2011 Heavy-Duty Hurt Locker: Davis Dam Grade Exhaust Brake Test

Words by Mike Levine, Mark Williams and Kent Sundling, Photos by Ian Merritt

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Davis Dam Grade Exhaust Brake Test

We didn’t just time the trucks up the grade. We also evaluated their exhaust-brake performance while heading back to Bullhead City with the 19,400-pound trailer pushing these dually HDs on their trips downhill.

An exhaust brake saves on brake and transmission wear by clamping down the engine’s turbo vanes, creating back pressure to engine-brake the truck. It also reduces the potential for brake fade during long descents, increasing downhill safety and overall wheel brake life.

The GMC Sierra and Ram 3500 have push-button-activated exhaust brakes that can work in or out of tow/haul mode, while the Ford F-350’s exhaust brake is enabled only when the truck is in tow/haul. Unlike the Duramax and Cummins, the Ford’s exhaust brake can't be turned off. Cruise control was not used.

Example graph of one of several exhaust brake runs in the Ford F-350 towing 19,400 lbs. (approximately 28,400 lbs. combined weight, including three adult males). Six brake applies can be seen here, immediately after speed peaks exceeded 60 mph. Wheel brakes were applied until speed was reduced to approximately 48 mph, to keep the truck in a narrow band between 50 mph to 60 mph.

At the start, we crested Union Pass westbound and set our speed to 55 mph. Then we waited for gravity to take over and the trucks to exceed 60 mph, at which point we applied the wheel brakes to lower our speed to approximately 48 mph to start the pattern over again. We counted the number of times the wheel brakes were applied. The truck with the fewest brake applies wins.

We’ve always liked the Ram’s exhaust brake, which was designed and engineered by Cummins. During last year’s HD Shootout, we considered it a stronger exhaust brake than the one recently added to the Duramax. That belief proved itself on the downhill run from the top of Highway 68. As measured for the trucks' best downhill runs, we had to apply the Ram’s wheel brakes only twice to keep the Ram one-ton in the 50 mph to 60 mph range. The GMC Sierra 3500 required four brake applies, and the Ford F-350 required five.

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Interesting how dominant GM is accelerating up the hill again. I thought for sure Ford would've figured out the issues. Maybe it's drivetrain related? Excess Ford drivetrain losses?

Kudos to Ford for dialing in the brakes. Wonder how trailer braking forces are guaranteed to be even across the different runs and different pickups.

It isn't surprising tha the Ram's engine brake worked the best. Isn't this engine used in industrial trucks ie. class 4 and up?

Way to go, Ram!

Curious why that "Buy American" chap would be rooting for a Fiat???

Can you clarify something real quick- if the cruise control wasn't used, how did you "set" the speed? was there manual downshifing, or was it all the truck's programming?

@Mrknowitall. The VBOX was mounted where we could see it and set truck speeds to its reading.

GM has decided to try to appeal to those looking at towing up hills at altitude as the most important criteria. Ford remains interested in selling trucks that work well under all conditions to the other 95% of truck buyers. This is why Ford remains the number one truck in sales for over 30 years running

@Obvious Troll: You guys asked for a low altitude mountain climb and we delivered, in addition to high altitude.

Ford trucks as a collective (incl. Lincoln) are not the best selling truck when compared to General Motors as a collective (Chevy+GMC)

@ML- sorry, I guess I still don't quite get how this works. The Exhaust brake just automatically starts working, anytime you begin to coast? That is the part I was unclear on, not a question of how accurately you set your speed (I completely trust your ability to perform a test in a scientificaly accurate manner).

@Mrknowitall - valid question. I had to read the story a few times myself. They used "pucker factor" to determine when to hit the brakes.LOL

@Tired-Ogre - go to the sales data posted every month on this site or go to "Good Car Bad Car" and do some math. The latter posts information on Canada and the USA.

Setting the cruise control will make the Ford's exhaust brake work much better. At least it does in my '08...setting cruise makes it really clamp down on the speed going down hill.

@Mrknowitall: Correct. When you're off the accelerator with the exhaust brake on and cruise control off, the engine brake will slow the truck. As you know, an exhaust brake's purpose is to extend the life of the wheel brakes -- especially going downhill. We could done the test with cruise control however applying the wheel brakes would have turned cruise control off. That's why we didn't test with cruise control on.

Yes, but a correctly designed (and rated) powertrain, should be able to hold the vehicle's speed without ANY brake applications.

That should be your test. A pass/fail.

@George - if that is the case all 3 trucks would of failed because all 3 required brake application.

@ Mike Levine
Do you guys downshift the transmission a gear or two while going down the mountain or just let the truck decide ?

@Taylor: We let the trucks decide.

Is this model of this truck available. I rarely see it now. Or maybe there's an upgrade of this model.

I was just thinking with the F350,if you cant turn the exhaust brakes on and off, would'nt that be dangerous on ice?

I have a tendency to run the cruise control a lot so I have to wonder how the test would've gone with cruise on. I know in my 05 ram with cruise control on the transmission down shifts if you get more than 5mph over the set cruise speed, that's pretty noticeable engine braking even without an exhaust brake. So I wonder, would any of these trucks actually need the foot brake on the downhill?

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