What to tow in--D -- 2 --or 3

[Amra]

Ive been reading other post on this forum and people say they always tow in D3 and that this is not bad on the truck. I have an 05' ext cab 4wd with a 5.3, 3.42 gears and a waitforme performance tune. The truck does way better now with the tune but i think it does not tow very good.

 

For some reason i thought driving in D2 or D3 would hurt my transmission. I tow my camping trailer about 3 hours away here from central Missouri with lots of hills on my way to camping.

 

So my question im wondering is if its ok to tow down the highway and everywhere in 3 without hurting my transmission.

[Bish]

I've put over 50K of towing about 5000lbs. Except for it's first tow, I always tow in 3. My Tahoe even gets better gas mileage in 3 when towing. I drive 70-80 on open highway when towing. I have a trans temp guage and the temps goes well over 200 if I tow in OD. When I tow in 3 it never goes above 200. The bottom line for me is whether or not it is locking and unlocking the torque converter or hunting gears as that's what heats up your trans and breaks down the fluid and eventually the trans.

 

Just my 2 cents of course.

[ZZebes]

Well the reason the truck is sluggish in tow is the 3.42

 

as for the D3 it wont hurt a d**n thing actually it will help prevent damage to the tranny because it keeps it out of O/D and prevents it from hunting for gears which creats enourmous amounts of heat thus killing the tranny

[RobDarden]

Use "3" to tow!!!!

[pwall]

And use the 'Tow/Haul' mode in your truck as well (assuming that the '05s have this).

[nitro882]

Yep use third gear to tow, towing in OD is a tranny killer.

 

I have the same deal with the 3.42's in my 06 and it tows just fine in 3rd gear. I pull a 3500# bassboat all over the place and it has no issue moving it. I have also hauled my fathers 25' ocean boat that wrighs in the neighborhood of 6000# with ease.

[BADGERMAN]

I tow it in overdrive with no problems, it doesn't hunt for gears and the tranny never gets above 175.

 

I tow a travel trailer that when it is loaded is about 6500# and usually have about 750 to 1000 # of wood in the bed of the truck.

[ken1mod]

Gentlemen,

 

Bish has it right when he talks about torque converter lockup. The only part of an automatic that makes heat in huge quantities is the tc. When locked, the trans is just like a manual and generates very little heat.

 

Most of us like trans coolers and so do I but driving with a load and heavy throttle with the tc unlocked will make more heat than the largest coolers can dissipate.

 

Lets say you are generating 250 hp under heavy throttle and load with tc unlocked.

TC slip under these conditions is about 10%. Let's calculate heat.

 

25 hp converted into heat thusly. 25 hp x 746 watts/hp=18,650 watts

18,650 x3.2 watts/btu=59680 btu of heat generated in trans under those conditions.

 

Gentlemen, I submit that there is no cooler on the planet that can do that much cooling.

 

Driving technique, as Bish says, is most important in towing.

 

Please feel free to check my math, thanks.

 

Ken

[mmmikkke]

The reason 60,000 btu sounds incredible is because it is. The "torque converter" converts torque. Your assumption about the 10% slip shedding 10% of the hp assumes no torque conversion.

 

Just for the exercise, ken, consider 10% slip to shed 3% of the hp.

[ken1mod]

Hey Mike,

 

You are thinking that a torque converter increases torque EFFICIENTLY. They can and do double torque at stall. but with a great cost in efficiency. Consider this.

 

When the tc is most effective at multiplying torque (stall) the truck is tied to a tree and you stomp on the gas. The tc is now putting 600 ft lbs (assuming 300 ft lbs from motor) into the unturning trans input shaft. 100 % slip. how much heat now?

 

If a tc were only associated with 3% loss, why would we need gears at all, anyone remember the old buick dynaflow?

 

Actually the normal loss in tcs before lock up units were made was considered 6%, I did add some considering heavy load trailering.

 

I would still think driving technique is really important.

 

Ken

[overkill]

I'm not mathematician so I'll take your word on the heat/friction/hp loss factors.

 

I do have a question though.... When using the tow/haul mode, do you still leave the tranny in OD or put it into 3rd also... I just got back from a trip this weekend and the engine just seamed to be racing and not wanting to upshift half the time (atleast when I thought it should). Is it ok for the engine to race for exteded hills and such.

[dewfpo]

In general, when using T/H mode I would use the trans in OD unless you are traveling over many hills where the trans cannot maintain your speed in OD and needs to downshift. Then you can just lock out OD on the stick until it flattens out again. If the engine is working too hard to maintain your speed, drop it down 1 gear at a time until the engine/trans. 'feels' comfortable maintianing your desired speed. It all depends on your load, speed and terrain.

 

DEWFPO

[bajakid2]

hey,i have a few questions,iv never towed before but the guy before me towed all the time with my truck i have now..but say if i was going to tow say a small trailer with 2 seadoos on it how would i go about this? tow/haul and just use 3 the whole trip?Thank you for the help-Travis

[pm26]

I think that you need to tow at least 1500 lbs to justify using the tow mode. Towing light loads in the tow mode is a nuisance, especially in town, because the transmission will not shift gears until about 3000 RPM and technically you will never shift into overdrive in the tow mode until you hit about 70 MPH.

 

Now in hilly terrain things may be diferent. I live in Florida, so everything is flat.

[mmmikkke]

Hey Mike,

 

You are thinking that a torque converter increases torque EFFICIENTLY.  They can and do double torque at stall.  but with a great cost in efficiency. Consider this.

 

When the tc is most effective at multiplying torque (stall) the truck is tied to a tree and you stomp on the gas.  The tc is now putting 600 ft lbs (assuming 300 ft lbs from motor) into the unturning trans input shaft.  100 % slip.  how much heat now?

 

If a tc were only associated with 3% loss, why would we need gears at all, anyone remember the old buick dynaflow?

 

Actually the normal loss in tcs before lock up units were made was considered 6%, I did add some considering heavy load trailering.

 

I would still think driving technique is really important.

 

Ken

 

<{POST_SNAPBACK}>

 

 

The one I miss is the THM-400 with variable vane torque converter. Mom and dad had one in our 66 Olds. It was like having an extra gear. Anything past 1/2 throttle and the vane angle would change, the torque was awesome!