T, for the 10-50t cassette.
• RD-GX-1-B2: largest cog 52T. SRAM says it is backward compatible and works with both 10-50t and 10-52t cassettes. Lunar color.

The Eagle PowerLock is marked "Eagle" on the side. It is not interchangeable with the 12-speed eTap AXS road PowerLock.

Specifications

On an e-MTB, SRAM's warranty requires the Eagle chain, cassette and derailleur to be used with a SRAM 1-Click shifter.

Torque figures

SRAM publishes no torque for the limit screws or the B-adjust screw. They are adjusting screws only.

Install the derailleur

Before you start: a gap between the B-washer and the hanger can let the derailleur work loose or break off the B-bolt. Check the washer sits tight against the hanger before you torque the bolt.

1. Check the hanger is straight with a hanger alignment tool. A bent hanger hurts shifting no matter how well the rest is set.

2. Do not grease the mounting bolt or the hanger threads.

3. As you fit the derailleur, push the B-adjust washer forward so there is no gap between it and the hanger.

4. Tighten the 5 mm mounting bolt to 11 N·m (97 in-lb) with a torque wrench.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, Derailleur Installation, pp. 9–10

Fit the trigger shifter as shown in the SRAM MTB Disc Brakes and Shifters User Manual. To set the paddle angle, loosen the T25 reach adjust bolt, move the paddle, and tighten to 3 N·m (27 in-lb).

Route the cable and set initial tension

1. Measure and cut the derailleur housing so there are no tight bends in the frame or at the derailleur. Fit metal ferrules and install the housing.

2. Shift the trigger to its furthest outboard position (smallest cog) while pulling the cable through the housing.

3. Turn the shifter barrel adjuster clockwise until it stops, then back it out one full turn counter-clockwise.

4. Run the cable through the housing, then through the derailleur and into the clamp groove under the anchor bolt.

5. Pull the cable tight and tighten the anchor bolt to 4.5 N·m (40 in-lb).

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, Cable Routing, pp. 22–23

Set the limit screws

The limit screws set how far the derailleur can move at each end of the cassette. They take a 3 mm hex key or a Phillips screwdriver.

1. High limit (H): with the chain on the smallest cog, turn the H screw until the center of the upper pulley lines up with the outboard edge of the smallest cog.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, p. 20

2. Low limit (L): shift to the largest cog and turn the L screw until the center of the upper pulley lines up with the center of the largest cog.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, p. 24

3. Check both limits again after you set the chain gap.

Size and fit the chain

Before you start: SRAM warns that a chain cut to the wrong length or joined wrong can break and cause a crash. The cage is spring loaded, so keep fingers clear of the pulleys when you lock and release it.

1. Full suspension: size the chain with the rear suspension fully compressed. Deflate or remove the shock to do this. Frames with an upper idler also need a lower idler.

2. Round X-SYNC or X-SYNC 2 chainring: wrap the chain around the chainring and the largest cog, skipping the derailleur. On full-suspension and idler bikes, add one inner and one outer link where the chain starts to overlap. On hardtails, add two inner and two outer links.

3. Break the chain so an inner link is left on the end. Throw away the outer link and the extra chain.

4. Oval X-SYNC 2 chainring: put the crank at the 1 o'clock position, wrap the chain around the ring and largest cog, and add the number of links shown in the chart in SRAM's manual.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, Chain Sizing, pp. 25–28

5. Put the chain on the smallest cog. Rotate the cage forward and press the Cage Lock button to lock it extended, then run the chain through the pulleys below the cage tab.

6. Join the ends with a new Eagle PowerLock, arrow pointing the way the chain travels.

7. Release the Cage Lock by rotating the cage forward and letting it come back gently.

8. Turn the crank until the PowerLock is above the chainstay, check both halves line up, hold the rear brake and push down hard on the crank until the PowerLock clicks. Check it moves freely. A PowerLock is single use and comes off only with chain link pliers.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, Chain Installation, pp. 29–33

Reinflate or refit the shock before you set the chain gap. More detail is on the chain length page.

Set the chain gap

The chain gap is the space between the upper pulley and the largest cog, set with the B-adjust screw. SRAM gives two ways to set it on 12-speed Eagle. Use the gauge if you have one.

With the SRAM Eagle chain gap gauge

Use gauge 11.7518.099.000 (RD Chaingap Adjustment Gauge Eagle V2). It works on 50T and 52T Eagle, mechanical and AXS. The older gauge 11.7518.082.000 is discontinued and does not work with 52T cassettes.

1. Shift onto the second largest cog (42T). On a full-suspension bike, set the bike at sag.

2. Snap the gauge onto the largest cog (50T or 52T) so the cog teeth touch the gauge surface in the window cut-out.

3. Rotate the gauge and cassette together until the ledge on the back of the gauge touches the upper pulley.

4. Turn the B-adjust screw until the center of the upper pulley bolt lines up with the tip of the pointer on the gauge. Keep the cog teeth on the gauge surface and the pulley on the ledge while you do this. Remove the gauge.

5. Check upper pulley alignment on the largest and smallest cogs and touch up the limit screws.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, pp. 34–36

Without a gauge

1. Shift onto the second largest cog. On a full-suspension bike, set the bike at sag.

2. Turn the B-adjust screw (3 mm hex or Phillips) until there is a 3 mm gap between the upper pulley and the tallest teeth of the largest cog.

3. Check pulley alignment on the largest and smallest cogs and adjust the limit screws if needed.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, p. 39

Adjust indexing

Do this with the chain gap and limits already set. Turn the barrel adjuster on the shifter one click at a time and shift through the range after each click.

1. Slow shifts from a bigger cog to a smaller cog: turn the barrel adjuster clockwise one click at a time until the shift is clean.

2. Slow shifts from a smaller cog to a bigger cog: turn it counter-clockwise one click at a time until the shift is clean.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, p. 41

If you cannot get clean shifts with the barrel adjuster, check the hanger is straight, then go back over chain length, chain gap and limit screws. SRAM says a good setup needs the right chain length, chain gap, limit screw settings and cable tension. The rear derailleur adjustment page has more general help.

Replace the shift cable

1. Shift to the smallest cog so the cable is slack. Cut off the end cap and loosen the derailleur anchor bolt.

2. Trigger with a cover: remove the cover bolt (3 mm hex or T25) and the cover. Push the old cable out of the shifter and pull it free. Feed the new cable through the shifter, refit the cover and tighten the bolt to 1 N·m (9 in-lb).

3. Trigger with a hatch: open the hatch, thread the new cable through the cable port and close the hatch.

   From the SRAM MTB Disc Brakes and Shifters User Manual, Cable Change, p. 25

4. Run the cable through the housing to the derailleur and set the tension as in Route the cable, then check indexing.

Replace the pulleys

1. Remove the upper pulley bolt (3 mm hex), the pulley and its spacers. Do the same for the lower pulley.

2. Fit the new pulleys with the etched letter facing outboard: U is the upper pulley, L is the lower. Refit the spacers flat side out.

3. Tighten each pulley bolt to 3 N·m (27 in-lb).

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, Pulley Replacement, p. 50

The B-bolt can also be serviced. Removing and refitting it means levering a circlip in and out of its groove with two picks while the bolt sits on a 5 mm hex key held in a vise. Wear safety glasses, because the circlip can fly off. SRAM's manual covers this on pages 44–49.

Cassette and chain wear

1. Grease the driver body threads and slide the cassette fully onto the XD driver with the splines engaged.

2. With a lockring tool that has a guide pin, pushing inward on the tool, tighten to 40 N·m (354 in-lb). If it gets hard to turn after a few turns, it may be cross-threaded. Back it off and start again.

3. To remove the cassette, wrap a 12-speed chain whip all the way around a cog and loosen with the lockring tool.

   From the SRAM Cassettes Digital User Manual, Cassette Installation XD and Cassette Removal

Clean the chain and cassette with biodegradable cleaner only, rinse, dry and lube. Do not use alkaline or acidic solvents, and do not soak or store the chain or cassette in cleaner. SRAM warns that parts can turn brittle and break. Replace the chain at 0.8% elongation.

Parts and consumables

Tools

• 3 mm hex key or Phillips screwdriver (limit and B-adjust screws; 3 mm also for pulley bolts and the trigger cover bolt)
• 4 mm hex key or T25 Torx (cable anchor bolt; T25 also fits the trigger cover and reach adjust bolts)
• 5 mm hex key (mounting bolt)
• Torque wrench
• Derailleur hanger alignment tool
• Chain tool approved for SRAM Eagle chains, and chain link pliers
• SRAM chain gap adjustment gauge Eagle V2, 11.7518.099.000
• SRAM Chain Wear Indicator
• Cassette lockring tool with guide pin (splines 7–8 mm long) and a 12-speed chain whip
• Cable and housing cutter

Troubleshooting by symptom

Slow shifts to smaller cogs

Cable tension too high. Turn the barrel adjuster clockwise one click at a time. See indexing.

Slow shifts to bigger cogs

Cable tension too low. Turn the barrel adjuster counter-clockwise one click at a time.

Poor shifting that tension will not fix

Bent hanger. Check it with a hanger alignment tool, then recheck chain length, chain gap and limit screws.

Shifting on a full-suspension bike changes once you sit on it

The chain gap was set with the suspension extended. Set it again at sag.

Derailleur works loose on the hanger

There was a gap between the B-washer and the hanger at install. Refit it as in Install the derailleur and torque to 11 N·m.

Related: SRAM Eagle Transmission, Adjust a rear derailleur, Set chain length, SRAM DB8 brakes