Lock up torque converter

The definitive answer please. (no guesses or maybe's)
I am towing 2300kg van with O/D switched off; i.e. in 4th gear.
Problem is revs are all over the place for the same road speed thus indicating the torque converter is not in "lockup" (even on still days on perfectly flat road)
Should I expect the torque converter to be able to ever lockup or is it because the converter will only lockup when the overdrive switch is in the "on" position?

There are several conditions required to make the TCC solenoid activate which pushes the clutch into the "Lock" position.

To answer your specific question, the selector lever must be in the "D" position and it must be able to get into gear 5. Refer to AT.PDF, p117/350 for this information (in the D40 workshop manual). The reference speed for testing the operation of the solenoid is 80km/h, although I've had mine lock at just over 70km/h.

I've never had my torque converter lock when not in overdrive. I wish it did! In fact I wish I could control it manually, sometimes.

Thanks for prompt reply but still a little confused.
"must be able to get into gear 5" does that mean capable of getting into gear 5 but will lock up in others (3,4 etc) or does it only lock up in 5th?
The big problem I am having is RPM variation of b/n about 2700 to 3200 rpm to maintain road speed. That must mean there is a hell of a lot of slippage most of the time thus reduced fuel economy and I assume increased heat.
Perhaps I should be just towing the load in overdrive and hope the transmission can handle it. (I'm a bit old fashioned and always thought overdrive was a "no no" when towing)

It means that the only time the solenoid will activate (and therefore lock the torque convertor) is when the vehicle is in gear 5.

gcaddaye said:

The big problem I am having is RPM variation of b/n about 2700 to 3200 rpm to maintain road speed.

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By those RPM, you must have the petrol engine. Is that a different tranny to the diesel?

08KINGCAB said:

By those RPM, you must have the petrol engine. Is that a different tranny to the diesel?

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They're the same model (RE5R05A) but have different codes.
The Diesel 2WD has the 95X09, the 4WD has the 95X0B, the petrol 2WD has the 97X0D and the petrol 4WD has the 97X0E.

Page 32/350 of AT.PDF actually has a table that I'll try to reproduce here.

Selector Lever __________|__ "D" position __|___ "3" ____|____ "2" __|
Gear Position ___________|__ 5 ___|__ 4 __|____3_____|_____ 2 ___|
Lock-up _______________|___X___|___ - __|___ - ______|_____ - ___|

No lockup occurs unless the vehicle is in overdrive.

Thank you Old Tony got it now.
To 08KINGCAB no I am talking Navara diesel auto Kingcab towing with O/D off thus in 4th gear. I truely get that much variation in 4th gear. I can kick it back to, or select, 3rd in which case rpm would increase to about 3300rpm for a similar road speed.

gcaddaye said:

no I am talking Navara diesel auto Kingcab .

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Well there's the problem. Welcome to my world of Kingcab crap. My definitive answer is sell the bloody thing that's what I'm going to do, if anyone will buy the $hitter!

Just wondering out loud....as I'm want to do periodically...does anyone know if it is possible to install a switch to control the torque converter on the D40 auto?

Get a manual cogswapper!

Pete22 said:

Just wondering out loud....as I'm want to do periodically...does anyone know if it is possible to install a switch to control the torque converter on the D40 auto?

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I was wondering the same thing. I'd like to lock it down so that the solenoid closes at "other times". It has to unlock for a gear change, so a manual switch carries a fair risk (unless it inhibits the changer). I don't know how the ECU or the TCM (Transmission Control Module) will react to being bypassed.

I'm almost positive that bypassing the TCM to lock the converter will void the warranty on the gearbox and possibly the engine as well.

But I will be researching how to do it, regardless.

gcaddaye said:

Thanks for prompt reply but still a little confused.
"must be able to get into gear 5" does that mean capable of getting into gear 5 but will lock up in others (3,4 etc) or does it only lock up in 5th?
The big problem I am having is RPM variation of b/n about 2700 to 3200 rpm to maintain road speed. That must mean there is a hell of a lot of slippage most of the time thus reduced fuel economy and I assume increased heat.
Perhaps I should be just towing the load in overdrive and hope the transmission can handle it. (I'm a bit old fashioned and always thought overdrive was a "no no" when towing)

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Hi, Rpm Bunbury did you get an answer to 4th gear lock up. I`m towing a 3tonne boat and have same problem, hoping to find electronic solution soon.

I towed a car trailer with a 1.5 ton car on the back plus my usual 600kg of gear on board for about 1000km's on both flat and hills and only changed out of overdrive for the steeper hills and the trans handled it fine.

I haven't looked extensively into hacking the transmission control to force a lockup, because if I ever forget, it could be downright dangerous.

I imagine that the TCM (Transmission Control Module) could be re-programmed to allow lockup to occur in 4th (selector on 'D', overdrive switch OFF) providing certain criteria (similar to when in 5th) are met.

I'd imagine once a certain speed was reached, and a certain level of accelerator, it ought to be able to lock in 4th just as well as it does in 5th - but I've no knowledge about the TCM and how it might be achieved, so that's just pie in the sky stuff for me.

These guys may be able to help??? Wholesale Automatic Transmissions

Bosshog said:

These guys may be able to help??? Wholesale Automatic Transmissions

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Interesting website. Nice work.

I found this in the workshop manual
Quote"
* The torque converter clutch solenoid valve is activated, with the gear selector in D5 , 2 and 3 by the TCM in
response to signals sent from the vehicle speed sensor and accelerator pedal position sensor. Torque
converter clutch piston operation will then be controlled.
* Lock-up operation, however, is prohibited when A/T fluid temperature is too low.
* When the accelerator pedal is depressed (less than 1.0/8) in lock-up condition, the engine speed should
not change abruptly. If there is a big jump in engine speed, there is no lock-up.

So going by this the torque converter will only lock-up in Drive, 3rd and 2nd but NOT 4th which is stupid if ya ask me.

I got my information from the table on page 32 of AT.PDF which shows the lockup only occurs in 5th gear (selector in Drive).

It confirms this again in text on p115. I can't find the section you're quoting, but my manual is for the European 2005 model, so maybe Nissan added lock-up for additional gears and eventually they'll do the whole box?

Next time I go for a drive, I'll have a go in 2nd and 3rd and see if the thing activates.

That quote comes from the top of page on page AT-110 in the European edition but the Australian edition I also have, now that I look at it only talks about D5 which is on AT-115 same as yours and both are 2005 editions printed in Europe so now I'm confused

And dammit I went out and forgot to try this out. When I finish reading these posts, I'll go do it.

The attached is, I think, the relevant page from the 2008 version of the D40 manual.