Here’s a fascinating look inside a NASCAR four-speed gearbox—simple, rugged, and rooted in old-time Detroit production technology.

Like most everything in the series, the transmissions used in NASCAR are the product of decades of slow and steady evolution. Back in the day, the gearboxes were off-the-shelf production four-speed units from Ford, Chrysler, Muncie, and Borg-Warner, but over the years they gradually they morphed into the highly specialized and purpose-built units used today. We can see that up close and in detail in this fine little video produced by Papadakis Racing.

The G-Force NASCAR top-shift gearbox disassembled here is laid out much like any Detroit-built four-speed, with a familiar-looking four-speed gearset in the main case and a reverse gearset in the tail housing. (The basic design was patented in the ’30s.) But instead of the production transmission’s silent-running helical gears, there are beefy straight-cut gears to reduce case thrust and handle the extreme torque loads. And in place of synchronizers, there are dog rings to negotiate the gear changes in a quick and positive manner. And of course, everything is stiffer and stronger than an OE gearbox and engineered for ease of service.

A top NASCAR Cup team will typically take three transmissions per car to every event, and each unit will see 4,500-5,000 miles of total service. Due to their ruggedness, simplicity, and strong supply chain, NASCAR-type gearboxes have become popular in other forms of motorsports, too—big-time professional drifting, in this case. Video follows.