Which gear when pulling over mtn passes?

Mountain driving, 4-speed overdrive automatic, 6.8 gas engine and 13,000 pound vehicle. I found it most useful to let the computer figure out which gear (2nd or 3rd) was needed to go up grade, but would manually shift into the lower of the two gears if it started hunting up and down. Which gear it is going to be depends on the speed you can maintain on the grade. My trip was US-50, thus curves designed for 45-55 mph; the Interstate can be different, roads capable of higher speeds than a RV or a tow can maintain.

Going down, it was always OD locked out, compression braking just isn't there at OD RPMs. On 4-6% grades, 3rd (direct) could hold speed to 65-75 mph, might work on Interstate but not good enough for US-50. To hold that 45-55 mph with only occasional braking I needed to lock in 2nd gear, to have the braking power of an engine spinning 4000-5000 RPM (engine braking HP is directly proportional to RPM).

My experience would be only a rough guide for you, because what gears depends on the grade, the combined vehicle weight, the speeds you want to maintain, and installed gearing. General guide, use the accelerator going up to try to maintain the spped you want, let the transmission tell you which gear. Going down a similar grade, lock into the gear you used going up. If still braking too much, slow down to the speed maintained on that grade in the next lower gear. I did a lot of 3rd going up, 2nd going down, to stay at a speed safe for the tighter curves going down.

Hardest part of mountain driving with a RV rig is figuring out where you want to be on speed. The big trucks may be down to 15-30 mph, cars going 55-70 depending on driver's tolerance for curviness, and your power to weight will put you somewhere in between. Do you bog down to truck speeds and use the right lane, or do you try to go past them, blocking higher speed traffic? I've found that I can get caught behind a heavy truck, let faster cars go by, and still have enough power to accelerate back up to my climb speed. May or may not work, depending on speeds, grades, and power to weight at in the gears available.

wintersun wrote:
The only reason to manually shift into a gear if is the transmission starts to upshift and then downshift a lot as when at an in-between speed going up a grade or having the transmission shift to a higher gear when you let up on the accelerator. .

Or to let the trans lock the torque converter...

All passes don't carry the same speeds. Some like I-70 or LaVeta pass have speeds up to 65 mph. Other passes may have lots of hairpins and 15 MPH speeds so learn to help the tranny by keeping the rpms in a happy range. This also varies by make and models and engine power. In other words one size don't fit all.

Other 1500 Hemi owners are a better source for how your 1500 Hemi/tranny will perform.

The only reason to manually shift into a gear if is the transmission starts to upshift and then downshift a lot as when at an in-between speed going up a grade or having the transmission shift to a higher gear when you let up on the accelerator.

With my last truck with a 4-speed transmission on a steep grade I would have to put it in third gear to keep it within the engine's peak power band and not have it shift into 4th and then lug. With my current truck's 6-speed transmission 4th is an underdrive gear and 5th and 6th are overdrive and I can leave it in auto mode all the time.

Colorado71 wrote:

It's 3% for every 1Kft. So ~ 30% loss of power over the Colorado passes.

30% is a huge amount of power to lose, right when you need it most.

Yep, makes a big difference. A 10K foot pass takes a 330hp Hemi and makes it a 243hp Hemi, 11K drops it to 236.. ouch!!

Since the 3% loss is referenced from the previous 1K feet here is a chart for anyone who doesn't want to do the math.

wilber1 wrote:

The 04 Hemi should be a 5 spd auto. The diesels used a 4 spd.

Bottom line. Make sure it is in the gear you want it to be. If D and tow/haul doing it for you, that's great. If not, do it yourself.

Yes it has a 5 speed, which is the problem with only have D, 2, 1 on the column. What about 3? No way to select it on a 545RFE.

The 545RFE also uses a gear called 2nd Prime, which is a taller ratio than 2nd. 2nd Prime is used when downshifting to get the gear to hold longer when passing. It's unclear when it will grab this over 2nd thou. My brother has an 06 with a 545RFE and feels it only grabs 2P when going from 4 down to 2, skipping 3.. as in romp to pass.

Peak torque occurs at 4400 and peak hp at 5400, so lets say that peak pulling power is going to be 4000-5500, if yo want to listen to it.

Looking at the gear ratio's if you are pulling a grade at 55-65 and you drop into 2nd gear your rpms will be anywhere from 3500-4500 probably pretty good. You make more power higher but to pull 5000 rpms in 2nd is around 70mph, might not need that much speed.

When the trans downshifts to 2nd I would move the shifter into 2nd and keep it there until the top. If the 545RFE is like other Dodge auto's this will allow tq converter lockup in 2nd and a cooler transmission.

I would personally wait for that to happen before manually putting it in 2nd. By going to 2nd you might skip 3rd, and on some hills 3rd may be enough rpms. Thou common sense does apply, 50 mph at 6K feet on a 7% grade will take 2nd.

I do recommend leaving Tow Haul on just about all the time, it does lockout the 2nd OD ratio thou.. so if you find yourself on a long gradual downhill turning TH off may let you use 5th. Once the long gradual downhill is done I would switch TH back on.

The highest gear that holds your speed. Too many variables otherwise, how steep the grade is, weight of your vehicle+load, etc. Generally stay about the speed of 18 wheelers. Object is to use your service brakes as little as possible, ideally not at all.

I have a 2014 Ram 1500 with a 5.7 Hemi, 8 speed auto transmission, intgerated brake controller with Tow / Haul mode.

Heading to Yellowstone in July, coming in through the North entrance, out through the South.

The stearing wheel has gear + / gear - buttons. If you would use 2nd on a manual transmission to come down, what gear would that translate to on a 8 speed?

5.7 tundra pulling aprox 7000lbs. I find myself downshifting to 2nd and holding 45 on I70 heading up. Usually 3rd is good for me on the way down. Definitely start low and move your way up if neciisary on the way down. Have never seen the temps move much up nor down.

Heat is not much of a problem going over the passes in Colorado.

Oregon Ms wrote:
Good advice on turning off the AC on the upside.

In addition to giving you back a little power, there's less heat being dumped in front of the radiator.