maybe it's the term itself "brake". i live in the n.w where log truck jake brakes are a common sound.they slow the rig down.i get that.why would you want to drive with a "brake on all the time. just isn't clicking for me.i can't understand having a brake on while i'm towing up a steep grade.it has got to be a totally different design.having read thru the search results confused me more.got a simple definition?

 

These are actually an exhaust brake, not a compression brake as you see in the big rigs. Basically all these ones do is close a flap inside the pipe on the 5.9's, and a vane style flap on the turbo of the 6.7's. It's computer controlled to come on under certain conditions, so its not actually on "all the time".

 

In bigger engines, compession pressure is released so that the force required to compress the incoming charge isn't returned on the power stroke.

On our trucks, exhaust backpressure is increased, either by a butterfly type valve in the elbow at the exit of the turbo in the case of 5.9's, or by clamping the variable turbo down on the 6.7.

In either case, when the exhaust brake is switched on, the ECU only activates the braking feature when the throttle position has been at idle for a couple of seconds.

The slight delay makes it possible to leave it switched on all the time, and not have it come on when you let off the pedal to shift. I would guess the delay may also protect the turbo from going instantly from full boost to brake on...

 

The Big Rigs run there E Brakes on most of the time too. They have a cut out switch on the throttle, and on the clutch, and a master switch on the dash, most now can select 2,4, or 6 cylinders.
Don't worry, your E Brake will not hurt anything if you leave it on all the time, and you should use it all the time, or it will soot up.

 

Unless they have changed something in the last ten + years, in my experience, most dont. But then the newest I have driven is a 94 Freightliner.

 

I leave mine on all the time on the freeway. Some nut cuts me off and I let off the gas the brake slows me down without having to hit the real brakes and gives me time to train horn the person that cut me off!

 

That got me laughing.

 

Only time will tell if use or lose it will be replaced with used it up as this is a very demanding design that involves high heat and pressures. The immediate question seems to be does leaving it on effect fuel mileage? Even at the idle if I turn it on there's a noticeable change in pitch and volume so it's hard to think that it's harmlessly laying in wait when I hear that.

 

Turning it on at idle does put additional load on the engine, and can be very handy for winter warm up.

Once the engine is up close to operating temp, the exhaust brake will not come on at idle when the vehicle speed is zero, even with the switch turned on.

There have been threads about the vacuum pump going out on the Jacob system, and sometimes if not used they build up carbon and have to be taken off and cleaned up. I don't think I've seen a thread about one wearing out.

With the 6.7 it just clamps down the variable turbo, which gets moved around all the time in normal operation anyway.

 

Check out this page.
http://www.holset.co.uk/mainsite/files/2_5_1_5-VGT.php
It has a little animation of how the brake works.