Shimano Freewheel Tool

Freewheels predate cassettes and never went away. The 1670.1/4 is the Unior tool sized to the Shimano-pattern freewheel; a 4-spline engagement that fits the most common freewheel pattern in the US market, including the Sachs, SunRace, and pre-cassette SRAM freewheels that share the Shimano spline geometry. Same back-end format as the modern cassette-lockring family: 24 mm wrench flat plus a 1/2" drive on the opposite face.

The Shimano freewheel pattern shows up on more bikes than the catalog age suggests. Most pre-1996 derailleur bikes use a threaded freewheel rather than a cassette-on-freehub design, and a large share of those use the Shimano-pattern spline. Vintage road, touring, classic mountain, fixie conversions built on freewheel-style hubs; they all back off with the 1670.1/4. The tool also serves current-production singlespeed and BMX setups whose freewheel manufacturer chose the Shimano pattern.

How to use it

The freewheel removal workflow is similar to the cassette workflow with one important difference: a freewheel threads onto the hub as a single unit, so there's no separate "hold the cogs still" step. The tool engages the freewheel, the wheel rim or skewer-mounted vise holds the wheel, and the 1670.1/4 turns counter-clockwise.

1. Remove the wheel; thread out the QR skewer.
2. Seat the 1670.1/4 into the freewheel's spline pattern.
3. Re-thread the QR skewer through the tool from the non-drive side, snugging the skewer nut against the back face of the tool. The skewer anchors the tool so it can't pop out of the splines under load; same trick as the cassette tool with guide pin, applied to freewheels.
4. Turn the 24 mm wrench flat or 1/2" drive counter-clockwise. Loosen the skewer a quarter turn each time the freewheel breaks free further.

Freewheels self-tighten under pedaling load, so the break-free torque can be high; well past what a freshly-installed cassette lockring takes. Use a 1/2" breaker bar if you've got one.

Compatibility

• Shimano-pattern threaded freewheels (4-spline engagement)
• SunRace, Sachs, and pre-cassette SRAM freewheels using the Shimano spline pattern
• Most current-production singlespeed and BMX freewheels on the Shimano pattern
• Not for SunTour freewheels; they use a different prong pattern (use 1670.3/4 or 1670.2/4)
• Not for cassettes (use the appropriate cassette lockring tool)

Specs

• Shimano-pattern 4-spline freewheel engagement
• 24 mm hex wrench flat
• 1/2" square drive socket on the opposite face
• Trivalent chrome plated to ISO 1456:2009
• Article number: 1670.1/4

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The 1670.1/4 is the freewheel-side equivalent of the 1670.5/4 cassette lockring tool: same back-end format, same trivalent-chrome finish, same construction quality. Workshops servicing both modern cassettes and vintage freewheels keep both tools, and they fit the same drawer.

Pro tip from our mechanics

Old freewheels can be stuck enough that a 1/2" ratchet won't break them free; the leverage on a ratchet handle is below what 20 years of pedaling has cranked the freewheel onto the hub. A 1/2" breaker bar; 18 inches or longer; gives you the leverage to break it. We've also had luck with a drop of penetrating oil on the freewheel-to-hub interface, left overnight, before the first attempt. The cassette-replacement workflow has more on the freewheel-versus-cassette call: When and how to replace your cassette →