Towing & Auto Gearboxes

[00falcon]

Morning All.

Quick question about Towing and Auto Gearboxes.

As I understood it, you should never tow in overdrive.
(my overdrive is quite high geared (1600rpm = 100km / 2002 Grand Cherokee)

But DieselBoy's comment over on the 'Auto Gearbox Prejudice' thread about the torque converter generating heat, apart from when the 'lock-up' is engaged has got me thinking...

When towing, should I just leave it in overdrive, and let the gearbox decide what to do, and lock-up at cursing speed.
Assuming the torque converter will lock-up while towing (...?)
or should I just not tow in overdrive...
or should I just selectively use OD on the down and flat...

------------

My GC has the 'Trailer Tow Group' listed in its build sheet...

Trailer Tow Group Class IV (requires V8 engine)
3.73:1 axle ratio
Power steering cooler
Transmission oil cooler
Frame-mounted receptacle for load-equalizer type hitch
7-into-4-way plug adapter

[Mr Revhead]

When towing, should I just leave it in overdrive, and let the gearbox decide what to do, and lock-up at cursing speed.

Is cursing speed when you find out your tow vehicle hasn't got the grunt to get up that hill?

[mudlva]

O/d on flats and easy downhills where speed isnt going to get away on you.
D on any section where motor starts to labour.
Higher rpm gets coolant moving around faster. Gets higher air flow going through motor. Gets engine up to where peak h/p is. Gets trans flowing more oil through cooler.
Just remember reving its head off will not achieve much either. Majority of engines pull well at 3000-3500 rpm once you exceed that all its doing is burning fuel and now generating more heat.
Its finding the happy balance and staying in that zone.
Trucks have a green range on their tachos anything above or below will create issues. Use the same theory with your motor

[00falcon]

O/d on flats and easy downhills where speed isnt going to get away on you.
D on any section where motor starts to labour.
Higher rpm gets coolant moving around faster. Gets higher air flow going through motor. Gets engine up to where peak h/p is. Gets trans flowing more oil through cooler.
Just remember reving its head off will not achieve much either. Majority of engines pull well at 3000-3500 rpm once you exceed that all its doing is burning fuel and now generating more heat.
Its finding the happy balance and staying in that zone.
Trucks have a green range on their tachos anything above or below will create issues. Use the same theory with your motor

So... common sense really...
no advantage trying to leave it in OD to get Torque converter to lock...

Engines don't really scare me... gearboxes do...

[Crash bandicoot]

Yep regardless of trans type, keeping the engine in its sweet spot will be of more benefit when accelerating, climbing hills.

[churchill]

What I do is if the TC unlocks on top gear I'll either back off the throttle or drop it down a gear.

[mudlva]

What I do is if the TC unlocks on top gear I'll either back off the throttle or drop it down a gear.

Bacf off and get the system working as a unit. If you do a lot of towing then get a farkkking huge cooler fitted. Bigger the better. And have your tranny serviced every 20-30k.
Fresh cool oil is the best you can do fir your trans.
If in ak talk to otahuhu transmission. Tony knows his stuff
Otherwise any shop that deals with working transmissions not just bone heads who turn spanners

[churchill]

What I do is if the TC unlocks on top gear I'll either back off the throttle or drop it down a gear.

Sorry, should've mentioned that I back off the throttle until the TC locks gain.

[suzolla]

Hi,

I thought the not towing in overdrive was more to do with some manuals as 5th is through a gear whereas 4th is straight through so can handle high sustained load.

Bit of experience with my 80 series landcruiser diesel with auto and only locks up in top, boost and fuel are increased and have also got external trans cooler. Need to fit an even bigger one
If you are going to tow I would highly recommend a trans fluid temp gauge and if a diesel an egt gauge.

To minimize trans temps I try and spend as much time as possible in top with trans locked up, if I need to put my foot down a bit such that it unlocks will then drop it back to 3rd to increase the engine speed and also reduce the TC slippage, if the trans temp keeps on rising will then drop back to 2nd to again keep the revs up and reduce TC slippage.

Quite often find that I am balancing trans temp and EGT temp, which is why I need a bigger trans cooler and also inter cooler.

Cheers
Tim

[Crash bandicoot]

Hi,

I thought the not towing in overdrive was more to do with some manuals as 5th is through a gear whereas 4th is straight through so can handle high sustained load.

Bit of experience with my 80 series landcruiser diesel with auto and only locks up in top, boost and fuel are increased and have also got external trans cooler. Need to fit an even bigger one
If you are going to tow I would highly recommend a trans fluid temp gauge and if a diesel an egt gauge.

To minimize trans temps I try and spend as much time as possible in top with trans locked up, if I need to put my foot down a bit such that it unlocks will then drop it back to 3rd to increase the engine speed and also reduce the TC slippage, if the trans temp keeps on rising will then drop back to 2nd to again keep the revs up and reduce TC slippage.

Quite often find that I am balancing trans temp and EGT temp, which is why I need a bigger trans cooler and also inter cooler.

Cheers

4th is usually a 1:1 Ratio, still require the lay shaft to transfer drive from ones end to the other.
Tim

[slide]

Hi,

I thought the not towing in overdrive was more to do with some manuals as 5th is through a gear whereas 4th is straight through so can handle high sustained load.

Very true. 4th (in five speeds, 6speeds can be different configurations) is straight through, no gears doing any work and very minimal bearing loading. You will never blow fourth gear- as there is none . Early mitsi's would blow 5th if you even thought about towing in fifth
Auto gears work very differently to manuals, is the same gears working, just different bands/clutches holding them differently.
Heat is the killer of autos. Driving style will dictate heat developed. (a cooler can be very beneficial)

[MihiT]

Quite often find that I am balancing trans temp and EGT temp, which is why I need a bigger trans cooler and also inter cooler.

Cheers
Tim

Or.... A manual...

[De-Ranged]

A few tips that haven't been mentioned....
Having towed some big loads with small auto cars, most modern cars cool the trans in the engine radiator so watch the temp gauge if you don't have a separate one for the trans.... this brings up another useful tip, don't forget you have another radiator in the car, your heater... turn it on full and the fan too you need to get the heat out! if you get hot wind the windows down lol

This one is a good driving technique anyway but helps alot when towing with an auto.... momentum, you have a dip coming up or a hill accelerate... use your momentum to get you further up the other side before you have to change down... how much you use this and where depends on your trailer and how well its balanced... how many friends in blue you have seen on the road..... the muppet in front who can't make his mind up if he is trying to hold you up or set the land speed record

As for the old thoughts of a manual box for towing lol its out dated, most modern autos and some older ones are alot tougher than people think.... torque converters have changed alot from the early slush boxes, heat is the only problem add some extra cooling... the mechanics of the auto box is better for load carrying as they run sun and planitery gear sets 3 contact points to transfer the load and no way for the gear set to spread under load... a manual on the other hand has an input gear that runs to a lay shaft this in turn drives the rest of the gears, this is all done on a single contact patch each time it transfers power, this under load causes the gears to try and push apart from each other and wear on the bearings the teeth
As for the other old comment about keep it in 4th so its straight through.... lol this incorrages bad driving, people get afraid to change gear admit it you do it labor the motor up this bit its not far or over rev going through the dip an auto wont do this
And oil changes should be more frequent for the gearbox and diff no matter what your gearbox if your towing

My personal preference is for an appropriate sized auto for towing.... in fact I'm going to ALOT of effort to have just that in my tow wagon
On advice given to me by one of my mates (senior oil tech for Total Oils) I'm not plumbing the cooling through the rad it will have a separate radiator with its own thermo switched fan