Locker vs Open

TeriAnn

Explorer
superpowerdave said:
I guess my thoughts on that are that it sounds as though a lot of people here travel solo (hence the number of Spot purchasers) or with just one more rig. Without a big group to help when things get tough some re-thinking needs to happen on a build.

I put on more miles alone than with another rig. I can set my own schedule, get distracted by something interesting, get lost in a book or spend hours waiting for the sun to move to a particular location. For me, 3 rigs together is a large group.

So for me, what happens on a build focuses first, second and third on reliability then on a design that can be field repaired. Then on increased capability where I want increased capability. Preferably with locally sourced parts. I do what work I can myself so I know how to do it and carry what tools I need to fix just about anything in the field.

I don't like to work on cars but I do love to travel in remote locations. Learning to work on my truck and every part on it is the price I pay to go where I want to go. In spite of designing for reliability I've had my share of broken parts. The important thing is that with my understanding of how my truck is built, so far it has never been a matter of if "I make it home". Its just been a matter of "when I make it home". Sometimes I think I'm at my best when in limp home mode, but I'm happiest when nothing goes wrong.

Build guidelines:

- Design for as bullet proof as possible

- know every bolt on your truck and how to field repair it or a good work around

- log lots of hours learning how get your rig where you want to without damage or at least limiting damage to non critical systems. I always find that my driving style is a lot more conservative if it just my out in the middle of nowhere.

I also design for comfort :)
 
expeditionswest said:
Another way to look at this is how the engineers specify the functional requirements for driver selectable lockers

Toyota E-Locker: Rear first, then Front. Front cannot be operated independently of the rear.

Mercedes G-Wagen: Center, then Rear, then Front. Front cannot be operated independently of the rear.

ARB Wiring Harness: Rear first, then Front. Front cannot be operated independently of the rear.

In all cases above, rear can be operated independent of the front, not vice-versa (without modification)

U500 is the same as G-Wagen, it uses a 4 position rotary switch (1st position is all 3 diffs open).

Charlie
 

JeepN95YJ

Adventurer
TeriAnn said:
The important thing is that with my understanding of how my truck is built, so far it has never been a matter of if "I make it home". Its just been a matter of "when I make it home". Sometimes I think I'm at my best when in limp home mode, but I'm happiest when nothing goes wrong.

Agreed, TeriAnn. I've found the "limp home mode" facilitates a creative mind that I normally have trouble accessing. In the 13 years I've owned my Jeep, the only time I've ever broken to the point of not being driveable happened on the street. I damaged a rear driveshaft ujoint pulling a friends broken vehicle out of the woods. That ujoint let go on the street and took the transfercase with it. U-haul was kind enough to "loan" me a truck and trailer to get home.

Even when I was much closer to stock, my driving style always got me home. People often used to comment how well my rig was built as I rarely broke anything. I always told them it had nothing to do with the build. I "like" my Jeep. I "rely" on it and I "respect" its capabilities. I can't, in good conscience, abuse it like a typical rock crawler.

I prefer selectable lockers F&R. I've used automatic lockers for many years but my ARBs are my favorites. I tend to use the lockers to avoid damage to both my vehicle and the terrain.
 
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kevb

Observer
R_Lefebvre said:
Well, my 2004 came with CDL. I have left the center open on some snotty muddy but otherwise non-technical roads, and the TC got along fine. But I can easily see how on technical climbs, the TC only is useless. Luckily for me I guess, the 04 has the best of both worlds. Lock the center diff, while still retaining TC to help torque distribution on each axle. The only time I ever saw a limitation, was on one steep climb which had a wash diagonally across it. The axles were all crossed up, I got the front axle through, but then the truck tipped alarmingly (for me) backwards. The TC only works when it senses a wheel spinning

And engine RPM is above tickover, I forget the exact figure.

[/QUOTE]...and the more I spun the low rear wheel, the bigger the hole it dug in the dirt became, the truck tipped over more and more ....until I felt comfortable enough to give it enough gas, get the wheels spinning, TC kicked in and pulled the truck out.[/QUOTE]

Exactly, once engine rpm was increased ETC is enabled and starts to do its thing. You can also encourage it with a bit of left foot braking as well. it takes a wee bit of practice but thats what its all about.


[/QUOTE] I hadn't expected something so hard as I'd been there before. The washout was new.[/QUOTE]

This is a lesson I have learned quite a few times and and no doubt will have to re-learn it again, seen people with far more experience than me caught out also.... never take anything for granted!

[/QUOTE] Not technically correct. Locked diffs can supply up to 100% of the engine torque to any one wheel.
In fact, it is open diffs that supply EXACTLY 50% of engine torque to each wheel on an axle. The trouble with open diffs is that when one wheel is in the air, that torque may be exactly zero, which means that exactly zero torque can go to the wheel with traction, which means you can apply exactly zero engine torque or else the wheel spins.[/QUOTE]

I have to disagree with this, torque is the turning force produced by the engine which is distributed to the wheels via the transmission system. Open diffs will allow 100% of the available torque to go to the wheel with no traction... the path of least resistance. In the case of the LR ETC/ABS system the brakes will then be applied to the spinning wheel (assuming engine rpm is high enough) and hopefully force the torque to the other wheels which hopefully have traction. In a mechanical locker situation with CDL, locking the CDL will split available torque 50/50 front to rear so as long as you have traction on at least one axle (both wheels) you will maintain forward progress. This is where a cross axle situation can be a problem and why suspension travel is important to some extent (without going silly). Weight on wheels equals traction. If you get cross axled then with no weight on opposing front and rear wheels you will lose traction and all your torque will again follow the path of least resistance and spin 2 of your wheels. Best case scenario is CDL with front and rear locker, 25% of your available torque is mechanically driven to each wheel so as long as you have traction somewhere you can maintain forward progress. Traction is the stickyness of your tires to the ground for want of a better description.


[/QUOTE]No, traditional 4wd transfer cases have no diff to lock, there is no diff in the center, at all. They are essentially like spools, only you can disconnect one of the axles completely.[/QUOTE]

Good description


[/QUOTE]Not having driven in deep sand, I have to ask why? I assume it's like driving in snow. And then, I have to ask, have you sampled ALL types of TC before you make that statement?

Some TC's cut engine power when they sense wheelspin. These SUCK in snow, and I imagine in sand. However, the D2 TC does not cut engine power at all. It just brakes the spinning wheel. It provides HUGE traction on snow, and I'd think it would help in sand too?[/QUOTE]

I am fairly familiar with the LR/Wabco ETC/ABS system, like you I had it in my 2000 D2 and currently have it in one of my Defenders. I like it as a factory option although it has its limitations. Like I said in an earlier post I also have f&r ARBs in my other Defender. In the Discovery the ETC actually has 2 functions, it maintains even torque distribution on wheels on the same axle by activating the brakes individually, up to about 30mph I think. It also maintains even torque distribution between front and rear axles (the idea here was to make the CDL redundant, unfortunately it didn't quite work). I think this is active up to about 50 or 60mph. On my ETC/ABS Defender traction control only works by the first system as Defenders always had a CDL. (it is a farm truck after all)! To add to Scotts 1-4 list above again, if we are talking about a D2 I would put a CDL pretty high on my list, maybe even above the Engel ;-) A D2 on ETC alone can be pretty hairy on loose slopes where you are breaking traction.

ETC sucks in deep sand because just as you sink in, requiring more torque to try and power out and maintain momentum the ETC in its wisdom applies the brakes. In most other scenarios I find it quite good, especially a few inches of snow, again as a non "extreme" factory option. It does not have a great reputation for reliability but as yet mine have been good. It is no where near as refined as the current LR traction control systems but that is to be expected.

I know FJ Cruisers have some form of engine limiting TC but to my mind this is for on road performance, correct me if I am wrong anyone but I think its the Trac (as opposed to atrac) fitted to the 2wd models?

Good points on the winch versus lockers, lockers will get you deeper in to trouble, hopefully a winch will get you out but its normally on the front of our trucks. What if the only way out is back the way you came? What other recovery options do you carry?

Terri Anne, great points from a leafer perspective that we can all learn from, thanks.
 
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seashore

Observer
superpowerdave said:
My wife drove her bone-stock P38 on a pretty challenging trail just outside of Mountain Home and folks were amazed. While you have your reasons for not taking her off-trail, I hope lack of confidence in performance isn't one of them :)

(By the way, at that time she still had the EAS!)

I'm not worried about performance, for sure. Although the only reason I miss the EAS (i've got springs in it) is for trail use...Basically we don't wheel it since we have the disco, which is plenty comfortable for longer trips. That and I worry about all those computers. Makes me think the p-38 should have air-recovery points like my old Sankey trailer...:(
 

R_Lefebvre

Expedition Leader
I have to disagree with this, torque is the turning force produced by the engine which is distributed to the wheels via the transmission system. Open diffs will allow 100% of the available torque to go to the wheel with no traction... the path of least resistance. In the case of the LR ETC/ABS system the brakes will then be applied to the spinning wheel (assuming engine rpm is high enough) and hopefully force the torque to the other wheels which hopefully have traction. In a mechanical locker situation with CDL, locking the CDL will split available torque 50/50 front to rear so as long as you have traction on at least one axle (both wheels) you will maintain forward progress. This is where a cross axle situation can be a problem and why suspension travel is important to some extent (without going silly). Weight on wheels equals traction. If you get cross axled then with no weight on opposing front and rear wheels you will lose traction and all your torque will again follow the path of least resistance and spin 2 of your wheels. Best case scenario is CDL with front and rear locker, 25% of your available torque is mechanically driven to each wheel so as long as you have traction somewhere you can maintain forward progress. Traction is the stickyness of your tires to the ground for want of a better description.

This is a very common argument to have, and is a common misconception, but it's wrong. An open differential always distributes torque 50/50. It must, because it is in fact nothing more than a complicated geared "rotational see-saw".

Locking diffs allow up to 100% of engine torque to be transmitted to only 1 wheel. That is why they break axles.
 

kevb

Observer
Hey Rob,

I'm having a discussion, not an argument :D

I see where you are coming from and maybe the word "torque" was technically a bad description. perhaps "drive" would be better. I was just trying to explain it is as simplistic term as my wee brain could handle. Torque being a measure of turning force, if you have no traction at a wheel you have no resistance and therefore minimal torque in the true sense. By the same token your statement about an open diff is only true if both wheels have traction, It only provides the same amount of torque to both axles if they both present the same resistance or traction. If you have one wheel hanging in the air spinning on an open diff there is no resistance.
 

R_Lefebvre

Expedition Leader
I know, I didn't mean argument as in the shouting type... I meant as in debate. ;)

Yes, if you said drive instead of torque, you'd be more technically correct.

But, open diffs do distribute torque 50/50. When one wheel is in the air, it has no capability for converting engine torque to "drive". It has zero resistive torque. Therefore, the diff will provide zero torque to the wheel on the ground. If one wheel only has a little grip, say it can only provide 10% tractive force, then you send 20% of the available torque to the axle, the diff splits it 50/50, 10% to each wheel. Any more than that, and the one wheel will start to spin. Once it starts to spin, it typically loses all traction. Once traction on the lose wheel is lost, the torque split again becomes 50% of zero, and you lose all drive again.
 

michaelgroves

Explorer
kevb said:
R_Lefebvre said:
In fact, it is open diffs that supply EXACTLY 50% of engine torque to each wheel on an axle. The trouble with open diffs is that when one wheel is in the air, that torque may be exactly zero, which means that exactly zero torque can go to the wheel with traction, which means you can apply exactly zero engine torque or else the wheel spins.

I have to disagree with this, torque is the turning force produced by the engine which is distributed to the wheels via the transmission system. Open diffs will allow 100% of the available torque to go to the wheel with no traction... the path of least resistance.

Rob is right, open diffs supply equal torque to both sides. Torque is the product of the engine/transmission acting against a resistance. The resistance is provided by the friction between the tyre and the ground - i.e. traction.

So zero traction (a wheel lifted, say) results in zero torque on that shaft (but lots of rotational movement as the wheel spins). An open diff will mean zero torque at the opposite wheel too, regardless of the traction under it. This equal torque split is an undesirable effect of the mechanism allowing the wheels to be driven at diffrent speeds.

kevb said:
In the case of the LR ETC/ABS system the brakes will then be applied to the spinning wheel (assuming engine rpm is high enough) and hopefully force the torque to the other wheels which hopefully have traction. In a mechanical locker situation with CDL, locking the CDL will split available torque 50/50 front to rear so as long as you have traction on at least one axle (both wheels) you will maintain forward progress.

ETC applies the brake to the spinning wheel, thus adding resistance, and thereby "artificially" raising the torque on the wheel without traction. The open diff then applies that same raised torque to the wheel with traction. An undesirable side effect of this is that the braking resistance can sap quite a bit of engine power, while (in itself) contributing nothing towards forward motion.

A locked diff will allow the resistance at each wheel to create whatever torque is possible on that shaft. So a raised wheel with zero traction will provide zero torque, but the opposite wheel with good traction will put a lot of torque on its halfshaft. An undesirable side effect of this is that the wheels are forced to rotate at the same speed.



Actually, to talk about "drive" is also misleading. Both wheels on an axle are "driven", in the sense that the engine/drivetrain supplies both of them with potential power. But neither of them "drive" unless there is sufficient total resistance from (traction at) the wheels. With an open diff, if one wheel is spinning and the other stationary, which of them is "driving"? The answer is that both of them are contributing the same amount of forward force, but their combined force is insufficient to make the vehicle move.

The misconception is common because to an onlooker it looks as if the stationary wheel is doing nothing - they can't see the strain on the shaft as it "tries" just as hard as the opposite (spinning) wheel.
 
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jfarsang

Adventurer
jfarsang said:
Ditto.

Tires and rear locker are a great combination.

Winch and front lockers come after the rear locker on my vehicles.

expeditionswest said:
When venturing into the unknown (i.e., not a day trip), always opt for a winch before a locker ;)

That one comes right from the school of hard knocks. :REOutCampFire03:

I agree. :cow:

I usually purchase the locker on a monday and the winch on a tuesday. :bigbossHL:

Also another plus of having the locker in the rear.

If you have to back out and can't use the winch in the front. Locking the rear end to use as a pull and using the front end to steering backwards makes for some good maneuverability.

Having only a locked front while having to back out may not work (depending on scenario) since you may have to steer.
 
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I Leak Oil

Expedition Leader
This most excellent discussion isn't quite long enough yet so I'll try to help it out......

Which locker is best.....?! Selectable, automatic, Lincoln, spool, pneumatic actuation, electric actuation, manual engagement? He he he.....

Jason T.
 
H

Hank

Guest
Jason T. said:
Which locker is best.....?! Selectable, automatic, Lincoln, spool, pneumatic actuation, electric actuation, manual engagement? He he he.....


Start a new thread. That debate will go on for pages.
 

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