D40 Torque Converter lock-up

[Anders]

Hi,

I am new to this forum and I don't own a Navara (yet) but I am thinking of buying one.
My question is re auto lock-up in 4th.
Does the auto lock up or not in 4th?
I am towing a caravan about 2700kg loaded and guess that 4th would be a very popular gear to use.

(I know this has been discussed before but interpreting the responses I am unclear of what is available for 4th.

Anders

 

[crack]

d40's are a 5spd auto. to get torque converter lock up you need to be to have overdrive on and be above 80km/h, if overdrive is off you will not get lock up. as for locking in up in 4th id say no as overdrive needs to be in the on position for this to happen. the torque converter lock up will unlock if you accelerate to fast or the accelerater is depressed more then hhalfway i believe.

i started a thread on towing tips a little while ago. if you do a search you should find it. theres a few bit written in their about it.

jack

 

[Old.Tony]

I'll confirm what Crack said.

The D40 Auto will only lock up when the following conditions are met:

* The vehicle is in overdrive
* The gear selector is in Drive position
* The gearbox has selected 5th gear
* Throttle position is below 50%
* Vehicle speed is 75km/h or higher

Once these conditions are met, the TCM (Transmission Control Module) signals the TCC (Torque Converter Clutch) solenoid to close, engaging the input and output of the torque converter directly.

Changing any one of those conditions will cause the TCC to disengage:

* vehicle slows below 75km/h (eg, when traveling up hills or into strong headwinds)
* throttle exceeds 50%
* Overdrive button is pressed turning OFF the overdrive function
* The gear selector is moved from Drive

Needless to say, the gearbox can't kick back a gear without that torque converter lock disengaging.

I've actually had mine engage going down a long hill without using the accelerator. We crested the hill slowly and rather than hammer it on the downhill I just let the thing gather speed - at 4.3T GCM it does that rather well. I was watching the tachometer, the revs were at about 1300 or so, but when the speed reached 75km/h, the TCC engaged and the rpm rose to about 1600. At this point, the vehicle stopped gathering speed as the engine braking effect took over - at least I knew it would work with only gravity providing the effort!

 

[sparra04]

. d40's are a 5 spd auto



jack

are they a 4 speed auto with lockup? or a 5 speed auto with lockup?
lockup isnt an extra ratio and should be avoided when towing

 

[Old.Tony]

My 2009 is a 5 speed auto.

The reason for the throttle position, gear selection and vehicle speed requirements for the lockup is to ensure that the engine doesn't suffer any strain while the torque converter is locked.

There are occasions when I wish I could manually lock the torque converter, because it does get frustrating to be cruising along at 90km/h (actual speed) and you have to use a little too much throttle, resulting in the TCC unlocking.

At that speed it seems to save about 500rpm. On ideal figures (these are not necessarily accurate figures but they'll be a fair guide) the vehicle should use about 0.0417ml per injection per cylinder (at 10LPHK, so unladen traveling). If you increase the RPM to 2500 for the same speed and duration, your LPHK increases to 12.5 immediately - just for a 500rpm increase. It will actually increase more, because now the engine/gearbox isn't linked, there's more throttle being used so the injector duration is slightly longer.

Here's how I calculated the fuel used per injection:

At 100km/h, engine rpm = 2000 revolutions per minute

There are 2 power strokes per revolution in a 4 cylinder engine (one cylinder gets either a power stroke or an exhaust stroke per revolution, or 0.5 power strokes per rev, times 4 cylinders = 2 power strokes per revolution).

This means 240,000 power strokes per hour (at 2,000rpm) so 10 litres divided by 240,000 is 0.0000417 litres or 0.0417ml.

At 2500rpm, times 2 power strokes per rev times 60 (minutes in an hour) times 0.0000417 gives you 12.5 litres used per hour (100km/h).

The nutshell is, basically, that for just 500rpm more, you're using 2.5 litres per hour more, so the moral becomes - if you can engage that torque converter lockup, let it happen.

Caveat on the calculations: you can't figure it for 1500rpm, because at 1500rpm you're traveling slower than 100km/h, so the calculation necessarily changes.

Further caveat: these figures are based on an unladen average. Laden, the figures will change. The instantaneous figures (taken at any point in time with, say, a ScanGauge) will show different figures.

 

[bluessv]

More importantly Old Tony, is that you came up with that very informative and technical reply at 5am!!

 

[crack]

are they a 4 speed auto with lockup? or a 5 speed auto with lockup?
lockup isnt an extra ratio and should be avoided when towing

lockup isnt an extra gear its just the torque converter manually locking up rather then slipping in the transmission fluid. old tony will be able to describe it better. so there are 5gears in total. to get 5th overdrive needs to be in the on position. with over drive off i beleive you remain in 4th gear. Nissan/holden dealership here told me not to tow in overdrive but after playing around towing a decent amount of weight i find towing in overdrive on works better as you can get the torque converter to lockup. as for damage i think it would be no exsistant as the torque converter will unlock and pick revs up or drop back to 4th gear if theres any unnecisary load on the gearbox.

hope this helps
jack

 

[Old.Tony]

That works for me, Crack.

Historically, automatics have been less fuel efficient than manuals because more RPM are needed to turn over the wheels at the same speed as a manual. It's just the same if the manual was driven with the clutch slightly depressed and slipping a little all the time.

The idea behind locking the torque converter is to remove that issue. The engine RPM is directly translated into the input shaft of the gearbox, just like fully releasing the clutch in a manual. This allows the autos to get much closer to the fuel efficiency of a manual.

As for should you do it or not: the thing is designed to take care of itself. If you push the throttle too hard, it disengages. If the vehicle slows too much, it disengages.

You could cram 5980Kg into and behind (max GCM) and do it in overdrive. If you go up a hill, it will kick back as it needs to. No harm will come to it.

If a problem DOES happen, it'll be the TCM that's flipped, or the ECU isn't sending speed data, and none of these will be because you're towing what the vehicle was designed to tow.

 

[hunter]

Is there a o/d button in the new navs with manual mode how dose the lockup converter work, and if useing manual mode in 4th gear will the auto kick back a gear if revs are low say towing and going up a hill?

 

[Old.Tony]

I haven't seen the new ones yet, and my manual definitely doesn't cover the new boxes, so as yet I've got no info on them.

I might go press my local dealer for some info on that, and see if he has one I could take for a test drive. The easy way to answer your question is to use the box in manual mode and try accelerating up a hill from 30km/h. If it can't kick back on its own, we will know that in manual mode, you have to do things manually.

Actually that's pretty bloody obvious, but I do wonder if there are built-in safeguards that might protect the thing from being pushed too hard.

 

[duck]

I believe what Old Tony says about towing in 5th with the auto but what annoys me is all the Nissan dealers I have had the D40 serviced all state don't tow in overdrive when I have pointed out that the owners manual makes no mention of it, even the towing section recommends leaving it in drive (overdrive on). The only time it is mentioned is where the vehicle changes up and down it is recommended to lock out the overdrive. So do Nissan dealerships service really know how the auto works? does locking out contributre to premature wear if so are they contributing to it because of ignorance.

I dont know what it costs to rebuild a motor or an auto I decided to take out the extended nissan new car warranty

 

[Old.Tony]

Back in the old days you'd have a Ford station wagon with a 3-speed auto box, a towbar and a York/Millard/Viscount 16-foot 1,200kg single axle caravan. You could get around hauling the thing in "D"rive but if you did and you got to a hill you'd have trouble, so "always tow in 2nd" became the common advice.

I think the guys are dinosaurs who don't have faith in their own product. 51,700km gone on my Nav now and half of that towing. Christmas saw us towing through the desert, through suburban areas and climbing the Alpine Way up to Thredbo - we started the morning in Walwa and by 8am we were at Lake Crackenback.

As for "locking out the overdrive" - the gearbox manages that itself quite nicely.

I don't know why they insist on scare campaigns. The auto box is solid and manages quite well without being fiddled around with.