Overdrive/ towhaul or 3rd, confused

[w5yne]

Hi again,
              TV is a 1500 Avalanche 3.73 ratio, rated for 7200lbs,  TT is a 19' Passport express about 5600lbs loaded, please bear with me this may become a long post.

around town i tow in 3rd with no problem and I'm happy with the truck response

Now the highway is a different story,

In tow/haul mode the truck holds gears for a longer time and will sit happy at 60mph @ 2000rpm
In D the truck seems to shift easier and does not seem to put as much stress on the transmission as tow/haul, then also sits at 60mph with 2000rpm,

I have been told to only tow in 3rd otherwise the transmission oil does not circulate fast enough to cool

Anyone got any preferences?

The truck is fitted with an AUX trans cooler but i have yet to install a Trans temp gauge, i never tow with the cruise control on because i prefer to use my own judgment rather than the truck reacting too late and shifting down to gears with sky high rpm's when a hill is encountered (better to speed up before the hill and ease off as you get to the peak) not that many hills here in Louisiana anyhow....

any advice or preferences very welcomed from the seasoned campers

Thanks
Wayne
W5yne
M1evk

 

[edjunior]

With any transmission that has Tow/Haul, put it in drive and let Tow/Haul do its thing.  As you have experienced, it does just fine.  The 3rd gear advice is for the older vehicles before Tow/Haul became more prevalent.  Even then, with a good rear gear, Drive was usually fine on the flatter roads and 3rd didn't really become needed until you hit a hilly area.

 

[Gary RV_Wizard]

I agree fully with Edjunior. A modern automatic transmission is best left to manage itself and that's what tow/haul mode is intended to do when towing a trailer.  You don't need to choose 3rd gear - or any other - as a matter of routine practice.  You only need to select a different gear if the transmission is obviously having trouble keeping up with road conditions, meaning it continually seeks another gear.

If "D" alone is giving the same results as tow/haul, then that's an ok choice too. On a more-or-less level highway at a steady speed, I would expect them to be the same. Tow/haul comes into its own on the hills, even the small rolling ones.

 

[COMer]

According to GM, the transmission and engine are designed to operate best in tow/haul IF the weight being towed is more that 60-65% (depends on the year) of the rated max for you TV.  Yours is.  Put it in tow/haul whenever you are towing and let the different shift points do their work.

 

[santurinos]

Our Trail-Lite crossover 189QB weight about 3800lb loaded.
We just came back from North Georgia Mountains, we had a great first weekend with our new camper and Tahoe.

Like you suggest, I had it on D with the tow button pushed, this worked perfectly. Also, after a few attempts I did not use the cruise control anymore because shifting into high RPM.

I don?t want to hijacking the thread but I have a question:
While driving very steep down on dirt roads in the mountains, I?ve shifted in the first gear to have the transmission helping with slowing down the rig.  Is this OK?

We?re new in the RV-hobby and need your experience and help!

Y?ALL take care ? have a great day ? Walter and Dianne.

 

[Lowell]

I too shift down when descending steep grades.  It doesn't hurt the engine as lng as you don't overrev the engine  and keeps your brakes from overheating.

 

[edjunior]

I don't know about other transmissions, but with the Torqueshift in the Fords, in Tow/Haul mode, it acts as an engine brake.  And boy, does it ever work.  Coming down a hill, if you lightly touch the brakes, it will kick down into a lower gear.  Sometimes rather abrubtly.  But it does work great.  If you want to test it without a trailer (I would suggest you do to get the feel of it), put your truck in Tow/Haul, get up to cruising speed, and lightly touch your brakes.  If it kicks down, you have a good engine brake like the Ford.

Otherwise, yes, downshifting coming down hill is definitely a good thing.

 

[Gary RV_Wizard]

I thought the GM tow/haul mode did that automatically too, but maybe only on the diesels with the Allison tranny? I don't know.  Maybe somebody  who has a 1500 with the tow/haul tranny can help???

 

[Carl L]

I don?t want to hijacking the thread but I have a question:
While driving very steep down on dirt roads in the mountains, I?ve shifted in the first gear to have the transmission helping with slowing down the rig.  Is this OK?

With a gasoline engine, that is how you get down a steep grade.  You use the lower gears (1 or 2) engine brake and touch the service brakes to keep the RPMs down and shed speed if it builds up.

There is no problem starting a new thread and it may well attract more answers.

 

[Joezeppy]

I don't know about other transmissions, but with the Torqueshift in the Fords, in Tow/Haul mode, it acts as an engine brake.  And boy, does it ever work.  Coming down a hill, if you lightly touch the brakes, it will kick down into a lower gear.  Sometimes rather abruptly.  But it does work great.  If you want to test it without a trailer (I would suggest you do to get the feel of it), put your truck in Tow/Haul, get up to cruising speed, and lightly touch your brakes.  If it kicks down, you have a good engine brake like the Ford.

Otherwise, yes, downshifting coming down hill is definitely a good thing.

I thought the GM tow/haul mode did that automatically too, but maybe only on the diesels with the Allison tranny? I don't know.  Maybe somebody  who has a 1500 with the tow/haul tranny can help???

I can't speak for the newer 1500's but my 2010 Sierra 2500 does this (6.0L gas and 6-speed tranny). As edjunior stated, "sometimes rather abruptly" (and with high revs!). Neither my 1999 Silverado 1500 or 2002 Silverado 2500HD had this feature (both 4 speed tranny). Not sure exactly when GM included this feature - I want to say with the restyle in 2007 but I could be wrong.

 

[longhaul]

My littlest truck is a 1500 GM 4L60 3.73 axle auto tranny and I never leave it in OD towing. The tranny TC clutch does to much locking and unlocking in hills and strong headwinds. In fact I don't use TH mode at all. It just  moves the tranny shift points/TC clutch lock points to 2450 rpm at light throttle. There is no software interface that the Allison or Fords Torqshift auto trannies use with their VVT system for braking. The 4L60 isn't in the same league so posting  replies will farther confuse the OP.

I use 3 (drive) which is a 1:1 or direct drive. The little 300 hp 5.3 won't pull much in OD. 

 

[Gary RV_Wizard]

Thanks, Longhaul. I suspected that might be the case on the 1500 with the light duty transmission.

 

[Frank B]

longhaul:

I had a 94 Chev 1500 with 5.7 liter (350) and 4L60E, with no tow/haul mode.  I had it reprogrammed to keep the TC clutch locked most of the time in OD.  It would pull our 23' lightweight 5th on the flat at 100 kph, but the engine didn't have enough power to do do any more than that.

IIUC, it is when the TC is NOT locked that heat builds up.  The slippage in the TC is what generates the heat.  No slippage, no heat.

Of course, with our 'new' 06 GMC 3500 crew/long Durmax / Allison, one hardly knows that lightweight 5th is there now. 

Frank.

 

[rbell]

I've got a Ford that I tow with. I did some testing with a Scan Gauge II  in different modes & conditions. The engine runs at 195 deg no matter what you do. The trans runs at about 145 not towing. When towing it'll get to between 155 & 165. I also found if I let it downshift by itself in rolling hills that the torque converter unlocks first. This starts heat buildup but it takes several minutes to notice it. If I take it out of OD then the TC stays locked when it starts uphill. Also the mileage is about .3 mpg better if I leave it out of OD in hills. Thats a bit hard to see though as the mpg reading changes very fast in those conditions.
I also found the trans temp gets to about 195 when I'm creeping around on the back trails taking wildlife pics. The TC is slipping all the time like that. So it stays cooler towing than it does driving very slow.

 

[trooper253]

I have a 1/2 ton 2004 Silverado 1500 and it has the Tow/Haul button.  As a pervious poster stated it only changes the shift points.  Also it does not help the engine hold back going down steep grades, I still have to down shift to get any assistance from the engine.

 

[MNBob]

I had this same question. When we picked up our new TT, I put it D and T/H like the book said. On a flat road it was fine, but the tranny temp went over 185, so I put it back in 3rd, and the temp went down right away. But what is a bad temp? On hilly roads with our boat, and even the old pop-up, I've always run in 3rd so it doesn't shift so much.

 

[rbell]

This will give you a rough idea.

 

[dvredc5]

Great advice from others here and I'd just like to add one thing regarding the cruise control and towing.  Best off not using it because unfortunately most cruise controls just mash the throttle as soon as they sense 1-2 mph loss which kicks your transmission down.  You can get pretty good an "modulating" the gas pedal yourself as you go over hills and things without unlocking the torque converter.  This will let the trans run at it coolest which adds to long life.  As with any tow vehicle, do change the trans fluid and filter more frequently than a vehicle you don't tow with.  It might seem costly what the time but all modern transmission are thousands to rebuild and replace.  Much cheaper in the long run to change trans fluid and filters more frequently.  If you can run in overdrive without it kicking up and down over every road crest or small hill you go over use it.  Otherwise you have to go down a gear. 

DV