The Difference between Synchronized and Unsynchronized Gearing in Manual Transmissions

By Mister Transmission

There’s a good reason why large commercial vehicles, motorcycles, and race cars still employ an unsynchronized gearbox

For stick-shift adherents, there is no greater joy than driving a car with a manual transmission. But what’s behind the mechanics of changing gears? And from a driver’s perspective, how does manual transmission synchronized gearing compare to manual transmission unsynchronized gearing?

Most modern urban vehicles fitted with manual transmissions likely feature a synchronized gearbox also referred to as a synchro-mesh gearbox. This device keeps the gears in mesh and rotating, or they can be locked to the shaft. In other words, when you change gears, you’re locking different gears to the transmission’s input or output shaft, thereby allowing you to increase your vehicle’s speed or slow it down. The manual transmission’s synchronized gearbox is what helps you smoothly lock gears into place.

It was a remarkable evolution in manual transmissions because the synchronizer did away with the need for motorists to perform double-clutching – releasing and re-engaging the clutch twice whenever changing gears – a requirement to operate a vehicle with a manual transmission unsynchronized gearbox.

Why the Manual Transmission Unsynchronized Gearbox Still Matters

A manual transmission unsynchronized gearbox is an older design (possibly the earliest design of a manual transmission) that required a lot of effort and skill on the driver’s part. It included a sliding-mesh gearbox, and the driver would need to carefully time when to shift gears to ensure the gears were rotating at the same speed, which was no easy feat. Do it improperly, and you’ll hear grinding and other noises.

However, the unsynchronized gearbox continues to exist. You will often find them installed in transmissions for large commercial vehicles such as heavy trucks and farming machinery, as well as in motorcycles and high-calibre race cars. Why? For two reasons: synchronized manual transmissions are more prone to breakdowns, and shifting gears on a synchro-mesh gearbox is slower than the unsynchronized version.

Are you experiencing a problem with your vehicle’s manual or automatic transmission or have questions about transmissions? Visit the Mister Transmission location nearest you and get the expert help and information you need.

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