I am assuming that the stock truck has an exhaust brake to help with towing. I have noticed it when you are cursing and then let off the gas the truck slows down noticebly, is that becasue the exhast brake is engaging. is there anyway to desingage it for driving around town, then engage it when hauling? i have a 06 LBZ

My '06 LBZ doesn't have an exhaust brake, sure wish it did.

Something tells me you may get your wish.

then if they dont have exhaust brakes what is it that is slowing me down when you let off the gas? Is it the turbo, or since the allison is so tight? its an auto too.

It's the compression from the engine and having the TC locked that causes the slowing down when you let off the peddle. If you do that in a lower gear without the TC locked it won't slow you down nearly as fast.

dont you alloson guys have "grade braking"? i thought i rember seeing that on hear its not like a exhausxt brake but jsut haveing the Trans locked up and using the engin a little bit you git some slowing like Lakingslayer said

hay Brayden will your new lil turbo box controle the vains of the turbo for braking?????????:ro) :ro)

Hmm That's a good idea the4wheeler ;) :muahaha:

Will it make the cool braaaaaaaap noise :D

So, then how does the LBZ brake the car and trailer. Does it have a "jake" brake (where the exhasut valve is lifted during compression)?

So, then how does the LBZ brake the car and trailer. Does it have a "jake" brake (where the exhasut valve is lifted during compression)?

Read Lakingslayer's post it is all done with compression.


Hmm That's a good idea the4wheeler ;) :muahaha:
Will it make the cool braaaaaaaap noise :D
:cool:

No... this is no detroit diesel... its a V8 duramax. You've got the TC in conjuction with automatic downshifting when letting off the gas and touching the break. No exaust breaks, no valves, no built in components in your engine either... just technology in a computer

Vanes one the trubo close in the medium duty stuff to act as a exhaust brake. Ours just inst programed to do this. Sounds like there may be a widget that will controll this a bit.

:exactly: I was just thinking if they can do it on the 4500 there's no reason some enterprising programmer person can't make it work on our trucks. Imagine that coupled with the grade braking feature of the Allison!:eek:

:exactly: I was just thinking if they can do it on the 4500 there's no reason some enterprising programmer person can't make it work on our trucks. Imagine that coupled with the grade braking feature of the Allison!:eek:

Sounds like another project for Brayden... ;)

I just might take that project on :D

OK beans are spilled, cat's out.. Check the Cubby Hole thread ;)

No... this is no detroit diesel... its a V8 duramax. You've got the TC in conjuction with automatic downshifting when letting off the gas and touching the break. No exaust breaks, no valves, no built in components in your engine either... just technology in a computer

Wouldn't it just freewheel and accelerate because the diesels do not have a throttle blade (what makes a gasoline decelerate). With larger diesels, they open the exhaust valve on the compression stroke to create a pumping loss. Where is all of the energy being expended when grade braking is turned on. Does anyone know of an advanced Duramax forum where I can learn about the more complex theories behind diesels?

The new DURAMAX 6600’s turbo system is the capability of the variable-geometry turbocharger to provide exhaust braking. You may notice the truck slowing down when you let off the gas but that is more of jut engine braking because of the transmission setup. If you put the truck in tow haul mode of course you will have a different shift pattern, but i belive that is when you are going to get your exhaust braking.

That system is not enabled in the pickup trucks. What you are feeling is only grade braking, nothing else.

The principle behind a diesel is simple.. No throttle required.

Cut the fuel, the engine doesn't produce any power. SO the drivetrain now has to spin the motor over by itself. Diesels run high compression, 17:1 or so on the duramax. This takes a great deal of energy to turn the crankshaft.

So essentially the engine while decelerating is one big high compression air pump. When grade braking activates, it spins the pump faster which creates a higher power draw.

Clear as mud?

Now if you add a TurboBrake to the system, then you've got lot's of extra braking ;)

I just might take that project on :D

OK beans are spilled, cat's out.. Check the Cubby Hole thread ;)

I can no longer find the whats in your cubby hole thread. Was it deleated?

I was very interested in finding out more.

They moved the thread.. Should have had a redirect in there though.. It was at the top as a sticky..

Click Here to see the TurboBrake thread (http://www.dieselplace.com/forum/showthread.php?t=78758)

That system is not enabled in the pickup trucks. What you are feeling is only grade braking, nothing else.

The principle behind a diesel is simple.. No throttle required.

Cut the fuel, the engine doesn't produce any power. SO the drivetrain now has to spin the motor over by itself. Diesels run high compression, 17:1 or so on the duramax. This takes a great deal of energy to turn the crankshaft.

So essentially the engine while decelerating is one big high compression air pump. When grade braking activates, it spins the pump faster which creates a higher power draw.

Clear as mud?

Now if you add a TurboBrake to the system, then you've got lot's of extra braking ;)



Where is the energy loss to slow a large truck and trailer. When the pistons compress the air mixture, it is similar to a spring, and wants to push the piston back down with almost the same force with which it was compressed. Unless you bleed off the compressed air (jake brake) you will not be scrubbing off, or losing energy. I am just trying to understand the diesels in these trucks.

You're forgettting the intake and exhaust valves still open and close. It takes energy to pull air in, and to expel it out, let alone from the compression. There are plenty of losses built into the system.

Trucks that have standard non VNT turbo's still grade brake well.

I am assuming that the stock truck has an exhaust brake to help with towing. I have noticed it when you are cursing and then let off the gas the truck slows down noticebly, is that becasue the exhast brake is engaging. is there anyway to desingage it for driving around town, then engage it when hauling? i have a 06 LBZ

I am assuming you are not in the tow haul mode and just sense the truck slowing more than other vehicles you have driven. I very much notice mine especially when coasting down through 35 MPH when I feel it change gear. A friend who has the 05 with the five speed drove it and says it feels like his so this must be normal. In the summer time it appears to be better than when I bought in the winter.

Hope that helps

Taken directly from a GM website used by dealership personel



Grade Braking and Cruise Grade Braking (Allison Transmission®)
Grade Braking and Cruise Grade Braking assists when driving on a downhill grade. It maintains the vehicle's speed by automatically implementing a shift schedule that uses the engine and the transmission to slow the vehicle. This reduces wear on the brakes system and increases control of the vehicle. The system constantly monitors the vehicle's speed, acceleration, engine torque, and brake pedal usage. It detects when the truck is on a downhill grade and the driver's desire to slow down by pressing the brake.

Cruise Grade Braking is available on the 6.6L Duramax® diesel engine. Cruise Grade Braking monitors a vehicle's cruise state, engine torque, acceleration, vehicle speed, and the cruise set speed. Using this information, it detects when the truck is accelerating on a downhill grade and will automatically downshift to slow the vehicle if it exceeds the cruise set speed by a certain amount.

See Cruise Control for more information.

The Tow/Haul mode and Grade Braking shift modes can be activated by pressing the button on the end of the shift control stalk. If your vehicle has the Duramax® diesel Engine or the 8.1L VORTEC™ gasoline engine, Grade Braking is only available while the Tow/Haul Mode is selected. While in the Range Selection Mode, Grade Braking is deactivated allowing the driver to select a desired range of gears

You're forgettting the intake and exhaust valves still open and close. It takes energy to pull air in, and to expel it out, let alone from the compression. There are plenty of losses built into the system.

Trucks that have standard non VNT turbo's still grade brake well.

Wouldn't the exhaust valve be closed on the compression storke, trapping the air inside, and creating a kind of "air spring" pushing the piston back down unless the compressed air is vented (via jake brake).

Maybe I am just mis-understanding how much braking can be done without evacuating the compressed air charge on the compression stroke.

Is there a web site that can explain all of this type of stuff in detail?

I am also looking for a site with images of the Duramax heads and block.

Any help would be appreciated.

If that is the case the "air spring" would only dampen the compression braking slightly.

Wouldnt the 'air spring' push down on the piston with almost the same amount of energy with which it was compressed, minus any energy loss from heat/friction?

Yes it would but that energy has no there near the energy of the cylinder firing.

Wouldn't the exhaust valve be closed on the compression storke, trapping the air inside, and creating a kind of "air spring" pushing the piston back down unless the compressed air is vented (via jake brake).

Maybe I am just mis-understanding how much braking can be done without evacuating the compressed air charge on the compression stroke.

Is there a web site that can explain all of this type of stuff in detail?

I am also looking for a site with images of the Duramax heads and block.

Any help would be appreciated.

Have you ever down shifted a manual transmition. No jake brake involved the engine slows the vehicle.

A jake brake or exhaust brake uses even more back pressure on the exhaust side by putting a valve that closes off the exhaust until a certain pressure is obtained. Hence the BRAP, BRAP, BRAP noise. I am not certain how the variable turbo works as a break as this is the first time I have been around one.

Have you ever down shifted a manual transmition. No jake brake involved the engine slows the vehicle.

A jake brake or exhaust brake uses even more back pressure on the exhaust side by putting a valve that closes off the exhaust until a certain pressure is obtained. Hence the BRAP, BRAP, BRAP noise. I am not certain how the variable turbo works as a break as this is the first time I have been around one.

Yes, I have. My daily car is a 6 speed LS1 Camaro. The reason that a gasoline motor creates an engine brake is because the throttle blade is closed (on deceleration), and creates a restriction in the intake tract. This restriction is what causes the motor to create a 'resistance' on deceleration. With no throttle on a diesel, it would suck more and more air in, with no resistance, and would continue to accelerate. Like I said earlier, maybe all the braking force comes from the friction alone.

Keep in mind you are still pumping air into and out of the engine.

Yes, I have. My daily car is a 6 speed LS1 Camaro. The reason that a gasoline motor creates an engine brake is because the throttle blade is closed (on deceleration), and creates a restriction in the intake tract. This restriction is what causes the motor to create a 'resistance' on deceleration. With no throttle on a diesel, it would suck more and more air in, with no resistance, and would continue to accelerate. Like I said earlier, maybe all the braking force comes from the friction alone.


not quite true. drive a manual transmission car and kill the ignition and see how fast it slows down. then start it back up, get back up to speed and kill the ignition again. this time, press the gas pedal with the ignition killed. you'll notice that the cars slows down faster with the throttle open than with it closed. you don't believe me? try it.

Like I said earlier, maybe all the braking force comes from the friction alone.


It not friction, its drag.

It's called pumping loss, and slowpoke is correct.