How does a dropper post work?
A dropper post lets you raise and lower the saddle while riding, via a remote lever on the handlebar. It revolutionized mountain biking by allowing riders to lower the saddle for technical descents and raise it for climbs — without stopping.
Mechanical principle
Most droppers use a sealed hydraulic (or pneumatic) cartridge. When you press the lever, a valve opens and allows movement. The internal spring (air or mechanical) pushes the post back up when the valve is open and you're not sitting.
The two main technologies:
- Sealed hydraulic (RockShox Reverb, Fox Transfer): hydraulic fluid + compressed air in a sealed cartridge. Reliable, but service requires specific tools
- Mechanical/air (OneUp V2, Brand-X Ascend, PNW): mechanical spring or compressed air for return, mechanical cable for activation. Simpler to maintain
Available travel
| Travel | Typical use | Frame size |
|---|
| 100 mm | XC, small frames | S |
| 125 mm | XC/Trail, medium frames | S-M |
| 150 mm | Trail/All-Mountain | M-L |
| 170 mm | Enduro | L-XL |
| 200 mm | Enduro/DH, large frames | XL |
When to service?
Regular maintenance is key to longevity. Here are recommended intervals:
- After every muddy ride: clean the stanchion (the part that enters the frame) with a damp cloth. Remove dried mud around the seal
- Every 50 hours (or every 3-4 months): basic service — upper seal cleaning, stanchion lubrication, cable/hose check
- Every 100-200 hours (or once a year): full service — cartridge disassembly, hydraulic fluid and seal replacement, bleed (for hydraulic models)
Basic service: what you can do yourself
1. Stanchion cleaning
The stanchion is the shiny tube (chrome or Kashima/DLC coated) that slides into the seat tube.
- Lower the post completely
- Wipe the stanchion with a clean cloth dampened with isopropyl alcohol
- Apply a thin coat of suspension fluid (RockShox Maxima Plush or Fox Float Fluid) to the stanchion
- Cycle the post up and down several times to distribute the lubricant
- Wipe off excess
Never use WD-40, degreaser, or chain oil on the stanchion. These products degrade internal seals.
2. Cable check (mechanical models)
- Check that the cable slides freely in the housing
- Inspect the ends: a frayed cable must be replaced
- Check tension: when the lever is at rest, the cable should not be tight enough to hold the valve open
- Lubricate the housing with cable lubricant (Shimano SP41 type)
3. Hose check (hydraulic models)
- Inspect the hose along its entire length: no kinks, no rubbing against the frame
- Check fittings: no visible oil leaks
- If the lever feels spongy → there's air in the system → bleed needed
Common issues and diagnosis
Post sinks on its own (sag)
Symptom: you sit down and the post slowly sinks, even without pressing the lever.
Possible causes:
- Insufficient air pressure (air models): re-inflate via the Schrader valve at the base. Typical pressure: 150-250 psi depending on model and your weight
- Worn hydraulic cartridge: fluid leaks past the internal valve. Full service needed
- Worn cartridge seal: cartridge or internal seal replacement needed
Slow or incomplete return
Symptom: when you press the lever and stand up, the post rises slowly or doesn't reach full height.
Possible causes:
- Cable too tight (mechanical models): the valve stays partially open. Release tension
- Excessive friction: the stanchion is dirty or scratched. Clean and lubricate. If deeply scratched, the stanchion needs replacement
- Low air pressure (air models): re-inflate
- Cold temperature: in winter, oil thickens and return slows. This is normal. Some manufacturers offer low-viscosity oil for winter
No movement at all
Symptom: the post doesn't move up or down at all.
Possible causes:
- Broken or disconnected cable: check the cable from lever to post
- Seized cartridge: internal corrosion. Full service required
- Faulty lever: test by disconnecting the cable and pulling manually
Lateral play
Symptom: the saddle wobbles side-to-side when you pedal.
Possible causes:
- Worn bushings: the plastic/bronze guide bushings are worn. Replacement needed. This is the most expensive fix if you don't do it yourself
- Insufficient clamping: check the seat clamp torque (5-7 Nm depending on manufacturer)
Brands and specifics
RockShox Reverb
- Type: sealed hydraulic (Connectamajig or Stealth)
- Service: full service with the RockShox kit (bleed kit + Maxima oil). The bleed is the most technical part
- Weak point: the internal hose can get stuck in the frame. Use cable lubricant when routing
- Special tool: IFP wrench (Internal Floating Piston) for full service
Fox Transfer
- Type: sealed hydraulic
- Service: similar to the Reverb. Fox service kit with Fox Gold 20wt oil
- Strong point: Kashima coating on the stanchion = less friction, more durable
- Weak point: the remote lever (1x Lever) can come loose. Check torque regularly (2 Nm)
OneUp V2 / V3
- Type: mechanical + air
- Service: simplest on the market. The cartridge is user-replaceable without special tools. Cable change takes 10 minutes
- Strong point: value for money, ease of maintenance, user-replaceable cartridge
- Tip: air pressure is adjustable to match return speed to your weight (150-250 psi)
Tools needed for service
- Torque wrench (2-7 Nm)
- Allen keys 2, 2.5, 3, 4, 5, 6 mm
- Snap ring pliers (for some models)
- Suspension fluid (Maxima Plush or Fox Float)
- Clean cloths + isopropyl alcohol
- Bleed kit (hydraulic models only)
Is your dropper showing signs of wear? Describe the symptoms to L'Atelier — it identifies your exact model and guides you through the right diagnosis and repair.
