Transmission Downshift

[RUSSELL5000]

Took a nice trip to West Virginia recently with the truck and trailer in signature; in West Virginia there are some 6% and 7% grades on the interstate, a number of these on the route to where we were camping, and an assortment of 9% grades on the route to camping (the longest 9% grade was three miles).

So far I have driven with the trailer by turning the exhaust brake button on, the tow-haul mode button on, putting the transmission in drive, and going on my way.

(1) In going up a few of the hills on the interstate the transmission would downshift; it seems strange to me though because engine RPM would suddenly rise way up, the downshift would occur, and engine RPM would drop back down. That seems weird to me, although with my first diesel truck and trailer I don't have direct experience with what "normal" is. Am I doing something wrong?

(2) I am impressed with how effectively the exhaust brake works. I go down the grades and pretty much do not touch the brake pedal - a couple of times for some tight turns was all. This is actually great as I watch other trailers with the brake lights constantly on. In fact, I think maybe it works too well: sometimes I am slowing, the truck downshifts (with an even more annoying sudden increase in engine RPM followed by a sudden decline), and we are braking way more than I actually want with speed rapidly dropping. Am I doing something wrong?


Thanks!

 

[Bug Out]

I owned a 2012 and now a 2013. The shifting is normal. As it shifts gears, the torque converter "unlocks, causing the rpms to raise up, once the shift is complete, the torque converter goes back to locked and rpms drop.

They cured the "it works to well" e-brake in 2013. You have a option of "AUTO" which keeps your vehicle at a steady speed downhill, rather then slow you to the point where you have to accelerate to keep folks from smacking into you from behind.

The 2012 I had would downshift and slow me sooo much, I had to accelerate. Not a bad thing because I dont have to worry about smoking the brakes like the others do... Just give it some fuel and it wont downshift as much... Once you buy a 2013 or newer, you'll just set it in auto and your good.. There are many experts on the board who will explain it much better then I.

 

[TJJEEPER]

On my '12 I just use the cruise control to keep the speed where I want it on the longer downhill runs. It will add more EB as needed just as it would add accelerator to the uphill side. As soon as you tap the brake it'll cancel the cruise and do as you're suggesting and slow way more than I want.

I'm up and down the I-5 Grapevine a couple time a year (6% grade) and never have to hit the brakes unless the traffic is heavy.

 

[PC12Driver]

My way around the big downshift is to manually click it down to 5th in anticipation of the hill. Not as much rpm flare that way. Otherwise, it almost feels like it drops from 6th to 4th, then back to 5th for the hill. It'll take quite a hill to trigger an automatic shift out of 5th.

On the long downhills I'll turn off Tow/Haul and then manually select a gear based on how much braking I want. That takes away the downshifting to redline tendencies that the '12 has for slowing.

 

[Newt]

My 09 on cruise will drop from 6th to 4th on a steep grade. The lower your speed the more you see this. I also have learned to anticipate. If I see a grade where I know it will downshift, I manually downshift it first. I also think it will provide better MPG. If you wait for it to downshift while using cruise control, it'll drop several MPH. Then the cruise control will give full throttle back to the set speed.

IMHO, it's much better to anticipate the shift, it's much easier on the transmission.

Newt

 

[RUSSELL5000]

I am going on another trip with the travel trailer next week - some of the same roads in West Virginia, some new ones. I'll practice using the manual shifter and anticipating.

 

[Bug Out]

Russell5000, if you happen to be at 60MPH or less, try keeping it in 5th and see how it acts.

 

[RikDavis]

When on Interstate 79 in WV I think 5th is a better choice, even with a light 5000 lb trailer. On some of the roads off the interstate you may never get into 5th. I think with the smart brake I did more downshifting going down hill than I did going uphill. The hills in WV were a lot steeper when I had a non turbo Chev. 6.2

 

[RUSSELL5000]

A good portion of the upcoming trip will be on I-79 in West Virginia. I like to go just under 65 mph with the travel trailer - it seems to be where I pick up the best fuel mileage. I'll try sticking in fifth in that hilly stretch as you enter WV from the north going south. That is where all the downshifts happened last time.

Thanks!