The Shimano RD-RX820 Tension & Guide Pulley Set (also sold under part code Y3JS98010) is a genuine replacement jockey wheel set for Shimano GRX 12-speed rear derailleurs.
Shimano RD‑RX820 Tension & Guide Pulley Set
What it is
This kit contains:
- Guide pulley (upper jockey wheel)
- Tension pulley (lower jockey wheel)
It’s designed specifically for:
- Shimano GRX RD-RX820
- 12-speed gravel/road drivetrains
What it does
These pulleys sit inside your rear derailleur cage and are responsible for:
-
Guide pulley (top wheel):
- directs the chain as it shifts
- ensures accurate gear engagement
-
Tension pulley (bottom wheel):
- maintains chain tension
- takes up slack when shifting gears
Together they ensure:
- smooth shifting
- stable chain line
- quiet drivetrain operation
Why replacement matters
Over time, pulley wheels wear due to:
- dirt and grit contamination
- chain friction
- long mileage use
Worn pulleys can cause:
- noisy drivetrain
- sloppy shifting
- slower gear changes
- chain skipping under load
Key characteristics
- Designed for Shimano GRX 12-speed systems
- Uses sealed bearings (on most versions)
- Engineered tooth profiles for precise chain control
- Lightweight but durable construction
Compatibility note
This set is typically NOT cross-compatible with:
- 10/11-speed Shimano road pulleys
- older GRX 11-speed systems
- MTB derailleurs (unless explicitly matched)
Shimano pulley systems are quite specific to:
- cage design
- chain width
- derailleur geometry
When to replace
Replace the pulley set if:
- teeth look hooked or sharp
- drivetrain becomes noisy
- shifting feels delayed or imprecise
- bearings feel rough when spinning
Bottom line
The Shimano RD-RX820 pulley set is a precision OEM replacement jockey wheel kit that restores smooth shifting and correct chain control on GRX 12-speed drivetrains, keeping the rear derailleur running quietly and efficiently under gravel and road conditions.
