the unnecessary usage of j-brakes, why????

Since you release the throttle to engage the Jake then no more fuel would be used then coasting down a hill. Instead of using your Jake to stop at a stop sign then coasting would save you more fuel because of the decrease of fuel used while maintaining your speed to the point of using your Jake. What I find interesting is the fact that some here will debate the minimal wast of fuel using the Jake while wasting fuel in all other aspects of your driving habits.

 

Debating this in a forum where it seems there is a minimal amount of understanding of how a diesel engine works, is kind of funny.

The theory that the turbo has something to do with fuel consumption while the engine brake is working also contain a certain amount of humor as well.

With Electronic fuel injection the fuel is completely shut off while the decompression valve is open. That would certainly deter the burning of something that is not there.

Besides that does anybody really care, I still prefer doubled up baseball cards...

 

You might want to think this one through a little more...

Many opinions...One correct answer!

And your answer wasn't it.


Computer controlled engines shut off the fuel supply to the injectors when the Jakes are activated...No fuel to the injectors, No fuel used, No fuel wasted.

 

1 Wrong answer.


Remember that use of the jakes is actually turning the motor into a sort of air compressor.

The turbo "boost" you see on that little dial on your dash is turbo pressure. In other words, it is the exertion of air onto the sensor that sends the signal to that little dial on your dash which tells you the pressure inside your turbo is 20 psi.

Your turbo whines up when using jakes because the added pressure inside it is requiring it to turn in order to release that buildup of air. This is why it whines up, the physical turning of the turbo itself adds friction to the whole works (it's a pretty powerful little part) and your vehicle slows a little more. The air is released, pressure goes down, the turbo disengages...you speed up a little as the air increases inside the turbo again....and so on. That black smoke some of us see when the turbo engages during jake use is unburned, recycled exhaust the turbo did not have a chance to get to before the jake was engaged.

Question, then, is how does the motor stay started when you disengage the jake if you weren't using any fuel? It's the same concept as push-starting a car. Even automatics will push-start if you can get them going fast enough. A diesel motor wants to run...it loves to run. So, when you disengage the jake, your diesel motor will pick up the slack as the crank shaft is still turning, engage the fuel pump and roll on.

There is no fuel actually being consumed during the use of your jakes.

I do not consider it to be "excessive" when I use them to stop quicker if something is going on in front of me or when (obviously) going down a grade. I do consider it excessive when you are just rolling up to a stop light in town or in a parking lot...and when you are upshifting. I actually get a giggle out of those who think the jake helps them upshift. All it does is put a strain on the fuel system with all that on-off-on-off nonsense. And make you look like a fool to those if us who know what the inside of today's aluminum-headed motors look like.

 

I think it's pretty much agreed that an engine brake (Jake) is primarily intended to assist the service brakes when descending grades. And they have proven their worth as a safety device in that respect. But, is there anything else a Big truck truck driver can do to create additional resistance to further aid the brakes and Jake?

Call me crazy, but in addition to the Jake, I flip the switch to ON, activating the fan behind the radiator, and turn the A/C on to the HIGH setting which engages the A/C compressor to run full time, --- both of which, I think, create drag on the Big motor, aiding the service brakes and the Jake.

I've been told those actions would have no effect, but when I do that before engaging the Jake, I notice a definite drag on the Big motor, and a slight reduction in road speed. And when I turn the Big fan and A/C off while descending, I notice an increase in road speed. Not all that much, but enough to require applying more service brake pressure to maintain a desired speed.

The reason why fan clutches are used is to reduce fuel consumption, and running the A/C compressor increases fuel consumption, so obviously there's an increase in resistance causing the Big motor to work harder to turn those pulleys and drive belts and fan blades and compressor parts.

What say y'all?
Is it real, Memorex, or my overly vivid imagination? :smt102

 

It works, though mine didn't have a high setting for the A/C. It was on or off.

 

I asked the Freightliner guy about that very thing...regarding the engine fan. The engine fan, if the jake is operating correctly, will engage itself automatically and you don't have to flip the switch. However, while the fan is turning, it adds about 40 hp worth of drag pressure to the whole picture, which, as you pointed out, assists in the slowing process.

I hadn't considered the A/C, but it makes sense. However, it most likely adds a fractional percentage to the slowing power and I'm not going to freeze my butt in the winter to slow down one mile per hour when I can touch the brake pedal one more time than if I had the A/C on. In the summer, the point is rather moot. It's on anyway.

 

All the A/C units in the Big trucks I drove could also produce warm air when set to do so.
Much better than using the heater/defroster during certain conditions when the warm, moist air from the heater/defroster fogs up the windows and windshield.
The A/C dehumidifies the interior air, preventing or removing the fog that accumulates on the glass.

Even if the A/C wouldn't blow warm, the dehumidifying effect would be worthwhile, and probably wouldn't lower an already cold temperature much, if any.

 

growing up in the back woods of Oregon, there would be A LOT of loaded logging trucks coming down the gravel roads hauling a full load of logs... you could hear the jake brake coming on long before you would see the truck, and you'd have time to find a wide spot and wait for them to pass you...

 

Yep...I know those back woods well...Roman Nose, Mount Nebo, Wolf Creek/Cougar Creek area, uphill from Seal Rock....just to name a few. Jakes never bothered me. It was the hotrod mudders that peeved me. Always making a big mess, leaving their trash and plowing through the wilderness at mach IV with their loud pipes and louder music. Messed up more than one quiet fishing trip.