The Brake that Jake Built


By Bob Vaccaro


Photo Jacobs Vehicle Systems

Most of you probably know about the Jake Brake. For those not familiar with it, the Jake Brake is an add-on engine brake for diesel engines and is produced by Jacobs Vehicle Systems. Brakes that serve a similar purpose are also made by other companies such as Pac Brake and Caterpillar.

Stopping and slowing down a large weight vehicle such as a fire truck requires a lot of energy and braking power, as well as friction that can cause heat build up and brake fade. This also requires the brakes to be replaced on a more frequent basis, which brings up the maintenance costs. This is where the Jake Brake and other add-on engine brakes come in.

They are a compression brake. The principal is that it is a hydraulic engine component that converts the diesel engine into an air compressor that absorbs power, and provides a retarding effect on the drive wheels.

It opens the exhaust valve just as the air reaches maximum compression, dumping all of the energy in an explosive release. The mechanical energy is converted to heat and then dumped.

By having a Jake Brake or other add-on engine brake installed when you spec out your vehicle, not only are you saving money on maintenance but also providing for safer braking.

Transmission retarders
There are other auxiliary braking devices such as transmission retarders and driveline retarders. The driveline retarder obtains the same result as a Jake Brake or similar brake, but operates differently. The driveline retarder uses an electromagnetic field to slow down the turning of the drive shaft. Because the retarder is activated before the brakes are applied, they provide approximately 85 percent of the braking horsepower needed to slow the vehicle down.

As long as there is current in the battery, the vehicle can be slowed safely. Also by only slowing the rear wheels, the retarder slows the vehicle while the operator maintains full steering control.

Meanwhile, an automatic transmission retarder is built into the vehicle's automatic transmission and is a system that is becoming more and more popular. The reason being is that it has shown to increase brake life by three times the normal rate.

Transmission retarders come in two different versions — an input and an output, each being mounted differently on the transmission.

I am by no means a mechanic and I recommend you read up on the operation of each device I have mentioned to get a better understanding of their operation and the pros and cons of their uses.

The one common result that they all produce is reduced cost of maintenance and safer braking. This is something that should concern all of you out there planning on an apparatus purchase any time in the future. This is a big item that you should seriously consider for the safety aspect if not anything else.

The best information can be gained by checking out the websites of manufacturers such as Jacobs Vehicle SystemsTelma and  Allison Transmission as well as reading the Fire Apparatus Purchasing Handbook by William C. Peters. 

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