Increase Traction w/o a rear locker? How?

muddyluxury

Observer
the QTII does send about 50 percent to the rear wheels, the other half goes to the front, being an AWD system of sorts. It also works the same way a the M998 hummers work. you get a wheel that will free spin, thats all you will do all day. Just ride the brake and give the free spinning wheel resistence to some power goes to teh stuck wheel. Its a "tourque biasing differential" as the army calls it, or for the rest of us OPEN.

as for a lack of traction options, i bet its because he has the V8 and the bastard child aluminum center section D44. If thats the case your only option is the aussie locker, or lunch box locker, i was under the impression that aussie had stopped production but somebody on another forum told me they had started production again.
 
M

modelbuilder

Guest
Unfortunately I called all the locker manufactures I could find and spoke with as many people as I could. Due to the fact that the WK has an odd housing for the rear axle a locker will not fit. I even took it to two 4x4 shops.

The same goes for the Jeep Commander. No one make a locker that will fit inside the housing...it's an odd shape.

My rear axle is the Chrysler 8.25" 29 Spline but it's the housing that keeps the locker from fitting on it.

I am just out of luck on this one. Only way to do it would be to swap axles. All the experts said forget it!!!

It's fine...it still gets me around!!!
 
Last edited:

xcmountain80

Expedition Leader
Unfortunately I called all the locker manufactures I could find and spoke with as many people as I could. Due to the fact that the WK has an odd housing for the rear axle a locker will not fit. I even took it to two 4x4 shops.

The same goes for the Jeep Commander. No one make a locker that will fit inside the housing...it's an odd shape.

My rear axle is the Chrysler 8.25" 29 Spline but it's the housing that keeps the locker from fitting on it.

I am just out of luck on this one. Only way to do it would be to swap axles. All the experts said forget it!!!

It's fine...it still gets me around!!!

Your in a Grand right and you say the Commander share the axle, didn't AEV build a snow bound expedition vehicle out of a Commander? Contact them and see what they did.
vehicles_show_iceland_xk.jpg


Aaron
 

xcmountain80

Expedition Leader
Well I read the descriptions on the AEV for both then Grand and the Commander and neither made any mention of altering the 4wd system. But I say call them or email them anyway.

Aaron
 
M

modelbuilder

Guest
Thanks guys but it looks like the only way to get a locker in there is to spend even more money. I was hoping for a quick fix from an Aussie locker etc.

I already called them and they confirmed that it will require extensive work to get a rear locker in there (lots of time and money)!

And that Commander in the above picture has Quadra Drive II...no need for a rear locker with that 4WD system.
 
Last edited:

xcmountain80

Expedition Leader
Thanks guys but it looks like the only way to get a locker in there is to spend even more money. I was hoping for a quick fix from an Aussie locker etc.

I already called them and they confirmed that it will require extensive work to get a rear locker in there (lots of time and money)!

And that Commander in the above picture has Quadra Drive II...no need for a rear locker with that 4WD system.

I thought you also had the QII system, was I mistaken?


Aaron
 

dust devil

Observer
Set the brake. when you push on the pedal again it unlocks the pedal and you now have control over how much pressure is applied.

Note: only if you have the sort of brake system that uses a second push on the pedal to unlock. If you have a pull handle with a button, hold the button and pull the handle and you have an unlocked hand brake. But if you have the kind of foot brake that uses a hand release, trying to use the brake as you suggest results in a foot/hand juggling act that usually does no more than interfere with driving in difficult situations. In any event, using equal braking pressures on both wheels in an open diff axle has only a very limited effect on the operation of the diff. The result may be enough to get you through what is stopping you, but often is not nearly enough because the amount of motive force allowed through the system is still not sufficient to roll the vehicle. The open diff is still going to limit you to the torque available at the wheel with least resistance. All the brake does is shift the threshold, not the balance.
 

Photog

Explorer
If you can't add a locker to the axle, and the Jeep does not use the ABS for traction control, you could add steering brakes for the rear axle. Then just increase brake pressure to the slipping tire to get moving again.
 
S

Scenic WonderRunner

Guest
I watched the video twice.

It looks like you are fully locked in 4LO.

The "4 all time" is ment to work on slippery AND dry surfaces. It has to offer some slippage or it will bind up and break on a dry surface. Is this not correct? Just thinking out loud.


(Last weekend I was out driving along the beach at the Salton Sea, just for fun! Dunno why...it stinks! I guess, just because I could.

As I pulled onto the pavement, I realized I forgot to take it out of 4x4 and unlock my hubs as I made a right turn on the pavement. I was hopping a little. I stopped right away and got out to flip my hubs to Free. I looked at my tires, and all 4 had scuff marks that took the sand/dirt off. No way can I drive on the street in 4x4 high.) ....just sayin....



.
 

michaelgroves

Explorer
In any event, using equal braking pressures on both wheels in an open diff axle has only a very limited effect on the operation of the diff. The result may be enough to get you through what is stopping you, but often is not nearly enough because the amount of motive force allowed through the system is still not sufficient to roll the vehicle. The open diff is still going to limit you to the torque available at the wheel with least resistance. All the brake does is shift the threshold, not the balance.

I'd be very interested to get your take on how this works. I've tried to identify a coherent theory might be behind it, but previous discussions about Brake Throttle Modulation on open diffs always seem to get bogged down by people asserting that it does work, rather than explaining how it works! I've yet to come across a convincing hypothesis. I can understand BTM working with a torque-biasing LSD, and I can understand how unequal braking can create useful torque... but equal braking on an open diff has me baffled.

If you have what you think is a good explanation, it may be worth starting a new thread, still under General Vehicle Modifications, as this might take on a life of its own!

Rgds,

Michael...
 

dust devil

Observer
First, brake/throttle modulation is not something I use, off road or anywhere else. Seems that in the past 30 or 40 years, I have tried it once or twice without any appreciable success, so, as with anything else that didn't really work for me, I didn't pursue it. I am not one of those who swear it works, I just don't swear it doesn't. My limited personal experience in this regard is not conclusive evidence one way or the other.

How could it work? Not being an automotive engineer, I can't resort to science, so all I have is observation and my own corrupt understanding of how things like differentials actually work.

As I understand the situation, an open differential is a torque sensing device, like your average LSD, except that it responds to torque opposite to that of the LSD. However phrased (sends torque, sends power, limits torque/power or whatever), the bottom line is that when there is a threshold level of differential resistance to rotational force occurring between two wheels on the same axle, the open diff will direct torque away from the wheel with the most resistance, e.g., traction, ** so that the other wheel spins at a higher rate. Not trying here to define how the thing works, but more the sense of what more or less happens and the fact that what happens is predicated on the difference in available traction or resistance as between the two wheels.

Commonly, when driving off road or in very slippery conditions, the differences between wheels that leads to getting stuck are usually pretty substantial, that is, one tire has enough grip, the other largely does not. If the tire without grip really has so little grip that it simply can not create enough drive to at least come close to shifting your vehicle, I can't see BTM working at all. If there is sufficient traction for two tires to drive the vehicle, but not enough for one, then perhaps BTM might work as long as you can limit the propensity of the open differential to run away with itself, and for this you need to keep throttle to a minimum and raise the break-free threshold of the differential to the point that, even if one wheel is moving faster than the other, both wheels are turning and the faster wheel is not moving so fast that it can not generate traction within the limits of the terrain.

It may also be that brake force evenly applied nevertheless has a differential effect on the two wheels in a stuck vehicle situation because with one wheel spinning freely (or at least faster than its partner), there is more area swept and more brake force generated on the spinning wheel, sufficient that it might shift the traction balance back towards the middle, and allow the wheel with traction to at least turn over and get you moving again.

So, I would propose that under the right circumstances there is at least a possibility that applying brakes while being cautious with the throttle could result in slowly turning wheels rather than one static and one spinning freely.

Most of us see and use science in out lives without understanding just why or how something works as it does. So, whether we can formulate a clear explanation for something is less important, in my opinion, than being able to demonstrate that something actually works. If someone has actually used BTM to get a vehicle moving again, why deny them their point of view or reduce the importance of their perspective simply because they can't put into words why and how that something really worked? Not saying you did say that or even suggest it, of course. Only suggesting that even without science on one's side, if they have used BTM to get moving again, it probably does work whether or not we understand why it should be so.

One might try a simple experiment. In two wheel drive in a vehicle with an open differential, jack one drive wheel off the ground. Then start the vehicle and try to drive away. The lifted tire will spin and you won't go anywhere. While the tire is spinning, tap the brakes and see what happens. If BTM simply does not work, nothing will happen. If it does, your vehicle will probably come down off the jack.


** I say 'directs torque away from' rather than 'limits torque to the lesser of' simply because I prefer to see it that way, and can understand better what I see happening. I believe the result is the same regardless of how defined. Personally, I believe that without resistance to torque, there is no torque other than in a theoretical, potential sense, and would rather describe open differential performance in terms of available traction rather than available torque. Drive lines don't produce torque, the engine does. The drive line only transmits it. Even when there is no available traction, there is still available a rather large amount of torque potential generated by the power plant, so saying that the differential limits torque to the amount at the free wheel rather misstates what torque is and how it is made, in my opinion.
 
Last edited:

michaelgroves

Explorer
** I say 'directs torque away from' rather than 'limits torque to the lesser of' simply because I prefer to see it that way, and can understand better what I see happening. I believe the result is the same regardless of how defined. Personally, I believe that without resistance to torque, there is no torque other than in a theoretical, potential sense, and would rather describe open differential performance in terms of available traction rather than available torque. Drive lines don't produce torque, the engine does. The drive line only transmits it. Even when there is no available traction, there is still available a rather large amount of torque potential generated by the power plant, so saying that the differential limits torque to the amount at the free wheel rather misstates what torque is and how it is made, in my opinion.

Useful that you made that point explicitly. Torque is the "twisting force" on a shaft, and is the product of what the engine/transmisson produces, and the resistance provided by traction. Without traction, there is no torque (as would be demonstrated by putting a suitable strain gauge on the relevant half-shaft, and measuring it). In other words, torque is produced by the engine and by traction, together - and the driveline, as you say, merely transmits it.

For our purposes, we can assume that the engine can potentially provide as much torque as could possibly be needed, and therefore, the torque on any shaft will be dependent entirely on the traction at that wheel. Also, we're only discussing the torque required to move the vehicle, rather than bothering about accelerating an already moving car, etc. So traction is indeed usually a proxy for torque.

In fact, though, the real issue is the force actually exerted between the ground and the tyre, which is the "motive" force that makes the vehicle move. Usually, this would just be equivalent to the torque - indeed, the torque is generated by that resistive force working against the engine. But as soon as we add the use of brakes into the equation, then we have resistance (and thus torque) that is unrelated to the motive force. A differential responds to torque, and not motive (tractive) force. What you have said so far shows that you clearly understand this, but it's worth saying explicitly, to distiguish between torque produced by brakes, and torque produced by traction.

One might try a simple experiment. In two wheel drive in a vehicle with an open differential, jack one drive wheel off the ground. Then start the vehicle and try to drive away. The lifted tire will spin and you won't go anywhere. While the tire is spinning, tap the brakes and see what happens. If BTM simply does not work, nothing will happen. If it does, your vehicle will probably come down off the jack.

Funny you should say that! :) I have previously described just such an experiment, and the results I got:

Here's one of the simple experiments I did, with a series Land Rover, in 2WD, and then the same with a Disco 1 (centre diff unlocked):

I jacked up one of the back wheels, using a trolley jack with casters, on a smooth concrete floor. Then I just put the car in various gears, and experimented with different brake/throttle techniques.

Result?

The Series truck didn't move at all. If there had been any positive effect from the BTM, it was completely offset by the front wheels being braked at the same time.

The Discovery jerked a little bit back and forth on the castered jack. I doubt it would have fallen off its own bottle jack, except perhaps on some of the more extreme wheel-spinning/slamming-on-the-brake attempts. (Incidentally, I also tried this with a front and a rear wheel up on castered jacks, and the centre diff both locked and unlocked).

This was more or less in line with what I would have predicted. Certainly there was no significant or systematic increase in driving force induced by BTM, else the car would have been driven forwards quite easily. I attribute the rocking/jerking to uneven braking forces and some internal friction in the diffs.
Subsequently Rob pointed out that the rocking would have been caused by the inertia of spinning up the heavy wheel under acceleration, not braking. The inertial resistance created torque which would have been balanced across the open diffs to the other wheels.

The good thing about this experiment is that it is easily repeatable. If anyone is interested, by all means try it for yourself.


Most of us see and use science in out lives without understanding just why or how something works as it does. So, whether we can formulate a clear explanation for something is less important, in my opinion, than being able to demonstrate that something actually works. If someone has actually used BTM to get a vehicle moving again, why deny them their point of view or reduce the importance of their perspective simply because they can't put into words why and how that something really worked? Not saying you did say that or even suggest it, of course. Only suggesting that even without science on one's side, if they have used BTM to get moving again, it probably does work whether or not we understand why it should be so.
I like other people having a point of view, (though I do have a philosophical aversion to perpetuating a belief in things without foundation). And the fact that so many other people claim to have had amazing success with BTM is the very reason I am trying to understand the mechanism. Given the experiment I've done, it's now also not just a case of trying to understand a possible mechanism, but also to reconcile claims of BTM working in the "real world", and not working under controlled conditions.

I can't think of any other driving technique or piece of hardware where the principles behind it are not understood. BTM with a LSD? I get that. Spinning a wheel in mud? Clears the tread. Using "fiddle" brakes? Raises the torque on the spinning side of the diff by means of braking, therefore raises torque on the side with good traction too. Keeping revs down? Takes advantage of static friction being higher than dynamic. Etc.

A lot of people who have earned wide respect (including mine), have said BTM works, but even on this forum where there is a huge wealth of knowledge of mechanical engineering and physics, no-one's come up with a consistent explanation of why equal braking across an open differential, should increase the force between the tyres and the ground.

It may also be that brake force evenly applied nevertheless has a differential effect on the two wheels in a stuck vehicle situation because with one wheel spinning freely (or at least faster than its partner), there is more area swept and more brake force generated on the spinning wheel, sufficient that it might shift the traction balance back towards the middle, and allow the wheel with traction to at least turn over and get you moving again.

The "bigger swept area" is intriguing possibility - though I can't really see how that in itself makes the braking force (and therefore the torque) higher on that side. (The energy absorbed is higher, but in principle that's a function of the same force being applied over a bigger distance). Unless, possibly, the brakes get hot on that side, and somehow bind more?

(I'm also still left with the issue of why it doesn't work in the controlled experiment).

Related: I did think at one point that maybe BTM works with drum brakes because the "leading shoe" effect only comes into play when the wheel is turning, so the spinning wheel is braked more effectively than the stationary one. But as many of the proponents of BTM are driving disc-braked vehicles, that doesn't seem satisfactory.
 
M

modelbuilder

Guest
I wonder if welding the spider gears will damage the 4x4 system my Jeep has....arghhh....I wish someone made a locker that would fit.

Is that even safe?

More info on how my 4x4 system works. The computer senses what wheel is slipping and applies brake pressure to the slipping wheel and sends torque to the wheel with traction.





.
 
Last edited:

Forum statistics

Threads
185,530
Messages
2,875,584
Members
224,922
Latest member
Randy Towles
Top