What’s a Jake Brake?

There's no doubt you've heard Jake Brakes being used on semi-trucks, but check here to learn how they work.
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If you’ve ever heard a semi-truck make an extremely loud noise while slowing down, that was probably an engine brake, sometimes referred to as a Jake Brake. They’re loved by truckers because they reduce wear and therefore maintenance as well as downtime. But what do they actually do, anyway?

A Jake Brake uses the truck’s engine to slow it down instead of the friction brakes mounted at each wheel. It’s an extremely useful function that helps bring heavy trucks and trailers safely to a stop. The concept has evolved some over time, though in a lot of ways, it’s similar to the device that first debuted in 1961.

What happens is the Jake Brake opens the engine’s exhaust valves slightly when the piston moves through its compression stroke, effectively turning it into a “power-absorbing air compressor.” That’s according to Jacobs Vehicle Systems, the company that originally patented the technology. In turn, the vehicle is slowed through the drivetrain rather than solely at the hubs, increasing the longevity of consumable parts like friction brakes.

The act of engine braking isn’t typically harmful to the truck so long as the engine doesn’t over-rev. This can happen if a vehicle carries a lot of speed into a steep downhill grade with a heavy load while engaging the Jake Brake, but it’s far from normal. At that point, it’s time to press harder on the brake pedal.

Yet another benefit of engine braking is potentially improved fuel economy. With the device engaged, the engine shuts off fuel consumption and is instead being “dragged” by the wheels, which turns the crankshaft and pistons. This is sometimes more efficient than relying on the friction brakes because the engine may not shut off fuel consumption when simply decelerating.

If you’re wondering whether or not your car has a Jake Brake, the answer is likely no. Maybe if you drive a commercial truck or a modern heavy-duty diesel pickup as some of those have factory engine brakes that operate in a similar way. Those aren’t nearly as loud as a semi’s, however.

You might have noticed that many towns prohibit engine braking due to noise restrictions. It’s one way of keeping the volume down and maintaining some sense of peace and quiet. More often than not, areas where engine braking is restricted often have lower speed limits, so it further reinforces the imperative to go slow.

All in all, Jake Brakes are handy devices installed on vehicles that need them. They have saved fleet operations a ton of money over the past six decades, both in maintenance and fuel costs. They work in a simple, clever way to slow trucks down, which means they’re just as significant for road safety. Not much in the automotive tech space hangs around for 60-plus years, so that speaks to the staying power of the original Jake Brake.