Exhaust Brake question?

The Tow Haul function is to save wear and tear on the transmission. GM recommends using it when the vehicle and trailer load exceed 75% of the GCWR of the truck. I use it even with a much lighter load when going up or down steep grades, where as mentioned, it helps the grade control system in the truck to keep your speed under control without having to do much in the way of braking.

The GM grade control system only works with the transmission in Range selection or manual mode. One situation where Range select mode is useful is if there is low traction as you can go into Range select and put the transmission into 2nd gear and this activates what GM calls "low traction mode".

I have never experienced anything workings nearly as well as the GM grade control using the transmission in auto and the Tow Haul mode engaged. It is a very impressive bit of engineering and the result of careful coordination between the Duramax, GM, and Allison engineers. About 10% of the time when using Tow Haul down a very long and step grade if I see the speed climbing I will engage the Exhaust Brake with the switch on the dash. With the newer trucks you can engage and disengage the exhaust brake at any time.

Ib516...thanks for your explanation. Everyone else, thank you too!

The exhaust brake is a much more technical way of stuffing a potato in the exhaust pipe. :)

The turbo in your truck is much like a fan, but it spins at very high rpm. Older design turbos were fixed vane designs, meaning the "fan blades" were of one shape and could not be adjusted. They were a compromise between fast "spool up" and the ability to flow hign volumes of air. Fast spool up reduces that delay between pedal down and the rush of power that sets you back in your seat. Small turbos spool up fast, but at the expense of being able to flow large volumes of air for high horsepower.

Large turbos spool slower, but support higher horsepower because they flow more air.

Always a compromise.

In comes the "VGT" or variable geometry turbo. What this does is, by being adjustable, it can spool quickly, and open up once up to speed to slow more air - best of both worlds.

Manufacturers then realized that by essentially "locking" the transmission to the engine and closing off the turbo vanes (the adjustable part) they could reduce the engine's ability to flow air, cause a restriction, and slow the truck. In comes the exhaust brake.

Why people say to use it often is because they have a tendency (over long periods of time) to get sticky by getting clogged with exhaust soot if not "excercised". Especially the first designs. Manufacturers then installed software that would exercise the vanes (move them through their full range of motion) without the driver knowing to keep them from sooting up. I am not 100 percent sure, but I don't believe it's as much of a problem as it used to be.

On to your next question about tow mode.

What this does is again eliminate a compromise. Manufacturers used to have to make the computer program that controlled the transmission work well in all conditions. Towing or not, mountains or cruising the flat terrain with no load.

Now with the tow mode, by prezsing the button, you are telling the trucks computer that you are goingto be hauling a load, and it would be best if it switched to the computer program the enegineers put in to be best suited for towing. Firmer shifts, less heat huild up, and more aggressive gearing down to hold back the load.

Couple that with the exhaust brake function, and you have a good 1-2 punch.

2013 silverado with exaust brake here use it all the time and very rarely use the brakes much it is awesome

RCMAN46 wrote:

ScottG wrote:
You need to run the exhaust brake often because it keeps the variable veins in your turbo free moving. If you don't use it you will more than likely end up with turbo problems.

And this is based on what information source?

For a while, when the 6.7 Cummins was new (07 to 09 primarily I believe), The turbos were manufactured with a cleaning port to take care of this problem. Today, not so much. At least that's from the Cummins POV. Seems like a procedure was even posted for the cleaning of the exhaust brake: Exhaust brake cleaning procedure

I use mine, they will save your brakes. GM trucks exhaust brake makes no noise at all, not the same thing as a Jake Brake. I use it with cruise control and it keeps the load in check, very good tool to have.

Love mine...I use it anytime I'm towing and also anytime I'm driving significant hills without the trailer. Saves brake use. Just have to watch for those little towns with exhaust brake ordinances. :)

I personally don't like the feel of the tow/haul mode on my truck, but the exhaust brake is great.

ScottG wrote:
You need to run the exhaust brake often because it keeps the variable veins in your turbo free moving. If you don't use it you will more than likely end up with turbo problems.

And this is based on what information source?

You need to run the exhaust brake often because it keeps the variable veins in your turbo free moving. If you don't use it you will more than likely end up with turbo problems.