Thread: Descending Hills - D2 Auto Lockup for braking

Hi Kev,

The app is the same. The module info appears to be read from the Nanocom so you just need to hook up with your existing app.


LR's docs seem to point to HDC being a second tier when engine braking in low 1st alone isn't sufficient to slow the D2, at least when used for steep descents. The reports in this thread seem to back that up.

Regarding TC lockup, the ZF pdf linked in the first post mentions low range TC lockup only occurs when engine revs are above 2000rpm, and there is 0% throttle. In my low range + 1st test, the two times the TC locks are when revs have been above 2000rpm and I've taken my foot off the throttle.

.... would have been nice if I was told that ! Thanks! I get to go play again.

If I remember correctly, in over-run, letting 1st or 2nd low drive the engine, mine locks-up about 1800-1900rpm give or take a bit (with 0% throttle), but when it locks, the revs then climb up sharply (and so they should), before the engine compression hauls the speed down with the locked tc.

Originally Posted by Fluids

.... would have been nice if I was told that ! Thanks! I get to go play again.

You were supposed to guess I think

Originally Posted by Fluids

If I remember correctly, in over-run, letting 1st or 2nd low drive the engine, mine locks-up about 1800-1900rpm give or take a bit (with 0% throttle), but when it locks, the revs then climb up sharply (and so they should), before the engine compression hauls the speed down with the locked tc.

That could be right. The first part of the PDF seems to be more generic coverage of the 4HP22-24, and the Disco II supplement doesn't give a specific lockup figure for 0% throttle. There are 2 versions of the Auto ECU, one fitted to all auto Disco2's and one to the P38 Rangie. According to the BBS website:

the main difference between the two being different shift points, different Gear lever switch inputs, and current gear indicator outputs

The PC app doesn't refresh data display particularly quickly so it's a bit difficult to see the nuances of what is actually going on.

cheers
Paul

...

... yes, I agree

Glad I'm not alone on that point then

Reading back on the RAVE content regarding TC lockup in Low it actually reflects what we are seeing if you replace a "a preset engine speed" with "2000 rpm".

Low range
To enhance off road control, particularly when manoeuvring at low speeds, torque converter lock-up does not occur when there is any degree of throttle opening.
When the throttle is closed above 2000 rpm, the lock-up clutch engages to provide maximum engine braking.

So to answer the original question I posed

I'm interested to find out what combination of control settings are required to lock the TC when descending.

- Low Range
- 0%
- Engine RPM above 2000rpm

The TC lock up in Low Range appears to be primarily designed to aid engine braking when decelerating, rather than to assist when descending. For an auto D2 in Low 1st and running stock tyre sizes 2000 rpm would equate to roughly 9.5km/h with the TC locked.

It worth noting that the D2 owners manual only mentions use of auto positions "1" and "2" in relation to engine braking:

1. Use on very severe gradients, particularly when towing, and when maximum engine braking is required.
2. This position also provides moderate engine braking for descending slopes.

I would concur Paul. That pretty much matches my experience.

Downhill, 0% throttle, Low 1st or 2nd the wheels drive the engine rev's to approx 1800-1900rpm then the TC locks.

Need to test this in High Range now ... just got to find a quiet, really long downhill run. I have one close by.

the bit thats missing is the need to achieve fluid coupling prior to getting on the hill.

if you dont get to the initial fluid coupling point of the TC then it will be "slow" in bringing the engine speed up and achieving the coupling point.

have a play with "driving through the brakes", pick a low box low gear (1 low) just prior to getting onto the descent and actually using engine power to drive over the crest onto the descent while maintaining an even brake pressure then back off the noise and modulate your speed with the brakes (or the HDC)..

get it just right and you wont even notice the engine speed pick up or the TC lock up.