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 > Towing up grades with "M" and 1 gears

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afidel

Cleveland

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Posted: 04/04/21 11:17am Link  |  Quote  |  Print  |  Notify Moderator

morley wrote:

This might be a dumb question so excuse me if it is. My 2009 Chevy Duramax with Allison has the engine brake for descending down steep hills (not a Jake brake), it works well and I use it all the time when descending. Now my dumb question and I ask myself this every time the engine brake is required and comes on.
Is more fuel used during this downhill braking scenario???


No, by definition engine braking is running the cylinders without fuel so you're using less fuel than letting the engine idle and using the friction brakes.


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mr_andyj

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Posted: 04/04/21 11:59am Link  |  Quote  |  Print  |  Notify Moderator

Please ignor all the post that start off saying "just..." With towing you dont "just" do anything.

If you are driving flat ground then keeping it in D is fine, tow mode or not. Tow mode will change the shift points of the trans, and there is nothing different about how the engine runs, just the transmission. Trans will rev higher before upshifting is what you will notice.

Yes, very much DO shift the trans into a lower gear for those white-knuckle downhills. Use the engine to maintain slow speed, not the brakes. I assume you have a gas engine? diesel engines will have very little engine braking effect without a Jake brake or exhaust brake engaged.
Gas engines do have a lot of restriction when off the gas pedal and coasting, so is useful.

Now, what gear to be in depends on the speed you want to maintain, the grade and the weight of the trailer.

Without researching the info you did not give us on your specific transmission, lets just assume you have a 4 speed with overdrive (5 forward gears). 5th gear is the O/D and the highest gear. With O/D off the truck will not shift into anything higher than 4th gear, and coasting speeds will be slightly reduced. In 3rd gear the truck will not shift higher than 3rd gear (no 4th, no 5th) and downhill speeds can be greatly controlled until the grade gets steep or your speed need to be dropped way down for turns.
Don't wait until the revs are high before dropping down to 2nd gear (truck wont shift into 3rd, 4th, or 5th) as is harder for trans to shift down when rpm's are so high (high revs in 3rd means way higher revs in 2nd).

Whatever buttons or levers or trickery you need to do to put the trans in the appropiate gear needs to be well understood by you before heading out.

Start dropping to lower gears, one at a time, well before you think you need to. This is not the emergency plan or back-up plan. Lower gears is your first solution to long downhill grades.

Using the trans/engine to slow the vehicle will save your brakes. Brake fluid will boil quickly and your brakes will fade or fail if you rely on them to maintain speed. This is not a good feeling. After brakes fail the engine can maintain speed, but then you have no way to further slow or stop the vehicle until they cool down.

Gdetrailer

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Posted: 04/04/21 03:41pm Link  |  Quote  |  Print  |  Notify Moderator

mr_andyj wrote:

Please ignor all the post that start off saying "just..." With towing you dont "just" do anything.

If you are driving flat ground then keeping it in D is fine, tow mode or not. Tow mode will change the shift points of the trans, and there is nothing different about how the engine runs, just the transmission. Trans will rev higher before upshifting is what you will notice.

Yes, very much DO shift the trans into a lower gear for those white-knuckle downhills. Use the engine to maintain slow speed, not the brakes. I assume you have a gas engine? diesel engines will have very little engine braking effect without a Jake brake or exhaust brake engaged.
Gas engines do have a lot of restriction when off the gas pedal and coasting, so is useful.

Now, what gear to be in depends on the speed you want to maintain, the grade and the weight of the trailer.

Without researching the info you did not give us on your specific transmission, lets just assume you have a 4 speed with overdrive (5 forward gears). 5th gear is the O/D and the highest gear. With O/D off the truck will not shift into anything higher than 4th gear, and coasting speeds will be slightly reduced. In 3rd gear the truck will not shift higher than 3rd gear (no 4th, no 5th) and downhill speeds can be greatly controlled until the grade gets steep or your speed need to be dropped way down for turns.
Don't wait until the revs are high before dropping down to 2nd gear (truck wont shift into 3rd, 4th, or 5th) as is harder for trans to shift down when rpm's are so high (high revs in 3rd means way higher revs in 2nd).

Whatever buttons or levers or trickery you need to do to put the trans in the appropiate gear needs to be well understood by you before heading out.

Start dropping to lower gears, one at a time, well before you think you need to. This is not the emergency plan or back-up plan. Lower gears is your first solution to long downhill grades.

Using the trans/engine to slow the vehicle will save your brakes. Brake fluid will boil quickly and your brakes will fade or fail if you rely on them to maintain speed. This is not a good feeling. After brakes fail the engine can maintain speed, but then you have no way to further slow or stop the vehicle until they cool down.


Your pretty much dead wrong and obviously have not used a vehicle with TOW/HAUL feature.

I HAVE towed BEFORE there ever was such a thing as TOW/HAUL, my first experience with TOW/HAUL was just amazing, all I had to do was just let off the gas pedal as I started descending a hill and the transmission downshifted and kept the whole rig from gaining speed the entire way down the hill.. Several hills were 6 miles long at 10%-11% grades! That truck was the 2006 F250, what a advancement in towing, before then, yeah, always manually poked the gearshift into the next lower gear..

Newer vehicles with advanced features HANDLE the upshift and downshift hill assent and descent gear changes WITH ZERO INTERVENTION AUTOMATICALLY.

This is far, far different from the days of old with a the manual "THREE ON THE TREE" or floor mounted "Handshaker".

OP HAS TOW/HAUL, they DO NOT NEED to "baby sit" every second of the gear selection. They can of course if they feel uncomfortable can OVER RIDE the gear selection that the TOW/HAUL selected just by TAPPING or TOUCHING the brake pedal lightly and the transmission will automatically downshift to the next available gear.

One of the nicest things I have found on TOW/HAUL on my Fords has been the fact that the shifts tend to be spot on the money and silky smooth.. I rarely have to tap the brakes to over ride or even ride the brakes..

Heck, I have a steep grade to get into the next town from me, 11% grade for 1 mile with not one but TWO stoplight intersections at the bottom.. My TOW/HAUL will and does downshift ALL THE WAY TO THE BOTTOM without me having to manually do a thing other than touch the brake pedal if needed. I only have to apply some brakes just before the stop lights and by that time the transmission is down to 2nd or 1st already.

Some folks just can't get that "trucker" manual mentality shift thing out of their head like you are stating..

And by the way, read the manuals, you NO LONGER have to take things out of "OVER DRIVE", that once again is an old school train of though that is not needed any longer.. Let the power train control figure out what gear to select and you will find that it does not "hunt" gears like older much more underpowered vehicles.

Newer transmissions also are designed to shift more since they have more gears to select, big difference in shifting between a 4 speed auto and a 10 speed auto.. If you don't like transmission that shifts a lot, don't buy a 10 speed as gears are very short between each..

Maybe GMs TOW/HAUL doesn't work as well as Ford but I can attest to the fact with my Fords, I am no longer trying to micromanage what gear I am in..

Perhaps you should try a Ford?

noteven

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Posted: 04/04/21 03:59pm Link  |  Quote  |  Print  |  Notify Moderator

afidel wrote:

morley wrote:

This might be a dumb question so excuse me if it is. My 2009 Chevy Duramax with Allison has the engine brake for descending down steep hills (not a Jake brake), it works well and I use it all the time when descending. Now my dumb question and I ask myself this every time the engine brake is required and comes on.
Is more fuel used during this downhill braking scenario???


No, by definition engine braking is running the cylinders without fuel so you're using less fuel than letting the engine idle and using the friction brakes.


Correct. When a diesel is in “deceleration” (foot off throttle above idle speed) mode zero fuel is injected.

morley

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Posted: 04/04/21 04:55pm Link  |  Quote  |  Print  |  Notify Moderator

noteven wrote:

afidel wrote:

morley wrote:

This might be a dumb question so excuse me if it is. My 2009 Chevy Duramax with Allison has the engine brake for descending down steep hills (not a Jake brake), it works well and I use it all the time when descending. Now my dumb question and I ask myself this every time the engine brake is required and comes on.
Is more fuel used during this downhill braking scenario???


No, by definition engine braking is running the cylinders without fuel so you're using less fuel than letting the engine idle and using the friction brakes.


Correct. When a diesel is in “deceleration” (foot off throttle above idle speed) mode zero fuel is injected.


Thanks guys now I know the answer, much appreciated.


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APT

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Posted: 04/05/21 07:23am Link  |  Quote  |  Print  |  Notify Moderator

M mode for GM is not quite manual. It is more like range limit for the top gears. The number displayed is the highest gear the transmission will automatically shift into.

I tow in M4 or M5 with Tow/Haul enabled depending on the situation. Same engine/transmission as your van. I tow around 70mph and have had the trans shift into 6th gear. There is not enough torque at 2000rpm to push through the air. So, speed drops, then double downshift to get back to target speed. I lose the grade braking feature in M mode, but I can do that myself by hitting '-'. That engine/trans can sing at 3000rpm for 300k miles.


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mr_andyj

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Posted: 04/05/21 09:24am Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:


Your pretty much dead wrong and obviously have not used a vehicle with TOW/HAUL feature.


Good for you.

No, nothing I said is wrong. All is correct for towing. Tow features on vehicles might differ, but the principal of shifting to a lower gear will not deviate. I have not driven your particular vehicle, but I imagine that it also shifts to a lower gear to engine brake, just as every other vehicle works.

What I left out is considerations on gearing and torque converters. That is a lot to get in to and will depend on the specifics of each individual vehicle trans.

It is very important to understand the engine and transmission and what it is doing or trying to accomplish when towing, especially when towing heavy. Just knowing to "press this certain button" is a foolish way to go about it.

Gdetrailer

PA

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Posted: 04/05/21 09:50am Link  |  Quote  |  Print  |  Notify Moderator

APT wrote:

M mode for GM is not quite manual. It is more like range limit for the top gears. The number displayed is the highest gear the transmission will automatically shift into.

I tow in M4 or M5 with Tow/Haul enabled depending on the situation. Same engine/transmission as your van. I tow around 70mph and have had the trans shift into 6th gear. There is not enough torque at 2000rpm to push through the air. So, speed drops, then double downshift to get back to target speed. I lose the grade braking feature in M mode, but I can do that myself by hitting '-'. That engine/trans can sing at 3000rpm for 300k miles.


The correct term would be "semi automatic" for "M", sort of like the olden days where you could by a vehicle that had a transmission that did not have a clutch nor had the automatic valve body. On those you had to manually move and select each gear one at a time but it did it without any clutch pedal..

As always, READ THE MANUALS.

I am sure Ford and GM vary a lot but once again, there should be zero reason to baby sit things..

Some folks seem to get scared that they are harming the engine (lugging or running too high of RPM).. The reality is, now days the power train controls are setup to PREVENT DAMAGE FROM OCCURRING.

If the power train control determines your engine as you are going up a hill is on the verge of "lugging" it WILL downshift to the next lower gear provided the RPM will not exceed redline.

Same happens when descending a hill, the power train control will only downshift to the next lower gear as long as that selection will not exceed redline.

The "M" mode is put there more to satisfy (appease) the folks that got upset when manufacturers dropped all manual stick shift transmissions offerings..

The advances made in automatic transmissions over the last 10+yrs has been amazing but I get it, folks ARE distrusting of advanced features like TOW/HAUL..

In older vehicles that offered 3 and 4 speed automatics it was typically recommended in the manuals to drop a gear if transmission was hunting gears or lock out overdrive when towing.. Those recommendations are no longer in the manuals.. And with older vehicles, a downshift at the wrong RPM could be catastrophic to the engine and transmission.

Here is some of the information in Fords manuals concerning TOW/HAUL, M mode.

Fords 2020 F250 manual..

HERE


"Page 206

Manual (M)
With the gearshift lever in manual (M), the
driver can change gears up or down as
desired. By moving the gearshift lever from
drive position drive (D) to manual (M) you
now have control of selecting the gear you
desire using buttons on the shift lever. See
Understanding your SelectShift
Automatic transmission later on in this
section.

Page 207

Your vehicle has a SelectShift Automatic
transmission gearshift lever. The
SelectShift Automatic transmission gives
you the ability to change gears up or down
without a clutch

To return to normal drive (D) position,
move the shift lever back from manual (M)
to drive (D).
The transmission operates through the full
range of gears.

Forced downshifts

Allowed in drive (D) with the tow/haul
feature on or off.

Press the accelerator to the floor.

Allows transmission to select an
appropriate gear.
Understanding Your SelectShift
Automatic

Transmission
E249567
Note:
When pressing the button on the
gearshift lever, you can cycle through the
available drive modes.
See
Drive Control
(page
267
).
Your vehicle has a SelectShift Automatic

transmission gearshift lever. The
SelectShift Automatic transmission gives
you the ability to change gears up or down
without a clutch.
In order to prevent the engine from running
at too low an RPM, which may cause it to
stall, SelectShift still automatically make
some downshifts if it has determined that
you have not downshifted in time.
Although SelectShift makes some
downshifts for you, it still allows you to
downshift at any time as long as the
SelectShift determines that damage to
the engine does not occur from
over-revving.
SelectShift does not upshift, even if the
engine is approaching the RPM limit. It
must be shifted manually by pressing the
+ button.
Note:
Engine damage may occur if you
maintain excessive engine revving without
shifting.

Page 208

Manual (M)
Moving the gearshift lever to the manual
(M) position allows you to manually select
the gear you desire. Only the current gear
displays. Use the buttons on the gearshift
lever to manually select gears. Press the
+ button to upshift or the

button to
downshift. Return the transmission to a
different gearshift position to deactivate
manual control.

Page 268

Tow/Haul

For improved
transmission operation when
towing a trailer or a heavy load.
This mode moves upshifts to higher engine
speeds to reduce the frequency of
transmission shifting. This mode also
provides engine braking in all forward
gears, which slows your vehicle and assists
you in controlling your vehicle when
descending a grade. The amount of
downshift braking provided varies based
on the amount you press the brake pedal."


As always folks READ THE MANUALS, MANY of the old recommended procedures of the days gone by have been changed or removed and no longer apply to newer power train systems.

Gdetrailer

PA

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Posted: 04/05/21 10:49am Link  |  Quote  |  Print  |  Notify Moderator

mr_andyj wrote:

Gdetrailer wrote:


Your pretty much dead wrong and obviously have not used a vehicle with TOW/HAUL feature.


Good for you.

No, nothing I said is wrong. All is correct for towing. Tow features on vehicles might differ, but the principal of shifting to a lower gear will not deviate. I have not driven your particular vehicle, but I imagine that it also shifts to a lower gear to engine brake, just as every other vehicle works.

What I left out is considerations on gearing and torque converters. That is a lot to get in to and will depend on the specifics of each individual vehicle trans.

It is very important to understand the engine and transmission and what it is doing or trying to accomplish when towing, especially when towing heavy. Just knowing to "press this certain button" is a foolish way to go about it.


Gearing, engine, transmission "considerations" HAVE already been taken in to account by the manufacturer of each said vehicle.

This forum continues to spout off all of the OLD SCHOOL methodology that one MUST manually intervene ALL THE TIME. That intervention typically is manually changing gears up or down or with vehicles with the feature to limit or lockout gears.

The advent of newer engine/transmission power train controls have outmoded that old advice.

Hence the reason I keep mentioning READ THE OWNERS MANUAL.

Todays systems collect a considerable amount of data, processes that data and then determines what gear to go to, what RPM to shift at and it does it fully automatically without any need for driver input. The systems are designed to protect the engine and transmission whether that is from "lugging", "overreving"and for best performance under those conditions.

For some weird reason folks think it is bad when a gas engine exceeds 2K RPM, perhaps back in the olden days it was because the redlines were often 3,200 RPM- 3,600 RPM? and the engines were screaming at 2K RPM because of the gearing and wide gear spread of 3 and 4 speed transmissions..Not to mention older engines had less than half the HP and TQ these newer engines have..

Don't know about GMs but Ford does use an "adaptive learn" strategy and when the power train control senses different loads and conditions it will learn and adjust shifting strategy to your new driving style.

I get it, you and many other folks are scared of new features and old habits tend to never die but perhaps you should try using those features and relax a bit before condemning them for everyone.

My advice to the OP still stands, DO NOTHING, you do not have to manually micromanage what gear to be in going up or down the hills, just put in drive and enable the TOW/HAUL as long as you are not exceeding recommended posted speeds and your not trying to win the hole shoot off the starting line it will be fine.

You always have the option to tap the brakes going down the hill which will over ride the current gear selection and downshift for you when in TOW/HAUL.

Grit dog

Black Diamond, WA

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Posted: 04/05/21 11:34am Link  |  Quote  |  Print  |  Notify Moderator

GDE, you’re appearing to get a little worked up and overly literal here.
There’s still a time and place, even with today’s amazing automatic transmissions that range limiting, manual shifting or M mode has its place. End of story.
Newer trans do a lot of the thinking for the driver but what they cannot do, in current form on pickup trucks anyway, is “anticipate”.
I know you understand those scenarios as well so maybe recognizing them would lead to a more productive discussion.


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