Limited Slip Faceoff: Detroit TrueTrac vs. ARB Air Locker

[rube bonet]

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.

The bronco gear rations are different because it is as close as the dana front and ford rear can be due to the different design of the gears. Most vehicles are the same ratio front and rear.

Metcalf, I agree with what you are saying. I have built quite a few crawlers, I always run ARBs front and rear. I used to crawl and rockrace professionally, I would typically crawl (and the rockcrawling portions of rockraces) with the fronts locked and the rears open, it allows the vehicle a much better turning radius, especially with cutting brakes, and keeps the rear end "on line". A LOT of the guys actually run a spool up front, and an arb in back for more reliabilty. I aways preferred ARBs front and rear, I like the rear locked and the front open for the high speed sections.

In daily driver/ expedition type applications, I have run quite a few different set ups, and I still prefer ARBs. Detroits are scary on icy mountain roads, not to mention sidehills. LSDs, if they are effective, will be almost as scary.

I like the idea of the lsd and locker combo a lot, I just don't know of any that hold up in heavy or abusive applications.


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[Buliwyf]

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? Rear.Two full case automatic lockers. Kinda hardcore? The Front autolocker will make snowy street use tough.
Three lunchbox lockers Crap.
Two or three limited slips Ok for light wheeling and smaller SUV's

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?
Because a F350 will snap those welds or a rear axle like a twig the first time you turn on dry pavement. 8000 pound truck with perfect grip from all that weight. The tires aren't going to let go too easy.

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....

Fullsize trucks, especially 250/350 and up, have stiff rear springs for towing. The front has more flex than the rear. And more weight over it. With open/open diffs one of the rear wheels will spin way before the fronts usually. Or at least the little bit of spinning from the rear is harder to overcome when climbing.

And my Superduty generally will lift a rear wheel before a front. I can't recall the last time I had any real loss of grip up front. The rear axle is the one to lock 1st on fullsize trucks. No doubt about it. Maybe it's different for smaller SUV's, but it's pretty conclusive with fullsize's.

I'm considering a Detroit locker up front as well as my rear one, but for now, it's a waste of money. My truck is allready far more capable than my needs.

 

[HillbillyfromAL]

I'd give the vote to the TruTrac up front and Full Detroit in the rear. I had that in my 04 F250SD and it was great. Selectable lockers IMHO are the perfect choice for anything with traction control, like my Discovery. For anything else I've pretty much used the other configuration. My two exceptions were a 04 Jeep Rubicon, and 83 Yota which had hydraulic steering and both ends with a full Detroit. The selectable will act as a full spool locked which causes the drifting and wanting to push straight forward on slick surfaces. While the Detroit can do that as well, it's not nearly as pronounced unless its in the front. Under throttle on loose surfaces it allows it to break traction much quicker than a LSD. So if there's snow or ice you need to use a light foot.

 

[1stDeuce]

I just found my club, so I'll take a swing at what's left of this horse too!

First, we're not talking about a flexible Jeep, or a rock crawler, we're talking about a stiff truck on bad roads. Second, IMO, and by the sounds of the OP's description, survivability ranks above ultimate mobility.

I'll consider my GMC 2500, which is similar. With a camper on the back, the truck is fairly well balanced, so the major limitation to mobility is when the truck gets crossed up, which happens a lot on tougher trails. Having just a rear locker worked well on my two previous (3/4 ton diesel) trucks to combat this. I have not yet taken the current truck up trails rough enough to need any locker at all here in CO. (Good thing, cause it doesn't work...) I briefly considered running a TT or E-locker in the front, but honestly, I don't want the temptation of taking this truck where is probably shouldn't go, and I don't want to front to do that much work.

I think a TT would be fine for front axle use, but I personally feel that there is too much possibility to engage a front locker in a "last resort" situation, and grenade the front end. Limiting the front to a TT, with a locker in the rear forces you to use the stronger rear axle and locker to get through tough situations, while allowing the front to do far more than it might do with an open diff if you ride the brakes a little.

Of course I'm waiting to see how Jack does with the E-locker in the front of his 2500... it sounds like he's used it, but not a lot. I find the same to be true of the rear locker in my jeep... I rarely engage it, as I find it easier to just pick a better line that doesn't cross up so badly, or add a little brake pressure and get through something (TT front, Rubi rear locker, which is a TT when it's unlocked.)

I think for the price, I would consider the lowest cost locker you can find for the rear (Selectable or auto, on a long truck it's less critical) and a TT in the front. Contrary to what I've read, a TT does NOT need wheel slip to bias, so that concern is out. (That's a gov lock's thing...) A TT DOES bias better with more torque flowing through it, which is why the brake trick works so well, and it will work without any wheel slip at all.)
$.02
C

 

[General Automag]

Another video for your collection

'Interesting video. I like the old 70-72? F-100! We have Auburn LSDs in our Toyota FJ40 and a stock LSD in the rear of our full-size Chevrolet, and they don't behave like the trucks in the video. When one wheel slips, the other wheel kicks in, or rather, starts turning.

With our Land Cruiser and Chevrolet, when you floor it, both vehicle will spin both wheels on grass and on pavement. Some LSDs must behave differently than others. I've been on uphill grades with slick and wet loose rocks haven't had any issues with traction. Again, we have been very satisfied with LSDs in our vehicles, and since we have winches installed and try to drive smart, we really don't worry about getting stuck.

 

[crawler#976]

I'm fortunate to have both a helical limited slip and electric locker in the rear axle of the Power Wagon. I rarely need the rear locker, but when I do, it's because the limited slip is no longer providing enough traction. We tow a StarCraft 10RT (loaded with gear and water, it's about 4000 lbs) into some pretty difficult places. If I had to have one or the other, there is no doubt about it - I'll take the selectable locker. The limited slip really does a fine job most of the time, but when it doesn't, you'd better have a winch (or a Power Wagon handy).

 

[drodio]

@crawler#976, that's super helpful. Is there ever a time you *don't* like having the helical limited slip? (BTW is it a Detroit TrueTrac or other brand)? I'm especially curious about snow or other slick road surfaces or tight turns in parking lots where others have said the limited slip sometimes becomes a liability.

 

[Metcalf]

@crawler#976, that's super helpful. Is there ever a time you *don't* like having the helical limited slip? (BTW is it a Detroit TrueTrac or other brand)? I'm especially curious about snow or other slick road surfaces or tight turns in parking lots where others have said the limited slip sometimes becomes a liability.

The rear locker on a Powerwagon is built by AAM. It is basically like a True-Trac with a locking function built onto one side....

I've been running a rear powr-lok ( good clutch style limited slip ) in the rear of my dodge truck for years. I have run it all over the place good roads and bad. It makes enough of a difference that I generally do not have to run 4wd that much. If the truck is going above 35mph I don't need 4wd. I would much rather deal with the odd time that both rear tires want to spin rather than not have it.

 

[drodio]

@1stduece,

Thx for the perspective.

It sounds like this might be an optimal way to go about it:

1 (now) Get an ARB rear locker as the first thing (I prioritize this as #1 because there are already situations where I've wished I had more traction)
2) Depending on results (i.e., am I ever stuck & can't free the truck?) then get a winch
3) Depending on results (i.e., do I have to use the winch in situations where I don't think I should have to?), get a TrueTrack for front axle

Maybe I go about steps 1, 2 & 3 over a 1 to 2 year period as I find myself in situations calling for the next step.

 

[PGT]

Not that its a direct comparison, but I've driven a few Subaru's in the snow/ice with both open diffs and LSD's (and a selectable one that can be locked 50/50..i.e. DCCD). The LSD will lock up when one tire is on an icy patch and another is not. This makes for some difficult driving....the car pulls hard to one side and you'd better be ready for it.

 

[Metcalf]

Metcalf, I agree with what you are saying. I have built quite a few crawlers, I always run ARBs front and rear. I used to crawl and rockrace professionally, I would typically crawl (and the rockcrawling portions of rockraces) with the fronts locked and the rears open, it allows the vehicle a much better turning radius, especially with cutting brakes, and keeps the rear end "on line". A LOT of the guys actually run a spool up front, and an arb in back for more reliabilty. I aways preferred ARBs front and rear, I like the rear locked and the front open for the high speed sections.

This is where I also picked up that idea. I lot of crawlers started running the rear open more often. I noticed a fair number of people going to a front detroit/rear ARB combo. A lot of the people that where class limited to one locker also ran it in the front....usually with cutting brakes in the rear as a workaround.

For high speed sections I usually just kick the front out. If I am going faster than 1st or 2nd low range I don't generally need 4wd. Heck, as an experiment I ran a LOT of stuff in high range granny gear in the Willys this last trip. That worked REALLY well. That is about 30:1 and allowed me to do most everything other than major obstacles. Running this way I could run 1-2-3 in high range and toggle 4wd in and out as needed. It worked fantastic....

In daily driver/ expedition type applications, I have run quite a few different set ups, and I still prefer ARBs. Detroits are scary on icy mountain roads, not to mention sidehills. LSDs, if they are effective, will be almost as scary.

Agree, daily driver can be different. Honestly, I don't think many daily drivers need any kind of locker. If they want to spend the money fine, but how often do they REALLY use them?

I like the idea of the lsd and locker combo a lot, I just don't know of any that hold up in heavy or abusive applications.

Not that it would have THAT many applications, but the rear axle of a powerwagon unit is pretty dang beefy. 10.5 ring gear, 35 spline shafts.

The rear of a JK rubicon is another option. Its basically the improved d44 design. They hold up pretty well. They are an odd 32 spline unit however. I have been trying to find a TJ rubicon air actuated unit for my Willys to retrofit. They are still 30 spline.....but require low air pressure ( like 6psi ). They are not the strongest, but in my sub 3000lb willys it should be fine.

What I would really like to see is a differential that could be selectable between open and an automatic detroit style action. That could be amazing....

 

[Metcalf]

The Front autolocker will make snowy street use tough.

It could, but what if you don't have to drive on snow/ice? I rarely use 4wd in my Dodge in snowy/icy roads above 2nd/3rd gear. I'm tempted to try a front locker just to see how bad it would really be....

Three lunchbox lockers Crap.

That is a pretty tough blanket statement. I ran a Spartan lunchbox locker all over some pretty hard trails in moab for over a week in a FRONT locker applicaion, in a dana 30, with heavy 35" tires without any issue? For the money a GREAT upgrade. As the axles get larger so does everything else.

Two or three limited slips Ok for light wheeling and smaller SUV's

For 'expedition' type use are vehicles really doing anything more than 'light wheeling'? From my perspective it seems that most of the terrain people are going over would rarely require anything more than proper air pressure and smart driving? It's not like people are taking there campers laden trucks up Pritchett Canyon. My dodge is open front/limited slip rear and I haven't run into many limitations with it yet....

I don't mean to get off on a rant, but I think a lot of people jump into adding a LOT of unnecessary upgrades to there vehicle before they have ever even had any issues?

On a long wheelbase rig, why not a spool or welded rear diff?
Because a F350 will snap those welds or a rear axle like a twig the first time you turn on dry pavement. 8000 pound truck with perfect grip from all that weight. The tires aren't going to let go too easy.

My first choice, no. A choice yes.

Fullsize trucks, especially 250/350 and up, have stiff rear springs for towing. The front has more flex than the rear. And more weight over it. With open/open diffs one of the rear wheels will spin way before the fronts usually. Or at least the little bit of spinning from the rear is harder to overcome when climbing.

I have a limited slip in the back of the Dodge. I have never noticed an issue spinning only one rear tire. Maybe a limited slip in the rear is enough for most situations?

And my Superduty generally will lift a rear wheel before a front. I can't recall the last time I had any real loss of grip up front. The rear axle is the one to lock 1st on fullsize trucks. No doubt about it. Maybe it's different for smaller SUV's, but it's pretty conclusive with fullsize's.

Maybe its because of the limited slip but I have never really need more traction from the rear axle? ( on my dodge )

I'm considering a Detroit locker up front as well as my rear one, but for now, it's a waste of money. My truck is allready far more capable than my needs.

I very much agree with this. My feeling is that most vehicles are WAY more capable than most people give them credit for. I think a lot of mods fix problems that don't really exist.

 

[Metcalf]

@1stduece,

Thx for the perspective.

It sounds like this might be an optimal way to go about it:

1 (now) Get an ARB rear locker as the first thing (I prioritize this as #1 because there are already situations where I've wished I had more traction)
2) Depending on results (i.e., am I ever stuck & can't free the truck?) then get a winch
3) Depending on results (i.e., do I have to use the winch in situations where I don't think I should have to?), get a TrueTrack for front axle

Maybe I go about steps 1, 2 & 3 over a 1 to 2 year period as I find myself in situations calling for the next step.

I would probably flip number 1 and 2 around. You WILL get stuck sometime in an inconvenient isolated location alone without help some day Adding a locker, unless you have PERFECT judgement will just get you stuck further from home and help.....

Moving a winch from one vehicle to another is WAY cheaper and easier than a locker in the long run also....

 

[crawler#976]

The helical limited slip is "transparent" to me - it probably isn't as tight as some LDS can be.

Over the years I've had Detroit Lockers, Spools, LDS, and selectable lockers. Believe it or not, my list as far as preference would be:

1. Selectable

2. Spool

3. LDS

4. Detroit (or other automatic locker)

Here's the reasoning - the first two are 100% predictable in all conditions. The selectable is either locked or not, the spool is locked, period. So, if you know what they do all the time, you can adjust to that. I put 55K on a dual spooled Toyota P/U - used it as a hard core trail rig and my daily driver. Yeah, it ate tires at an alarming rate, but I knew that going in. Yeah it barked like a big dog on pavement, but it really wasn't all that bad to drive. Obviously, a selectable is open until you need it. ARB is king - almost instantaneous actuation, so in rough stuff, you can cycle an ARB off to turn, back on to pull. Makes U-Joints much happier. On the Power Wagon, actuation is slow, and requires some fore thought - they better be locked before you need them.

An an LDS, while better than no locker, isn't a true locker. They are a lot easier to drive on pavement since they are open until a wheel spins.

I had Detroits in the ol' beater, and hated them with a passion. A Detroit and a 5 speed is completely unpredictable - I never knew when it would exhibit locker wiggle when shifting or turning. Since the Detroit is locked until there is enough bias to overcome the mechanism, it does some strange things when it does. On a 5 speed, if the truck was under load, like going up hill on the highway, the locker stayed locked. Sometimes when coasting or just rolling down the road, I'd upshift and the backend would go sideways when the locker released. Sucked. So, I went to dual spools. I broke the front Detroit on Outer Limits, so replacing it with another wasn't even considered as an option. When I splashed the rear gear set, I pulled the Detroit, sold it, and put in the other spool.

 

[Metcalf]

ARB is king - almost instantaneous actuation, so in rough stuff, you can cycle an ARB off to turn, back on to pull. Makes U-Joints much happier. On the Power Wagon, actuation is slow, and requires some fore thought - they better be locked before you need them.

What about unlocking when the locker is bound up? It seems to me that unlocking usually takes some differential in wheel rotation. You might turn off the air, but then you turn and everything is all bound up and the locker won't release. I have noticed this on everything from ARBs to factory electric lockers. Kinda sucks.

I had Detroits in the ol' beater, and hated them with a passion. A Detroit and a 5 speed is completely unpredictable - I never knew when it would exhibit locker wiggle when shifting or turning. Since the Detroit is locked until there is enough bias to overcome the mechanism, it does some strange things when it does. On a 5 speed, if the truck was under load, like going up hill on the highway, the locker stayed locked. Sometimes when coasting or just rolling down the road, I'd upshift and the backend would go sideways when the locker released. Sucked. So, I went to dual spools (for a couple reasons - I broke the front Detroit on Outer Limits, and I hated it on the street, so replacing it with another wasn't even considered as an option. When I splashed the rear gear set, I pulled the Detroit, sold it, and put in the other spool)

You broke a detriot straight out? What application? I have seen a few Detroit lockers destroy themselves but it is usually from a violent axle break causing the dog teeth to sheer off from the wind up in the axle. I don't think I have ever seen a detroit fail before an axle.....

I do agree that a detroit locker in the rear axle can be a total pain on the street.