overdrive for towing?

[outragex]

What do you experienced tow people think? I have a new Tundra DC that I use for towing a light utility trailer now, and I plan to tow a heaver trailer in the future. The owner's manual says nothing about avoiding overdrive for towing, though I have always been told that it is best to shift out of OD when towing.

So far I have left it in OD for towing a light trailer (less than 1,000 lbs.) with light load in vehicle. What if I tow a 2-3k camper?

I live in CO so will be towing over steep, high and long grades (10,000 ft.). I know about shifting out of OD or into second if necessary for slowing descents. If towing in OD is okay at all, should I use OD for level spots and go to third for climbing before the tranny shifts for itself?

What about changing rear diff fluid after towing? (I have limited slip.) Is it really necessary to change it after 3k miles of light or medium duty towing as I have seen referred to in other forums?

[RockyMtnRay]

Originally Posted by outragex

What do you experienced tow people think? I have a new Tundra DC that I use for towing a light utility trailer now, and I plan to tow a heaver trailer in the future. The owner's manual says nothing about avoiding overdrive for towing, though I have always been told that it is best to shift out of OD when towing.

So far I have left it in OD for towing a light trailer (less than 1,000 lbs.) with light load in vehicle. What if I tow a 2-3k camper?

I live in CO so will be towing over steep, high and long grades (10,000 ft.). I know about shifting out of OD or into second if necessary for slowing descents. If towing in OD is okay at all, should I use OD for level spots and go to third for climbing before the tranny shifts for itself?

What about changing rear diff fluid after towing? (I have limited slip.) Is it really necessary to change it after 3k miles of light or medium duty towing as I have seen referred to in other forums?

I live in Colo also and tow a 3600 lb low profile TrailManor travel trailer over our steep, long, and high altitude grades.

You might be able to tow the light trailer with OD left on; my experience is you best turn OD off anytime you're pulling a 3000 lb or heavier trailer. The key is whether or not the transmission torque converter stays locked...if it unlocks (you'll see about a 200 RPM rise on the tach when it does)...or if it downshifts to 3rd, the torque converter creates a great deal of heat. Additionally the constant engagement/disengagement of the torque converter clutch and OD clutch pack causes wear and even more heat.

One little known fact about turning OD off on the Tundra transmission is it will allow the torque converter to lock in 3rd gear...with OD on, the TC will only lockup in OD. With the TC locked in 3rd, I find I can pull up to 5% grades at 60 to 65 mph without having it downshift to 2nd...and a locked TC in 3rd gear provides enough engine braking that I seldomly need to use my wheel brakes on descents of grades of 6% or less.

I have a pan mounted transmission temp gauge and normally see 150 to 160 degree ATF temperatures when pulling hard with the TC locked in 3rd (ambient temps in the 70s) (when not pulling hard, the temp is more like about 130). But when the TC unlocks and I drop into 2nd for the steeper (6% or greater) climbs, the ATF temp fairly steadily rises to about 185 to 190...those are still acceptable temps but it's obvious an unlocked torque converter produces a huge amount of heat and heat is what kills a transmission. I should add that my truck does have the towing package with the external transmission cooler in addition to the cooler in the bottom of the radiator. If you don't have the towing package with that external cooler, you should immediately add one.

So to answer your question, try towing in OD...if you see even semi-frequent TC unlocking or downshifting to 3rd, just turn off OD and be done with it...as soon as OD is turned off, the transmission will go to 3rd and the TC will immediately lock.

[DCTUNDRA]

My Tundra manual reccommends towing with OD "off" but states that this is for braking effectiveness: ie being able to take advantage of "engine braking" for minor speed reductions. I have towed over mountains and usually will switch the OD "off" unless I am "loafing" along on pretty-much flat terrain. I don't like the idea of trying to lug the drivetrain and then having the transmission kick-down abruptly. The engine seems happy as a "high-revver", so I just let it work at the higher rpm's.

[Mike Donofrio]

Originally Posted by RockyMtnRay

I live in Colo also and tow a 3600 lb low profile TrailManor travel trailer over our steep, long, and high altitude grades.

You might be able to tow the light trailer with OD left on; my experience is you best turn OD off anytime you're pulling a 3000 lb or heavier trailer. The key is whether or not the transmission torque converter stays locked...if it unlocks (you'll see about a 200 RPM rise on the tach when it does)...or if it downshifts to 3rd, the torque converter creates a great deal of heat. Additionally the constant engagement/disengagement of the torque converter clutch and OD clutch pack causes wear and even more heat.

One little known fact about turning OD off on the Tundra transmission is it will allow the torque converter to lock in 3rd gear...with OD on, the TC will only lockup in OD. With the TC locked in 3rd, I find I can pull up to 5% grades at 60 to 65 mph without having it downshift to 2nd...and a locked TC in 3rd gear provides enough engine braking that I seldomly need to use my wheel brakes on descents of grades of 6% or less.

I have a pan mounted transmission temp gauge and normally see 150 to 160 degree ATF temperatures when pulling hard with the TC locked in 3rd (ambient temps in the 70s) (when not pulling hard, the temp is more like about 130). But when the TC unlocks and I drop into 2nd for the steeper (6% or greater) climbs, the ATF temp fairly steadily rises to about 185 to 190...those are still acceptable temps but it's obvious an unlocked torque converter produces a huge amount of heat and heat is what kills a transmission. I should add that my truck does have the towing package with the external transmission cooler in addition to the cooler in the bottom of the radiator. If you don't have the towing package with that external cooler, you should immediately add one.

So to answer your question, try towing in OD...if you see even semi-frequent TC unlocking or downshifting to 3rd, just turn off OD and be done with it...as soon as OD is turned off, the transmission will go to 3rd and the TC will immediately lock.

Ray, this is by far the best and clearest explanation I have seen regarding this oft asked question.

I generally leave the OD off when towing, although if I am on a long smooth and flat stretch of highway and I have something small being towed I might turn it on for a while to save a few RPMs and gas...

[RockyMtnRay]

Originally Posted by Mike Donofrio

Ray, this is by far the best and clearest explanation I have seen regarding this oft asked question.

I generally leave the OD off when towing, although if I am on a long smooth and flat stretch of highway and I have something small being towed I might turn it on for a while to save a few RPMs and gas...

Thanks, Mike

Yeah, after reading about a gazillion discussions here and on various trailer towing forums, I gradually concluded that hard and fast rules (e.g. "always tow with OD off") just aren't a good answer.

For one thing, transmission designs vary widely between manufacturers and sometimes between models or even years of a model for a given manufacture. Even for we Tundra owners, we with the '03 and newer models with a beefed up transmission probably can more safely tow in OD than those of you with the earlier model transmissions.

But another factor that has to be considered...especially by those of us who tow on Colorado's high altitude mountain roads...is the greatly reduced power we have available. At 11,000 feet (a very common elevation of mountain passes in Colorado), the Tundra V8 is only putting out about 110 HP. Even at a "low" Colorado elevation like mile-high Denver, the engine is only making about 160 HP (30% less than sea-level). With so little power available, it takes almost no grade at all when towing to necessitate enough throttle movement that a TC unlock or downshift will happen if OD is left on. Even though I'm towing a moderate weight, low profile trailer, my truck will only keep a TC lock in OD on a downgrade ...just maintaining 65 mph on level ground causes the TC to unlock in OD. With OD off though, the TC locks and stays locked even on some pretty good grades.

And finally, trailer weight and profile (aerodynamic resistance) has a lot to do with whether or not OD towing is wise. A low profile, light weight trailer presents much less of a load on the drivetrain than a big box, slab front, 5000 lb travel trailer.

Too many variables for hard and fast rules, IMHO. So I think that watching the TC's behavior is the only good clue we have. My recently installed, pan mounted tranny temp gauge (so I'm seeing the temp of the ATF as it goes into the transmission's innards) has been a very useful confirmation of what I suspected was happening in the transmission.

[Montfort]

A good subject and as noted one that has been tossed around a fair amount. You might want to do a search under 'planetary gear'. This would seem to be the main reason why, in the case of the Tundra, towing with OD ON is not recommended. This component would appear to be the weak link in early Tundra transmissions and I'm not certain whether or not it has been corrected in later models. It would be great to have an update from a Tundra transmission expert. Dave

[outragex]

Thanks to all for useful info, esp. RockyMtnRay. I never realized the trans would lock in third gear until you explained this. I think I will turn OD off whenver I notice the lock cutting out, or whenever climbing long, steep grades. I know from experience with manual trans that moderate high engine revs are better than lugging engine.

Compared to my old 91 Trooper the new Tundra is a Lexus and Porsche rolled into one. I am enjoying it. I knew that my old 8track was obsolete, but who knew they wer putting CDs in cars! Who knows maybe our children will even have TVs or satelite radios in their trucks some day.

Look for me in the mountains Ray, I will be in the green DC with half-dozen canoes and kayaks hanging from roof and trailer.

[RockyMtnRay]

Originally Posted by outragex

Thanks to all for useful info, esp. RockyMtnRay. I never realized the trans would lock in third gear until you explained this. I think I will turn OD off whenver I notice the lock cutting out, or whenever climbing long, steep grades. I know from experience with manual trans that moderate high engine revs are better than lugging engine.

Most welcome...really glad to be able to offer some helpful advice to a fellow Coloradan. Because of our altitude and steep, long grades we have arguably the most challenging situation in the nation for towing...it's so different than anywhere else that I sometimes feel like it's trying to describe life on another planet when I discuss towing with folks from the low altitude flatlands.

And yes, be prepared to do a lot of revving with your engine...not just in 3rd gear but on the steeper (6% and up) grades also in 2nd gear at about 4500 RPM. Not just for short spurts either...but continuously for 5 to 10 miles in 2nd gear! Those long periods in 2nd are why I put a tranny temp gauge in mine...and did it the right way (also the much more complicated and expensive way) by putting the sensor in the pan.

Look for me in the mountains Ray, I will be in the green DC with half-dozen canoes and kayaks hanging from roof and trailer.

I'll be looking...and if you see a pure white '03 SR5 Access cab with a folding Peragon tonneau cover pulling a fairly unique TrailManor trailer...with a blue mtn bike on a hitch mount carrier, that'll most likely be me. And I might even see you on the water...I bought a Folbot Edisto folding kayak this season...got it in the very speedy Red color. It folds up into one backpackable bag that fits quite nicely in the bed for transport and storage, though by mid-summer I plan to buy a TracRac so I can carry it assembled. So add red boat on rack to the previous description...I doubt anyone else in the nation will have that combination.