4R70W towing in overdrive

[95busa]

All, my uncle recently advised me that no matter how well it is pulling, not to pull on terrain that is not level in overdrive. My truck has 4.56-1 gears in the back, and recently pulled a 2000lb camper while hauling 5 people, three dogs and a bed full of camping gear (probably 1500 pounds) with no issues. It pulled up hills in OD without hunting a bit,and did not need a lot of gas pedal to do it. On his advice I locked out OD and kept it locked out after that little experiment. It obviously pulled very well in 3rd, but RPMs were on the high side (2900 at 55mph). Mileage was OK (15.5MPG). I want to keep RPMs under 3K, but would like to go a bit faster, so if I can pull at 65MPH at about 2400-2500RPM in overdrive that would be awesome. Opinions? Facts? Thoughts? To all the guys that commented on my previous post about gear selection- if I had it to do over again, I would probably run 4.10s.

 

[demarpaint]

I'm old school and agree with your uncle, and would lock out OD if I were towing. It is better for the transmission, and for braking. MPG always suffers when towing, but overheating a tranny, or worse, is a lot more expensive. JMO

 

[SwampSurvivor]

It won't overheat if the torque converter is locked, will it? I also think the "no overdrive when towing" is for when you have stock gears. When you have 4.56 gears ... very little strain (other than RPM) is being placed on the transmission

 

[01rangerxl]

That's a tough call.

Personally, I can't bring myself to tow with OD on. Even if the engine is running over 3000 RPM, I'm not as worried about that as I am putting additional strain on the transmission. I don't have a 4.56 gear ratio though, so as Miller said maybe in your truck it's not so much of an issue anymore.

I would get a Scangauge or install a trans temp gauge and go by that. If the fluid temp is good with OD on, I would think you are okay using it.

 

[Zaedock]

Originally Posted By: 01rangerxl
If the fluid temp is good with OD on, I would think you are okay using it.


X2.

I've towed my Jeep across country in my '03 F150 (tow package, etc) and the tranny was fine. The only time I manipulated the transmission controls (OD off/tow mode) was in the Rockies.

Check your manual to be sure. The no OD for towing stemmed from the GM 700R4/early 4L60 days when the pump did not provide enough fluid flow while towing in OD. That situation was resolved in the late 90's.

3500 pounds of load for your truck should be a piece of cake.

 

[Roadkingnc]

It will be fine with the 4.56 gearset

 

[Mud]

I've rebuilt a number of these units.
If you looked at the OD band in a 4R70W you would be surprised at how thin it is. In comparison the reverse band is built like a tank, I've never figured that one out, seems that the construction should be the opposite by how much each is used.
The OD band is activated by the OD servo to grab the reverse sun gear. Depending on load and mechanical condition, you may not be able to feel a slight amount of slippage. Slippage = heat and can accelerate deterioration of the band and fluid.
IMO going down a flat highway especially with your gearing you can probably get away with OD but for other (hill) conditions you may see longer tranny life with deactivating OD.

 

[eljefino]

What's the wind load of that camper? Glad it pulled well. I'd expect a pretty big hit in MPG going faster. Crunch the numbers and you may find you're paying yourself $15-20 an hour to go 55 compared to 70.

Hard to argue with the 1:1 3rd gear being efficient and strong.

This is with the 4.2 V6? IDK its torque curve but it's surely at higher RPM than a big block. "They" say you can run 80% throttle at 80% of redline RPM "forever".

I would be concerned about a V6 trans being made weaker than a V8s: fewer clutch packs or whatever. This would mean careful notation of others' anecdata if it's not your V6 setup. Can you get some codes off its labels that show it's a V6 only?

 

[95busa]

Wind load shouldnt be bad at all, its a pop-up. I can surely give it a try. I pulled off the trans pan and changed oil and filter last month. It had been flushed at the dealership at around 70K (113K now), but had never had a pan drop. I threw on a B&M aluminum pan that holds 3 more quarts with cooling "heat sink" fins while I was at it. I expect a small drop in temp, but more than anything I suspect the pan and extra oil will smooth out the peaks and valleys associated with torque converter unlocking/locking and gear changes. I didnt notice labels or codes when I was under it. If the weather changes for the better I might get under it this evening and have a peek.

 

[Chris142]

what's The speed limit when towing?

 

[95busa]

interesting question. I usually roll about 5-10mph under posted. With O/D locked out its 55mph for me.

 

[meep]

the issue is actually not the TC. yes, if it's hunting you'll get fluid temps.

BUT---

the general concern is in OD you have a big gear essentially turning a smaller gear. all of that force is being placed on a smaller surface area of the driven gear for an extended period of time. The smaller diameter leaves it with little mechanical advantage and presents 1) more strain to the teeth 2) more compression of the lubricant in those areas.

this is one of those areas where "well it drove just fine" doesn't really tell you if it's acceptable or not for your trans, and I'm willing to bet some trannies handle it better than others.

m

 

[AVB]

If it is a 4.2, they are used in industrial applications that are run at 3000rpm constant. I do not know if the internals are the same but externally they look identical. I wouldn't worry too much about the rpm.

 

[95busa]

Good advice all....sounds like 3rd is definately safer. Might switch to 10w-30 hdeo...

 

[OVERKILL]

Originally Posted By: meep
the issue is actually not the TC. yes, if it's hunting you'll get fluid temps.

BUT---

the general concern is in OD you have a big gear essentially turning a smaller gear. all of that force is being placed on a smaller surface area of the driven gear for an extended period of time. The smaller diameter leaves it with little mechanical advantage and presents 1) more strain to the teeth 2) more compression of the lubricant in those areas.

this is one of those areas where "well it drove just fine" doesn't really tell you if it's acceptable or not for your trans, and I'm willing to bet some trannies handle it better than others.

m


Very good point. If he had the 4R100, towing in OD isn't an issue, as it was designed for it, just like the 5R110/5R120...etc. But IIRC, the 4R70W was not designed to tow in O/D, and it should state so in the manual.

 

[95busa]

IIRC it says something like...if transmission is hunting between gears or downshifting frequently then lock out overdrive.

 

[OVERKILL]

Originally Posted By: 95busa
IIRC it says something like...if transmission is hunting between gears or downshifting frequently then lock out overdrive.


Could you check? I'd be interested to read the verbiage.

 

[CBR.worm]

One of my owners manuals (Tundra?) said not to tow in OD to maintain charging system efficiency. It also said to limit speed to 45mph. Since I did not do the second, I did not do the first.

 

[95busa]

Use a lower gear when towing up or down steep hills. This will
eliminate excessive downshifting and upshifting for optimum fuel
economy and transmission cooling.
² Anticipate stops and brake gradually.

 

[OVERKILL]

That's not bad at all. Sounds like it should be OK then.