NNBS 07 Siearra tow haul mode questions

[ProStreetCamaro]

I tried the tow mode only twice in our 07 2500HD. Both times when I hit the brakes the trans downshifted hard and sky rocketed the rpms. We bought the truck new and it now has 18K on it. I assume that is a function of the feature but personally I would rather replace a set of rotors than I would a transmission. Anybody else feel the same way?

So what all does the tow haul mode really do other than downshift the trans when brakes are applied? Is there any certain weight range where they suggest you use this mode? Does it modify the shift points and such?

[kcb37]

If I can reemeber all of it.
It does change the shift points. Shifts later when shifting up. More rpm more power. Shifts sooner shifting down. More rpm more engine braking.
It also locks the torque converter sooner for more power and keeps it locked longer slowing down for more engine braking. Having the TQ locked also reduces trans temps due to less slip. Less slip less heat.
Unloaded as you said it does kick when it shifts. But with a load you won't feel it, unless you are pulling something real small.
I pull my trailer empty in T/H, it's right around 1,500 pounds empty. It shifts smooth up and down shifting. (This is with my 03 2500HD Dmax)

[ProStreetCamaro]

Originally Posted by kcb37

If I can reemeber all of it.
It does change the shift points. Shifts later when shifting up. More rpm more power. Shifts sooner shifting down. More rpm more engine braking.
It also locks the torque converter sooner for more power and keeps it locked longer slowing down for more engine braking. Having the TQ locked also reduces trans temps due to less slip. Less slip less heat.
Unloaded as you said it does kick when it shifts. But with a load you won't feel it, unless you are pulling something real small.
I pull my trailer empty in T/H, it's right around 1,500 pounds empty. It shifts smooth up and down shifting. (This is with my 03 2500HD Dmax)

Ahhh sounds pretty good. I did notice even with one of our cars behind it the downshift while braking was pretty severe. Down shifted so much that it brought the rpms darn near 5K.

This was a 160 mile trip to the beach for a huge cruising the beach weekend. This was last year and the first time I had tried the tow haul mode.

[Underpowered]

yes, teh tow haul mode modifies the shift points, and on your D-max it makes better use of engine braking.

i only use mine on a loaded trailer, i never use it while towing unloaded.

[kcb37]

It helps with engine braking with every engine not just diesel. Does the same thing gas or diesel, 1/2 ton to 1 ton.
I will add that my tach won't jump like that though. But you also have a gas engine and it redlines higher. Mine redline's around 3,200 RPM. That may be why you have such a kick. Also that isn't a real heavy load.
Well worth having a 3/4 ton for, but not heavy for it.

[Underpowered]

Originally Posted by kcb37

It helps with engine braking with every engine not just diesel. Does the same thing gas or diesel, 1/2 ton to 1 ton.
I will add that my tach won't jump like that though. But you also have a gas engine and it redlines higher. Mine redline's around 3,200 RPM. That may be why you have such a kick. Also that isn't a real heavy load.
Well worth having a 3/4 ton for, but not heavy for it.

but it helps more on a Diesel than on gas motors

on my 5.3, tow haul does virtually nothing as far as engine braking is concerned. it helps more on my brothers 6.0, but on my buddies D-max it makes a huge difference.

[dozerboy]

I see a gasser not a dmax? You will do more harm to your trans and brakes by not using T/H. 5K is nothing I run around in T/H all the time when I'm getting on it. Have to be careful on slick roads with it though a hard down shift can lock up the rearend and put you in a skid. Engine braking is more on a gasser then a diesel that doesn't have a engine brake on it or a throttle body. And Dmaxs rpms will get way up there too like 4800

[kcb37]

It does so little on your 5.3 because it's a 5.3
Little engine little engine braking.
That's why the 6.0 does better and a Dmax 6.6 better still.

[unseen]

the trany will down shift in tow hual mode at about 1500 2000 rpn ists mor for long down hill grades so you dont have to ride your brakes. If your load is to light and you use it to stop the truck on a steep hill it will drop rpms quickly and down shift sudinly. If the hill is steep eas the rpms down with the breaks till you hit the shift. your lq9 motor is not your aveage ls engine in was built as a boat motor and was desind to rev your hardend valvtrain and 6 bolt main will hold up. your hd should have the 6 spd and is built very well