Overdrive on/off

[4Factor]

Ok, I'll be towing a trailer in the 2200-2300 lb range. I know it's the smarter thing to drive with the overdrive OFF (or locked out) because simply that's what everyone says to do. What I really want to know is
1. What's going on behind the scenes, why does it ALWAYS have locked out of overdrive when towing?
2. Is there any time when towing that it's ok to press that button and let it go into the overdrive gear.

 

[Corwyyn]

Ok, I'll be towing a trailer in the 2200-2300 lb range. I know it's the smarter thing to drive with the overdrive OFF (or locked out) because simply that's what everyone says to do. What I really want to know is
1. What's going on behind the scenes, why does it ALWAYS have locked out of overdrive when towing?
2. Is there any time when towing that it's ok to press that button and let it go into the overdrive gear.

Kind of answers both: if you are at highway speed on a nice flat road you should be able to run with the OD engaged. If you encounter climbs or descents you would want to engage the OD lockout so that your transmission isn't constantly searching for the correct gear on the uphills, also allows the transmission to take some of the braking load going downhill.

To answer the first question, the main reason locking out OD is recommended when towing is simply that you have more load and the transmission is more sensitive to changes in speed (particularly any increase in speed); locking out the OD limits the amount of shifting. And since U-tug and some other major equipment renters recommend that you not exceed 45mph having the OD locked out puts you in a better part of the power curve (I believe, could be wrong).

Anyway that's my take on towing. Pretty sure others will chime in to prop me up or shoot me down

 

[4Factor]

Done some research, this is what I found...
CONDITION #1 - in overdrive, torque converter "locked up"
CONDITION #2 - in overdrive, torque converter "unlocked"
CONDITION #3 - in third gear, torque converter "locked up"

If you're in OD and cruising at constant speed on flat ground you're in CONDITION#1. If you need to accelerate slightly you move to CONDITION#2 which causes a rise in RPM's thereby creating more power. In this "unlocked" state the torque converter creates tons of heat which is (obviously) bad for the transmission. If you further press the throttle you'll move to CONDITION#3, there's a bigger rise in RPM's and power, but the heat issue is not a problem because the torque converter is "locked up" again.

Now from what I understand the reason for pressing the button and being in "OD OFF" mode is to prevent changing through these above CONDITIONS because constant gear changing in itself creates heat and is bad for the transmission. Most importantly it's to avoid CONDITION#2... this is the one that creates tons of heat and can quickly shorten your transmissions' life expectancy.

Now if this above research I compiled is correct, my question are...

1. Are there ANY other times that the torque converter becomes "unlocked" (OD OFF or ON)?
2. As long as there's no gear "hunting/searching" going on, does it matter whether the OD is OFF or ON? (ie. if I pay attention, can I cruise on the highway with the OD ON)

 

[LibertyFever]

I spent the last week towing a heavy vehicle trailer (about 5000 lbs). I left the OD off and cruise. On the occasional steep hill I'd take it out of cruise to limit the engine racing. With OD on the engine labored and the transmission shifted wildly. My fuel mileage sucked big time (as low as 12 MPG) but I doubt your's will be that low.

Does your state require a 2200 to 2300 lb trailer have brakes?

 

[tjkj2002]

Depending on ****** you have if you tow anything with the KJ in OD you have a real good chance of burning up your TC.The 42RLE's TC is not stong enough to handle that much stress,the 45RFE is just barely strong enough.Remember we have plastic stators in our TC's.

 

[4Factor]

Depending on ****** you have if you tow anything with the KJ in OD you have a real good chance of burning up your TC.The 42RLE's TC is not stong enough to handle that much stress,the 45RFE is just barely strong enough.Remember we have plastic stators in our TC's.

Perfect! That's what I needed to know... if the thing will self destruct in OD.
Looks like it will, so I'll keep the OD off and just pay the cost of fuel (cheaper than a new ******).
Oh BTW it's a 2004 (the 42RLE).

For those that care... (Canadian costs)
It's about 400 kms (250 miles) one way so round trip should cost me a bit, I'm estimating 20L/100km (11.75 MPG) just to be on the high side, so it's basically a bit over one tank to go one way. I've budgeted $250 for fuel (basically 3 tanks) and I'm currently spending $80 per tank so I'm right on target!

 

[Atrus]

Remember we have plastic stators in our TC's.

Woah, didn't know that!

 

[tjkj2002]

Woah, didn't know that!

The CRD guy's are having a terrible time with there TC's because of the stator(and the fact it's tuned still for HEMI and not the CRD engine),some have replaced them with a HD unit from SunCoast.There are aftermarket TC's for the 45RFE,the 42RLE will be more expensive since a custom converter will need to be made.

 

[JeepJeepster]

I believe you can get converters from APS precision trannies for the 42rle. Kyliberty has talked about it a few times.

4factor, you forgot condition#4-in third and unlocked.

When you give it gas to pass someone, it goes into 3rd with the torque unlocked. When it does that push the o/d off botton and watch the rpms, they will go down.

 

[4Factor]

I believe you can get converters from APS precision trannies for the 42rle. Kyliberty has talked about it a few times.

4factor, you forgot condition#4-in third and unlocked.

When you give it gas to pass someone, it goes into 3rd with the torque unlocked. When it does that push the o/d off button and watch the rpms, they will go down.

Well, back from the trip with the trailer... didn't know about the above mentioned condition #4, but similar to condition #2 it likely creates lots of heat (bad).

So I left it in the "OD Off" mode for the trip and didn't have any problems. My mileage was way better than expected (got 14.9L/100km or 15.8mpg), but the fuel price was WAY worse than I thought it would have been so with $25 to spare out of the $250 budgeted I guess I did ok.
The cruise control.. or shall I say SPEED control did excellent up and DOWN the hills, I'm impressed by the ability of it to not allow me to go too fast down the hills by down gearing for more braking assist... nice little helper. After nearly 800kms (500 miles) of trailering the next day felt weird driving without it, felt like it had tons more get-up-and-go! That feeling went away as I got used to no trailer again.
One HUGE disappointment is the spare tire had to be removed from the rear of the Jeep, the locking handle on the trailer tongue wouldn't fit under the tire, so the tire went inside the vehicle instead (the trailer was already packed before I realized this and the spare couldn't go anywhere else). Although this didn't cause any problems, I was disappointed it had to be removed. I'll be looking for a different hitch in the future, it only needed to be lower by about 1/2 an inch (for better clearance, I'll drop it a full inch if I can find the right one).

 

[JeepJeepster]

The downshifting is nice but I usually cancel out the cruise and just use the brakes. It down shifting like that puts more wear and tear on things I cannot easily replace in the driveway, I can replace brakes anytime.

With my Draw-Tite hitch the spare has never been a problem. I usually use a 2" drop, I do have a 3" lift though.