Please forgive my ignorance.

Also, are they worth having even it you don't do alot of heavy towing?

From what I've read so far it's a good thing to have for slowing down while towing heavy loads downhill.

Thanks alot,

DT.

 

http://www.jakebrake.com/content.php4?doc_uid=25

This should expain it for you.

 

A diesel engine inherently lacks a retarding effect in zero throttle position. In a conventional gasoline engine, when you take your foot off the throttle, a butterfly in the intake system closes off the air supply creating a vacuum. This causes the engine to work harder when it's in the 'intake' mode as it trys to draw in air against this vacuum resulting in the engine absorbing energy, causing it to decelerate. In a diesel engine the throttle controls the fuel flow and not the air so the engine does not create vacuum. Even though the fuel and resulting combustion is reduced, air is still being pumped into the engine. The only deceleration characteristic in the diesel engine is the friction of its moving parts. There are two differing methods of creating retarding power in a diesel engine - engine (compression release) brakes or exhaust brakes.

The exhaust brake is gate in the exhaust flow which when closed prevents much of the exhaust from leaving the manifold. Instead of the engine working hard on the intake stroke as with a gas engine, it now has to work hard to exhaust. It basically creates backpressure that each cylinder works against providing a dramatic slowing effect.

 

Thanks for the info guys.

I just checked out Jakebrake link, that thing ain't cheap.

$2000.00?

It would probably be worth it if one did alot of heavy towing and therefore went through many brake jobs, but to make your money back via just normal brake wear it'd probably take a very long time.

Thanks again,

DT.

 

Essentially the business end is a big butterfly type valve (like a throttle inside a carb) mounted in a housing that replaces the elbow at the turbo exhaust outlet. When turned on, the valve will close when the throttle is in the idle position, building up exhaust backpressure, so that the engine provides more compression braking/resists being turned by the drivetrain more.

The valve is closed by a vaccum actuator, and opened by spring force. Vacuum is provided by an engine driven vaccum pump, which was standard on earlier engines (attached to the power steering pump) and has to be added on to newer trucks (bolts onto the front of the engine, driven by a longer fan belt). A switch in the cab allows the driver to turn the Jake on or off, and it is hooked to the engine management computer. The engine management computer controlls an electric/magnetic valve between the vacuum pump and the acuator on the Jake Brake its self, and also uses input from the throttle position sensor.

In operation, if I'm going down a long grade and have the Jake turned on, if I let the throttle come up all the way the valve in the Jake will close. This will help slow the truck and prevent having to drag the brake pedal. Once you give it some throttle, the Jake deactivates. There is a slight delay built into the system between when you let off the throttle and when the Jake comes on, so the driver can shift without having to shut the system off.

Its also helpful for warmups in cold weather. With the Jake turned on, the engine control unit automatically increases fuel to maintain the same idle speed with the increased resistance.

You can also go to the excellent page spots posted and download the installation instructions, which give great detail.

I find mine worth having, but not an absolute must have...

P.S. I see some other people posted while I was composing this. I think I paid around $1200 for mine from the dealer, and I suspect a Cummins parts house may be able to do better. Install is pretty straight forward...