Should I use overdrive when towing?

[NL_ASHIE]

He guy's
This xmas I will be towing my jayco camper up to Qld and was talking to my mechanic recently and asked about using overdrive when towing and he said no problems, but a few weeks ago I had my NL put on gas and that mechanic said I shouldnt use overdrive when towing.Just wondering what some seasoned Paj drivers have found when pulling a van.
Cheers Ash

[NJ94]

I'm not sure about that Ash? I tow with my NJ with o/d engaged. If it hits a steep climb it changes back. Unless mechanic was saying something about the LPG? Can't imagine that being a problem even though it obviously burns hotter but the engine is designed for it.
Peter

[chippy4x4]

well I would say NO
the way it was easily described to me was that the input shaft to the gearbox can become "bent" due to the tourque being forced down the shaft. Similar to the way that a small drill bit will bend when being pushed hard while drilling. The shaft will return to its normal shape when the tourque is backed off but it is while the "bend" is present ,that it may cause a slight miss alignement with the meshing of the drive gears and spigot bearing
hope this helps

[Alex86]

Have also been recommended to not use it.

Auto box can overheat according to some.

[Matatak]

i reckon it all depends on how heavy your load is that youll be towing.

[NL_ASHIE]

Hi matatak
I will be towing around the 1300kg mark I reckon.

[Sbazz]

I was told when i had a new transmission put in that the most likely reason the old one was cactus was from towing too much with the overdrive on - something to do with heat dissipation being better when the overdrive is off

[dank54]

I reckon as long as its not working hard 'lugging' in o/d its fine. The clutch in the torque convertor are quite small and cant handle huge amounts of torque through them.

The problem with towing while it isnt in o/d is that the engine is spinning harder and working the fluid in the convertor harder which generates more heat.

The enemy of the auto trans is heat so think about having an external trans cooler fitted if towing is going to be a common task.

[Goody]

I have towed for years in my Paj, I used to tow a 16ft poptop and always in OD. I now tow a 2 tonne monster full van and after having my gear box shit itself I now tow with OD OFF. I dont let the rev's go much over 3 grand and so far on this trip ( one month on the road) all is fine. Economy is as per expected ( 250 kms on a tank of LPG 65 litres)and I dont find the Paj hunting for gears. We average about 85-90 kph on good roads.
For the longitivity of your tranny I would recommend towing in OD OFF.

[sharky]

I would say o/d off but if you were going along a straight stretch slightly downhill I dont see why you couldnt engage it then.

[Blu Ballz]

It has to do with your gear ratios for an automatic transmission. Third gear is generally about 1.3:1 or about that and overdrive brings it to about 0.75:1 so the engine is going slower than what the engine is trying to put out. This puts extreme pressure and heat onto your torque converter trying to go from rotary flow back to vortex flow. If you stay in third without overdrive on you will stay in rotary flow and will have minimal heat.

So when towing overdrive off.

Hope this helps

[nj swb]

well I would say NO
the way it was easily described to me was that the input shaft to the gearbox can become "bent" due to the tourque being forced down the shaft. Similar to the way that a small drill bit will bend when being pushed hard while drilling. The shaft will return to its normal shape when the tourque is backed off but it is while the "bend" is present ,that it may cause a slight miss alignement with the meshing of the drive gears and spigot bearing
hope this helps

Sorry, this is simply wrong.

1. The drill bit bends because there's an axial force. The gearbox input shaft shouldn't be experiencing an axial force.

2. The input shaft torque comes from the engine. The engine can only produce so much torque, and the gearbox is designed to cope with this torque.

Any reliability issue would come down to heat; allowing the transmission to labour in OD would create extra "slip" in the torque converter, which will increase heat generation. Too much heat for too long and things fail.

[Rayw1]

It has to do with your gear ratios for an automatic transmission. Third gear is generally about 1.3:1 or about that and overdrive brings it to about 0.75:1 so the engine is going slower than what the engine is trying to put out. This puts extreme pressure and heat onto your torque converter trying to go from rotary flow back to vortex flow. If you stay in third without overdrive on you will stay in rotary flow and will have minimal heat.

So when towing overdrive off.

Hope this helps

Bluey..
I'm probably going to show a whole heap of ignorance here, but... are you talking about taking the automatic off and driving in manual and using 4th gear as your top gear when you are saying taking the O/D off?

When I tow I have got into the habit of driving in manual based on a discussion on this forum several months ago. However I have often wondered about the differential in heat generated by driving in auto and causing the extra heat in the torque converter as opposed to driving in 4th gear and having higher revs than if in auto. Does a higher revving engine mean it is working harder, therefore more energy more friction more heat?

Hope my query makes sense.

Ray.

[Blu Ballz]

The highest gear in a manual or an auto box is always a ratio of 1:1 or better like 0.89:1.
In a three speed the gear ration is just not quite low enough for a good cruising range so they throw in an overdrive to bring the engine speed down. In a manual or an auto to stop the engine and gearbox from working to hard you should not have your gear in a ratio of 1:1 or less.

[Spursman]

DO NOT use overdrive or cruise control while while towing. I believe MMAL does not recomend the use of overdrive and this stated in the owners Hand book.
Cheers Spursman.