Idle-Jack Dangerous in low range reverse Puma

[MrLandy]

Originally Posted by MrLandy (in jeep vs defender thread)
"It's low reverse where the problem lies. I had a frightening experience in my Puma, with low range reverse down a steep driveway! It accelerates! Anyone else had this experience?"

Originally posted by Tact:
"Both in low reverse and low first in TDCi defenders: When the clutch pedal is almost fully up the position sensor on the clutch pedal signals and the ECU ramps idle speed up a few hundred rpm

Normal (for TDCi defenders in low range and first/reverse)

That (little) speed increase can give you a scare. But the crawling speed of the vehicle is still damn slow and controlled.

And yes... If you press the brake (only) to stop the vehicle when it's motoring in low range 1st/rev (on slope or level ground!) it's not going to stop easily!"
__________________
Neil
(Really shouldn't be a...) Grumpy old fart!
MY2013 2.2l TDCi Dual Cab Ute


Hey Tact, I've moved this post over here bc this is important and has nothing to do with jeep comparo. (Mods, sorry you may want to move this again, or move our other related posts?)

So your experience is that low range reverse is slow low enough? But then getting into low reverse on a steep hill the idle jack gives a burst as you take foot off clutch. My experience is that this is very dangerous!

And to stop in such a situation all you can do is jump on the brakes! Then the clutch and then you lose all traction.

Low reverse may be ok in some circumstances, but starting in low reverse down a steep hill is frightening! I think it's a serious issue. Obviously my Tdi would never do that and has heaps of compression to safely start in low reverse on a hill.

There needs to be a way to shut idle jack off in certain circumstances. I suggested in other thread that perhaps it could somehow become part of a remap. Not sure how viable this might be...maybe Pete Bell can answer?

[tact]

Yeah I reckon the low reverse on a TDCi is plenty low. In the situation you describe. On the hill and stopped, low range and reverse selected, I just let the clutch and brake go and it starts off super slow and when the idle Jack feature raises the idle speed a second or three later you speed up a little - but still plenty slow. It's like engine idle was 800rpm and ups to 1000 (ish?)

On the worst slopes where you key off or stall stop. Select reverse, key it started, and again you reverse nice and slow.

I don't doubt your experiences. I know what my experiences are. Just cannot figure why there is any difference.

[tact]

The only dangerous part of the idle Jack feature is when a driver doesn't know about it .... Is in low 1st/rev, trying to move millimetre by millimetre super carefully. When the clutch pedal is below a certain point the activity goes to plan, but a second or two after the clutch reaches a point up its travel and the idle speed gets a 200-300rpm boost, if sure does FEEL like a sudden uncontrolled surge - scares the proverbial out of a man.

But it's not an uncontrolled surge. It's a gentle raising of idle engine speed by 200-300rpm.

In normal operation, low 1st or low rev, the vehicle speed is fine on steep stuff, up or down.

[debruiser]

I use low range to reverse trailers, yes it's cheating. I know it's going to lift the revs and drive accordingly. I guess going downhill ti could be a bit of a pain though.

I don't remember mine doing it going downhill though; for REALLY steep hills - I'm talking stuff on the passenger seat falls on floor steep. Maybe I was too busy clenching... :wasntme:

[cuppabillytea]

It hasn't bothered me yet but I've been driving clutch versus break at idle for decades.

[alien]

It is something I've got used to now.
I also use low range for backing most trailers, it actually allows you concentrate in the mirrors with out fear of stalling.
Off road it will idle over rocks, ruts, and fallen branches with the anti stall trying to maintain 1'000rpm.
On downhill decents I find 1st is quite low and the anti stall is helpful as I drop in and out of ruts to chose the best line.

[MrLandy]

I agree it's fine going forward, so far. But Interesting that you don't mind that lurching out of the blocks experience in reverse Tact. ...I think it's something that needs to be addressed / disabled when in reverse gear. The 2.2 should have enough compression to keep running in low reverse without the idle-jack function. My TDI has no problem with doing so. ...I had a frightening experience in my Puma, with low range reverse on a steep slippery driveway! Rather than a slow controlled uptake in low reverse, with the engine braking keeping the descent safe and steady, it lurches back when idle-jack kicks in and accelerates! ...Anyone else had this experience?

[tact]

I agree it's fine going forward, so far. But Interesting that you don't mind that lurching out of the blocks experience in reverse Tact. ...I think it's something that needs to be addressed / disabled when in reverse gear. The 2.2 should have enough compression to keep running in low reverse without the idle-jack function.

Just to be clear. My TDCi doesn't "launch out of the blocks" in reverse. Reverse or 1st in low range behave the same: There is a raising of idle from around 800rpm to around 1000rpm a second or two after the clutch pedal is fully up.

Jacking the idle speed up a few hundred rpm has nothing to do with compression or lack thereof. It is about ensuring the vehicle speed is not too slow for good control on very slippery descents. Thats a LR decision. Not a bad decision I think.

There are times when maybe it would be nice to be able to over ride the feature. Like when trying to maneuver in millimetre precision through tight spots. But knowing how and when idle Jack kicks in mitigates this need somewhat.


Edit: MrLandy - quick check. When the vehicle seemed to have not enough compression and "lurched off" ... Did you have the centre diff locked? Steep slippery descents (low first or low reverse) will see you careening downhill if just one wheel loses traction while CDL is unlocked.

[tact]

My driving style on steep slippery downhills is to generally "trust the vehicle" by keeping feet off pedals and just steer. CDL locked of course.

If I touch a pedal at all it will be the accelerator, counter intuitive as that may be, to bring things back under control if any slippage occurs.

I have done long greasy slippery clay downhills where there is wheel slip all the way down. But keep the wheels turning all the way, driving the throttle, blipping throttle now and then to get some semblance of steerage. A bit like driving a jet boat - no rudder - you have to hit the throttle with wheel turned to get any change in direction.

On steep rock/shale downhills - again no feet on pedals. Trust the vehicle and steer. So long as the nose is steered/pointed downhill (steering into tipping moments) the savior in sphincter moments is always "Our Blessed Lady of Acceleration".

again - all the above goes out the window if you are needing to creep/crawl through tight spots with millimeters between your vehicle and panel damage - if you care about that.

[Gerokent]

I've had the idle up come on in a car park several times, in high range :eek:

[alien]

Having not read the RAVE cd I bought from Dave's shop I'm going to have guess.

The idle up would require a low range signal and use the clutch fluid preasure switch.
When in low range has anyone tried pulling a wire from the clutch switch under the bonnet?
This switch is used for the cruise control I fitted and works on gear changes but not on a light touch of the pedal which is why I'm making the suggestion.
If it works it would not be hard to rig a dash mounted inline switch to disable the switch when required.

Just a thought.

[tact]

Another drop dead cool feature of the TDCi (off-road) comes as a byproduct of the way the throttle never seems to snap quickly back to zero. Instead it gradually reduces.

Likely this is an anti pollution thing. Throttle positioners are even on petrol engines going back a few decades.

But on those looooong slippy slidey, wheels always slipping slopes where I described turning the steering and blipping the throttle to get some kind of steerage way... It's great to be able to blip throttle and know it will slowly droop back to lower revs itself. This is how you keep any little grip you caught and bring vehicle speed back down again.

In a vehicle without this kind of feature you have emulate this with right foot. If the throttle (and with it the road wheels) suddenly drop back to idle speed the sudden action gives away any grip you gained by the blipping of the throttle.

See it in action easily. You are cruising along and lift throttle. At first it's like you don't have much compression braking. But then gradually the compression braking increases. Blip the throttle and immediately it seems you don't have a lot of compression braking again... But it comes.

[tact]

Having not read the RAVE cd I bought from Dave's shop I'm going to have guess.

The idle up would require a low range signal and use the clutch fluid preasure switch.
When in low range has anyone tried pulling a wire from the clutch switch under the bonnet?
This switch is used for the cruise control I fitted and works on gear changes but not on a light touch of the pedal which is why I'm making the suggestion.
If it works it would not be hard to rig a dash mounted inline switch to disable the switch when required.

Just a thought.

The idle Jack feature (not anti stall) requires all the following to be true:
- low range selected
- first or reverse gear selected
- clutch pedal close to fully up

There has to be switches/sensors on t'fer lever or box, main shift lever or box, and the clutch pedal to detect it's near top of movement.

Defeating any of those sensors may do the job.

Not sure which is the best to tackle. Likely stay away from the t'fer case/shift sensor/switch as this one is likely also used as ECU input for the changed throttle curves when in low range

(When low range is selected the throttle response curves are vastly different to when in high range)

You'd stay away from the main shift sensor too. I guess you'd want this to still work so reverse light and sensors all keep working.

[Col 110]

So - I have learnt this when in carparks with speed humps - when you approach a (killer) speed hump you need to time the 'lift' of the throttle - when you get it right in 2nd it slows perfectly to get over the speed hump to then go again for the next one.

At first I thought I had no engine compression - then I learn't that it holds the rev's to a point - then it it drops and the engine compression shows up.

Perhaps I am nuts - but I enjoy this in the Defender!


Another drop dead cool feature of the TDCi (off-road) comes as a byproduct of the way the throttle never seems to snap quickly back to zero. Instead it gradually reduces.

See it in action easily. You are cruising along and lift throttle. At first it's like you don't have much compression braking. But then gradually the compression braking increases. .

[tact]

At first I thought I had no engine compression - then I learn't that it holds the rev's to a point - then it it drops and the engine compression shows up.

Perhaps I am nuts - but I enjoy this in the Defender!

Not nuts at all. Enlightened. I enjoy it on road and love it off-road.

[debruiser]

Not nuts at all. Enlightened. I enjoy it on road and love it off-road.

Handy offroad, but I would prefer it to drop a fair bit quicker on road, but there again I don't like using brakes :p

[manofaus]

Just wondering when you are crawling along and the idle jack feature is being used why the brake pedal does not cut out this feature, at least back to low idle. Surley the abs and traction control would be able to sort it out instead of the engine providing a constant rpm or are the wheels turning too slowly to enable use of the supplementary systems.

[tact]

Just wondering when you are crawling along and the idle jack feature is being used why the brake pedal does not cut out this feature, at least back to low idle. Surley the abs and traction control would be able to sort it out instead of the engine providing a constant rpm or are the wheels turning too slowly to enable use of the supplementary systems.

Apparently the LR thinking is that when in low 1st/rev the gear ratios in the TDCi result in the wheels turning too slowly for a safe descent in loose/slippery conditions - when engine is ticking over at normal idle speed (~800rpm).

LR solution: bump engine idle speed up to ~1000-1100 rpm to raise vehicle speed at idle to something similar to the earlier Defenders.

Just guessing: If the above is all true (paraphrased: 800rpm in low first/rev is "unsafe") then allowing provision to drop idle rpm back to 800rpm is unsafe.

Am not advocating or defending the thinking. Just regurgitating what I gleaned from several different reading sources.

Edit: certainly in that use case (steep slippery downhill) brakes are a bad thing to touch!
Our Blessed Lady of Acceleration is the patron saint for this use case.

[MrLandy]

Apparently the LR thinking is that when in low 1st/rev the gear ratios in the TDCi result in the wheels turning too slowly for a safe descent in loose/slippery conditions - when engine is ticking over at normal idle speed (~800rpm).

LR solution: bump engine idle speed up to ~1000-1100 rpm to raise vehicle speed at idle to something similar to the earlier Defenders.

Just guessing: If the above is all true (paraphrased: 800rpm in low first/rev is "unsafe") then allowing provision to drop idle rpm back to 800rpm is unsafe.

Am not advocating or defending the thinking. Just regurgitating what I gleaned from several different reading sources.

Edit: certainly in that use case (steep slippery downhill) brakes are a bad thing to touch!
Our Blessed Lady of Acceleration is the patron saint for this use case.

Not if the idle-jack is forcing you to go too fast in reverse down a very steep slippery hill and you're headed for a rock wall! Brake! Nothing! Clutch in Brake! Slide! **** that was close! Give me no idle-jack compression anytime.

[tact]

Not if the idle-jack is forcing you to go too fast in reverse down a very steep slippery hill and you're headed for a rock wall! Brake! Nothing! Clutch in Brake! Slide! **** that was close! Give me no idle-jack compression anytime.

Mate. The difference between 800rpm and 1100rpm is 300rpm. (To be generous - the real numbers likely end up less than 300rpm difference.

300 on 800 is ~27% difference.

I don't know what speed the vehicle would be doing in low reverse. But a 27% speed increase looks like this:
2km/h at 800rpm becomes 2.54km/h at 1100rpm
3km/h at 800rpm becomes 3.81km/h at 1100rpm
4km/h at 800rpm becomes 5.08km/h at 1100rpm
5km/h at 800rpm becomes 6.35km/h at 1100rpm

I would guess the actual vehicle speed in low reverse is closer to 3km/h than 6km/h. Not a lot of difference at such slow speeds.

If you are in such a tight spot near a rock wall in your direction of travel that the difference between 3km/h and 3.81km/h makes safe progress turn into unsafe progress - you are already in a bad situation before the descent started.

[MrLandy]

Mate. The difference between 800rpm and 1100rpm is 300rpm. (To be generous - the real numbers likely end up less than 300rpm difference.

300 on 800 is ~27% difference.

I don't know what speed the vehicle would be doing in low reverse. But a 27% speed increase looks like this:
2km/h at 800rpm becomes 2.54km/h at 1100rpm
3km/h at 800rpm becomes 3.81km/h at 1100rpm
4km/h at 800rpm becomes 5.08km/h at 1100rpm
5km/h at 800rpm becomes 6.35km/h at 1100rpm

I would guess the actual vehicle speed in low reverse is closer to 3km/h than 6km/h. Not a lot of difference at such slow speeds.

If you are in such a tight spot near a rock wall in your direction of travel that the difference between 3km/h and 3.81km/h makes safe progress turn into unsafe progress - you are already in a bad situation before the descent started.

Appreciate your calculus, but I have to disagree. 25% faster, suddenly, in reverse and no brakes because of idle jack is not acceptable. I only came near the rock wall because I had no choice but to drop the clutch, stand on the brakes and slide to a stop. The lurch backwards as you lift the clutch in low reverse is a problem no matter how you look at it.

Now that I know I need to allow time and space for the idle jack lurch, I would have been safer in high reverse.

[cuppabillytea]

So - I have learnt this when in carparks with speed humps - when you approach a (killer) speed hump you need to time the 'lift' of the throttle - when you get it right in 2nd it slows perfectly to get over the speed hump to then go again for the next one.

At first I thought I had no engine compression - then I learn't that it holds the rev's to a point - then it it drops and the engine compression shows up.

Perhaps I am nuts - but I enjoy this in the Defender!

Not nuts I enjoy it too......... Except when I've been driving something else and forget to do it. Its sends a shiver up my spine when that happens.

[DiscoMick]

I like the anti-stall feature.

Sent from my GT-P5210 using AULRO mobile app

[MrLandy]

I like the anti-stall feature.

Sent from my GT-P5210 using AULRO mobile app

Yes I should say I like it too in certain circumstances, but not in low reverse.
The rev holding feature can be good and takes getting used to - letting clutch fully up before accelerator - for gear changes, but it is also inconsistent at times while changing gears, sometimes it's great, but it can also be non existent ...bizarrely I find it often disappears when changing from 1st to 2nd. Perhaps BAS remap fixes some of this?

[Graeme]

Appreciate your calculus, but I have to disagree.300 rpm over 800 rpm is 37.5% faster!

[tact]

300 rpm over 800 rpm is 37.5% faster!

Yes you are right.
So instead of 2km/h @ 800rpm becoming 2.54km/h @ 1100rpm, it should be 2.75km/h.

Which actual experimentation on the ground pretty much confirms:

I took a little time this afternoon to try and put to bed any such errors and "calculus" distractions.

The attached image refers:
On level ground at 1100rpm idling in low first - 3km/h
On level ground at 1100rpm idling in low reverse - 3km/h
On a steep hill (20 degrees) at 1100rpm idling in low first - 3km/h
On a steep hill (20 degrees) at 1100rpm idling in low reverse - 3km/h

(All above tests: started from a standstill, feet off all pedals, and regards the hill tests - didn't matter going up or down)

Standing on the brakes to drop revs to 800rpm in low reverse or low first - 2km/h

[tact]

If this bit of trivia helps:

While idle speed is 800rpm when in neutral, or in gear but clutch disengaged, when you are idling along in high range the engine speed is raised to 900rpm.

In high range first or reverse, on level ground, start from standstill, feet off all pedals: 900rpm and 6km/h. Exactly double low range. Must check ratios and see if that agrees.

[MrLandy]

If this bit of trivia helps:

While idle speed is 800rpm when in neutral, or in gear but clutch disengaged, when you are idling along in high range the engine speed is raised to 900rpm.

In high range first or reverse, on level ground, start from standstill, feet off all pedals: 900rpm and 6km/h. Exactly double low range. Must check ratios and see if that agrees.

Yeah but in high reverse, it doesn't artificially jump out of the blocks suddenly and disable the brakes! Give me 6km/hr, full control and brakes eased off from stand still over that anytime.

Ps: still loving your calculus tact 😝 Cheers mate

[tact]

Yeah but in high reverse, it doesn't artificially jump out of the blocks suddenly and disable the brakes! Give me 6km/hr, full control and brakes eased off from stand still over that anytime.

Ps: still loving your calculus tact �� Cheers mate

So there it is. The real issue is your vehicle apparently "jumps out of the blocks suddenly and disables the brakes" when in low range.

Mine does not. The transition from 800rpm to 1100rpm is so smooth it's usually barely perceptible.

Not shooting at you Mr Landy or denying your experiences. I just don't understand the differences in vehicle behavior:
- is there a fault in your vehicle, or is mine faulty?
- is it the BAS tune I run?
- is it a difference in tyre sizes? (I run 33")
- is it the driver is the difference?

I'd love to know.

Anyone else experience their vehicle "jumps out of the blocks suddenly and disables the brakes" when in low range reverse gear?

[MrLandy]

Gee impressive tact. Good luck with that.

[FV1601]

I assume that my 2010 2.4 shares some of these features, certainly in reverse low range. I also had the backing the trailer (empty) down a steep gravel and wet leaf hill experience when the Landy accelerated, almost Jack knifed before I could stop. Scared the Bejesus out of me.
Rich.

[MrLandy]

I assume that my 2010 2.4 shares some of these features, certainly in reverse low range. I also had the backing the trailer (empty) down a steep gravel and wet leaf hill experience when the Landy accelerated, almost Jack knifed before I could stop. Scared the Bejesus out of me.
Rich.

Cheers Rich. Sounds very similar. It's definitely a problem in certain circumstances.

[cuppabillytea]

Cheers Rich. Sounds very similar. It's definitely a problem in certain circumstances.
On the other hand, if you are reversing up hill on gravel or dirt with large rocks and ruts it is a definite bonus. Now that you're aware of this feature it probably won't effect you adversely again, because as soon as you reach the point where you know it kicks in you will automatically depress the clutch. You won't even have to think about it.

Cheers, Billy.

[MrLandy]

On the other hand, if you are reversing up hill on gravel or dirt with large rocks and ruts it is a definite bonus. Now that you're aware of this feature it probably won't effect you adversely again, because as soon as you reach the point where you know it kicks in you will automatically depress the clutch. You won't even have to think about it.

Cheers, Billy.

Yes like anything you get used to it (or you just don't use it!). But it's good for others to know in advance...

Cheers CBT :)

[cuppabillytea]

Yes like anything you get used to it (or you just don't use it!). But it's good for others to know in advance...

Cheers CBT :)

Yes indeed. You do them a big favour.

[FV1601]

Revisiting an old thread I know, but has anyone actually found reference to the idle jack in the drivers handbook or associated material?
Or are we all supposed to learn the hard way? ( and then search AULRO...)


On the plus side, after my scary introduction (reversing empty trailer down steep gravel/wet leaves scenario) I have been experimenting with it of late after fitting the lockers, and the combination is quite impressive.
Rich.

[debruiser]

Revisiting an old thread I know, but has anyone actually found reference to the idle jack in the drivers handbook or associated material?
Or are we all supposed to learn the hard way? ( and then search AULRO...)


On the plus side, after my scary introduction (reversing empty trailer down steep gravel/wet leaves scenario) I have been experimenting with it of late after fitting the lockers, and the combination is quite impressive.
Rich.

the feature is a very useful tool offroad... the car will climb by itself with only steering input needed! I love it... makes me look like a genius and makes my 90 look like a weapon hahahaha

[tact]

Revisiting an old thread I know, but has anyone actually found reference to the idle jack in the drivers handbook or associated material?
Or are we all supposed to learn the hard way? ( and then search AULRO...)


On the plus side, after my scary introduction (reversing empty trailer down steep gravel/wet leaves scenario) I have been experimenting with it of late after fitting the lockers, and the combination is quite impressive.
Rich.

Am still stunned you and others have had an issue with this. In my vehicle, after selecting low range, selecting reverse/first, letting out the clutch normally, the transition from around 800rpm (normal idle) to 1100 rpm (jacked up idle) is barely perceptible, gradual, controlled and smooth. Even when at 1100 rpm even the slowest garden snails leave me in their dust.

I should video it and share it....

If yours lurches off dangerously there has to be a fault somewhere and needs a warranty fix!

[tact]

the feature is a very useful tool offroad... the car will climb by itself with only steering input needed! I love it... makes me look like a genius and makes my 90 look like a weapon hahahaha

Thats anti-stall.

Idle Jack kicks in only in low first or low reverse after the clutch pedal is fully raised. You should then notice your idle speed goes up a few hundred rpm. (Normal is around 800rpm. It goes up to about 1100rpm in the above circumstances).

If you so much as touch the clutch pedal the idle speed will drop again to 800 in a few seconds.

The reason given for raising the idle speed when motoring along in low first and low reverse is that those gear ratios result in too slow a rate of turn at the wheels for safe descents on slippery hills

[Col 110]

Thats anti-stall.

[SNIP]


And I also love Anti-Stall - great feature - not just off road but also when doing hill starts in traffic!

[Col 110]

Am still stunned you and others have had an issue with this. In my vehicle, after selecting low range, selecting reverse/first, letting out the clutch normally, the transition from around 800rpm (normal idle) to 1100 rpm (jacked up idle) is barely perceptible, gradual, controlled and smooth. Even when at 1100 rpm even the slowest garden snails leave me in their dust.

I should video it and share it....

If yours lurches off dangerously there has to be a fault somewhere and needs a warranty fix!
So - I do get a slight lurch in high range in reverse when going down my driveway - nothing serious but it is there (and my driveway does not need low range).

I'll need to go out and test the low range when engaging the clutch in reverse.

Recently I attended a LROC Sydney training day where we did a hill stall recovery i.e. drive up a steep hill - pretend to stall (i.e. break and then stop engine) - put it in reverse (low range) - no hand break - take feet off the peddles - and start the engine = very smooth decent - no lurch at all.

Not sure what result I would get being half way up the hill and stop - with engine running and then selecting reverse (low range) - taking the foot off the break and letting the clutch out to go in low reverse - i.e. would I get a "lurch"?

May need to depend on brake / clutch operation

Note: if I had to start a steep reverse down hill decent (be it a drive way or other) - I would do it using the method taught on the course i.e. start the car in low range reverse gear and feet off the pedals

Cheers,
Col.

[FV1601]

Tact/Neil
Please don't feel stunned about me!
The concern raised in that post was why information about this feature/s was not presented in the drivers handbook (I have not yet found reference to it anyway) as this is new technology for many.
Do I have both idle-jack and anti stall, or just one of them,etc.
After sliding down 100m of clay at Mt Stanley on the weekend, I can assure you that any extra revs provided were not appreciated.
Rich.

[MrLandy]

Am still stunned you and others have had an issue with this. In my vehicle, after selecting low range, selecting reverse/first, letting out the clutch normally, the transition from around 800rpm (normal idle) to 1100 rpm (jacked up idle) is barely perceptible, gradual, controlled and smooth. Even when at 1100 rpm even the slowest garden snails leave me in their dust.

I should video it and share it....

If yours lurches off dangerously there has to be a fault somewhere and needs a warranty fix!

Hey Neil, in my experience it's not so much that it lurches in low reverse, but that when reversing down hill in low the idle jack acceleration can be dangerous because it makes low reverse faster than it should be and it strongly resists braking. I have found that in low reverse on a steep driveway, when I tried to slow the vehicle by applying the brakes, the idle jack fought the brakes, artificially keeping engine revs / speed relatively high. Obviously it would be better not to touch the brakes in this situation, but the vehicle speed was way too fast for a safe descent ...Now I never reverse downhill in low.

In my 300tdi, low reverse is entirely predictable, allows engine braking to hold the vehicle back and is also responsive to the foot brake. In the Tdci engine braking and foot brake are strongly counteracted by the idle jack.

[tact]

Tact/Neil
Pleas don't feel stunned about me!
The concern raised in that post was why information about this feature/s was not presented in the drivers handbook (I have not yet found reference to it anyway) as this is new technology for many.
Do I have both idle-jack and anti stall, or just one of them,etc.
After sliding down 100m of clay at Mt Stanley on the weekend, I can assure you that any extra revs provided were not appreciated.
Rich.

It's not documented in the owner's manual or even the workshop manual as far as I can see.

My experience with the vehicle speed when idling along in low reverse or low first is that it is very slow! Slow enough for even the steepest slippery slopes you'd want to tackle. (And here in Malaysian rainforests/jungle we get some fantastic, looooong, steeeeeep, slippery slopes).

What I have found is that on the steepest long greasy descents your wheels have almost no traction at all and basically are sliding all the way down anyway. With the wheels turning at something approximating vehicle actual speed (as opposed to being locked up on brakes or turning way too slow) you do get enough traction to see steering inputs have an effect.

In fact many times I use a technique more often used to maneuver a boat - turn the steering where you want to go and give the throttle a bit of a blip, turn steering agin and blip throttle again... when the vehicle is pointing where you want give it a little longer blip of throttle. Back to idle. Wash/rinse/repeat to the bottom of the hill.

With wheels not rotating at all, or rotating way too slow and arguably not much difference to not rotating at all, of course you just slide uncontrolled down the entire hill.

Related to idle Jack and anti stall, though not getting as much attention, is that the throttle return after a blipping as described above is a very controlled and slow affair before getting back down to idle revs. This slowing of the throttle return to idle is GOLD in the slippery downhill described above. Imagine this:
- you are sliding downhill, blip throttle to get some tyre bite and steerage. If after the blip your engine instantly goes back to idle speed (huge compression) as would be the case in older diesels without electrickery - you instantly break the traction you had for a moment. Been there, done that (in toyotas). You need skills to blip throttle just right and then with your right foot slowly reduce revs again
- the TDCi does that last bit for you. Your right foot can hit/release throttle as roughly/fast as you like and the ECU ensures a nice gradual return to idles revs after every blip.

[tact]

Who here has a TDCi and a TDI? Can you do a slow race for us as an interesting comparo?
Which vehicle is slower at idle in first low?
Which vehicle is slower at idle in reverse low?

One of the assertions made to explain the need for idle Jack on TDCis is that it compensates for lower gearing and brings the vehicle speed back UP to what older models would do in low range.

A "slow race" between two stock tyred/geared defenders (TDCi/TDI) would close the book empirically on whether TDCi speed at idle is too fast.

[DiscoMick]

I used to have a Tdi Disco but it was an auto so not comparable to a manual. The auto was too fast downhill, even in low first.
All I can say is the idle jack/anti-stall on the TDCi hasn't been a problem for me. In fact, low first is so low that at times I've had to accelerate to keep moving downhill at the desired speed.
I haven't noticed a problem in reverse, even on a steep 4WD course near Lismore a while ago. The anti-stall certainly seems to do a lot to prevent it stalling on a steep climb, which makes backing downhill a less frequent problem.
Interested to hear others' experiences.

[MrLandy]

Who here has a TDCi and a TDI? Can you do a slow race for us as an interesting comparo?
Which vehicle is slower at idle in first low?
Which vehicle is slower at idle in reverse low?

One of the assertions made to explain the need for idle Jack on TDCis is that it compensates for lower gearing and brings the vehicle speed back UP to what older models would do in low range.

A "slow race" between two stock tyred/geared defenders (TDCi/TDI) would close the book empirically on whether TDCi speed at idle is too fast.

My post above describes exactly that comparison. 300tdi is definately slower and safer in low reverse than Tdci in my experience. First low forward in Tdci is excellent, slightly better than Tdi. I've never had an issue with either in low first forward.

[tact]

My post above describes exactly that comparison. 300tdi is definately slower and safer in low reverse than Tdci in my experience. First low forward in Tdci is excellent, slightly better than Tdi. I've never had an issue with either in low first forward.

Reverse gear is slightly taller than 1st in the TDCi gearbox. (Ratios below).
(Edit: as is the case for some R380 and LT95 boxes as fitted to some older landys - so a quick Google reveals)

Will be interesting to get a real measure how TDCi compares to the speed of a TDi in low reverse. (As there may be ratio differences elsewhere in the drivetrain)

Gearbox ratios:
1st 2nd 3rd 4th 5th 6th Rev
5.441 2.840 1.721 1.223 1.00 0.742 4.935

[tact]

Who here has a TDCi and a TDI? Can you do a slow race for us as an interesting comparo?
Which vehicle is slower at idle in first low?
Which vehicle is slower at idle in reverse low?

One of the assertions made to explain the need for idle Jack on TDCis is that it compensates for lower gearing and brings the vehicle speed back UP to what older models would do in low range.

A "slow race" between two stock tyred/geared defenders (TDCi/TDI) would close the book empirically on whether TDCi speed at idle is too fast.

http://www.aulro.com/afvb/90-110-130-defender-county/240601-defender-slow-race-tdci-vs-tdi.html#post2584448

[PAT303]

Tact/Neil
Please don't feel stunned about me!
The concern raised in that post was why information about this feature/s was not presented in the drivers handbook (I have not yet found reference to it anyway) as this is new technology for many.
Do I have both idle-jack and anti stall, or just one of them,etc.
After sliding down 100m of clay at Mt Stanley on the weekend, I can assure you that any extra revs provided were not appreciated.
Rich.

Nothings going to help you there except snow chains,pumping up the rev's is an old trick when sliding down a slope but your seriously in the crap in that situation. Pat

[PAT303]

I think one problem is that people could be over driving their vehicles,try driving without doing anything but steer and see how you go. Pat

[DiscoMick]

So it appears from the above posts that the TDCi is slower than the Tdi in low first forwards, but the Tdi is slower in low first reverse - is that right?

[tact]

So it appears from the above posts that the TDCi is slower than the Tdi in low first forwards, but the Tdi is slower in low first reverse - is that right?

Yeah it seems to be the case. (Check latest posts in the slow race thread).

[tact]

As revelation progresses, or goal posts move, it seems more likely that MrLandy is describing a perception that maybe the TDCi doesn't have the same level of available compression braking as the TDi, MrLandy mentions the wonderfully controlled and predictable compression braking of the TDi (contrasted to TDCi) in an earlier post. However:
- it is clear that overall gearing in the TDCi is lower than the TDi for both low first and low reverse.
- it is very likely true that the vehicle speed of the TDCi at engine idle in low first and low reverse is slower than the TDi (even when the TDCi idle is jacked to 1100rpm against the TDi running 800rpm)
(Hasn't been "slow-race tested")
- but the question is asked, does all this hold true on a steep sloping driveway (where of course the available compression braking will come into play)

So the focus is now on whether the TDCi is lacking in the compression braking department.

My experience (not empirical) is that on the steepest high traction slopes reversing at idle in low reverse gear - my 110 doesn't lack for any compression braking. Speed doesn't run away.

What I do notice is that if I were to feed in some throttle to go faster and then release the throttle - the TDCi takes its merry time to slow right back to crawl speed (idle revs - 1100rpm). This can sure give the impression the TDCi lacks in the compression braking dept. but if you wait a bit....

This is a result of that other undocumented feature I wrote about earlier, and if on slippery slopes is much valued!

In really tight situations like reversing a trailer down a steep slope - it may not be so appreciated.

[jx2mad]

You should try a stall recovery in a rural fire service truck! You have to start the engine with the gearbox in reverse and of course low range. It frightens the hell out of new recruits sitting in the back as it takes off backwards down the incline before the gearbox slows it down. The look on their faces reminds you of the first time you were in their position .:eek::eek:

[tact]

[...]Recently I attended a LROC Sydney training day
[...]
:thumbsup:



Not sure what result I would get being half way up the hill and stop - with engine running and then selecting reverse (low range) - taking the foot off the break and letting the clutch out to go in low reverse - i.e. would I get a "lurch"?

May need to depend on brake / clutch operation

You got it right - Depends on how good you are coordinating brake/clutch. If the slope is really steep getting it wrong can be disastrous.

One technique that can limit the risk is to "drive through the brakes". ie a bit like what happens when you forget to release parking brake and drive off, then release the brakes.

Hard to do if you are in a sphincter clenching situation so stick to the engine off approach. ;)

[tact]

(Sidetrack - Heheh... Sphincter clenching:
Have you ever been in such a scary situation, on a such a steep lean, that if you relax the sphincter your butt loses traction and you slip off your seat!)

:twisted:

[debruiser]

(Sidetrack - Heheh... Sphincter clenching:
Have you ever been in such a scary situation, on a such a steep lean, that if you relax the sphincter your butt loses traction and you slip off your seat!)

:twisted:

hahah yes... forward and backward too..... although forward you have to stand on the firewall.... :D

[tact]

Likely these posts belong here more than over there:
http://www.aulro.com/afvb/90-110-130-defender-county/240601-defender-slow-race-tdci-vs-tdi-2.html#post2585331

http://www.aulro.com/afvb/90-110-130-defender-county/240601-defender-slow-race-tdci-vs-tdi-2.html#post2585386