D40 auto gearbox question

[Stevolution]

Hi all.

I have a 56 plate Auto Aventura - 78k. All going well.
But, I have noticed lately that the auto box does seem to be 'searching' for a gear and being a bit dithery over finding the right gear.
Its not terrible, but my mate noticed it straight away.


I asked my local Nissan dealer and they asked a local transmission specialist to have a look. He hasn't actually test driven it yet - he is waiting for a dry day ??? What difference that makes I have no idea.

There is talk of it either being something to do with the torque converter or a clutch part (what part I don't know - the clutch pack?).

It was orignally thought to just be out of adjustment, but apparently the computer says all is well.

Thoughts? The auto gearboxes were not exactly popular for being reliable so I am amazed its lasted 78k.

Just wondered if anyone had any ideas.

Thanks, Steve

 

[the_bluester]

I can not offer too many thoughts on your own problem, but I would not really agree about them having big reliability issues. I have an r51 Pathfinder instead of a Navara (Same car from the headlights to the middle of the back doors) and it is at 165,000 km without any problems. I changed the transmission fluid recently and it was still nice and pink and smelled fresh. I could not find any evidence that Nissan had changed it any any service before that so it had done about 140,000km when I changed it.

I have only heard about one failure (On another forum) where the valve body gave up and it was a very expensive exercise to replace, however I have since found a supplier that rebuilds them in Australia for a third of the cost (Nissan sell them as a complete unit)

 

[Old.Tony]

Welcome to the forum.

Mine's a baby, having only done 34,500km. There are no major issues with mine, but I've noticed some things and learned some things about the way the gearbox works when researching and discussing stuff.

The choice of gear is not made by any mechanical means. Embedded within the sump of the gearbox is a "TCM" - Transmission Control Module. This is the device that is responsible for things like gear changes, engine braking, torque converter locking etc.

The TCM obtains information from the ECU relating to throttle position, brake application, vehicle speed (obtained by averaging the ABS sensor readings) among other things. It also reports things to the ECU like several temperature sensor values and current gear choice.

If you're driving along at a constant speed on flat ground below 70km/h (use the cruise control) and the gearbox is unable to stay in the one gear, then I'd suggest there's an issue with either the TCM itself, or an electrical connection. This connection could be the brake light switch (which is where the ECU gets its information about brake application), or the connectors on the side of the gearbox, or even just the earth connection to the motor (although that would likely cause other issues).

There may be some contaminant that has entered the gearbox at some stage and caused some damage that an oil change can't fix. Has the vehicle ever been submerged, and are the breather hose and gearbox seals intact?

What exactly is being experienced here? Please be precise with the symptoms, eg "driving at 90km/h on a slight uphill and small variations in throttle cause it to change gear when towing 2.5T or more" (and for THAT, I'd say "yep, expected").

No guarantees we can help - it might be pitting in one of the valves inside the gearbox, but at least we might be able to narrow down the possibilities which is better than nothing.

 

[Dave]

If its hunting for gears it could be a sensor playing up or could do with a service of the trans.

However the torque converter rings a bell, I think someone had theres replaced under warrenty.

Dave.

 

[Old.Tony]

The torque converter issue is probably a TCC Solenoid failure or something extremely closely related to it.

At the speeds where the problem is experienced (vibration of the vehicle), the TCC solenoid is active (ON, so the converter is LOCKED) but is being triggered by the ramped-up power from the engine as you're just entering maximum boost range. The TCC solenoid would be engaging and disengaging constantly, thus causing the vibration.

It doesn't happen below 85km/h. The turbo isn't up to speed at this point, but the TCC is ON - the TCC solenoid is activated by the Transmission Control Module at 75km/h or over if the throttle is below 50%. Because there's no vibration at these speeds, I suspect it's because there isn't the power coming into the gearbox.

I've noticed that even on medium throttle (say a third to near a half), if I reach 95km/h or so my TCC will disengage the lock and my tacho will start varying, indicating the torque converter is no longer locked. I have to back off completely (removing the power generated by the turbo boost) for the converter to lock again. It's especially annoying when I'm towing, because I'd like to remain in top with the converter locked, and between 95km/h and 120km/h the thing just won't stay locked. I either have to drop under, or go over - and 130km/h with the whole rig weighing some 4.5 tonnes is a little dangerous, and needlessly wasteful on fuel.

But that's a different issue to this one, I think. I'd like the problem described a little better before trying to really nut it out though.