Will someone tell me what jake braking is?

 

More correctly termed "ENGINE BRAKING". It's the system that produces the loud noise when a large truck descends a hill. It was designed to help drivers maintain control over their speed going downhill without using the brake shoes. Think of it as "the opposite of acceleration".

The term "JAKE BRAKE" comes from what was the most popular system for years made by "JACOBS BRAKE SYSTEMS".

 

Oh. It'd be kind of like putting it in reverse and giving it just a little bit of acceleration to slow it down.

How does it work? Is there a button you press that causes it to come on?

 

Its a function of mechanical and quick adjustment of the timing of the valves to cause detonation in the cylinder at a different time than the acceleration stroke.... causes the truck to slow or maintain speed down a hill.

Some are automatically turned on when you take your foot off the accelerator, or when the on/off switch is set to on. Or some trucks even have an automatic feature that if the truck exceeds more than a couple of mph over its set speed on cruise control....the jakes will come on in stages.

 

...its a wonderful sound..

 

When your cylinders pump in a normal car the air gets compressed. When compressed on the top of the stroke it's super hot and that's when the little bit of gas is pumped in. That explosive energy is used to make your car go.

http://or.essortment.com/jakebraketruck_raio.htm

 

Ummmmmmm. Yummy! Nothing like a set of 7" straights roaring.

 

As a four-stroke internal combustion engine, each piston in a diesel normally moves up and down twice in each cycle. The process begins when the fuel and air valves are closed and the piston moves upward. This compresses the air in the cylinder to as much as 25 times atmospheric pressure. This is much higher compression than a gasoline engine (typically ten times atmospheric pressure) and results in the air getting very hot. At this time fuel is sprayed into the superheated air which immediately begins burning. The second stroke, the power stroke, is the downward movement of the piston as fuel burns. The third stroke is an upward movement with the exhaust valve open to clear out the combustion products while the fourth stroke refills the cylinder with air.

The Jake brake completely changes all this, redefining what the valves do as each piston moves up and down. With the fuel flow terminated, the upward moving first stroke still compresses the air to very high pressure. As we said above, this transfers mechanical energy into heat as the air becomes highly compressed. If nothing else were done, most of this energy would be recovered, except for frictional losses, as the cylinder moved back down and the compressed air expanded. The Jake brake, however, opens the exhaust valve just as the air reaches maximum compression, dumping all of that energy in an almost instantaneous explosive release. The result is a very effective slowing of the vehicle as mechanical energy is converted to heat and then dumped. The Jake brake effectively transforms the internal combustion engine into an air compressor.

 

I had the elbow just below the muffler fall off (ya, it fell off) on my last local truck. Mind you, it was a day cab, with the exhaust literally 6 feet from me. Also, no A/C, so the windows had to stay down.

You want to talk about loud? I couldn't hear anything for 2 days after I drove that thing 40 miles with the missing elbow.

 

Cool! 8)