Limited Slip Faceoff: Detroit TrueTrac vs. ARB Air Locker

[Metcalf]

Basics first......air down the tires to the proper pressure for the terrain, have a way to air them back up, and have a strong selection of recovery gear. I would highly recommend investing in a winch before the expense of lockers particularly if you are going to be traveling alone.

You can drive around most locker quirks. Most selectable lockers fail to the open mode so you can generally always get home ( note the above statement ).

 

[mogwildRW1]

Unless you're rock crawling, I can't see the need for locking differentials.

There's an area I hunt in, the access is though a fence, then an immediate left hook, and straight up a hill. The hill is loose dirt on top of hard pack, and there's nothing to put a winch on. Lockers are the only way to make it up, as soon as your done the left turn your already at 70% or better grade, hit the locker switch, and crawl up. Tire spin (which Unimogs don't do well anyway) only makes you slide sideways or backwards, towards the fence, and you can't get a run at it.

I use my lockers all the time offroad, I see them as a tool to keep from getting stuck, not a "I'm already stuck, time to winch or turn the lockers on"

that being said, I already have a recovery winch, and its a vital tool just as much as lockers are.

 

[locrwln]

^^Gotta agree^^

Winches are great if you have something to hook to.

Here I was at just under 10k feet last weekend and it took the front locker to get there. "Moguled" loose shale hill climb.



And I do carry a pull-pal.

Jack

 

[Metcalf]

Air pressure?

 

[mogwildRW1]

I've been down to 8psi, usually wheel at 1.4bar (20psi) and still times I click the lockers on, again, to keep from getting stuck and minimize the destruction to the ground, I know it sounds funny, most people thing locking the diff's rips up the ground, but quite the opposite, it keeps the tires from spinning.

This is 20psi. I already had the air pressure low because I was pulling a huge stump (1500lbs or more) into the back yard to the burn pile, so I had the tires nice and low to maximize traction and floatation (hard to tell because they are caked in mud). The stump tipped over (it was roots and all) and turned into a ground anchor, sinking the mog, I was floating nicely on top of the mud and grass up to that point. If I hadn't clicked the lockers on, wouldn't have mattered if the tires were flat.

Having lockers kept me from having to get out, and chain up, chaining up in the mud, when your already sunk, sucks @$$.

Sometimes, you just need all 4 tires spinning at the same time. (this is my own back yard, so no worries about ripping up the landscape )


Another advantage to all 4 wheels locking, is, in a straight line (no turning, at all) all 4 wheels will turn at the same rate (assuming the vehicle is a real 4wd, some kind of center locker or in the Unimogs case, no centre differential), so if one wheel or more contacts a soft spot, say, loose gravel during a climb, that wheel won't spin, because all 4 wheels are locked, turning at the same rate, if that wheel doesn't spin, it won't break though or slide. They call that "forced slip"

Edit:

They explain it better than I can here:

http://youtu.be/fZRews1U1K4?t=8m25s

 

[Metcalf]

I'm not against locker at all. I am just saying that they are not the 1st thing you need to buy.
In the end I think most people would agree that having selectable lockers front and rear is the ultimate goal.
I just think that if money is an issue spending 'locker' money elsewhere is probably a smarter bet......OBA, recovery gear, winch, etc.

 

[mogwildRW1]

I certainly agree, to a point. I put lockers up higher on the list, but that's entirely depended on the type of terrain I wheel in (so, I guess, IMHO). Lots of open prairies up here and quite often, nothing to anchor your winch to. Pul-pal's are great but I'd need two for my vehicles weight, and yeah, I could bury the spare tire, but you and I know what a mog tire and rim weigh's, and just rolling it around is hard, let along burying it And for slippery hills, I'd have to climb the hill first, attach the winch, and pull myself up, or, just hit the lockers, and crawl up.

The OP's post wasn't "winch or locker" it was "limited slip or locker", from how I read it. So my money is on true, full locker (ARB) since having onboard air is good for airing the tires up and down anyway, as well as running air tools, blowing off dust, blowing off light snow, etc.

No doubt proper sized winch, and adequately sized recovery gear is also on the list.

IMHO, selectable lockers will help you keep from getting stuck in the first place, so you'll have to winch less. And, if you do get stuck, quite often, the winch is on the front of most installations, when, you should actually be pulling yourself out the way you went in. So, budget for 2 winch's. Or, just lock both diff's, and probably back out

 

[Metcalf]

True.....so trying to back on topic here, or give it another twist...

Say you have $1000 budget for lockers....

You can just about get....

One selectable. Which end do you run it in?
Two full case automatic lockers.
Three lunchbox lockers
Two or three limited slips

Putting a dollar figure on it gives is a better scope I think? Not everyone has the money for selectable lockers front and rear. Perhaps we should discuss other options and combinations?

On a long wheelbase rig, why not a spool or welded rear diff?

Personally, I have been VERY surprised with the FRONT autolocker, REAR limited slip combo in my Willys. I did it to test a few theories and seems to be panning out really well so far. Just another out of the box idea....

 

[mogwildRW1]

The problem (IMHO) with limited slip, is in all the systems I've seen, it works on the torque multiplication method, when one wheel slips, it multiplies the torque to the other side by binding in the diff (worm gears, or the newer grooves and gears system, etc). Usually a pre set amount of multiplication can be setup, such as 3to1, 5to1, however the worm-gears or device is setup. Awesome. But if one side has zero traction, zero times anything is....zero. No power will be sent to the other side. As the OP mentions, this can be overcome by applying brake pressure, but doing that in all situations isn't always the easy, or the best idea. You can't just brake the front axle, so you'll be binding up the whole drive-train and if your back axle for instance has full traction, your killing the power to it, while trying to get the front to stop slipping, or vise versa. So in short, if one wheel has zero traction, you have an open diff.

Limited slip is wicked when there's at least some grip available, so the torque multiplication can work. On dirt roads etc you'll likely always have some grip at one tire for it to work, on sheer ice, rocks where your tire will lift, (or in an Audi rally car, hard corning causing tire lift...not a problem in the mog ) ditch crossing where one tire might lift, or snow where you get high centred or spin and melt into ice, not so much. Tire lifts, or is on ice, or very slippery aggregate, you have zero power to the other side.

Modern vehicles get away with this using computerized traction control systems that are capable of braking just one axle, or, even, one wheel on some systems, using the ABS system. You can't do that on a retrofitted system. On the back axle you can use the handbrake (in the case of a RWD car) but on a 4wd, if the center isn't open, your again, binding the whole drive-train, and cutting power to the front.

I wheel a lot in snow up here, open diff's and limited slip don't cut it 20"+ of snow, locker, or nothing, pressing the brakes to transfer power to the wheel with grip when pushing drifts is not an option and that's also hard on the drivetrain. I'd rather have an open front diff and a rear full locking, so when I get to the top of the hill, I can still steer (open front) and have the rear locked to finish the hill climb. Or better yet, open diff's or limited slip for ice (highway driving, as in daily driving), full locking for icy hills, backroads, and the deep stuff (fully locking both diff's on sheer ice is....not fun).

Again, just my type of wheeling.

 

[Metcalf]

One thing I really wanted to test with my front autolocker/rear limited slip idea is the bind between the front and rear axle....

The short version. Almost all of the bind went away ( vs autolocker/autolocker or spool/spool )

A front autolocker seems to unlock and lock MUCH faster and with MUCH less bind than with a selectable locker. One common trait I see with selectable lockers is that once locked, and basically a spool, if they have any bind on them at all they don't like to unlock. Some are better or worse than others, but it seems to be a common trait. A lot of time you see a little steering wheel sawing to try and get the bind out of the locker.

The other thing I noticed. The rear end 'pushes' less. When running a spool, auto-locker, or locked selectable the chassis always seems to be binding on itself with nowhere for the any tension in the system to be released. To me, it seems like the best place for the bind to go is out the inside rear tire. This seems to cause the minimal upset to the chassis.

The other thing I really like is that the rear end doesn't want to kick downhill as much and the front end goes in the direction it is pointed, even when turning and trying to go uphill.

In my situation with a short wheelbase on the Willys I rather have the front end do more work than the rear axle. This helps keep the chassis more stable when climbing. And it climbs pretty good. Escalator in Moab, 85" wheelbase, autolocker front, limited slip rear.


I kinda wish someone made a selectable 'automatic' style locking diff.

There are some limited slips that can lock up 100% without the torque multiplication issues of the old tru-trac design.

http://www.wavetrac.net/

Not cheap however....ouch.

 

[mogwildRW1]

Hmm, interesting. I like the idea, makes sense because the rear axle wouldn't be "pushing" and keeping tension on the front axle, not allowing it to unlock and thus, not causing it to bind. Rather, the front axle would be pulling. Innovative (nice willys too!)

I've seen that wavtrac, for the money, I'd go with full lockers. I also think you can get a Torsen with an E-locker? Not sure, haven't looked in a long time since I got the mog I haven't needed any other 4wd. There's so many variation and different systems its hard to keep track, and lots of re-branding going on.

 

[Metcalf]

Hmm, interesting. I like the idea, makes sense because the rear axle wouldn't be "pushing" and keeping tension on the front axle, not allowing it to unlock and thus, not causing it to bind. Rather, the front axle would be pulling. Innovative (nice willys too!)

I've seen that wavtrac, for the money, I'd go with full lockers. I also think you can get a Torsen with an E-locker? Not sure, haven't looked in a long time since I got the mog I haven't needed any other 4wd. There's so many variation and different systems its hard to keep track, and lots of re-branding going on.

Thanks

Yeah, wavetrac is WAY expensive. Neat technology though. You can get a limited slip with an over-riding locker in a few applications. The most common is the rear end of just about any new powerwagon, JK rubicon, or TJ rubicon. That is basically what I am trying to find to swap in the rear of my Willys when I regear again....

 

[78Bronco]

Typically your front end is geared slighty off the rear ratio so the front axle is pulling the vehicle...for instance my bronco has 4.09:1 Up front and the rear is 4.10:1. Thus the front tires turn faster than the rears based on the same input rpm. Binding in the driveline is common.

Personally I would not throw your money away on a limited slip as they require both tires to have some traction to work properly. Look at the rear ARB and add a winch for go anywhere capability. Your rear axle is stronger and when you are carrying a load off road you will want to take advantage of the weight bias giving you much more traction out back. Locked front makes turning a biotch.

 

[locrwln]

Air pressure?

30psi. Truck weighs 9200lbs loaded. I could probably go a little lower, but based on over 20 years of wheeling everything from Jeep, Toyota, Mazda, Chevy, Ford, motorcycles, Scouts, 2.5t, and humvees, over most every kind of terrain, I feel confident, that I needed the front locker to make it an easy no spin climb out of what would have been a tire spinning endeavor as evidenced by the mogul effect that the other (non-locked I assume) vehicles have turned the road into. The last part up to the summit was very steep and loose. Could you have made it sans locker? Sure, but it was much more relaxing with it.

Again, my current set up is the factory g80 "gov-loc" rear and Eaton E-locker front. Works very well for me and I have used the locker much, much more than the winch. To paraphrase Ferris Bueller, "If you have the means, I highly recommend it."

Jack

 

[Metcalf]

Typically your front end is geared slighty off the rear ratio so the front axle is pulling the vehicle...for instance my bronco has 4.09:1 Up front and the rear is 4.10:1. Thus the front tires turn faster than the rears based on the same input rpm. Binding in the driveline is common.

Personally I would not throw your money away on a limited slip as they require both tires to have some traction to work properly. Look at the rear ARB and add a winch for go anywhere capability. Your rear axle is stronger and when you are carrying a load off road you will want to take advantage of the weight bias giving you much more traction out back. Locked front makes turning a biotch.

I don't think what I am experimenting with is binding from different gear ratios. What I was referring to is the bind created by all the tires going along a different radius when turning. There is not only bind with the front and rear axles doing different distances, but also bind between the left and right tires.

My willys is locked in the front, limited slip rear....it turns WAY better than a locked/locked vehicle. The rear end doesn't 'push' or torque the chassis over. The front just does it thing.

If you have a bunch of weight bias to the rear do you really need the locker? Most vehicles are not going to lift a REAR tire while trying to climb, they are going to try and lift a front tire.