Clutchless Shifting | Dog Engagement Gearboxes [TECH NUGGET]

Dog engagement gearboxes are commonplace in motorsport and offer the advantage of incredibly fast gear changes. A conventional dog box doesn’t require the clutch in order to change gears, however, it still requires an engine torque reduction in order to allow the dogs to disengage and the shift to take place.

This torque reduction can come from a fuel or ignition cut, or a brief lift of the throttle but either way it impacts on the ET and can cause a large turbo to drop off boost, resulting in lag in the next gear. In a drag application, a slightly different take on the dog box is the ‘clutchless box’, made by the likes of GForce Transmissions and Liberty Gears. This style of gearbox still uses dog engagement, but it uses a two-piece selector with a normal dog on the drive side and a ramp on the opposite side. How this works is that when the driver selects 1st gear, the drive dogs will engage as normal. When the driver wants to change from 1st to second they will pull the lever which moves the other selector ring across into 2nd gear.

In this way, the gearbox is momentarily in two gears at once. Normally this doesn’t end well but as soon as 2nd gear is engaged, the shaft speeds up and the result is that the dogs on first gear contact the smooth ramp on the selector ring which disengages it. The result is that no throttle lift or ignition cut is required and the engine retains full torque across the shift. The downside is that you can only shift up the gears (hardly an issue for a dedicated drag car) and if the driver has to lift out of the throttle the gearbox will jump out of gear, meaning the run is aborted.

Irrespective of what gearbox you are using, if you want to learn how to be the best you can be behind the wheel the Race Driving Fundamentals course is for you.