Using lower gear and 4 wheel low to control down hill speed

[Gallowbraid]

Picked up a 2019 Ram 1500 Laramie a few months ago after coming from a long line of 4WD vehicles that I've modified heavily for camping and off road exploring. Over this past week I had a chance to get up into the Cherokee National Forest in Tennessee to do some camping and exploring on the forest service roads. Other than ensuring the 4WD system worked during my test drive, this was the first time I'd gotten a chance to really use it. In navigating some of the steep descents in the NF I wanted to save the brakes and prevent any brake fade so I dropped the truck into 4WD low and used the gear limiting option to, initially, limit the truck to 3rd gear. This did not have the desired result. The truck would hold a low speed and then seemingly drop into neutral causing the truck to accelerate for a moment before dropping back into gear and slowing down. If I selected 4th or 5th gear as the highest limited gear the truck would do what I was expecting it to do which was use the transmission/transfer case to maintain a slow and steady decent speed.

Since this only happened in the lower gears (3rd or below) I have to assume this is a design or safety feature of the 8 speed transmission and not a malfunction. In reading the manual I don't see anything listed about using low range and the gear limiting to slow the vehicle, just the use of the downhill decent control which my truck isn't equipped with (and which uses the brakes, defeating the purpose of preventing brake fade). In any of my past vehicles: F150s, Rangers, Tacomas, Wranglers, 4Runners, a Sequoia and an F250, I could place them in 4lo and drop as low as 1st gear to use the gearing to maintain a downhill speed. Can anyone confirm this is just how the 8 speed transmission works in the Ram?

 

[SD Rebel]

What was the max speed you were driving during your descent where it would disengage and go into neutral?

 

[Gallowbraid]

What was the max speed you were driving during your descent where it would disengage and go into neutral?

Started from a complete stop, put the truck in 4lo and chose 3rd gear as the upper limit. Let off the brake and never touched the gas. Truck probably got to 5 or 6 mph, would then accelerate to 8 to 10 mph before slowing back down and then repeating. Not sure it was actaully dropping into neutral, thats just what it felt like. Choosing 4th or 5th gear as the limit the truck would maintain approximately 8 mph down hill.

 

[HSKR R/T]

There should be no brake fade if you are going that slow. Takes a lot of speed and brake pressure to really heat up the brakes. Maybe if you are talking miles upon miles of that.

Also 3rd gear is still pretty fast and the acceleration you felt was probably a shift into 3rd due to speed. Try using a lower gear

 

[SD Rebel]

That makes sense, you should have locked it in first or 2nd gear. Because it will try to shift into the highest gear possible naturally and that could be the feeling as HSKR mentioned.

 

[Gallowbraid]

Sorry, I should have mentioned this happened when locked into any gear 3rd or under. Putting it in 1st or 2nd resulted in the same "surging". The surging only stopped when I selected 4th or 5th as the highest allowable gear, and even when selecting 5th gear it would hold 4th gear for an extended period of time.

 

[SD Rebel]

Sorry, I should have mentioned this happened when locked into any gear 3rd or under. Putting it in 1st or 2nd resulted in the same "surging". The surging only stopped when I selected 4th or 5th as the highest allowable gear, and even when selecting 5th gear it would hold 4th gear for an extended period of time.

Oh gotcha, that is interesting, and now beyond my scope. Hopefully someone here will chime in, there are off-road members here who likely have better experiences, I would check out the off-roading section and PM some of those folks in case they didn't see this thread.

 

[hogger]

I've noticed similar behavior on my '22. On mine, it's not that it's going in and out of neutral, rather it's going in and out of fuel cut off. I can see this on the fuel economy screen, the instantaneous MPG switches between 99 and something in the mid teens, corresponding to the surges. In the first couple gears, it basically doesn't go into fuel cut off until about 3500RPM, then the compression takes over and slows the truck until it drops somewhere around 2500-3000 RPM, where it starts feeding fuel again. Kinda irritating. I've noticed it doesn't seem to behave like that in the higher gears, pretty much stays in fuel cut off until below about 20mph.