Auto box Soft Sand Problem?

Hi folks
I don't see to many Petrol autos on the forum but have experienced an odd problem with mine and would like to know if anyone can shed some light on it.

The Petrol auto has been great on the sand.....until it hits the really soft deeply rutted track. I have the standard suspension (looking to upgrade soon) so it doesn't take much to start dragging gear, however when its in these conditions and the going is tough the drive through to the wheels seems to be interrupted or reduced. ie if I have stopped in the soft stuff and then try to set off, the engine revs but no wheel movement/drive - and yes its in gear and 4L. it does not rev as freely as if it were in neutral though. First time this happened I thought perhaps the Auto box was overheating but no warning lights on dash. Second time I had to be snatched out. Of course tried to assist but no drive, then after 1st snatch it started to drive but would then stop driving as revs climbed. I found if I throttled off then on again the drive would come back but then fade once more. By 4th snatch I was mostly out of the soft stuff and drive was restored to normal.

I have always had manual diesel 4WD's before so I don't have a lot of experience of auto boxes. Does anyone have any idea why this might be happening?

Next time I head in to a Nissan dealer I will ask them to hook up the computer and see if there are any fault codes or messages that may explain it, apart from this the D40 has been great and returns economy figures almost as good or better than some of the diesels I have read about on the forum. 13.5 to 14L/100 city cycle better on the freeway but thirsty when towing probably about 20L per 100 towing a Ton trailer as aerodynamic as a brick

Cheers
JonO

I'm not sure if there are any warnings for a over heating trans, but that what your symptoms sound like. Very common for any auto 4WD in sand.

There are temperature sensors in the auto transmission and these report to the TCM located inside the gearbox which should report a fault up to the ECU. I've not read where it might indicate that level for the ECU to actually display in real time - someone with a ScanGauge might be able to shed some light on that.

But I have no doubt that:

* Excessive over-temperature conditions in the gearbox may cause the TCM to make adjustments to the gearbox, including encouraging the gearbox input to turn over faster in order to pump the oil around faster. This could be perceived as "slippage".

* Excessive over-temperature responses from the TCM may cause the ECU to enter "limp" mode.

On sand, particularly soft sand, the car has to work a lot harder. Also, because the torque converter won't lock up (TCC solenoid activated) until >70km/h in overdrive, the converter is always slipping therefore generating more heat. Unfortunately autos never do sand as well as manuals.

I would have to check the manual again but I am pretty sure that there is a transmission temp warning on my R51. No idea if it goes into a protective mode before the warning pops up though.

Thanks guys, there I was thinking an auto box would be good for sand as no momentum lost with the manual gear change :-( it certainly drives well on sand until the really soft deep sections.
I appreciate the feedback and will follow it up further with the dealer and see what faults or history the computer logged.

Cheers
JonO

Hi Guys,

I used to have an Ford Explorer V6 auto and had trouble with auto in soft sand. An auto trans specialist advised me to use the auto as if it was a manual in sand by going up through the gears manually. Dropping tyre pressures helps too!!

Hope this helps

Alan

Thanks Alan, I will try that out

We had a similar issue in the mrs's xtrail while at beachport over the long weekend, could possibly be a bad trait with the later model nissan auto gearbox? Or autos in general which personally id rather not use for 4wding. we dropped tyre pressure and that got us out of trouble though (after some digging!)

Autos are not a fixed driveline unless you get the vehicle over 75km/h in overdrive with the throttle below half.

In a manual gearbox, once the clutch pedal is released, one single revolution of the crankshaft equates exactly to one single revolution of the input shaft of the gearbox.

In an automatic, you get something less - I don't know the average percentage slip, but it could easily be 50% judging by the variation in rpm while moving on flat level ground.

Let's assume for the moment that you indeed only get 50% of the revolution transferred to the gearbox. This means the engine has to do twice as many revs to maintain gearbox input that ends up as drive power. Just when you need the power the most, you have half of it and even then it's slippery. This makes the auto box quite unsuitable for sand.

My auto suits me for the driving that I do - mostly forest trails or highway with a 1.8T van behind. If I want to do sand, I'll stick to firm stuff, have my tyres at about 12-14psi and I'll take my time. If I can't do all of those, I won't go there.

A quick update for those interested in this thread.
My Nav just had its 40K service and I asked them to have a close look at the Auto Transmission, change fluid, comment on the adequacy of the oil cooler etc. Incidentally my D40 has a 2 piece set of bash plates that provides cover from the base of the ARB bullbar to the back of the Transmission case. These were supplied and fitted by Opposite Lock 4wd.

Well observation 1) the Nav actually has quite a sizable Auto Transmission Oil Cooler located at the center front. This is almost 100% obscured by the Bash Plate and Bull bar. Solution Drill 20 1inch holes in said Bash Plate to let the air actually reach the oil cooler. (Now why wouldnt the manufacturer of this D40 specific Bash Plate have thought of that?)

Observation 2) the A/T oil has probably been overheated and while not burnt or pungent was a bit black ie overheating has occurred and this probably led to the gearbox power delivery problem reported earlier.

Observation 3) the D40 does have an AT temp sender however this reports to the ECU only and is not readily readable via a ScangaugeII (I have tried). However Wholesale Automatics in Melbourne supply a kit including their own sensor that can be easily fitted to the D40 and will provide the very necessary AT Temp gauge. It cost me $272 including freight (ordered today). They are also producing an upgraded Nomad valve for the D40 with claims it will improve shifting, response, cooling and towing performance.

I will report back when the Temp gauge is fitted and maybe link a picture of that and the Bash plate with the holes drilled (it actually looks quite good and should not impact the structural integrity or strength of the unit.

I am considering the Nomad valve but its a but more exy and I will wait and see what the temp is doing in off road and towing situations.