Why does your rear derailleur have no spring tension?
Diagnose a slack chain and a rear derailleur that will not spring back by separating chain routing, mounting, clutch, pivot, cage, and broken-spring faults.
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A rear derailleur should take up chain slack through its cage spring. If the lower chain run hangs loose and the cage does not pull it taut, stop turning adjustment screws. First establish whether the chain is routed correctly, the derailleur is mounted in the position shown by its maker, a clutch or cage lock is engaged, a pivot is stuck, or a spring or stop has failed.
The short answer: shift to the smallest chainring and smallest rear sprocket, stop riding, and gently move the derailleur cage by hand. A healthy cage resists forward movement and springs back. If it does not, use the checks below; do not try to cure missing spring tension with cable tension or limit screws.
Why this question causes so many wrong diagnoses
A current r/bikewrench thread about a new bike whose derailleur had no tension produced conflicting guesses about chain routing, mounting position and a failed spring. That disagreement is the useful signal: several faults can create the same photograph.
Reddit comments are not a service manual. The exact derailleur model, hanger design and manufacturer instructions decide what “correct” looks like. Shimano’s general dealer manual, for example, shows that the B-tension stop and hanger stop must meet correctly and warns against deforming them during installation.
Begin with a no-pedal inspection
Put the bike in its smallest front chainring and smallest rear sprocket. Support it securely and do not put fingers near the chain while turning the cranks.
Check these four things before touching a bolt:
- Chain path: the chain should pass over the upper guide pulley, between any cage guide tabs, and under the lower tension pulley.
- Cage position: the cage should point generally down and forward enough to tension the lower chain run, not fold behind the cassette without resistance.
- Derailleur body position: compare the bracket and B-tension stop with the exact maker diagram. Do not use a random product photo as the authority.
- Wheel and hanger area: stop if the hanger is bent, the derailleur is near the spokes, or anything is cracked or loose.
If the chain does not follow the correct route, fix that before judging spring tension. Our rear-derailleur chain-routing guide explains the common guide-tab mistake.
Test the cage spring without dismantling it
With the bike stationary, pull the lower derailleur cage gently forward. A normal cage should resist and return when released. Compare the feel through a small range only; never force it around a stop.
The result narrows the fault:
| What you feel | More likely explanation | Next move |
|---|---|---|
| Firm resistance and a clean return | Spring probably works | Check routing, chain length and mounting |
| Cage is locked and barely moves | Clutch, cage lock or seized pivot | Check the model manual before applying force |
| Cage moves freely and does not return | Disengaged, unwound or broken spring; broken stop | Stop and arrange service or replacement |
| Cage returns only part-way | Dirty or seized pivot, damaged spring or interference | Inspect for contact; service to the maker’s procedure |
| Derailleur works without the chain but not with it | Chain may be too short or incorrectly routed | Verify chain length and compatibility |
Some derailleurs have a clutch switch. Some have a cage lock intended to help wheel removal. Others have neither. Identify the model number and read its manual instead of copying a control from another brand.
Mounting position matters
The derailleur’s attachment bolt can be tight while the body sits incorrectly against the hanger. On many conventional systems, a stop on the derailleur must sit against a matching stop on the hanger. Direct-mount and newer interfaces differ.
Do not loosen and spin an unfamiliar derailleur until you have its installation diagram and torque value. Incorrect repositioning can damage the hanger, bracket axle or stop. Shimano’s general procedure specifies the relationship between the B-tension adjuster and hanger stop and gives model-family torque values; your exact manual takes priority.
If this is a newly assembled boxed or department-store bike, treat incorrect assembly as a warranty and safety issue. Photograph the fault, stop riding, and ask the seller to correct or replace it. Use the boxed-bike safety check before the first ride.
What the adjustment screws cannot fix
Three tempting adjustments do not restore a missing spring:
- Cable tension controls lateral shifting, not the cage’s chain-take-up force.
- High and low limit screws restrict sideways travel; using them blindly can create a shift into the spokes or frame.
- The B-tension screw sets guide-pulley clearance on compatible designs; it does not repair a failed cage or body spring.
If the derailleur is spring-loaded but the chain remains slack, check chain length. A chain that is much too long can leave insufficient cage take-up. A chain that is too short can overextend the derailleur and damage it. Follow the component maker’s sizing method or use our chain-length diagnosis.
When replacement is the sensible repair
Many entry-level derailleurs use riveted construction and are not designed for spring replacement. A failed internal spring, cracked cage stop, bent parallelogram or damaged bracket can make complete replacement safer and cheaper than exploratory disassembly.
Replacement still requires compatibility. Match the shifter’s cable-pull system, number of rear speeds, cassette range, mounting interface and required capacity. “It has the same number of gears” is not enough.
Have a shop handle it when:
- the spring has no return force;
- the hanger or derailleur appears bent;
- the derailleur can contact the spokes;
- the mounting interface is unclear;
- a new bike arrived this way;
- you cannot verify chain length and compatibility.
Your next step
Record the derailleur model number, take clear photographs from the drive side and rear, and download that model’s installation manual. Verify chain path and perform the gentle return test. If there is no spring return, stop there: take the bike and evidence to the seller or a qualified mechanic rather than riding or opening a riveted mechanism.