Seneca - Tackling Steep Grades

[Crossingover]

For example, the 4-6% grade on I-24 west of Chattanooga (Monteagle), the 5% grade on I-24 north of Nashville, or the 5% grade on I-40 between Nashville and Knoxville. What are the ascending and (most importantly) descending best practices to safely run these grades when loaded to capacity?

[WinnieView]

The rule of thumb we have always followed with our motorhomes is whichever gear was needed to get up the hill should be the same one used to get down the hill.

[Tumbleweed44]

I've also heard that the computer will do a better job climbing the hill on cruise control than when using the foot throttle. I've not had mine long enough to verify. The old school rule of thumb is to use the same gear up or down, as previously stated. I'm not sure about modern engines/drivetrains/brakes/aerodynamics and computer modulated controls if that is still the best current practice.

[crumgater]

I take off cruise, take off over-drive, and set the RPMs around 2200 on the uphill side (and/or just push the pedal to the floor). Downhill, turn on the engine brake and stay under the curve max speed limits and go slow enough on the straights to minimize braking.

In our F350, we burned out the turbo letting the cruise control try to keep up with the set speed (pulling a 5er up a grade)... it just kept dumping in fuel trying to accelerate... I think the M2 is smarter than that, but having been burned once, I'm leery to test that theory.

[Mountain Cajun]

I us the cruise going up no matter what the grade, and take the cruise off going downhill so the exhaust brake will work correctly!


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[Robbbyr]

With a 2016 and up Seneca I am sure you have air brakes, so using the transmission and exhaust brake are wise as mentioned by the other posters. I say this about air brakes because however unlikely it might happen, repeated applications (pumping) of your air brakes to maintain speed could deplete the air. Pressure too low and the parking brake pops on automatically applying the rear brakes only. Not desireable at all! And having drum air brakes, continuous riding of the brakes of a heavily loaded coach (possibly also towing a heavy load) down a long grade could cause brake fade resulting in reduced effectiveness. It could happen on disc brakes also, but discs are inherently more fade resistant. And Senecas (with air brakes) have air-actuated drum brakes on each wheel.

The above air loss failure scenario is not likely in a newer Seneca compared to a larger truck with considerably more brake air demand. The air compressors might even be oversized for what air demand there is on a two axle Seneca. Especially overkill on my 2014 with 4-wheel hydraulic-actuated disc brakes. My compressor is barely working at all to maintain my parking brake off, air springs, engine cooling fan, and my (added) air horns. But air brake-equipped Seneca owners would be wise to be aware that as time and miles accumulate, you will need to make sure your automatic slack adjusters are working properly keeping the brakes in adjustment and that the air compressor is still putting out what it is supposed to. Or at some point years from now you might unexpectedly experience some air brake malady!

I'll also take this opportunity to get up on my safety soapbox (again!) and recommend that any driver of an air brake-equipped Seneca please take some time and get better acquainted with how your air brakes function. They are not the same as in your car, and they operate and fail differently. Most people who drive air brake-equipped vehicles have to have a CDL, and that testing and licensing incorporates air brake knowledge. But in many states that is not required for RVs.

[ready2retire&drive]

Since having my transmission reprogrammed it climbs the hills much better but on the really steep long pulls I will still shut off the o/drive and mat it. As for descending I had the engine brake reprogramed to come on at 3 miles over the set cruise limit so I do not get the speed run up like before, again on the really steep descend's cruise off eng brake working, and slight tap on brakes to assist if needed

[RVermont]

A good video resource for working with air brakes is SMARTDRIVETEST.com.
They present clear driving information for working with heavy trucks.

He explains brake fade and how to use your engine brake correctly. We are driving 25,000 -35,000 lbs rigs and a mistake can be fatal.

To avoid brake fade use of the correct gear is important, use of engine brake, as well as proper use of brakes .

Brake fade is not unique to air brakes and can occur in any vehicle however large heavy units are more likely to have this issue when the driver is using the brakes constantly causing overheating. For those of us of an age, remember all the runaway trucks on CHIPS, very exciting watching the big rig run down the hill.

I think the main thing is to know and read the grade signs before descending down any hill. make a conscious decision on each and every descent.

[Crossingover]

Great input from everyone! Thanks so much. We travelled the Monteagle grade last month by car and saw two tractor trailer rigs safely up in the emergency runaway ramps. Got me to thinking about keeping our Seneca out of that predicament.

[repacs0103]

One of those situations where the question illustrates why CDL knowledge is highly applicable to rigs this size. Descending grades in any vehicle but especially air brake equipped trucks should involve stab braking- pick a safe speed you desire, say 55. Let the vehicle accelerate to 5 over that, then “stab” the brakes and apply firm pressure until speed drops to 5 under the safe speed. Repeat as necessary and use the jake brake to assist; this technique will control speed and prevent brake overheat, fade and failure, and excessive air pressure loss.

Other than that just mind your air pressure gauge and keep in mind that 5% isn’t really much of a grade unless it’s about 10 miles long!


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