What is a jake brake?

A Jake brake (also known as a compression release brake, engine brake, or Jacobs brake) is a supplementary braking system for large vehicles, such as trucks, buses, and some locomotives. It doesn't rely on friction like conventional brakes (disc or drum brakes), instead using the engine itself to slow the vehicle.

Here's how it works:

• Compression Release: A Jake brake works by releasing the compression in the cylinders of the engine during the power stroke. Normally, the downward motion of the piston compresses air in the cylinder, creating pressure that drives the crankshaft. With the Jake brake engaged, a mechanism (usually pneumatic) opens valves in the cylinder head, releasing this pressure. This sudden release of pressure slows the engine's rotation and, consequently, the vehicle's speed.

• Exhaust Brake: Some systems also incorporate exhaust braking. This involves restricting exhaust flow, which increases backpressure in the cylinders and further assists in slowing the vehicle down. This is often combined with the compression release function for greater braking effect.

• Benefits: Jake brakes provide significant advantages:

  • Increased braking power: They greatly augment the braking power of the vehicle's service brakes, especially important on long, steep descents. This reduces wear and tear on the service brakes and prevents brake fade (a reduction in braking effectiveness due to overheating).
  • Improved safety: By reducing the reliance on service brakes, Jake brakes improve safety by reducing the risk of brake failure and providing more control on steep grades.
  • Reduced brake maintenance: Decreased reliance on service brakes translates to less frequent and less costly brake maintenance.

• Drawbacks:

  • Noise: Jake brakes are notoriously loud and produce a distinctive characteristic "Jake brake" sound, which is often considered a significant nuisance, especially in residential areas. Many jurisdictions have regulations restricting their use in certain areas.
  • Engine wear: While generally durable, using a Jake brake excessively can contribute to increased engine wear, especially in older engines.
  • Cost: Jake brakes are an additional expense when outfitting a vehicle.

The name "Jake brake" is a registered trademark of Jacobs Vehicle Systems, but has become a generic term for this type of braking system. Many manufacturers now produce similar systems.