How to Install and Adjust a Rear Derailleur: Cable, Shimano Di2, SRAM AXS & Transmission

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Updated September 2026: rewritten from Robb’s original 2009 cable-era guide to cover mechanical, Shimano Di2, SRAM AXS, and SRAM Eagle Transmission. The electronic-shifting steps follow Shimano, SRAM, and Park Tool procedures checked in September 2026. They are not a new BIKE198 hands-on session on every system. The photos are from the original cable-era guide. Your derailleur’s own manual always wins over any general guide, including this one.

Quick answer: Start with a straight derailleur hanger. Then bolt the derailleur on using the torque spec printed on the part or in your derailleur’s manual (for Shimano mechanical derailleurs, that’s typically 8–10 N·m per Shimano’s dealer manuals and Park Tool; the 12-speed Di2 derailleurs in Shimano’s dealer manual DM-MARD011 are 10–12 N·m), with the B-screw stop sitting correctly against the hanger tab. If they disagree, follow the current manual. Size and route the chain, and set the low and high limit screws so the chain can never go past the largest cog into the spokes or off the smallest cog into the frame. Then set the B-gap and adjust indexing. On a cable derailleur you do that with cable tension and the barrel adjuster. On Shimano Di2 you use adjustment mode, and on SRAM AXS you use MicroAdjust. SRAM Eagle Transmission is the exception: it has no hanger and no H, L, or B screws, and it is set up with a Setup Key, Setup Cog, and chain length from SRAM’s AXS app. Whatever you run, re-check shifting under load before a real ride.

Which system are you on?

Four drivetrain families cover almost every mountain bike you’ll work on today. Find yours, then jump to that section. Everyone should read the foundations first.

Tools you’ll need

• Derailleur hanger alignment gauge: Park Tool DAG-2.2 (MSRP $93.95 at Park Tool). For every system that uses a hanger. Not used on SRAM Eagle Transmission, which has no hanger.
• Cable and housing cutter (mechanical only): Park Tool CN-10 (MSRP $48.95 at Park Tool). Cuts shift cable and housing cleanly. It’s not meant for hydraulic brake hose.
• Chain tool for sizing and joining chains (for example, Park Tool’s CT-3.3).
• Torque wrench that covers the torque spec printed on the part or in your derailleur and frame manuals (if they disagree, follow the current manual). For Shimano mechanical derailleurs, that’s typically 8–10 N·m per Shimano’s dealer manuals and Park Tool; the 12-speed Di2 derailleurs in Shimano’s dealer manual DM-MARD011 are 10–12 N·m, and SRAM’s Transmission mount bolt is 35 N·m.
• Metric hex keys: 5 mm for the mounting bolt on many derailleurs, and small hex keys (often 2 mm) for limit and B-screws on many modern models. Some older derailleurs use a Phillips screwdriver for the limit screws.
• System-specific: the correct SRAM chain gap gauge for your cassette (AXS), Shimano’s TL-EW300 plug tool (wired Di2 / e-bike), and a phone with the SRAM AXS app (AXS and Transmission).
• Threadlocker or grease for the mounting bolt threads, per your derailleur’s instructions.

Building out a home tool kit? Our must-have bike tools list and home bike workshop guide cover the rest of the bench.

Foundations before any indexing

Shifting problems get blamed on cable tension or MicroAdjust when the real cause is further upstream. Sort these first, in this order.

1. Check and straighten the derailleur hanger (skip for Transmission)

The hanger is the small, usually aluminum part the derailleur bolts to. It’s designed to bend or break in a crash so your frame doesn’t. That’s why it’s so often slightly bent. SRAM’s own service guide says hanger alignment is the foundation for good shifting, that it can’t be judged by eye, and that it should be checked with a hanger alignment tool before any other adjustment. That includes new hangers and new bikes, which can get knocked in shipping.

Why it matters for safety: a bent hanger can let the chain shift off the largest cog into the spokes, or off the smallest cog into the frame, even when the limit screws were set correctly before. That can wreck a wheel or derailleur and cause a crash. Check alignment after any crash or knock to the derailleur.

A gauge like the Park Tool DAG-2.2 threads into the hanger and measures against the rim at several points around the wheel. If the hanger is out, straighten it gradually. Aluminum weakens every time it’s bent, so a hanger that’s been straightened several times may need replacing. If you don’t want to own a gauge, a shop can check it. SRAM Eagle Transmission has no hanger, so the DAG-2.2 doesn’t apply there.

2. Mount the derailleur and torque the bolt

• Prep the mounting bolt threads with threadlocker or grease as your derailleur’s instructions specify. Some bolts come with dry threadlocker already applied.
• Thread the bolt in square to the hanger. If it binds, stop and check the threads rather than forcing it.
• Make sure the B-screw stop (the tab or plate behind the mounting bolt) ends up sitting against the hanger tab, not hanging below or in front of it. Shimano’s newer derailleurs call for no gap between the stopper plate and the hanger tab.
• Use the torque spec printed on the part or in your derailleur’s manual. If they disagree, follow the current manual; for example, SRAM says early Transmission mount bolts marked 25 N·m should be tightened to 35 N·m. For Shimano mechanical derailleurs, that’s typically 8–10 N·m per Shimano’s dealer manuals and Park Tool; the 12-speed Di2 derailleurs in Shimano’s dealer manual DM-MARD011 are 10–12 N·m. The original version of this guide gave 8–10 Nm (70–85 in.lbs). SRAM says its derailleur bolts have specific torque values that must be followed, so use the figure in your manual.
• If the derailleur has a clutch (Shimano Shadow+ or a SRAM cage lock), switching it off or locking the cage makes installation easier. Many manuals call for this. Turn the clutch back on before you ride.

3. Chain length and routing

The original version of this guide used the classic method for traditional derailleurs: wrap the chain around the biggest chainring and the largest cassette cog without threading it through the derailleur, then add two links and cut there. Modern 12-speed systems and SRAM Transmission use their own methods (Transmission gets its chain length from the AXS app or SRAM’s Full Mount chain length guide). Follow your drivetrain’s manual rather than a rule of thumb.

Before you join the chain, route it through both pulleys and inside the cage plates. If you’re replacing a derailleur, take reference photos of the old routing and B-screw position from a few angles before you remove anything.

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Mechanical (cable) setup

This is the cable-era core of the original guide, updated. Order matters: limits first, then the B-gap, then the cable, then indexing.

High and low limit screws

The limit screws stop the derailleur from moving past the smallest and largest cogs. In the original guide’s words, they prevent “the chain from falling off the backside of the cassette into the spokes or off the front side into the frame.” Set them before the cable goes on.

• Low (L) screw: with the cable disconnected, push the derailleur inward by hand while turning the cranks, and set the L screw so the upper pulley lines up center-to-center with the largest cog. The derailleur must not be able to go any farther inward than that. This is the screw that keeps the chain out of your spokes.
• High (H) screw: let go of the derailleur so it rests on its spring and set the H screw so the upper pulley lines up center-to-center with the smallest cog. The chain should run there without clicking or skipping.

B-gap (chain gap)

The B-screw sets the gap between the upper pulley and the cassette. Too close, and the pulley can hit the big cogs and you may not get the full range. Too far, and shifting gets slow and vague. Set it with the chain on the cog your manual specifies (usually the largest), then check that the pulley clears the cassette in every gear.

For the 9- and 10-speed derailleurs of 2009, the original guide said: “In the Shimano instructions, they recommend you get the pulley as close to the cassette as you can. I tend to stay with the SRAM recommendation of 1/4″ in both cases.” Modern wide-range 12-speed systems use model-specific methods instead: a SRAM chain gap gauge, or a marking on the derailleur on some Shimano models. On those, follow the manual rather than a fixed measurement.

Install the cable and housing

1. Make sure the housing is secured to the frame and seated correctly at the derailleur, with no kinks, and not limiting derailleur movement.
2. Shift the shifter to the smallest cog (hardest gear) to release the most cable.
3. Turn the barrel adjuster all the way in (clockwise), then back out one full turn so you have adjustment both ways.
4. Pull the cable snug through the derailleur’s cable path and tighten the cable fixing bolt to the manufacturer’s torque spec.
5. Shift up and down through the gears several times while turning the cranks to seat the housing ends, then re-check for slack and re-tension if needed.
6. Cut the cable an inch or two past the fixing bolt with a proper cable cutter like the Park Tool CN-10 and crimp on an end cap so it can’t fray.

If you’re replacing housing too, a clean square cut matters as much as the cable. We covered one sealed cable kit in our Gore RideOn cable review.

Barrel-adjust indexing

With the bike in the stand, turn the cranks and click through every gear. Adjust the barrel adjuster one click (or a quarter turn) at a time:

• Slow or hesitant shifts toward bigger cogs: not enough tension. Turn the barrel adjuster out (counter-clockwise) to add tension.
• Slow or hesitant shifts toward smaller cogs: too much tension. Turn it in (clockwise).

Some cable derailleurs, including older Shimano SIS models like the one below, have a second barrel adjuster on the derailleur as well as the one on the shifter. Either one does the same job.

Then re-check the low limit with the cable connected. Shift firmly to the largest cog and make sure the derailleur stops there. If it can overshift toward the spokes, tighten the L screw until it can’t.

Shimano Di2 setup (wireless and wired)

There’s no shift cable to tension. Indexing is done electronically in adjustment mode, but the hanger, B-screw, and limit screws still matter. The steps below follow Shimano’s procedure for the 12-speed wireless MTB and gravel derailleurs (XTR RD-M9250, XT RD-M8250, Deore RD-M6250, and GRX RD-RX827, including their wired e-bike versions). Other Di2 rear derailleurs, including the RD-RX717, should be set up from their own dealer manual. Button layout and adjustment-mode entry differ by model and generation, so check your dealer manual. For older road Di2 context, see our Dura-Ace Di2 review.

Charge, pair, and connect

• Wireless: charge and install the derailleur battery, then pair the derailleur and shifter. Shimano’s E-TUBE Project app handles pairing checks, firmware, and settings.
• Wired e-bike versions: no derailleur battery. Connect the EW-SD300 wire to the derailleur with Shimano’s TL-EW300 plug tool, and refit the wire cover.
• Mount the derailleur as in the foundations section: straight hanger, no gap between the stopper plate and the hanger tab, and the mounting bolt at the torque spec printed on the part or in your derailleur’s manual (if they disagree, follow the current manual). For RD-M9250, RD-M8250, RD-M6250, and RD-RX827, that’s 10–12 N·m per Shimano’s dealer manual DM-MARD011. RD-RX717 isn’t in that manual, so use the figure in its own manual.

B-gap

Size and route the chain first. Shift to the largest cog. Adjust the B-screw: Shimano’s dealer manual DM-MARD011 says to align the contour of the outer plate with the tip of the tallest tooth on the largest sprocket.

Micro-adjust in adjustment mode

1. Shift to the 5th-largest cog.
2. Enter adjustment mode: hold the function button on the derailleur, or the designated shifter button, until the derailleur LED shows adjustment mode.
3. Turn the cranks and step the derailleur inboard until the chain just starts touching the next-larger cog and you hear it.
4. Step it back outboard the number of clicks your manual specifies (five on the 12-speed wireless models above), then exit adjustment mode.
5. Shift through all the gears to confirm.

On older Di2 systems, adjustment mode is entered from the junction box and each press moves the derailleur roughly 0.2 mm.

Set the L and H limits

Electronic shifting doesn’t remove the limit screws or their job. Shift to the largest cog and turn the L screw in until it just touches the stopper. Shift to the smallest cog and do the same with the H screw. A Di2 derailleur with loose limits can still put the chain into the wheel or frame.

SRAM AXS setup (Eagle AXS with a hanger)

AXS derailleurs have no shift cable (some e-MTBs run a power cable to them). They still bolt to a hanger, so hanger alignment, the chain gap, and the limit screws all apply. For why wireless shifting took off, see our GX Eagle AXS explainer.

Pair and use the AXS app

Charge the battery and pair the derailleur with its controller. The SRAM AXS app shows your components, updates firmware, and handles settings. If you also pair an AXS dropper into the same system, that’s a separate job. For choosing a dropper, see our best dropper posts guide.

Don’t force an AXS derailleur by hand. The derailleur is moved by a motor. Shift it with the controller or app rather than pushing the cage or parallelogram into position.

Chain gap with the correct gauge

SRAM sets chain gap with a plastic chain gap gauge that clips onto the upper pulley. You turn the B-adjust screw until the tallest teeth of the specified cog line up with the gauge outline for your cassette size. The gauge has to match your cassette. SRAM’s current Eagle gauge is the Eagle V2 chain gap gauge (part 11.7518.099.000). Older Eagle gauges (11.7518.082.000 and 11.7518.095.000) are discontinued and don’t cover 52T cassettes. SRAM’s road/XPLR gauges are for road cassettes and shouldn’t be used on Eagle 50T or 52T MTB setups. Follow the manual for which cog to use and whether to set the gap with the rear suspension sagged.

MicroAdjust

MicroAdjust is AXS’s version of the barrel adjuster. SRAM describes it as a single trim position for the whole cassette, set from the controller or the app. It isn’t set cog by cog. On most controllers you hold the AXS button and press the shift paddle in the direction you want to move. Each step is small (about 0.25 mm on road AXS and roughly 0.2 mm on Eagle), and the derailleur LED flashes to confirm each command even if you can’t see it move.

Limit screws

Shift to the largest cog and set the L screw so it lightly contacts the derailleur’s stop, then shift to the smallest cog and do the same with the H screw. As with every hanger-mounted derailleur, the L limit is what stops the chain going into the spokes.

SRAM Eagle Transmission (T-Type): different rules

Transmission, in both its wireless AXS models and the cable-actuated Eagle 90/70 T-Type, isn’t a hanger-mounted derailleur with a different badge. It mounts directly to the frame at the rear axle, which SRAM calls Full Mount, so the usual steps change. Our GX T-Type Transmission review covers the groupset itself. This section is only about setup.

SRAM also makes cable-actuated Transmission (Eagle 90/70 T-Type). It uses the same Full Mount, Setup Key and Setup Cog method, with the derailleur held at the Setup Cog by a 4 or 5 mm hex key, and cable tension in place of MicroAdjust.

No hanger, no H, L, or B screws

SRAM’s support documents are explicit: Eagle AXS Transmission has no high limit, low limit, or B-adjust screws, and the cable-actuated Eagle 90/70 T-Type uses the same Full Mount, Setup Key and Setup Cog method. The derailleur’s position is fixed by the frame interface, which is designed to line up with the rear axle. There’s no hanger to align, so a hanger gauge doesn’t apply. Don’t try to set it up like a cable derailleur. There are no screws to adjust. Skipping the Setup Key and Setup Cog steps, or setting them wrong, gives the wrong chain gap and, SRAM warns, may damage the derailleur or frame.

Transmission only fits frames built to SRAM’s UDH standard. You remove the UDH hanger (its bolt is left-hand threaded, so turn it clockwise to loosen) before fitting the derailleur.

Setup Key, Setup Cog, and chain length

• Get your bike’s chain length, Setup Key position (A or B), and Setup Cog from the SRAM AXS app or SRAM’s Full Mount chain length guide.
• According to SRAM, the Setup Key in the correct position, used with the correct Setup Cog, pre-sets the chain gap in the stand without sag so that it’s correct once the bike sags under you.
• The exception: for frames not listed in SRAM’s database, and for idler-pulley frames, the Transmission manual says the final tightening must be done with the rear suspension at sag, not unweighted in the stand. For unlisted frames it also gives default setup data (Setup Key position A, Setup Cog 21T / gear 7) along with a chain length table.
• Tighten the mount bolt to SRAM’s spec (35 N·m in the current Transmission manual; SRAM says to use 35 N·m even on early bolts marked 25 N·m), and the thru-axle to your frame or axle maker’s spec. Don’t reuse hanger-derailleur numbers.
• SRAM says to repeat the full setup if you change chainring size, chainstay length (flip chip), or a lower idler pulley position, or after replacing the chain.
• Transmission has no clutch switch. It uses a Cage Mode button (Open, Setup, and Ride modes). Release the cage from Setup Mode to Ride Mode when you’re done.

MicroAdjust only after Full Mount is correct

Once the derailleur is mounted correctly with the right chain length, Setup Key, and Setup Cog, use MicroAdjust from the controller or app to fine-tune. If a small MicroAdjust doesn’t fix it, check axle and mount-bolt torque, chain length, and the Setup Key/Cog rather than chasing it with more trim. For chain wear, SRAM’s Transmission manual says to use a SRAM-approved chain wear tool (replace at 0.8% elongation) and its Transmission Service Matrix.

Ride check under load

A bike that shifts perfectly in the stand can still misbehave on the trail. As the original guide put it, most bikes shift differently in the stand than they do under load. Before a real ride:

• Ride on flats and a climb somewhere safe and shift through every gear under pedaling load.
• Confirm the chain can’t go past the largest cog or off the smallest cog.
• Make small corrections (one barrel-adjuster click or one MicroAdjust step at a time), then check again.
• Confirm the clutch is back on if you switched it off (on Transmission, that the cage is released from Setup Mode to Ride Mode).
• Re-check indexing and limits, and hanger alignment where the bike has a hanger, after any crash or knock to the derailleur.

Troubleshooting matrix

FAQ

How do I adjust a Shimano Rapid Rise derailleur?

Rapid Rise (low-normal) derailleurs rest on the largest cog with no cable tension, so the logic flips: you push the derailleur to the smallest cog by hand to set the high limit, and you start cable installation in the easiest gear. It’s a legacy design mostly found on older bikes.

What torque should the derailleur mounting bolt be?

Use the torque spec printed on the part or in your derailleur’s manual. If they disagree, follow the current manual. For Shimano mechanical derailleurs, that’s typically 8–10 N·m per Shimano’s dealer manuals and Park Tool. The 12-speed Di2 derailleurs in Shimano’s dealer manual DM-MARD011 (RD-M9250, RD-M8250, RD-M6250, RD-RX827) are 10–12 N·m. SRAM specifies torque values per derailleur; the Transmission mount bolt is 35 N·m, and SRAM says to use 35 N·m even on early bolts marked 25 N·m.

Can I use a hanger alignment gauge on SRAM Transmission?

No. Transmission has no derailleur hanger. It mounts directly to the frame at the axle, and SRAM’s hanger guidance says it doesn’t apply.

Should the clutch be on or off during installation?

Many manuals call for switching the clutch off, or locking the cage, to make installation and chain routing easier. Turn it back on before riding. SRAM Transmission has no clutch switch; it uses a Cage Mode button, so release the cage from Setup Mode to Ride Mode when you’re done.

Can I mix brands or speeds?

SRAM’s guidance is to stick to the correct speed and intended ride type within one component ecosystem. SRAM doesn’t verify or endorse third-party chains, chainrings, or derailleur cages with its drivetrains. Check your manufacturer’s compatibility charts before mixing parts.

Do I need to re-index after replacing the chain or cassette?

Re-check it. New parts can change how the chain sits, and new cables settle in after the first few rides. A quick stand check and ride check catches most of it.

Where to buy the tools

The two tools that matter most for doing this job safely at home:

• Park Tool DAG-2.2 Derailleur Hanger Alignment Gauge on Amazon: for any derailleur that bolts to a hanger. Not for SRAM Eagle Transmission, which has no hanger.
• Park Tool CN-10 Cable and Housing Cutter on Amazon: for mechanical shift cable and housing.

Also useful, depending on your system: a chain tool (such as Park Tool’s CT-3.3), a torque wrench that covers the spec in your derailleur’s manual (typically 8–10 N·m for Shimano mechanical derailleurs per Shimano’s dealer manuals and Park Tool, 10–12 N·m for the Shimano Di2 derailleurs in dealer manual DM-MARD011, and 35 N·m for SRAM’s Transmission mount bolt), the SRAM Eagle V2 chain gap gauge for Eagle AXS, and Shimano’s TL-EW300 for wired Di2. Buy SRAM gauges as genuine SRAM parts, because lookalike listings exist. Prices and stock change, so check the listing before you buy.

Official references: SRAM rear derailleur adjustment guide, Park Tool derailleur removal and installation, and Park Tool DAG-2.2.

Robb Sutton

I founded Bike198 back in 2008 and started riding bikes seriously in 1994. A lot has changed since that time and one of the greatest releases is still getting out on the bike and shredding trail or tearing up the road.

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