AWD and Slip

[Third From Texas]

I've been stuck before and had people say "you're not in four-wheel-drive" to which I reply "it's not a four-wheel-drive truck" which always results in a puzzled look. Heh

Something GeoPen and I briefly discussed a couple years ago came to mind the other day as I was driving. As I understand it, with the LMTV all-wheel-drive system, if a wheel loses traction, the diff applies all power to the opposite wheel. In many situations (like soft sand, mud, etc) that can result in only one tire turning per axel and you basically make matters worse.

Some owners opt for lockers to resolve this issue but as we all know, they are all-or-nothing (due to the lack of e-lockers or air-lockers). If you have Detroit-style lockers, you basically create a one piece axel to improve traction. This of course presents issues (skipping in turns, etc) that aren't desirable.

So back to the discussion GeoPen and I had sometime back. We were talking about the inability to independently apply brake pressure to each tire. Of course, the trucks aren't set up to allow for that. On a hydraulic brake systems, you can use a proportioning valve to adjust your braking front or rear (but I don't have the slightest clue if this can be done with air brakes but I suspect that it very well could). And you can take things a step further with rear cutting brakes that can limit each rear tire independently on sand cars, etc. But as I said, our air systems aren't really designed with that in mind.

But lets say you could in fact use a handle to apply pressure to the brakes in one axel or the other (or even each tire independently) via something akin to a cross between a proportioning valve and a set of "cutting brake" handles that would allow you to apply enough pressure to an axel (or a tire) to trick the diff into keeping power to both wheels on that axel. Not enough to stop the wheel, just to create enough resistance so the diff doesn't go into slip mode and the wheel stays under power. If you had such a handle(s) in the cab, wouldn't that technically result in all wheels then staying under power when they would normally crap out and let one on each axel slip?

My A1R has ABS and I'm not sure how that comes into play (I still assume that it functions per axel and not per independent tire), but again it's a point I'm ignorant of with regards to the LMTV braking system. If the ABS *does* control the braking of each tire independently, then I think it could also be used to negate the limited slip issue. Even if not, I wonder if pulsing the ABS would be enough to stop the diff from slipping.

Just something that I think about from time-to-time. Especially when the Jeeps are circling my stuck LMTV and yelling "BRO, YOU'RE NOT IN FOUR WHEEL DRIVE DOOD"

 

[GeneralDisorder]

The ABS system is capable of modulating brake application, and when manufacturers implemented "traction control" it was basically just a software upgrade to the ABS systems. Which is why they did it.... it's not great or even good.... it's mostly a marketing ploy and it was essentially free.

The problem with using the brakes to lock down wheels that are slipping to transfer power to wheels that (we're guessing) aren't slipping is that in the real world when the vehicle is in a traction challenged situation (mud, ice, etc), there's a fine line between "the other wheel has better traction" and "no wheel has better traction" and you setup a situation where you just bring the vehicle to a dead stop because the software's only solution is to apply brakes...... and that results in you going nowhere. You see this with consumer vehicles that have inferior AWD systems that are essentially open diffs with software traction control that relies on the brakes to artificially transfer power through an open diff. You see the conundrum between using brakes to propel the vehicle forward right? You rapidly approach an unworkable solution. Having all the wheels spin like crazy and dig and fling mud can sometimes be the better solution. And a mechanical locker that locks the wheels together due to differential rates of rotation gets power to the wheels without the need to absorb power from the brakes.

What you really want in such situations is for all the wheels to get power mechanically, not to brake the vehicle to a dead halt. Applying the brake at one wheel is useful in only very limited situations - rock crawling where you have hung one wheel in the air and locking it down won't really be any detriment to moving forward a foot or two......

 

[Third From Texas]

The ABS system is capable of modulating brake application, and when manufacturers implemented "traction control" it was basically just a software upgrade to the ABS systems. Which is why they did it.... it's not great or even good.... it's mostly a marketing ploy and it was essentially free.

The problem with using the brakes to lock down wheels that are slipping to transfer power to wheels that (we're guessing) aren't slipping is that in the real world when the vehicle is in a traction challenged situation (mud, ice, etc), there's a fine line between "the other wheel has better traction" and "no wheel has better traction" and you setup a situation where you just bring the vehicle to a dead stop because the software's only solution is to apply brakes...... and that results in you going nowhere. You see this with consumer vehicles that have inferior AWD systems that are essentially open diffs with software traction control that relies on the brakes to artificially transfer power through an open diff. You see the conundrum between using brakes to propel the vehicle forward right? You rapidly approach an unworkable solution. Having all the wheels spin like crazy and dig and fling mud can sometimes be the better solution. And a mechanical locker that locks the wheels together due to differential rates of rotation gets power to the wheels without the need to absorb power from the brakes.

What you really want in such situations is for all the wheels to get power mechanically, not to brake the vehicle to a dead halt. Applying the brake at one wheel is useful in only very limited situations - rock crawling where you have hung one wheel in the air and locking it down won't really be any detriment to moving forward a foot or two......

Rgr all.

What I *really* want is the ability to engage and disengage a mechanical locker. But that seems to be beyond the scope of technology somehow for these trucks. What I don't want are fulltime locked diffs front and rear (or even just rear, honestly).

 

[Weldman]

.

 

[Ronmar]

The secret of traction control is in NOT braking the wheel to a stop, only applying enough additional drag to the slipping wheel with a brake so that the diff thinks it has two wheels with traction and sends more torque to the wheel that actually has some. I do this with my tractor on occasion as it has split rear brakes And it works just fine. Dune buggies have been using it also for a very long time.

Now the issue with traction control on a hydraulic brake system is you need a high pressure hydraulic source and the method to control it(ABS pump and modulator). The cool thing about airbrakes is you already have a full pressure brake source available and easily manipulated. The hard part on my A0 is collecting wheel RPM. The A1 axles and hubs have tone wheels and places for sensors for the ABS, the A0 does not(But I have an idea)…

I actually sketched out a fairly simple one chip circuit that would use a single control module for each axle, 2 wheel sensors and two solenoid valves and a adjustable pressure regulator and flow control to fine tune the application Speed and force. What I am envisioning is a simple crawl control that you would manually activate with a pushbutton at a specific power application that you would tune it for. It would only be active as long as you hold the button. It could be interfaced with each wheel brake actuator using DOT approved 2way check valves, the same way the front blue glad-hand is interfaced with the service brake system(either source, or the stronger source can override and activate the brakes). You could override the system simply by stepping on the pedal any time you wanted, and when the button was released and power removed, the system is disabled and would have no effect on normal brake operation. if a wheel was not slipping it wouldn’t have any effect anyway, perhaps in a really tight turn… How this would be looked upon from a legal perspective is of course questionable… Ahhh so many projects, not enough time, so this one is still in my sketchbook…

Youtube search “Toyota crawl control”. Thats what got me thinking of the possibilities…

 

[Third From Texas]

The secret of traction control is in NOT braking the wheel to a stop, only applying enough additional drag to the slipping wheel with a brake so that the diff thinks it has two wheels with traction and sends more torque to the wheel that actually has some. I do this with my tractor on occasion as it has split rear brakes And it works just fine. Dune buggies have been using it also for a very long time.

Now the issue with traction control on a hydraulic brake system is you need a high pressure hydraulic source and the method to control it(ABS pump and modulator). The cool thing about airbrakes is you already have a full pressure brake source available and easily manipulated. The hard part on my A0 is collecting wheel RPM. The A1 axles and hubs have tone wheels and places for sensors for the ABS, the A0 does not(But I have an idea)…

I actually sketched out a fairly simple one chip circuit that would use a single control module for each axle, 2 wheel sensors and two solenoid valves and a adjustable pressure regulator and flow control to fine tune the application Speed and force. What I am envisioning is a simple crawl control that you would manually activate with a pushbutton at a specific power application that you would tune it for. It would only be active as long as you hold the button. It could be interfaced with each wheel brake actuator using DOT approved 2way check valves, the same way the front blue glad-hand is interfaced with the service brake system(either source, or the stronger source can override and activate the brakes). You could override the system simply by stepping on the pedal any time you wanted, and when the button was released and power removed, the system is disabled and would have no effect on normal brake operation. if a wheel was not slipping it wouldn’t have any effect anyway, perhaps in a really tight turn… How this would be looked upon from a legal perspective is of course questionable… Ahhh so many projects, not enough time, so this one is still in my sketchbook…

Youtube search “Toyota crawl control”. Thats what got me thinking of the possibilities…

That's more along the lines of my thinking.

But I admittedly don't know what's possible and what's not. I've built sand cars and desert pre-runners but my LMTVs have been my first introduction to air brakes. When GeoPen mentioned this in a sort of "wouldn't if be cool if" sorta way, I agreed. But thinkking about my truck being ABS the other day got me thinking about it a bit harder.

Just food for thought, but the back of my mind harbors this "what if I could drop in a $100 mod myself instead of spending thousands to have a locker installed that I really don't want to have for on road/around town use".

 

[Skyhawk13205]

The secret of traction control is in NOT braking the wheel to a stop, only applying enough additional drag to the slipping wheel with a brake so that the diff thinks it has two wheels with traction and sends more torque to the wheel that actually has some. I do this with my tractor on occasion as it has split rear brakes And it works just fine. Dune buggies have been using it also for a very long time.

Now the issue with traction control on a hydraulic brake system is you need a high pressure hydraulic source and the method to control it(ABS pump and modulator). The cool thing about airbrakes is you already have a full pressure brake source available and easily manipulated. The hard part on my A0 is collecting wheel RPM. The A1 axles and hubs have tone wheels and places for sensors for the ABS, the A0 does not(But I have an idea)…

I actually sketched out a fairly simple one chip circuit that would use a single control module for each axle, 2 wheel sensors and two solenoid valves and a adjustable pressure regulator and flow control to fine tune the application Speed and force. What I am envisioning is a simple crawl control that you would manually activate with a pushbutton at a specific power application that you would tune it for. It would only be active as long as you hold the button. It could be interfaced with each wheel brake actuator using DOT approved 2way check valves, the same way the front blue glad-hand is interfaced with the service brake system(either source, or the stronger source can override and activate the brakes). You could override the system simply by stepping on the pedal any time you wanted, and when the button was released and power removed, the system is disabled and would have no effect on normal brake operation. if a wheel was not slipping it wouldn’t have any effect anyway, perhaps in a really tight turn… How this would be looked upon from a legal perspective is of course questionable… Ahhh so many projects, not enough time, so this one is still in my sketchbook…

Youtube search “Toyota crawl control”. Thats what got me thinking of the possibilities…

There is a designed system the sort of acts like you are describing. The WABCO ECUs on the A1s can be programmed to use active traction control.

After I got my truck I could not get my ABS light to go off, I got a code reader and found that my WABCO ecu was looking for an ATC valve and would not allow ABS to function. I had to reset the ECU by wiring in a temp abs switch.

I think an ATC system would be possible to install but it would also require an inhibit if the center differential is locked.

 

[Keith Knight]

I’ve been running a Detroit locker in the rear of mine for 5 years with over 5,000 mile on the road and I don’t even realize it’s in there except for the rare occasion while make a slow turn in a parking lot and I accelerate a little to much and the locker locks up and makes a clunk noise which is typical. The Detroit locker is not a spool it actually does separate and allows for differential to ack as normal in a turn until power is applied which causes it to lockup.

Search Detroit lunch box locker how it works videos to understand it better. The lunch box style locker is the type of locker that is available for our vehicles. It was developed in the mid 90’s by easy locker then sold the company then the patent wore out and now everyone makes it.

 

[Third From Texas]

I’ve been running a Detroit locker in the rear of mine for 5 years with over 5,000 mile on the road and I don’t even realize it’s in there except for the rare occasion while make a slow turn in a parking lot and I accelerate a little to much and the locker locks up and makes a clunk noise which is typical. The Detroit locker is not a spool it actually does separate and allows for differential to ack as normal in a turn until power is applied which causes it to lockup.

Search Detroit lunch box locker how it works videos to understand it better. The lunch box style locker is the type of locker that is available for our vehicles. It was developed in the mid 90’s by easy locker then sold the company then the patent wore out and now everyone makes it.

I've read a few comments from LMTV owners about noticing control/skid issues in the rear while driving on ice that were not present before installing their rear lockers (sounded like they were describing unexpected "spinout"). Granted, big heavy trucks on ice are a handful, but I don't like the idea of introducing extra issues (I knida want to do the Rockies, Alaska sort of thing with my truck some day). And I've read a lot of feedback saying not to install lockers on the front axel (so that still leaves the truck with a potential 25% traction loss). But yeah, I've had trucks with lockers before and I'm familiar with the the turning "clunk". I was making more of a simplistic statement about how they work. You are quite correct in that they don't really create one big solid axel.

Twenty years ago I'd have gone up to the shop and ripped the diffs open, slapped in new ring/pinions, and locker just because I could. Sadly, I don't have the tools, the shop, the physical capability any more, nor the $7-10K at this point to have someone else do it for me. I don't know what the cost of just installing the rear locker would be, but I suspect the labor is no less than doing the ring and pinion swap (so IMO you'd do it all at the same time if it's being done). Honesly though, if I were going to throw down that sorta cash I'd really rather have air-lockers (if they existed). But if there was a solution I *could* install myself and only cost me a couple hundred bucks, I'd jump at that in a heartbeat.

Appreciate the feedback. Just gathering thoughts, really.

 

[Mullaney]

I've read a few comments from LMTV owners about noticing control/skid issues in the rear while driving on ice that were not present before installing their rear lockers (sounded like they were describing unexpected "spinout"). Granted, big heavy trucks on ice are a handful, but I don't like the idea of introducing extra issues (I knida want to do the Rockies, Alaska sort of thing with my truck some day). And I've read a lot of feedback saying not to install lockers on the front axel (so that still leaves the truck with a potential 25% traction loss). But yeah, I've had trucks with lockers before and I'm familiar with the the turning "clunk". I was making more of a simplistic statement about how they work. You are quite correct in that they don't really create one big solid axel.

Twenty years ago I'd have gone up to the shop and ripped the diffs open, slapped in new ring/pinions, and locker just because I could. Sadly, I don't have the tools, the shop, the physical capability any more, nor the $7-10K at this point to have someone else do it for me. I don't know what the cost of just installing the rear locker would be, but I suspect the labor is no less than doing the ring and pinion swap (so IMO you'd do it all at the same time if it's being done). Honesly though, if I were going to throw down that sorta cash I'd really rather have air-lockers (if they existed). But if there was a solution I *could* install myself and only cost me a couple hundred bucks, I'd jump at that in a heartbeat.

Appreciate the feedback. Just gathering thoughts, really.

.
Agreed!

 

[Ronmar]

There is a designed system the sort of acts like you are describing. The WABCO ECUs on the A1s can be programmed to use active traction control.

After I got my truck I could not get my ABS light to go off, I got a code reader and found that my WABCO ecu was looking for an ATC valve and would not allow ABS to function. I had to reset the ECU by wiring in a temp abs switch.

I think an ATC system would be possible to install but it would also require an inhibit if the center differential is locked.

Yea i don’t see the need for center diff interaction control with what I am envisioning, as it is on a per axle basis(controller for each axle). I envision it more like an on demand electronic locking diff, and when you would use it the center diff is probably already locked in mode. It would simply resist the escape of torque to a wheel that has less traction, and direct more to the wheel that does.

 

[CONJIN]

The secret of traction control is in NOT braking the wheel to a stop, only applying enough additional drag to the slipping wheel with a brake so that the diff thinks it has two wheels with traction and sends more torque to the wheel that actually has some. I do this with my tractor on occasion as it has split rear brakes And it works just fine. Dune buggies have been using it also for a very long time.

Now the issue with traction control on a hydraulic brake system is you need a high pressure hydraulic source and the method to control it(ABS pump and modulator). The cool thing about airbrakes is you already have a full pressure brake source available and easily manipulated. The hard part on my A0 is collecting wheel RPM. The A1 axles and hubs have tone wheels and places for sensors for the ABS, the A0 does not(But I have an idea)…

I actually sketched out a fairly simple one chip circuit that would use a single control module for each axle, 2 wheel sensors and two solenoid valves and a adjustable pressure regulator and flow control to fine tune the application Speed and force. What I am envisioning is a simple crawl control that you would manually activate with a pushbutton at a specific power application that you would tune it for. It would only be active as long as you hold the button. It could be interfaced with each wheel brake actuator using DOT approved 2way check valves, the same way the front blue glad-hand is interfaced with the service brake system(either source, or the stronger source can override and activate the brakes). You could override the system simply by stepping on the pedal any time you wanted, and when the button was released and power removed, the system is disabled and would have no effect on normal brake operation. if a wheel was not slipping it wouldn’t have any effect anyway, perhaps in a really tight turn… How this would be looked upon from a legal perspective is of course questionable… Ahhh so many projects, not enough time, so this one is still in my sketchbook…

Youtube search “Toyota crawl control”. Thats what got me thinking of the possibilities…

Any more thoughts on this Ron? I think it would be awesome!

 

[Ronmar]

Any more thoughts on this Ron? I think it would be awesome!

No, too many other things I want to get done. Still need to figure out wheel speed Sensors…

 

[Third From Texas]

Yeah, saw this on FB today and that old spark lit up thinking about this thread.

 

[coachgeo]

I got rear locker... still got stuck in that kind of mess.

 

[chucky]

Not saying this would have got him out but any time you do get one of these trucks in a greasy spot ! Use one foot on brake pedal and one on throttle doing light power brake will usally transfer spinning wheel torqe to non spinning side and cause it to turn so like a hillbilly limited slip and this works on just about anything non locker/pos and really helps on ice to get out of spin divit your made in the ice !

 

[Ronmar]

The key, is to stop the spin before it digs in, which can happen very quickly. If you look at just about any pic of one of these stuck when stuck, one corner is way down(thats the tire that dug in in AWD), which raises the opposite corner, and allows the torque to escape from that axle Which gives you zero thrust even in mode.

So as soon as a wheel starts to spin, STOP! Get out and figure out how to keep that wheel from spinning and digging any further. Don’t hope you can get it moving by spinning it more, you must stop the spin or you better hope whatever comes to pull you out has enough mass and pull to actually do so while you are buried to the axle…

It would be nice if these wheel rims had welded loops inside and out. Then it would be easy to attach a Y lanyard or even a set of tire chains to a wheel that has no traction/spins. Then you could enhance traction or connect a pull line back to an anchor BEFORE you bury it to the axle…

you either need another vehicle to provide enough thrust to pull against the edge of the hole you have dug to climb that anchor wheel out of its pit, or you must find a way to stop the spinning wheels and force torque to the wheels that still have traction. Here is where differential breaking comes in.

i have thought something like a bush winch might be very effective on these vehicles, as it can serve two purposes. Apply braking to a spinning wheel, and also applying pull/traction on that wheel back to an anchor point, but so could some sets of rings(chain links) welded to the rims…

I think my tractor is a good analog to these trucks. High weight compared to a relatively low tire footprint. I have dug it in and gotten it stuck on several occasions, halfway up the engine block once and nothing but soup to push against with the front end loader. and that with a locking differential on the back. But it has pass-thrus on the rear rims. Put a line thru and hook it to itself, run it back to an anchor and it will back right up the line…

 

[ckouba]

Put a line thru and hook it to itself, run it back to an anchor and it will back right up the line…

One of the things I am struggling with the most currently is what exactly is the anchor? I am familiar with the concept of deadman anchors but haven't any hands on experience in this realm. It feels like it'd be a pretty tall order for a deadman to provide functional assistance in something like sand. That's the environment I am most concerned about, and probably most likely to actually get stuck in- fine beach sand or silty river bank.

I know it's a bit of thread drift, but has anyone had practical experience in those situations and can share their tricks? I'm also happy to start another thread to expand this subject independently.

 

[Ronmar]

The anchor can be the hardest part... that is one reason it is best to not let it get too dug in before you figure out how to lock down the slipping wheel. The shallower the hole the lower the force required to pull your truck out...

 

[Keith Knight]

An old Jeep trick is dig a hole put your spare tire in the hole, attach your winch to the tire, bury the tire and start winching. In our case same thing but, dig a really big hole really deep. Desperate times require desperate measures. But for a little comfort I had my M1079A1 converted to a Expedition vehicle weighing in at 27,000 lbs on the very soft sands of the outer banks on North Carolina shores. With the the tires aired down it performed very well, stopping and starting in the sand slow u turns basically I was testing it’s limits and getting an understanding of how it performs in those conditions.