Auto gear selection for towing.

[Mudnut]

After completing some small trips, I got to wondering what should I do with the auto transmission. I have never towed a heavy load with an auto before. In my TD5 Defender, I did not use 5th gear when towing unless going down a slight grade, and there was no stress on the transmission. Do people use manual mode, and not cruise in 8th? Want to preserve this transmission, and the vehicle for a long time. I do plan on using manual mode for steep downhill grades, to preserve the brakes, even with a braked trailer.

 

[Eric]

After completing some small trips, I got to wondering what should I do with the auto transmission. I have never towed a heavy load with an auto before. In my TD5 Defender, I did not use 5th gear when towing unless going down a slight grade, and there was no stress on the transmission. Do people use manual mode, and not cruise in 8th? Want to preserve this transmission, and the vehicle for a long time. I do plan on using manual mode for steep downhill grades, to preserve the brakes, even with a braked trailer.

Have towed heavy loads (3.5 T ) occasionally for decades in an auto. 5 number auto L/R Discoverys before the Grenadier. In that time of ownership of I have never used the manual functionality. The Grenadier pulls and tows better than the L/R. You are using the same gearbox whether it is auto or manual mode and the torque in the gearbox will be the same. For going down very steep hills you can always use the downhill assist function.

 

[Jeremy996]

Let the auto make the decisions! (unless you are going downhill and need engine braking or similar).

The manufacturer has gone to a lot of trouble to optimise the gearing and the shift points for towing and normal driving, so for the vast majority of the time the truck will be able to make a decision at least as good as the one you would make. Where this comes unstuck is situations where the truck does not know the lie of the land or the friction coefficient of the ground surface. Here you would be advised to make a decision for the truck!

(As a general rule, automated systems make a poor driver at least average; a truly excellent driver might find the automated systems a bit of a drawback, but the vast majority of drivers are less than really excellent). ABS is a good example; the very best drivers can out-brake an ABS equipped vehicle in a vehicle not equipped with ABS, BUT drivers that good are very, very rare and ABS makes a suitably equipped vehicle at least consistent for most drivers.

 

[Eric]

Let the auto make the decisions! (unless you are going downhill and need engine braking or similar).

The manufacturer has gone to a lot of trouble to optimise the gearing and the shift points for towing and normal driving, so for the vast majority of the time the truck will be able to make a decision at least as good as the one you would make. Where this comes unstuck is situations where the truck does not know the lie of the land or the friction coefficient of the ground surface. Here you would be advised to make a decision for the truck!

(As a general rule, automated systems make a poor driver at least average; a truly excellent driver might find the automated systems a bit of a drawback, but the vast majority of drivers are less than really excellent). ABS is a good example; the very best drivers can out-brake an ABS equipped vehicle in a vehicle not equipped with ABS, BUT drivers that good are very, very rare and ABS makes a suitably equipped vehicle at least consistent for most drivers.

I agree with what you say, if your towing is on tarmac and no extreme off road then there is no need to take it out of auto.

 

[Tinerfeño]

Gearbox and engine have been mainly optimised for fuel efficiency. For this engine revs are kept as low as possible.

Torque is the factor causing gearbox wear and ultimately failure. Same driving force can be achieved by lower gear where engine runs at higher revolutions and torque on gearbox is lower.

I would recommend the use of manual function. At low resistance (downhill, tailwind) you can use high gears, but already on "normal" resistance one gear lower is better. Uphills one more.

I did this for he entire running-in period even though I didn't tow anything.

 

[Mudnut]

Gearbox and engine have been mainly optimised for fuel efficiency. For this engine revs are kept as low as possible.

Torque is the factor causing gearbox wear and ultimately failure. Same driving force can be achieved by lower gear where engine runs at higher revolutions and torque on gearbox is lower.

I would recommend the use of manual function. At low resistance (downhill, tailwind) you can use high gears, but already on "normal" resistance one gear lower is better. Uphills one more.

I did this for he entire running-in period even though I didn't tow anything.

That is what I was thinking. I have always towed in a lower gear with my manual cars. This is my first auto box that I have towed with in 40 years.

 

[Tazzieman]

I also use the manual option when towing uphill on steeper gradients.
Maybe if I drove a diesel I wouldn't.

 

[landmannnn]

That is what I was thinking. I have always towed in a lower gear with my manual cars. This is my first auto box that I have towed with in 40 years.

Your old Defender used a manual gearbox that was developed for the SD1 in the early 70s. It was never great and did need some looking after. That ZF auto is strong enough too not not cause any concern, so let it do its thing.

On the downhills, I would tend to use the brakes unless really long and steep. They are relatively cheap to replace.

 

[Mudnut]

Your old Defender used a manual gearbox that was developed for the SD1 in the early 70s. It was never great and did need some looking after. That ZF auto is strong enough too not not cause any concern, so let it do its thing.

On the downhills, I would tend to use the brakes unless really long and steep. They are relatively cheap to replace.

Thanks for that. The Defender R380 gear box defiantly had it's weaknesses. I was still able to look after it for over 300 thousand k's with out an issue (except reverse light switch) Just trying to do the same with the ZF box in the Quartermaster.

 

[MattA]

When towing it’s also about the engine temps, the auto is designed and programmed to improve fuel efficiency so it holds the lowest gear possible
Lower gear can cause the engine to labour which increases temps so holding it in a higher gear can be better for longevity

 

[TheDocAUS]

View: https://www.youtube.com/watch?v=uc7Z5gEDtRA&pp=ygUXZ3JlbmFkaXIgY2FyYXZhbiB0b3dpbmc%3D

View: https://www.youtube.com/watch?v=dTcSRFjsVT8&pp=ygUXZ3JlbmFkaXIgY2FyYXZhbiB0b3dpbmc%3D

 

[Mudnut]

When towing it’s also about the engine temps, the auto is designed and programmed to improve fuel efficiency so it holds the lowest gear possible
Lower gear can cause the engine to labour which increases temps so holding it in a higher gear can be better for longevity

I do like the Transmission temp, and Engine temp on the tyre temp page. I am surprised that there is no EGT temp. There would be sensors in the exhaust, but the info is not displayed.

 

[TheDocAUS]

I do like the Transmission temp, and Engine temp on the tyre temp page. I am surprised that there is no EGT temp. There would be sensors in the exhaust, but the info is not displayed.

Correct it is there. INEOS should add a Towing Tab to the Console including EGT and turbo PSI.

 

[Tinerfeño]

I also use the manual option when towing uphill on steeper gradients.
Maybe if I drove a diesel I wouldn't.

Especially with diesel because of better low rev torque.

 

[Tinerfeño]

Your old Defender used a manual gearbox that was developed for the SD1 in the early 70s. It was never great and did need some looking after. That ZF auto is strong enough too not not cause any concern, so let it do its thing.

On the downhills, I would tend to use the brakes unless really long and steep. They are relatively cheap to replace.

My Disco 200Tdi -93 has a LT77 gearbox with over 600´ km and it has been towing a lot. Still going strong.

Why automatic gearboxes are thought to last forever? Especially with diesel engines they have problems with clutch plates (gearbox and torque converter) and also with cutch housings. Picture from ZF 4HP22 D-clutch:

Downhill engine braking is preferred not for lower brake pad wear but for avoiding brake fluid boiling and conseguent loss of braking. It also reduces fuel consumption. I use this a lot.