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Bank_of_Dad's avatar
Bank_of_Dad
Explorer
Aug 19, 2013

6 speed transmission questions.

So I came out of the ice age and got a Suburban with the new 6 speed transmission (PRNDM_1). Reading the manual, it seems a little daunting.

So how do you use it when towing? And what about steep downhill grades (short or long) when towing. I'm used to just downshifting into 2nd.

Thanks

Judy
Tow Vehicles

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  • Tystevens's avatar
    Tystevens
    Explorer
    Aug 21, 2013
    TomG2 wrote:
    What is different about the GM transmission? My 2500HD seems to operate exactly the same way when M5 is selected. I do tap down to M4 if I see a particularly steep hill coming up. When you say you lock it in 5th, do you mean is will "never" downshift? Even with WOT on a 6% grade?


    In an auto with true manual control (I don't know if the Ford is this way or not, but my Subaru and Acura have this feature), you can force an up-shift as long as you're going fast enough to allow the transmission to shift into that gear, and the vehicle will hold that gear as long as mechanically possible. So yes, you can stand on the gas pedal and it will not downshift as long as it can keep the speed within the operating range for that gear.

    In the GM transmission, if you have it in M5, for example, and step on it, it will shift down to 3rd or 4th gear to get power to respond to your input. It won't make any effort to stay in 5th gear. Just as it would if you had the transmission in "D" and the truck happened to be operating in 5th gear at the time you stepped on it.
  • Hybridhunter's avatar
    Hybridhunter
    Explorer
    Aug 21, 2013
    I had a Chevy 1 ton, and a Ford 1/2 ton. The Ford has true manual control, if you order the tow package, it's my favorite feature when towing. I lock it in 5th on mostly flat terrain, turn on cruise control, no torque converter unlocking, no downshifting. Perfect.
  • fickman's avatar
    fickman
    Explorer
    Aug 20, 2013
    Great info. . . saved me from asking the same question as I'm new to towing with the 6-speed.

    I'm 99% sure I have the 3.42 gears and I've found I tend to lug in 6th even with a lighter PUP. I do use T/H (although according to a few posts here I don't need to).

    I smiled from ear to ear the first time I experienced the transmission assisting me with braking. . . complete unexpected. . . but very appreciated.
  • Tystevens's avatar
    Tystevens
    Explorer
    Aug 20, 2013
    ktosv wrote:
    Do you have a 1/2 ton or 3/4 ton? If 3/4 ton, I am thinking you might be able to just drop it into Drive and be good with that size trailer. When approaching a steep downgrade and you think you will need to shift down, just drop it to M. It may automatically drop to the next lower gear than you are in (if cruising in 6th, it might drop to 5th when you go to M). Just shift up and down as needed when needed.

    If you have the 1/2 ton with the 3.42, you may have to use M all the time and limit the truck to 5th gear.


    Not really. The transmission does a very good job avoiding hunting or other issues. I've been quite impressed with it, even when towing near the max ratings as we do. It also does a good job downshifting to control speed. The only time I have really had to intervene is on steep mountain highways where we need to keep speeds down in the 25-35 mph range for curves and stuff. Overall, I am very happy with the transmission programming. Like others said, mine is just in D, t/h on for 95% of my towing.
  • Tystevens's avatar
    Tystevens
    Explorer
    Aug 20, 2013
    TomG2 wrote:
    Hybridhunter wrote:
    ....snip...... It only limits up-shifting, ........................snip...........


    Funny, mine downshifts with a tap. I often anticipate the extra power needed to climb a hill and tap it down a gear to save the transmission from doing it for me half way up the hill.


    Of course it does, if you are in a gear above the gear you tapped down into. If you are in 6th, and you select 5, it will force the downshift. But if you are in 4th and you select 5, it probably will not do anything.

    Basically, the same as the old 1-2-3-D setup. If you have it in 3, it will shift thru gears 1, 2 and 3, but will not shift into 4th (or od or D or whatever you want to call it). It is simply less cumbersome to have a button to select range rather than have 6 individual positions for the gear shift lever.

    The operation is quite different from an auto with true manual shifting capability, such as my Subuaru or the Acura TL we used to have. In my Subaru, if I select 3, it will will stay in 3 unless I let the speed get to where it cannot physically maintain the gear. I can stand on the gas, and it will not downshift. In my '10 Suburban, if I select 3 and step on the gas, it will downshift to whatever gear it needs to respond to my request.
  • Tystevens's avatar
    Tystevens
    Explorer
    Aug 20, 2013
    The Texan wrote:
    ktosv wrote:


    Also, if you select 2, it will start in 2nd gear and stay in 2nd gear. Awesome for a 2wd vehicle like mine in deep sand or snow.
    Nope, select 2 and it will start in 1 and shift to 2. It is NOT a manual transmission, just a top gear selector.


    You're right, it is just a range limiter, which is a poorly understood feature or function of this transmission.

    With the exception of 2, however. From a stop, it will start in 2 if that range is selected. It is to reduce torque and improve traction on slick roads. My '05 4 spd had the same feature. Seems needless since the truck has traction and stability control, too -- it will limit wheel spin on ice in 1st gear -- but that is the feature.
  • wnjj's avatar
    wnjj
    Explorer II
    Aug 20, 2013
    TomG2 wrote:
    Hybridhunter wrote:
    ....snip...... It only limits up-shifting, ........................snip...........


    Funny, mine downshifts with a tap. I often anticipate the extra power needed to climb a hill and tap it down a gear to save the transmission from doing it for me half way up the hill.


    Nothing funny here; you both agree. If you limit up-shifting to a lower gear, it must downshift. The difference is if you are going slow enough of under heavy throttle and tap it up a gear it won't necessarily upshift.

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