Nissan Patrol 4x4 (Africa)

I dont know if anybody has read the topic on the Aus. forum about steep descent with an auto.
The guys mention you put it in reverse gear when going down a steep forward descent and control the speed of descent with he accelerator, according to them it works for short descents ect. The only thing you got to check is for the transmission not to overheat.
If I understand the theory correctly , the converter does all the work.Gerrit whats your call on this?
Has anybody done it before?
I personally dont owe an Auto , but will in the near future.
Koos

Could work but how will it impact the torque converter in the long run. I would much rather use the brakes to go down.

Koos, I have heard of this trick, but have never tried it myself. In principal, running the transmission in a gear appropriate to the opposite travel direction won't harm the torque converter (or other parts), but will generate some heat: Effectively the torque converter is performing the function of a retarder and the energy dissipated in maintaining the vehicle's speed down the hill ends up as heat. In my opinion, this heat load will not be severe for the typical short descents (<100m) done in off-highway driving. One would need quite a long and steep descent to send the transmission temperature into the red, but remember that is only a gut feeling.

In order to make a controlled descent, one would have to modulate the braking effect by careful operation of the throttle pedal. If this is not done, the engine might even stall. Of course, controlling descent speed by pressing down onto the throttle pedal to go slower is highly counter intuitive to most drivers and will require some practice in safe circumstances (Dry high grip surface with good run-off area and nothing to hit ).

Another concern with the technique is the fact that some vehicles with electronically controlled transmissions and engines may do strange things when detecting that the vehicle is moving in the "wrong" direction, such as cutting the engine if the vehicle speed is anything higher than a mere crawl (my DiD Pajero is one of them). This could be rather undesireable in a hill descent situation (because you immediately loose steering and braking power assistance, which renders all your carefully learned brake feathering skills totally uncalibrated and leaves you with the engine and drivetrain effectively disconnected from one another), so one needs to be fully aware how the particular transmission will react (by testing in safe circumstances) before using the technique in anger.

I am not sure whether the best results would be obtained in low range or high range.

Another technique that can be used is to drive through the brakes on the descent. The idea is that the drivetrain ensures that the wheels keep turning while you control the descent speed with the left foot. Of course it also takes practice to learn to modulate the brakes with the left foot and some heat is also generated when driving through the brakes. I have experimented with this technique a bit, but am as yet not proficient at the left-foot braking.

Gerrit, very interesting. Still very uncomfortable with the whole idea of the box in reverse, especially wrt what the ECU may decide to do.
Left foot braking on the other hand is very handy way of doing things. I have done it even with my manual GQ. It works really well especially where you have to keep the engine tiking over at very low revs. Right foot keep the engine going and left foot keep the speed down. It is just not natural to press the brake with your left foot. In an auto I am sure you would get used to this very quickly as you dont have to worry about the clutch.

Abri Hoffman wrote:Still very uncomfortable with the whole idea of the box in reverse, especially wrt what the ECU may decide to do.
Left foot braking on the other hand is very handy way of doing things.

Both of these techniques must be practiced in safe circumstances so that one knows what to expect before one needs to use them in "real" situations. Then one would have had the opportunity to get to know the way that the variouos ECUs in the vehicle might react to what is happening and to acquire the necessary car control skills.

The reverse thingy just sounds wrong, if something goes wrong and you need to power out of it, you are in reverse...! I vote for the left foot braking mechanism(hill decent control)

It will be very interesting to see how the ECU react in various situations. Where would we find such a safe playground to test it?

Yes , its strange for me to, but seems to be done.
Thx Gerrit your technical knowledge always let me understand the knitty gritty behind whats going on inside the drive train.
Koos

Interesting WWW