Ask A Trucker: Running Late With Jake Brake At The Top Of My Slate

The following letter landed in the “? A Trucker” mail bag on February 25th, right around the same time I went into a writing slump. I’m still not quite out of my funk, but I’m gonna give this a try anyway, so here we go:

• Q:

My old man has a 75′ Pete (1975 Peterbilt) and has tried to teach me how to drive…while I understand most of the basics, how the heck do you use the Jake brake? I get so nervous that I’ll kill the engine.

• A:

For those that don’t know, Jake Brake is a trademarked nickname for Jacobs Brake, and has become a generic term for similar brake systems, much like Q-Tip for cotton swabs, or Kleenex for facial tissue. A more appropriate generic term would be auxiliary brake, engine brake, or engine retarder.

So, what is an auxiliary brake? The auxiliary brake is a brake system completely separate from the service brake system (the brake pedal). The auxiliary brake helps the service brake in slowing the vehicle, controlling the vehicle when slowing or descending a grade, and by saving wear and tear on the service brakes.

How do auxiliary brakes work? Let me keep this very simple, because there’s way to much to this topic to get into. When the auxiliary brake is turned on it starts doing it’s job when ever you take your foot off the accelerator, or when your vehicle begins to accelerate a few miles per hour over the speed at which your cruise control is set.

And now for the real question “how the heck do you use the Jake brake“. Most auxiliary brakes have two on positions, high and low. When getting started, your auxiliary brake should be off. Some can be used in town, but most cannot. For safety’s sake we won’t turn it on until we’ve reached highway speed. Likewise, I make it a habit to turn them off when I get off the highway, at approximately 45 MPH.

Once I turn it on, I tend to leave it in the “high” position. The low setting in my truck doesn’t seem to do enough to justify ever using it. This may vary from truck to truck, or from auxiliary system to system. In normal driving conditions, at a maintained speed of 45+ MPH you can leave your auxiliary brake on.

When not to use the auxiliary brake: when traveling under 45 MPH or in stop and go traffic, when driving conditions are slippery (use in slippery condition can increase the risk of skid or jackknife), while bobtailing (driving without a trailer), while driving with an empty trailer (use while bobtailing or pulling an empty trailer may result in wheel lock up), or where auxiliary brakes are prohibited.

Auxiliary brakes prohibited? What’s up with that? Some auxiliary brake systems are rather loud. Because of this fact you often time see signs when driving into towns prohibiting the use of auxiliary brakes. I’ll let you be the judge of just how loud your auxiliary brake system is, but keep in mind, if the police officer disagrees with your choice, you could be looking at a hefty fine.

This was a bit of a technical question so if you have any further question I suggest refering to your auxiliary brake owners manual. With so many makes, models and types out there, that’s probably a great place to start anyway.

I still have some catching up to do, so keep an eye out for more installments of Ask A Trucker in the near future.

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