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BigJimnyMeet (North) 2024 (12 Jan 2024)


BigJimnyMeet 2024

14th July 2024
Parkwood Nr. Leeds

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For those who have an auto

  • Lambert
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19 Apr 2024 14:18 #255666 by Lambert
Whatcha auto fam. I am partial to watching rock crawling especially in Moab.  What I'm noticing is that many of the drivers are left foot braking which I don't regularly do.  Apparently they use it as a means of  maintaining loading on the transmission for technical climbs to avoid the vehicle rolling back and also avoiding shock loading. Essentially you keep the revs on with your right foot and control your progress with your left.  Is this something that is new only to me and I should be putting time into mastering? 

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
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19 Apr 2024 14:51 #255667 by Roger Fairclough
I used left foot braking when I was trialling my SJ. This had a manual box but I see no reason that the technique cannot be used with an auto. Basically it is used as a simple traction control. You con the diffs. into the belief that there is equal traction on each wheel by braking, with the left foot, whilst applying power with the right. It might sound a bit Heath Robinson but it really does work and the modern traction control system is just a copy of the idea. As the Jimny Gen 3 and 4 already have traction control, however crude, do you need to try left foot braking? Maybe the Moab drivers do not have traction control. I would class a lockable diff. as all or nothing with a good traction control as variable.

Roger

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19 Apr 2024 18:17 #255674 by LesNewell
I have to admit that technique is new to me as well. I suspect it's one of those things that you need to try to see if it works for your particular driving style. I can see it being useful as you go over a large lump. It would stop the car lurching forward.
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19 Apr 2024 19:13 #255679 by Lambert
Replied by Lambert on topic For those who have an auto
I think that is more what it's about is control rather than traction and round here lanes are rock and quite technical rather than swamps. I will have to have a practice.

Temeraire (2018 quasar grey automatic)
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19 Apr 2024 19:20 - 19 Apr 2024 19:23 #255680 by facade
Replied by facade on topic For those who have an auto
I don't rock crawl, but I've been left foot braking on the roads in autos for about 40 years.

Apparently, it is Really Dangerous, I don't see why. The worst that can happen is in an emergency I get all confusicated and press the brake with both feet, but the ABS will deal with that. I suppose I could imagine I was driving a manual and press it like it was a clutch, but I did that 40 years ago, and you don't do it again.

I can drive a manual, but I don't like it, my left foot can work brakes or clutches (and gear shifters), I suppose it is only the same as the right one can work accelerators, and brakes in cars and on 'bikes, and my left hand can do clutches and brakes.

The only time I had a problem was when I had a Vectra auto.

This had the great idea of dropping into neutral when the brake lights were on at idle.
Right foot brakers would lift off and whilst they were moving to the accelerator it could drop back into gear.

I start off by mashing the accelerator into the floor and lifting off the brake at the same time, so the vectra would go CLANG!!!!! every time as it jolted back into gear at about 2000 RPM.

I assume I wasn't the only person doing it as that "feature" seems to have faded away.....


The transmission loading thing I did when I took my part 1 test on a honda 90, wind on constant throttle and control the speed with the brake so it kept the clutch engaged and there was only one control to worry about doing figure 8s round the cones.





 

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)
Last edit: 19 Apr 2024 19:23 by facade.
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19 Apr 2024 20:29 #255683 by 300bhpton

Whatcha auto fam. I am partial to watching rock crawling especially in Moab.  What I'm noticing is that many of the drivers are left foot braking which I don't regularly do.  Apparently they use it as a means of  maintaining loading on the transmission for technical climbs to avoid the vehicle rolling back and also avoiding shock loading. Essentially you keep the revs on with your right foot and control your progress with your left.  Is this something that is new only to me and I should be putting time into mastering? 
Ultimately I'd say no, probably not worth it unless you want to invest the time. Don't get me wrong, I think it has a purpose. The slack that the torque converter needs in order to make the wheels move can be hard to judge, aka unpredictable. Left foot braking can give you much more finite control. But by and large this is only going to really help rock crawling, messing about in typical British mud, grass and loose surfaces I suspect it will be far less useful.

To some extent the same technique can work even with a manual, more on slowing your speed than starting from a stand still though, but a similar principle.

If you get opportunity I'd say have a play around and see how you get on, but I really wouldn't expect it to transform how you currently drive off road.
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20 Apr 2024 13:23 - 20 Apr 2024 13:24 #255692 by rogerzilla
Replied by rogerzilla on topic For those who have an auto
I think the braking-as-traction-control only works well in certain circumstances, basically with certain types of LSD.  Otherwise the torque you are gaining at the non-spinning wheel is exactly that lost in the braking.  The traction control systems only brake the spinning wheel.

I have a friend who used to drive a JDM MX-5 and he got home in fairly bad snow by using the handbrake.  The JDM cars have a Torsen LSD and, while this can't cope with really low grip at one wheel (it will still spin up and take all the power), loading up both rear wheels with the handbrake enables the Torsen to do its job.  An LSD with friction clutches may cope better without the handbrake trick.
Last edit: 20 Apr 2024 13:24 by rogerzilla.

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20 Apr 2024 14:30 #255693 by fordem
Replied by fordem on topic For those who have an auto

 Is this something that is new only to me and I should be putting time into mastering? 

If you do intend to use this technique I would suggest you consider adding an external transmission cooler and, at the very least, fitting a transmission temperature gauge.

Based on what I have read the automatic transmission used in the Jimny is close to the limit on the power it can handle - what I know from experience, (not with a Jimny automatic), is that holding the car on the brake with the throttle open causes fluid churn in the torque converter and the fluid temperatures "sky rocket" - research "torque converter stall test" for more detail.

I'm not into rock crawling, but, my experience with automatics in sand, again not in a Jimny, is that they run hot, to the point that I feel anyone driving an automatic in any sort of serious/frequent off road usage should have at the very least, a transmission temperature gauge, that way you'll know how hot you're running the transmission, long before you "cook" it.

It might also be an idea to review the "severe driving conditions" maintenance schedule, I think the fluid change recommendations are very different.

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21 Apr 2024 18:19 #255718 by Manxman
Replied by Manxman on topic For those who have an auto
I've driven Moab a few times in automatic Jeeps. Yes, a lot of people do use a little left foot braking, for the reasons you've given - but it's only really necessary on really technical, steep hill climbs. Worth remembering that in Moab you're driving on slick rock - which despite the name has phenomenal grip - so crazy climb angles and side slopes are feasible, and the potential for shock loading the transmission is high. I've used this a few times in a Jeep XJ in the UK and Europe, buts been much less useful/necessary. Can't comment on how this would apply with a Jimny, I'll defer to the other guys on that one.
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