Differential Question

[milo12]

I am in the process of designing a camper for a Dodge 5500. The 5500 has brand new axles that have ratings of 7000 lbs front and 13,500 lbs rear. Since my gross weight will be around 12,000 lbs I figure it should be a pretty reliable package. My dilemma is no one makes any lockers for these axles. Dodge offers a rear limited slip as an option.

So here is my crazy idea. I have read on other 4x4 forums of rock crawlers using line locks on the individual brakes. The idea is when a tire spins/ is airborne, lock that brake and the other side gets driven through the diff. This also is convenient for making very tight turns, which may be very convenient on a large truck. The turn is done by locking the inside rear and then when you apply power the truck pivots about the locked rear tire.

So will this work on a vehicle designed for more "expedition" type use? I figure the wheel brake feature will help me since without lockers I am more liable to get stuck.

I plan to order the truck soon and I need to decide whether or not to get the limited slip diff. I expect you can not use the wheel brake feature with the LSD since the LSD will be fighting you if one wheel is locked.

Any comments appreciated.

 

[Robthebrit]

I would first drive the truck with the standard axles and the LSD - which will help. I very rarely use the lockers on the mog and when I do you could most certainly get by without them. With such a heavy (probably top heavy) vehicle you are not going to be climbing rocks and driving on real nasty trails so the only thing you really have to contend with is mud and snow. In these situations its debateable whether or not lockers help. My mog is more squirmy in snow with the lockers on that when they are off. On trucks this size the first thing it to make sure the front wheels are directly driven either by a tcase or a locking center diff in the case of a perm 4x4.

Using the brakes is a definate option but you really need to understand the system on your truck and the situations you'll be in, it might get old quick when you need to use it. One of the most useful techniques for driving a Hummer H1 is knowing when to use the brakes. Sides effects of the torsion diff can leave a H1 stranded, for example diagonal wheels off the ground. The torsion diff can only multiply the torque going to the lowest power wheel on the axle - 5x (for example) the torque required to spin an airbone wheel is not enough to move the truck. Gently holding the brakes gives 5x times the brake force to the other wheel which is enough to overcome the brakes and move the truck. Even with a torsion diff it can take a huge amount of brake effort to force the other wheel to go around.

Rob

 

[TheRoadie]

Some good detail, Rob. Do you mean "Torsen" diff.?

 

[Grim Reaper]

Some good detail, Rob. Do you mean "Torsen" diff.?

Its a type of limited Slip that uses a worm gear set up instead of clutches like most LS's use. Torsen in the brand.

http://www.torsen.com/

 

[Robthebrit]

Some good detail, Rob. Do you mean "Torsen" diff.?

Yes, I do.. Its one of those days..

Rob

 

[cruiseroutfit]

Rockcrawlers don't use the Line-Locks for axle control (they have lockers, no need), rather they use them to "pivot" or "front burn" using the front drive only and one rear tire or the other locked. We ran this way in the comb buggy I competed in, very useful.

The way you are describing is basically how the Toyota A-Trac system works (as I understand it), it basically uses ABS senors to detect unequal spin, and applies the brakes as needed.

In the real world, short of it being computer controlled, I think it is very impractical at best. While there may be certain situations where it is useful, I don't know that you'll find your 12k lb beast in them. Mud, sand, snow... I'd think that by they time you even realized you needed to operate the linelock (which requires pressing the brakes and then locking the fluid at the tire), its too late, your stuck.

What axles are they?

 

[Tucson T4R]

I run a 4Runner with Atrac. It works great when you pick a line and drive through it at a consistant RPM. If you are starting and stoping on rocks, a mechanical locker is far superior. In most overland conditions Atrac is all you need. If you plan to run more technical trails, A locker is the way to go.

 

[madizell]

I don't believe that line locks will accomplish what you want. Even for something more suitable for hydraulic locks, such as locked wheel pivots, your heavy and longer wheelbase truck won't respond to a locked wheel the way you think it will, in my opinion. More likely to happen is if you lock one wheel, the truck will simply drag that tire down the trail. Besides, pivot brakes, as used on sand buggies and rock crawlers, are generally not line lock units (lift button locks), but hand-brake type devices so that the amount of brake force to a given wheel can be modulated. A line lock does not modulate brake pressure, it simply interferes with release of hydraulic pressure in the line that you lock. Trying to set it at other than full lock probably won't work the way you wish.

As mentioned above, lockers don't get used all that often when use of the locker is selectable. I rarely use my ARB's, even in the mud. The limited slip should be sufficient and is a factory item, which means it will come installed and warranted. A good LSD could be all you need. If you plan to go where you can or likely will get stuck anyway, you will need a winch whether or not you have a locker.

 

[milo12]

Thanks everyone for all the great input.

Looks like the LSD is the way to go. Time to get out the checkbook.:yikes:

I'll post an update as I progress.

 

[ntsqd]

Steering or Turning brakes would accomplish what you're looking for in the line-locks. Sand rails use them almost exclusively for turning under power. In some places they are known as the "poor man's posi."
Still, I'd go with the advice against them, at least until proven to be needed.

 

[Ron B]

the torsens will definately leave you stranded if you don't use the brakes/know how to drive the hummer (using brake-throttle-modulation/btm). You rarely have to mash the brakes unless you are doing a really crazy obstacle. I like it better than a traction control system, which is reactive (usually won't engage until you are having issues). It'll go just about anywhere a locked truck will go.

That being said, I like to wheel crazy stuff so I put a detroit in the rear. Heavy btm puts a tremendous amount of stress on the t-case/tranny and I've seen a few t-cases go in the boonies -- rather not have it be me!

rb