Complete Drivetrain Overhaul: From Cassette to Crankset

A complete drivetrain overhaul transforms a neglected bike into something that shifts like new. This guide covers everything: cassette removal, chain replacement, chainring inspection, cable replacement, and derailleur adjustment. Budget three to four hours for your first time. With practice, you’ll do it in under two.

When to Overhaul

Drivetrains don’t fail suddenly—they degrade gradually until shifting becomes unreliable. Signs that indicate overhaul time:

Chain skip under hard pedaling, especially in smaller cogs
Visible shark-fin wear on cassette teeth
Chain stretch exceeding 0.75% (we’ll cover measurement below)
Shifting that won’t stay adjusted despite repeated tuning
Grinding noise that persists after cleaning and lubing

If your chain measures past 0.5% stretch and your cassette shows wear, replacing both together prevents the new chain from skipping on worn cogs. Mixing new chains with worn cassettes causes problems. Same goes for chainrings—worn teeth chew up fresh chains.

Tools Required

Gather these before starting:

Chain whip (holds cassette during removal)
Cassette lockring tool (matches your hub type—Shimano/SRAM or Campagnolo)
Chain breaker or quick-link pliers
Chain wear indicator gauge
Cable cutters (regular wire cutters damage cable ends)
4mm and 5mm hex wrenches
Phillips screwdriver
Torque wrench (optional but recommended)
Clean rags and degreaser
Fresh chain lube

Don’t skip the chain whip. Trying to remove a cassette without one strips lockring tools and damages knuckles. The $15 investment pays for itself immediately.

Step 1: Assess Chain Wear

Chain wear tools measure stretch—the elongation that occurs as pins and rollers wear against each other. A new chain measures exactly 12 inches across 12 full links. Worn chains measure longer.

Insert your chain checker according to its instructions. Most have a go/no-go design:

0.5% wear: Replace chain only. Cassette and chainrings likely fine.
0.75% wear: Replace chain and cassette together. Check chainrings.
1.0% wear or beyond: Full drivetrain replacement often necessary.

Chains ridden past 0.5% wear begin damaging cassettes. That’s why regular chain measurement—every 500 miles or so—extends drivetrain life significantly.

Step 2: Remove the Rear Wheel and Cassette

Shift to the smallest cog before removing the wheel. This reduces cable tension and makes reinstallation easier.

Remove the wheel. Insert your cassette lockring tool into the lockring—it fits into the splines of the lockring, not the smallest cog. Wrap your chain whip around one of the middle cogs, holding it in place to prevent the cassette from spinning.

Turn the lockring tool counter-clockwise while holding the chain whip. The lockring should break free with moderate force. If it’s stuck, penetrating oil and a longer wrench handle help.

Once the lockring is removed, the cassette slides off the freehub body. Note the orientation of any spacers behind the cassette—they need to go back in the same order.

Step 3: Inspect the Freehub Body

With the cassette removed, examine the freehub body. Look for:

Deep spline wear: Grooves cut into the aluminum freehub by the cassette under pedaling force. Minor grooves are normal. Deep gouges that prevent the new cassette from seating require freehub replacement.
Freehub play: Grab the freehub and try to rock it. Side-to-side movement indicates worn bearings inside.
Engagement feel: Spin the freehub backward. It should click smoothly. Grinding or hesitation suggests contamination or wear.

Clean the freehub body with degreaser and a rag. Don’t spray degreaser into the freehub internals—it washes out lubricant. A light wipe of grease on the splines prevents corrosion and makes future cassette removal easier.

Step 4: Remove the Old Chain

If your chain has a quick link (also called a master link), use quick-link pliers to disconnect it. Squeeze the plates together while pushing the link inward, and it pops apart. Much easier than chain breaking.

For chains without quick links, use your chain breaker. Position a link over the tool’s supports and drive the pin until it just barely clears the inner plate. Don’t push it completely out—you’ll need to reuse that spot if reconnecting without a quick link.

Pull the chain through the derailleurs and set it aside for length comparison.

Step 5: Inspect Chainrings

While the chain is off, examine your chainrings. Fresh teeth have a symmetrical, rounded profile. Worn teeth look like shark fins—hooked in the direction of chain travel. Run your finger across the teeth. Sharp, pointed tips indicate wear beyond service life.

Also check for:

Bent teeth: From impacts or poor shifting. Bent teeth cause chain skip.
Loose chainring bolts: Snug all bolts to spec (typically 8-12 Nm depending on manufacturer).
Spider cracks: Rare, but check where chainrings attach to the crank spider.

Chainrings last longer than cassettes—often two or three cassette replacements per chainring set. But if your chainrings show shark-finning, replace them with the cassette and chain.

Step 6: Install the New Cassette

Slide the new cassette onto the freehub body. The splines are keyed—one spline is narrower than the others, so the cassette only fits one way. If it won’t slide on, rotate it until the key aligns.

Ensure any spacers from the old cassette go back in their original positions. Some cassette/freehub combinations require a spacer behind the cassette; others don’t.

Thread the lockring on by hand, ensuring it catches the threads properly. Tighten to spec—typically 40 Nm, which is firmer than you’d expect. Under-torqued lockrings can loosen during riding and damage freehub threads.

Step 7: Size and Install the New Chain

New chains come longer than needed. You must size them for your specific bike. Two methods work:

Comparison method: Lay the new chain alongside the old chain. Match them link-for-link, outer plate to outer plate. Cut the new chain to match the old chain’s length. This only works if the old chain was correctly sized.

Big-big method: Route the new chain around the big chainring and big cassette cog, bypassing the rear derailleur. Pull the chain ends together until they just meet, with minimal slack. That’s your required length, plus add one full link (two half-links) to account for the chain passing through the derailleur.

Cut the chain at the appropriate link using your chain breaker. For chains with quick links, cut so you have two inner-link ends that the quick link can connect. For chains using connecting pins, you’ll need one inner-link end and one outer-link end.

Step 8: Route the Chain Through Derailleurs

This step trips up beginners. Pay attention to the path:

Front derailleur: The chain passes between the derailleur cage plates. Nothing special here.

Rear derailleur: The chain wraps around the upper pulley (guide pulley) then around the lower pulley (tension pulley). Looking from behind the bike, the chain goes clockwise around the upper pulley and counter-clockwise around the lower pulley. The chain should NOT pass between the rear derailleur cage and the frame—a common mistake.

On many derailleurs, there’s a metal tab between the two pulleys. The chain must pass in front of this tab, not behind it. Routing behind the tab prevents proper chain tension.

Step 9: Connect the Chain

With the chain routed correctly, bring the ends together.

Quick link connection: Insert each quick link plate into one chain end. Bring the plates together so pins engage holes. Pull sharply on the chain (or pedal forward with brakes held) to snap the link fully engaged. Verify both pins are fully seated in both outer plates.

Connecting pin method: Bring chain ends together overlapping one half-link. Insert the connecting pin from the inside of the chain toward the outside. Drive it through with your chain breaker until it’s centered. Snap off the guide tip if present.

Flex the new joint side-to-side. If it’s stiff, gently flex it until it moves freely. Stiff links cause skipping.

Step 10: Replace Shift Cables (Optional but Recommended)

While the drivetrain is apart, consider replacing shift cables. Old cables fray, corrode, and develop kinks that resist movement. Fresh cables shift crisper.

For each shift cable:

Shift to the position that gives maximum cable slack (usually smallest cog, smallest chainring)
Locate the cable anchor bolt on the derailleur. Loosen it and release the cable.
Pull the old cable out through the shifter. Note how the cable end seats inside.
Feed the new cable through the shifter, through all housing sections, and to the derailleur
Pull the cable taut by hand and secure the anchor bolt

Don’t forget cable housing. If the old housing is kinked, cracked, or contaminated, replace it too. Cut housing with proper cable cutters, then clean up the cut end with a pick or small file.

Step 11: Adjust the Derailleurs

With fresh components installed, derailleurs need adjustment. Start with limit screws, then B-tension, then cable tension.

High limit (H-screw): Shift to smallest cog. Looking from behind, the upper derailleur pulley should align directly under the smallest cog. Adjust H-screw until alignment is correct. This prevents the chain from falling off the cassette toward the frame.

Low limit (L-screw): Shift to largest cog. Same deal—pulley should align under the largest cog. This prevents the chain from shifting into the spokes.

B-tension: With the chain on the largest cog, the gap between the upper pulley and the cassette teeth should be approximately 5-6mm. Clockwise B-screw rotation increases the gap.

Cable tension: Shift to the middle of the cassette. If upshifts (to easier gears) are slow, add cable tension via the barrel adjuster. If downshifts (to harder gears) are slow, reduce tension. Work in quarter-turn increments.

Step 12: Test Ride and Fine-Tune

Shifting on the stand doesn’t replicate riding loads. Take a test ride that includes:

Shifting through all gears under easy pedaling
Shifting under moderate power (climbing simulation)
Rapid multi-gear shifts
Cross-chain positions (big-big, small-small) to verify limits

Expect to make minor barrel adjuster tweaks after the test ride. New cables stretch slightly during initial use—many shops recommend a free tune-up at 30 days for exactly this reason.

Maintenance Schedule Going Forward

Your freshly overhauled drivetrain will last longest with regular attention:

Every ride: Quick wipe of chain if it’s dirty
Every 100-200 miles: Chain cleaning and fresh lube
Every 500 miles: Chain wear check with gauge
At 0.5% wear: Replace chain before cassette damage begins

A chain wear gauge costs $10. Checking regularly and replacing chains at 0.5% stretch—rather than waiting until they skip—typically doubles cassette life. The economics are clear: chains cost $30-50, cassettes cost $40-150, chainrings cost $50-200.

Troubleshooting Common Problems

Chain skips under power: Usually worn cassette that wasn’t replaced with chain. Can also be stiff chain link or severely worn chainrings.

Won’t shift to largest cog: Cable tension too low, or L-limit screw too tight. Increase cable tension first; if still won’t reach, loosen L-limit slightly.

Won’t shift to smallest cog: Opposite problem. H-limit may be too tight, or cable tension too high.

Grinding noise in big-cog positions: B-tension likely too low (pulley too close to cassette). Increase B-tension.

Chain drops off when shifting: Limit screws need adjustment. If dropping toward frame, tighten H-limit. If dropping toward wheel, tighten L-limit.

A properly overhauled drivetrain should shift crisply across all gears without hesitation or noise. If problems persist after methodical adjustment, look for bent derailleur hangers, damaged pulleys, or housing contamination.

Conclusion

The complete drivetrain overhaul intimidates beginners, but each individual step is straightforward. Take your time, work systematically, and you’ll finish with a bike that shifts better than when it was new. The skill pays for itself—professional drivetrain service runs $100-200, and you’ll need it every 2,000-4,000 miles depending on conditions and maintenance habits.

Build the competence now, and your bikes stay running for decades.