Idle-Jack Dangerous in low range reverse Puma

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Originally Posted by tact

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.

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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.

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Originally Posted by 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!

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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.

I like the anti-stall feature.

Sent from my GT-P5210 using AULRO mobile app

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Originally Posted by DiscoMick

I like the anti-stall feature.

Sent from my GT-P5210 using AULRO mobile app

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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?

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Originally Posted by MrLandy

Appreciate your calculus, but I have to disagree.

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300 rpm over 800 rpm is 37.5% faster!

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Originally Posted by Graeme

300 rpm over 800 rpm is 37.5% faster!

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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

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.

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Originally Posted by 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.

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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

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Originally Posted by MrLandy

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

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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?

Gee impressive tact. Good luck with that.