Descending Monteagle Mountain: I-24 east.

[jstdreamin]

I'm planning a trip this summer that will take me from Nashville to Atlanta on I-24. Which means descending Monteagle mountain. According to Mountain Directory East, there are two separate grades. 3.5 miles of 5% with a 45mph curve at the bottom and another 4 miles at 6%.

I'm real comfortable driving my rig but haven't driven this kind of descent as yet and the DW gets a bit anxious. I've driven this route before many times in a car or SUV towing a boat but am wondering about what gear to start in when leaving the summit.

I have a 40' DP, Freightliner, 6 sp Allison, 360hp Cummjngs, with an exhaust brake. Coach will weigh about 30,000 and will be flat towing a 4,400lb small SUV with a Patriot brake system. Coach is rated 32k GVWR, 42k GCWR.

Do I leave it in "Drive" and turn on the exhaust brake? Or put it into 5th? 4th?

[Vaflatlander]

Last May we headed west from VA.spent 22 weeks and 10,000 coach miles in that time I went by the maxim that you desend a mountain in the same gear that you climb it. Your rig is similar to mine and I have found that the exhaust brake should be used and it will keep you safe.

[RV Wizard]

Turn on exhaust brake and have speed down to about 50-55 and put the trans in 4th at the truck inspection station at the top.

[Coma]

Your exhaust brake equipped ISC will make about ~240BHP in decent with EB on. You can climb in a higher gear than you should descend. I suggest you select one gear lower than the gear used to climb. The goal is to not use your service brakes for descent. You want to save them for an emergency stop.

The ECM may allow RPM's to go as high as ~2400 using the exhaust brake. You get your highest BHP at the upper end of the allowable RPM range.

[Spk64]

I think you should be fine. Made my first trip down the same hill this past spring. 40' DP with engine brake pulling a suburban. I tried to keep my speed around 45 going down. Tapped the brakes occasionally. Just be sure to be slowed down before going down the hill. I left my tranny in normal driving and just switched on the engine brake it handled the downshifting. Only problem was when I came upon a trucker that decided 10-20mph was his speed and I had no room to get over so had to stand on the brakes more than I liked.
On the return trip I set the cruise at 55 and maintained that all the way up the hill.

[MisterT]

exhaust brake works fine, dont sweat it - our first trip
was from Atlanta thru the Smokies to Gatlinburg, a little
hairy, as my first trip in a DP, but it is designed to handle
these situations - you CAN manual downshift, but I never
did... : )
[also traversed mountain passes from Montana thru Idaho to Washington state, and even better, the Big1 California CLIFFS coast!]

[fountain42]

Don't sweat it turn on the exhaust brake and tap the brakes if your speeding up to fast. no need to shift gears the exhaust brake will take over. We just passed over the Rockies and the exhaust brake made it very easy.

[alpha99]

I've driven that and much, much steeper and longer grades in the west with my DP towing a Chevy Avalanche. I just use the exhaust brake, rarely use pedal brake, no problems whatsoever. I leave the transmission alone and let it downshift as needed with the exhaust brake. I have invisibrake on the truck.


BTW, that's not a mountain, that's a hill. There are mountains out west.

Cheers!

[Papa_Jim]

Originally Posted by jstdreamin

I'm planning a trip this summer that will take me from Nashville to Atlanta on I-24. Which means descending Monteagle mountain. According to Mountain Directory East, there are two separate grades. 3.5 miles of 5% with a 45mph curve at the bottom and another 4 miles at 6%.

I'm real comfortable driving my rig but haven't driven this kind of descent as yet and the DW gets a bit anxious. I've driven this route before many times in a car or SUV towing a boat but am wondering about what gear to start in when leaving the summit.

I have a 40' DP, Freightliner, 6 sp Allison, 360hp Cummjngs, with an exhaust brake. Coach will weigh about 30,000 and will be flat towing a 4,400lb small SUV with a Patriot brake system. Coach is rated 32k GVWR, 42k GCWR.

Do I leave it in "Drive" and turn on the exhaust brake? Or put it into 5th? 4th?

Our rig is much like yours, in that we have the Cummins diesel engine, 6 speed Allison, exhaust brake, and probably weigh in about the same with a toad.

I regard any down grade with extreme caution.

I firmly believe in an old trucker's quote," You can go down a grade a thousand times too slow. You'll go down that grade too fast only once."

6% grade for 4 miles. At the top of that grade, I slow down to 45 MPH, shift the transmission to 4th and activate the exhaust brake. To further control the speed, when needed I will firmly push on the brake pedal for only a few seconds. I do not ride the brakes for fear of heating them. I find this is the most stress free way of floating down the grade.

You will learn with experience if you can go down a 6% grade in a higher gear and faster. That's fine as long as you know you have good control of your rig. Just remember, if the speed gets away on you, you might not be able to get things under control.

The other thing I often think about, if I'm going down grade too fast, and something happens that requires me to stop suddenly, how would I ever do that?

Just approach those down grades with caution, and you'll live to enjoy many happy trails.

Jim

[TMan59]

We have descended 6%, just use the exhaust brake and left the tray in 6th.
Tapped brakes a few times, but was very comfortable.
Hope that helps.

[ChasA]

We went down Monteagle last year. Transmission in D, exhaust brake on. Let the computers handle it.

[Fatfendr38]

As an ex truck driving instructor in non exhaust brake trucks, we taught students to use what ever their final gear was going up hill is the gear to select at the top of the grade before going down hill. We also taught "stab braking". Push firmly on the brake, slow the vehicle down and then release. Let the tranny take over again. This allows the brakes to cool off. With an automatic and exhaust brake I would use the exhaust brake and at least the gear you went up the hill. If you are unsure go 1 gear lower. There is no rush going down a grade. Beware that semis may be slower than you if the are running heavy. Its far better to ease it down the grade than run someone over.

[Steve Ownby]

Originally Posted by jstdreamin

I'm planning a trip this summer that will take me from Nashville to Atlanta on I-24. Which means descending Monteagle mountain. According to Mountain Directory East, there are two separate grades. 3.5 miles of 5% with a 45mph curve at the bottom and another 4 miles at 6%.

I'm real comfortable driving my rig but haven't driven this kind of descent as yet and the DW gets a bit anxious. I've driven this route before many times in a car or SUV towing a boat but am wondering about what gear to start in when leaving the summit.

I have a 40' DP, Freightliner, 6 sp Allison, 360hp Cummjngs, with an exhaust brake. Coach will weigh about 30,000 and will be flat towing a 4,400lb small SUV with a Patriot brake system. Coach is rated 32k GVWR, 42k GCWR.

Do I leave it in "Drive" and turn on the exhaust brake? Or put it into 5th? 4th?

You are smart to be prudent and I predict that you will have no problem whatsoever with this grade.

I assume that with the exhaust brake switch on, when you lift your foot off the throttle, the Allison displays 2 or 3 and downshifts to whatever gear your current speed/rpm allows. The key to a safe descent is the speed/rpm that you are at when the brake activates. Since this is your first experience with a moderate grade of several miles the thing to do is to start conservatively. If you know the speed at which the Allison will downs shift to 4th, then be at that speed when the brake activates. If you don't know then set you speed at 45 mph since that is the posted speed for the mid descent curve. I'm guessing that with that target speed, you will not increase speed as you descend. If you do start picking up speed, let it build to about 50 and apply the service brake aggressively for about 5 seconds and release. This is known as "snub braking". That should get you down below 45 again. If you slow as you descend, before you get a downshift to 3rd, apply a little throttle which will deactivate the exhaust brake. When your speed builds back to your target speed then close the throttle & the brake will activate again.

Since this is your first experience with a down grade like this, use it as a learning experience and experiment a little. You will learn some about the capability of your coach and you will become a better driver.


Steve Ownby
Full time since '07

[ernest917]

We took or Berk down numerous 6% grades on our 2013 trip and never had a single issue