Towing with OD off.

[dodge man]

Something I don't understand is why towing with the OD off is easier on the transmission. Does this also unlock the torque convertor? I know if you tow a heavy load in OD, you can overheat the transmission.

I have rebuilt a 727 torqueflite in a 70 Challenger once, so I have a good idea of what goes on inside a transmission. It seems like it would be easier on the transmission if it was in OD and the torque converter was locked up. The only thing I can think of is maybe the transmission is being overloaded in OD and the bands and/or clutch packs are slipping making the transmission overheat.

 

[deerefan]

Something I don't understand is why towing with the OD off is easier on the transmission. Does this also unlock the torque convertor? I know if you tow a heavy load in OD, you can overheat the transmission.

I have rebuilt a 727 torqueflite in a 70 Challenger once, so I have a good idea of what goes on inside a transmission. It seems like it would be easier on the transmission if it was in OD and the torque converter was locked up. The only thing I can think of is maybe the transmission is being overloaded in OD and the bands and/or clutch packs are slipping making the transmission overheat.

You have the gist of it. In OD, you are dealing with a "lazy" ratio, economical, not towing, based. It also keeps the truck in its minimal powerband. By turning OD off, say on a 4 spd auto, you are keeping the truck in its sweet spot, not building up a ton of heat in the tranny. The truck as a whole will run better and tow better with OD off and your tranny will do a lot less gear hunting, which also increases wear.

 

[Bird]

I always thought it was OK to tow in OD if the load was light enough that the transmission wasn't frequently shifting up and down. If the load is heavy enough and the road hilly enough to cause frequent shifting, then I'd turn off the OD. Is that not the case? I know when I had a 17' aluminum bass boat with a 55 hp outboard, it was light enough that I towed it in OD with my Ford Ranger pickup with the 4.0L V-6 engine.

 

[dave1949]

The '03 automatic 6.0L F250 I had would absolutely scream before shifting - uphill or down - before shifting with OD off and towing. I didn't care for that and could have done a better job with a manual. Uphill was no problem, just hold the throttle at something reasonable. Downhill was another story. Just doesn't seem right to let a diesel run that fast. I would end up turning OD back on til I got to the bottom of a hill sometimes. People would actually turn their heads and look at what was making all the noise.

Maybe it wasn't set up right from the factory? Sold it a couple years back, so it really isn't an issue now
Dave.

 

[Diamondpilot]

I do not have a real good answer for you but I know on a trip we took to Lake Of The Ozarks I had a friend turn the OD on in his Dodge 4x4 with a 360 to try to break 10 mpg. Within ten miles it was boiling out the tranny fluid though the dip stick. He was pulling a 7,500# boat and there were about 6 others traveling with him in a convoy. It made a mess.

I only use OD when I am towing a empty car hauler or boat trailer. The rest of the time its in tow mode.

Chris

 

[Egon]

On my 1996 dodge with the auto transmission with OD engaged the converter locks up at 80 KPH in the fourth or OD gear. With the OD disengaged the converter locks up at 60 KPH but in third gear.

When towing a heavier load in hills the anemic engine will not pull in OD and I have to lock it out. That means at 2300 rpm I'm at about 95 KPH and usually have no problems with the pulling.

 

[wvpolekat]

I never turn the OD off on my 01 F250 unless it is hunting. Believe that is what the owners manual states. I routinely tow 10,000 lbs with OD on and no issues. I have a trans temp gauge and have never seen it go over 200. With 130,000 on it, I don't see any reason to change what I am doing.

 

[Reg]

Something I don't understand is why towing with the OD off is easier on the transmission. Does this also unlock the torque convertor? I know if you tow a heavy load in OD, you can overheat the transmission.

I have rebuilt a 727 torqueflite in a 70 Challenger once, so I have a good idea of what goes on inside a transmission. It seems like it would be easier on the transmission if it was in OD and the torque converter was locked up. The only thing I can think of is maybe the transmission is being overloaded in OD and the bands and/or clutch packs are slipping making the transmission overheat.

Basically it keeps you in a lower gear, by blocking the top (overdrive) gear.
There is less tendency toward "lugging".
The increase in revs for any given road speed also means the cooling fluids in both the rad and trans are pumped at a faster rate, so there is better cooling of both.

"Overdrive" is somewhat of a misnomer these days anyway, since "Top" gear is rarely a "direct" 1:1 ratio.

Tow/Haul mode is a little more complex, and different between manufacturers.
In it's simplest form it raises all the shift points, on some transmissions it also locks out the highest gear, or maybe the two highest gears.
Some just raise all the shift points and O/D doesn't come in until ~55 or above.
In others there is "intelligence" to cause downshifts if the brakes are applied but there is no significant slowing within 1/2 a second or so. Don't ride your brakes on long down grades with these, or you will have very high revs in low gears. Normal upshifting is not restored until you get on the gas again for 1/2 second or so.

 

[carpenter383]

Yes the torque converter clutch (tcc) will still lock in drive (1 to 1 ratio) and even in second gear if you're moving fast enough.
The main reason not to tow in overdrive (aside from shifting back and fourth) is because the overdrive clutch or band typically dosen't have sufficient holding power to keep from slipping under heavy loads. This is especially true in the older o/d trannies. In the newer ones with tow/haul the computer raises line pressure, and shift points which makes it less likley to slip.
A shift correction kit will help an auto tranny survive under heavy duty conditions, They typically address/fix factory issues and common problems and don't necessarilly make the trans shift hard.
Auxillary trans coolers are cheap, easy to install, and should be considered a must have for anyone towing on a regular basis, Heat is the worst enemy.
If you ever get a trans rebuilt that you know is gonna see alot of towing, the builder can install extra clutches, wide bands, bigger servos, stronger hard parts, etc. that will make the trans alot more durable.

 

[Tul01]

Sorry, not trying to hijack the thread, but what about heavy loads in a half ton. My father in law routinely drives with up to 8 hours with 1500-2000lbs in his 07 tundra. I've wondered while driving with him if it should be in tow mode or is this realistically not even similar to what a trailer will cause?

Brent