Buzball

Hello guys

When towing a trailer does the O/D Have to be turned of im guessing it does?

nickxj94

Yes unless you like your tranny well done.

Buzball

Ok thanks

Could anyone go into detail on why it needs to be off?

Kalali

What overdrive? Are you talking about the torque convertor?

Fruid

If you are talking about 4th gear then no it doesn't. I regularly tow my boat 150mile round trip to the lake and it weighs approx 1ton (2200lbs) , I sit on the motorway at 60mph to keep the mpgs as high as poss.
It will only go into 4th if it can handle it, up hills I kick it down or it dies.

djb383

How would u turn it off? It's computer electronically controlled. A number of highly educated folks did the programming parameters. Put it OD, it'll figure out the correct gear depending on the driving/operating conditions all on it's own.

salad

To turn it off, put the shifter in the 3rd gear position. D includes 4th which is the overdrive gear - this is actually in the vehicles manual. Pretty much every other light vehicle manual says the same thing. The transmission computer is based on sensory input like RPM, vehicle speed, and throttle position. However, there is no sensor for weight, so the shift pattern is not adjusted appropriately.

You turn need to turn OD off because of the torque converter. In a way an automatic transmission is sort of like an 8-speed because with each of the 4 gears the torque converter can either be in hydraulic mode or locked. The problem with towing and overdrive is that frequently the computer will think that you're going the correct speed and throttle to get into 4th. However, you never get to a point where it actually locks the converter unless you're going downhill with the wind at your back or you're towing something relatively light (with low wind resistance) on flat terrain. As a result the torque converter spends WAY too much time unlocked in hydraulic mode which creates a LOT of heat and burns more fuel than locked in 3rd gear at a higher RPM. It runs the risk of overheating the transmission and causing some nasty damage. The torque converter is meant to aid in shifting. For cruising it should be locked. It is for this reason that when towing heavy loads you need an auxiliary or HD transmission cooler - the torque converter does a lot more work.

djb383

Maybe a very loose interpretation of a 7 speed. Converter will not lock-up in 1st hear, according to the FSM. Haven't seen anything about not towing in OD, but then it's a big manual also.....still looking.

RenegadeT

try the owners manual

salad

Fruid

Good Information

How do you know, or is there a way of getting a signal to let you know if the converter is locked. Like I said , regularly tow my 2200lb boat and other stuff, my XJ came with factory tow package so has the trans cooler, when on the motorway it glides along as though there was no boat but when you come to a steepish hill it starts to die and kicks down into 3rd, I don't feel like it's overdoing it, besides on the Jeep tow hitch it says OK for 3200kg (7040lbs).
Thats pretty normal for big trucks but I wouldn't want to do that with the little XJ.
Interesting to know if there was a signal available for the converter locking in.

Fruid

Or a transmission fluid temp gauge!

salad

Technically yes sorta, you'd have tear into the TCU to get it though. Somewhere around here on these internets there's actually a write up on making a shift controller for the AW4 that includes a manual torque converter lock.

Though if I were you I'd just make sure I have the 75w140 in the rear, aux tranny cooler up front, and leave it in 3rd. Remember lower RPM doesn't always equate to less fuel.

salad

Haha yeah a few people have fitted these

djb383

Yep, I've read the owner's manual and it does not say "do not tow in OD", as previously stated, nor does it make any reference to the torque converter locking or unlocking. The owner's manual does suggest using a lower gear in hilly areas and on severe grades thus selecting a lower gear will eliminate excessive shifting. Sounds like common sense to me as it's easy to hear the motor reving/feeling the tranny shift, no? If one can't hear the motor/feel the tranny, they must be deaf in one ear and can't see out of the other, no? LOL

Since there is a sizable and very noticeable difference in both engine rpm and engine noise (3rd gear, 4th gear), I just presumed one would have enough common sense to slow down and select a lower gear IF the tranny was frequently shifting gears back and forth. IF the tranny down shifts out of OD occasionally, then there's no need to tow in a lower gear than OD. The owner's manual seems to say the same thing but maybe using a slightly different wording....but again, the manual does not say 'do not tow in OD'. Listen to what the motor of the tow vehicle (with a auto tranny) is tellin' ya.....and use some common sense.

Now, If one is towing with a manual tranny, there ain't any intelligent life (regarding programming) involved.....it won't do anything automatically () .....and that's why virtually any light duty vehicle with a stick shift tranny has a lighter tow rating than a apples-2-apples auto tranny equipped vehicle.