what is locked/unlocked ctr differential? AWD and 4WD?

[FoxChung]

what is locked centre differential and unlocked centre differential? which one is good the offroad and why please?

and

what is different between 4WD and AWD?

 

[hyde]

what is locked centre differential and unlocked centre differential? which one is good the offroad and why please?

and

what is different between 4WD and AWD?

jeepjeepster will answer your first question, he has no-slip differential. Simply put it allows no slip between your wheels. If one turns other must turn. Some limiteds and renegades come with limited-slip differential. It slips but not so much to lose traction. That's what happens when you are stuck in the mud, and those sedans have one wheel spinning crazy while other is standing still, no torque.. all power is sent to slipping wheel.. while no slip distributes evenly..

Nowadays many cars come with AWD, it is junk for off-roader. It is good for rainy weathers, slippery surfaces and light snow. You don't need to disangage it, it can be used all year long (in most cases you cannot disangage it).
4WD is meant to be used for what we have in our jeeps as 4x4HI or 4x4PART TIME. It must be disangaged in dry pavement, so that it doesn't damage your drivetrain. Although it is changing nowadays. Forget both and get 4x4 O

Jeeps are 4WD squared. With selec-trac you are getting 4WD + AWD (sort of). With select-track, you can use your 4x4 all year around, or slip it into 4WD kind of operation.

this is just basics, and more experienced wheeler might give you more info

 

[JeepJeepster]

Hehe, Im here to save the day!

Anyway, with an open differential only one wheel is guaranteed to get torque. With a 4wd jeep that has open differentials front and rear, it will only have 2 wheels guaranteed to receive torque when in 4wd.

On-to the transfer case. The transfer case is what controls the amount of torque that goes to the front and rear diffs. In part time, it spilts it 50/50 and makes the front and rear diffs spin at the same speed. The reason you DO NOT use this on dry black-top is b/c the front and rear wheels take different arcs resulting in different speeds. The select trac transfer case has an extra option over the command trac transfer case and lets you put it into full time 4wd which allows the front and rear diffs to spin at different speeds. This option is kinda like an AWD car and isnt very good offroad in mud or snow. It works best in rain and light or patchy snow on the road.

A locker goes into the front or rear diff and makes the two wheels spin instead of having one wheel guaranteed to get torque. This means in 4wd, you would have 2 rear wheels spinning(the rear diff has a locker) and one front wheel spinning.

Does this clear things up? O

 

[Fjellfinn]

Hehe, Im here to save the day!Does this clear things up? O

All clear !

Please also explain us why I should get me a locked diff instead of the LSD (Limited slip)
and perhapse some words why choos ARB air-locker or the one you have... (Aeh)

 

[grogiefrog]

Hehe, Im here to save the day!Does this clear things up? O

All clear !

Please also explain us why I should get me a locked diff instead of the LSD (Limited slip) and perhapse some words why choos ARB air-locker or the one you have... (Aeh)

I didn't write this, but this about says it all! (Cheers)

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The Difference between Lockers, LSD's and open Diffs
There are basically three differenct types of differentials. Open, limited slip, or locked.

Open differentials:
This is the most common type of differential (diff). Most jeeps come stock with open diffs, though the rubicon comes locked and the limited slip (LSD) was an option in certain years. An open diff is designed to allow the two wheels on the axle to turn at different rates during turns. As you may know, the outer wheel on the axle must turn faster than the inner wheel during cornering to cover the larger distance. An open diff allows this to happen with a set of smaller spider gears between the two axle shafts. . The down side is that it transmits power to the wheel that has the least resistance, or traction. This is good for normal, on pavement driving since it minimizes tire wear in turns, but In terms of off road performance, this is a bad thing. As soon as one tire starts slipping in the mud or sand, the tire that still has traction will stop receiving power. All of the power is sent to the spinning tire and unless you can add resistance to that spinning tire, you lose pushing power on that axle. If you spin a tire on both axles, you lose forward movement. Thus, with two open differentials you really only have a true 2wd system.

Limited slip devices:
LSD's are a step up from open diffs. These diffs use spring loaded clutch plates in addition to the spider gears of an open diff to transmit power to the axle shafts. when moving straight, the clutches allow the wheels to turn together normally. when one wheel wants to turn faster than the other, the clutches resist the faster wheel's movement. it must first overcome the friction on the clutch plates, which is a result of the spring force, before it can turn at a different speed. if the turn is sharp enough, the clutches will release, allowing the LSD to operate like an open diff for the duration of the turn. at the end of the turn, the clutches re-engage and keep the wheels turning at the same rate. Going back to our "stuck in the mud" scenario, the plus side to this setup is you still have a limited amount of power being transmitted to the tire that still has traction. until the amount of torque applied to that wheel can overcome the clutch friction, you still have forward movement on that tire. If you are stuck hard however, the amount of torque needed to move you forward can be more than the clutch friction and the clutches will break free on both tires, leaving you with an open diff. There is also the downside of having to replace the clutch plates every so often (~30K miles on some models) and that can get expensive. If the clutches wear out, you are left with an open diff. with an LSD, you have a psuedo 3wd or 4wd system (3wd if you have one axle with an LSD and an open diff on the other, 4wd if you have two LSD's). it's only a psuedo system because they can be defeated and rendered into an open diff in the right situation.

Lockers:
Lockers are the ultimate form of differential from a traction stand point. locked diffs do exactly what they sound like: they lock both wheels together so that they turn at exactly the same rate all the time. Unlike the LSD's, there is no defeating them short of breaking something. the tires will always turn together. a locked diff wll give you a "true" 3wd or 4wd system (1 or 2 lockers again) because all four wheels will always be turning even when there are tires that are slipping without traction. the only way you lose forwad movement is to lose traction at all 4 tires. Modern lockers now offer either a selectable option (you can turn them on or off as needed) or an automatic option. Auto lockers will still allow the wheels to turn at different rates during cornering so you don't totally lose the benefits of a diff on road but still retain the benefits of turning both wheels off road. Selectable lockers offer the benefit of open diffs on road and locked diffs off road at the touch of a button. There are two main types of lockers: lunchbox type, and full carrier lockers. the lunchbox style replaces the spider gears in the stock carrier. This means that the competent home mechanic can install one with basic tools without having to reset the complex measurements on the ring and pinion gears (on most vehicles). The down side is if your stock carriers are weak and some axles do have weak carriers. Be sure to check to see what axle you have and where it's weak points are before adding a lunchbox style locker (or any locker for that matter). The full carrier style locker replaces the stock carrier with the locker assembly itself. the ring gear is mounted to the locker itself, which is usually stonger than the stock carrier. This style however requires that the gears be reset by a professional mechanic and is usually best installed when regearing to account for larger tires or to achieve a lower crawling gear ratio so you don't pay for the gear reset twice. The benefit is a stronger axle due to beefier locker acting as the carrier. both styles do the same thing however.

What about Spools and mini spools, or welding the spider gears?
Spools are the "old fashioned" lockers. Basically all they are is a solid piece of metal to replace the carrier that the ring gear mounts to and couples the axle shafts together. There is no provision for the tires to spin seperately like a locker would allow. The tires are joined no matter what as if a solid piece of metal connected them. Mini spools do the same thing, but replace only the spider gears leaving the stock carrier for the ring gear, much like the lunchbox locker. Welding the spider gears together and to the carrier accomplishes the same thing as a mini spool without the cost. Done right, there is no difference as far as performance. Spools will wear tires much faster and increase the risk of broken axle shafts more than any of the other diff options in a vehicle that sees the road at all. For a trail only rig, they are a cheap option. They are also very predictable as far as handling characteristics where as a locker can disengage and engage on pavement with sometimes surprising results.

What should I put on my rig?
It depends on your driving habits, what kind of traction you want off road, what you're willing to spend and how much maintenance you want to do. LSD's are a great traction compromise, but are high maintenance. open carriers are best for on road DD's but can be a problem off road. Spools are cheap, but cause tires to wear fast on road. Lockers are expensive, but offer great traction off road and the newer models have excellent on road manners. If your rig is a trailered rig, spools might be the way to go. if it's a weekend warrior and has a way to disconnect one axle (locking hubs or a front axle disco can allow one or both wheels to freewheel during turns even with a locker or spool), a single locker up front might be enough. a full time 4wd vehicle is best equiped with LSD's and lockers interfere with such a system. mixing and matching the options between front and rear axles offer some versatility. for instance a spooled or locked front with locking hubs could be combined with an LSD or selectable rear for great off road traction with good on road manners. Whatever you decide, be sure that your axle can take the added stress before adding any of the above traction devices. Extra traction isn't worth anything if you break an axle shaft!

 

[Fjellfinn]

I didn't write this, but this about says it all! (Cheers)

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The Difference between Lockers, LSD's and open Diffs:

What a wonderfull and superb explanation !!

Next step -- tell us why I should go for Powertrax in light of this explanation, how this is implemented on a 2003 Liberty with LSD (not Dana) and how this will work on a highway in 100 mph O

 

[JeepJeepster]

I didn't write this, but this about says it all! (Cheers)

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The Difference between Lockers, LSD's and open Diffs:

What a wonderfull and superb explanation !!

Next step -- tell us why I should go for Powertrax in light of this explanation, how this is implemented on a 2003 Liberty with LSD (not Dana) and how this will work on a highway in 100 mph O

Haha, why are you going 100mph in the libby? Are you on the autobahn or something? Id say you wouldnt know it was in there at 100. The only time it pops and carries is when Im going slow in a parking lot or pulling out and i need to get on the gas.

 

[Fjellfinn]

I didn't write this, but this about says it all! (Cheers)

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The Difference between Lockers, LSD's and open Diffs:

What a wonderfull and superb explanation !! O

Haha, why are you going 100mph in the libby?.

Like in your PM I just sent you I often mix up NOK / USD and now in km/t <--> mph (Aeh) ...
(It was 421 USD for the lunchbox locker)

OK - I will refrase - on ordinary dry road at high speeds about or somewhat over speedlimit and cruising along in high speed for several hours on a road with lots of curves-
will you notice the Powertrax in any way ?