D2 TD5 Auto Use eg Towing

[gavinwibrow]

I tried a few experiments while towing my rather heavy van back to Perth on pretty flat roads after the weekend, and a couple of questions arose. I know virtually nothing about the realities of how an auto works, despite having seen the internals of quite a few and a little reading to boot.

I've known and had re-affirmed many times that 3 Sport is the best gear for heavy highway towing on the flat, but it got me to questioning how our autos work.
In 3S with my 31.6 inch diameter oversize tyres I think I recall I'm doing about 2600 rpm at 90 kmph. If I drop into D, not only do EGTs rise, but with the pedal "pressure" required to maintain that speed it does not quite go into 4th lockup.

Question 1 - is it purely transmission oil manipulations/magic in the trans causing the slippage pre lockup, or would I be at risk of damaging clutches like would occur if slipping a manual clutch?

Question 2 - I also have a still yet to be connected Heavy Automatics Lockup (mainly cos I do quite a bit of 70 kmph light throttle travel, and it would be nice to slip into 4th lockup in those conditions) and I wonder if heavy towing using this system could do any clutch type damage in the scenario above?

Question 3 - what is the maximum sustainable EGT without damaging the TD5? It has been suggested that no more than 600 sustained (and preferably lower), with short bursts only to 650 should be OK??

[discorevy]

Hi Gavin
The slippage ( for want of a better word )you refer to is all taking place in the torque converter, sort of like 2 fans facing each other but with fluid instead of air , so no slipping clutches , but if towing a heavy load while out of lock up you are generating a lot of heat (the by product of wasted energy in the torque converter) , which can damage the clutches in the trans if too hot.

Light throttle 70 kph is fine if you can manually lock it up, you could also for now get it to lock up in 4th above 80 then ease back down to 70 by keeping enough throttle on so it stays locked up, you won't damage anything ( except for the voice boxes of the drivers behind:-)


Egt will be well and truly safe at those levels , wouldn't stress even hitting 700 for a few seconds

[Pippin]

My comment on 1 & 2 only based on my understanding:

1. The slippage or the smoothness of changes are a consequence of the torque converter out of lock up, the damage may occur when heavy towing out of lock up due to excessive heat generated over time in the fluid by the torque converter.

2. Damage may occur if you are changing gears while still in lock up due to shock loading of the clutches.

Nick

[gavinwibrow]

Thanks - makes sense, and just as well I have extra cooling capacity for my ATF - its never gone above 85.

Going up to 80 then easing back to 70 is not an option unless you like $100 contributions to the Police - this is mainly on west coast highway where there is often a presence.

Have hit 700 a few times inadvertently and once panicked at 770 - inattention climbing the big hill ex Melbourne en route to Ballarat on a 45 degree day towing a camper trailer.

[Pedro_The_Swift]

You need to lower the 4th lockup point.
8 words and a million dollars;)
towing at 2600 is way past where your TD5 makes its torque,

The more weight, the taller the tyres, the bigger the chip(or V8) the harder it is to get our auto's to lock up. The standard TD5 is pretty woefull in that regard.

nothing wrong with towing in 4th,
as I've said previously, I'd rather it lug in 4th down to around 1900rpm (that's why I built it the way it is) than "Sport" change downs occurring under full load into a non locked-up 3rd.

Put the van on, get it up to around 95 and "Heavy Auto Lockup"- it into 4th, keep yours eyes on your egts and away you go:D

[Pedro_The_Swift]

Have you thought about changing centre diff ratio's,,
1.411 from a defender TD5
just think'in--;)


late edit, was just trawling through Ashcrofts site and they actually recommend this ratio for Disco towing,,
great minds huh,, :lol2:

[Pinelli]

An Auto mechanic recommended that when taking off, treat it like a manual. Start in 1st, and manually shift through 2nd & 3rd. He also recommended cruising in 3rd (haven't tried 3s - is the ration different?), but I've found 4th just as good for cruising.

Towing 2T up hills is rather heavy going though - EGTs climb fast.

[Blknight.aus]

heres the auto primer for you

http://www.aulro.com/afvb/technical-chatter/31741-grey-box-evil-aka-autotransmission.html?highlight=grey+box+evil