General Land Rover vs other makes 4wd system

[bguetter]

Just a quick general question. I understand what the CDL is in my 04 and how it works.

Sorry for the Noob question. I guess im wondering if CDL is a standard factory feature in other vehicles like wranglers, SUVs, or trucks?

I'll admit i had a wrangler in the past and i have found the disco much easier to drive offroad. Thats what made me wonder how unique the CDL is.

 

[Surf]

The traction control is what makes it better than a regular ol' unlocked from and rear 4wd system. If a wheel starts to slip, the traction control applies some brake to that wheel to make the one with more traction turn instead of the one that is spinning faster than the others. It works ok most of the time. It's not nearly as nice as having lockers though.

 

[MUSKYMAN]

a center locking diff is only needed on 4wd systems that have a center diff. Most 4wd systems are designed to drive in 2wd on the dry roads so the front drive shaft is disconnected when it rolling down the road.

 

[bguetter]

Muskyman- So vehicles that operate in 2wd, then are selectable to 4wd split the torque 50/50 front and rear while in 4wd like our CDL equipped Discos?

Surf- the reason i asked this question was i took my 04 out today for the first time in very wet offroad conditions and only saw the TC twice. Meaning i wasnt slipping very much at all despite the conditions and only using all season tread tires. Which got me thinking about how effective the CDL is and if other vehicles were similarly equipped or a unique feature of land rovers.

 

[ratboy]

So vehicles that operate in 2wd, then are selectable to 4wd split the torque 50/50 front and rear while in 4wd like our CDL equipped Discos?

correct.

 

[p m]

Muskyman- So vehicles that operate in 2wd, then are selectable to 4wd split the torque 50/50 front and rear while in 4wd like our CDL equipped Discos?

In our Discos, the torque is only split 50/50 front and rear while CDL is UNLOCKED.
When CDL is locked, the front and rear driveshafts are forced to turn at the same rate regardless of traction, the same as part-time 4WD trucks with front axle engaged.

ratboy: wrong answer.

 

[91 PBP 5079]

It was an option on the jeep cherokee (XJ) called the NV242 but was only availible with the auto box and was not labled like the land rover. I dont think they are very common. Not something most Jeep buyers understood. I wanted it when I got the jeep for my wife but did not want the automatic.

It had a full time 2 wheel drive position a full time and part time 4 wheel drive position. But only a 4 low part time no 4 lo full time.

I find the low range very helpfull when backing up trailers. It is easier to go slow. Kinda of hard to back up a part time case in low range on hard pavement smoothly.

 

[robertf]

tons of stuff has a center diff lock, but it has different names
jeep called it "emergency drive" in the 70's in wagoneers and automatic CJ7's
hummers have it (real ones, not the gm garbage), but I forget what the shift plate says. 4lock low or something like that
anything with an np203 has it, so that accounts for many fullsize ford, chevy, and dodge vehicles in the 70's

 

[p m]

jeep called it "emergency drive" in the 70's in wagoneers and automatic CJ7's

To be precise, all jeeps from 74 to 79 had an option called "Quadratrac" - full-time 4WD case with a limited-slip, lockable center differential. "Emergency drive" is when the center diff was locked.
Good transfer case (Borg Warner 1305/1339), I broke three.

 

[robertf]

To be precise, all jeeps from 74 to 79 had an option called "Quadratrac" - full-time 4WD case with a limited-slip, lockable center differential. "Emergency drive" is when the center diff was locked.
Good transfer case (Borg Warner 1305/1339), I broke three.

to be precise, cj5's didnt

yeah, I meant they called "diff lock" emergency drive. How did you break them? Were you running the AMC t-case lube that is refined from unobtanium?

 

[gmookher]

In our Discos, the torque is only split 50/50 front and rear while CDL is UNLOCKED.

When CDL is locked, the front and rear driveshafts are forced to turn at the same rate regardless of traction, the same as part-time 4WD trucks with front axle engaged.

This is not correct.

When the center diff is UNLOCKED, alslo known as open, torque is NOT 50/50 to both output shafts. Its the opposite, power will flow to the path of least resistance. It can be that almost all or all the torque goes to one output shaft, 90/10, or 70/30 or whatever, resulting in one side spinning faster than the other. This is what an open diff is designed to do. It lets one shaft spin at a different speed than the other hence there is a differential.

I agree with you, When you LOCK the center diff, torque will be split 50/50 irregardless of resistance. When the CDL is Locked, both front and rear output shaft spin at the same speed, driving both drive shafts at the same speed.Thus, it is locked, as in 'locker'

Similarly when one installs a locker, it forces both left and right side axles to turn the same rate and get the same torque when locked, and lets the two differentiate when OPEN, which is what our discos center diff is set to for 'normal' open 4x4 driving.

Just wanted to clarify.:victory:

 

[garrett]

In our Discos, the torque is only split 50/50 front and rear while CDL is UNLOCKED.
When CDL is locked, the front and rear driveshafts are forced to turn at the same rate regardless of traction, the same as part-time 4WD trucks with front axle engaged.

ratboy: wrong answer.

I too am assuming you accidentally typed the wrong thing.

LOCKING the CDL splits the power to the front and rear 50/50. With an "open" (no lockers) truck, the power will go to the path of least resistance. ie. The wheel that is spinning, has little to no traction or least amount of weight on it.

You can use brake modulation in order to help transfer the power to the wheel that does need the traction.

Having your CDL locked is not always the best option in off road conditions either. While turning in limited traction situations you might not want the front tire to rotate at the same speed as you rear wheel (since they are not "locked" in and rotate at the same speed now).........likely breaking traction and your momentum.

 

[MUSKYMAN]

I too am assuming you accidentally typed the wrong thing.

LOCKING the CDL splits the power to the front and rear 50/50. With an "open" (no lockers) truck, the power will go to the path of least resistance. ie. The wheel that is spinning, has little to no traction or least amount of weight on it.

.

wrong

come on Garrett you know better then this.

you too Gem...wrong

:rofl:

do we really need to go through all this again

 

[MUSKYMAN]

This is not correct.

When the center diff is UNLOCKED, alslo known as open, torque is NOT 50/50 to both output shafts. Its the opposite, power will flow to the path of least resistance. It can be that almost all or all the torque goes to one output shaft, 90/10, or 70/30 or whatever, resulting in one side spinning faster than the other. This is what an open diff is designed to do. It lets one shaft spin at a different speed than the other hence there is a differential.

I agree with you, When you LOCK the center diff, torque will be split 50/50 irregardless of resistance. When the CDL is Locked, both front and rear output shaft spin at the same speed, driving both drive shafts at the same speed.Thus, it is locked, as in 'locker'

Similarly when one installs a locker, it forces both left and right side axles to turn the same rate and get the same torque when locked, and lets the two differentiate when OPEN, which is what our discos center diff is set to for 'normal' open 4x4 driving.

Just wanted to clarify.:victory:

wrong

wrong

and not clearly correct

Gem ...time to shut back up again and learn how a differential works

 

[fishEH]

do we really need to go through all this again

Apparantley we do. Here's my understanding. A disco is an all wheel drive vehicle. Meaning drive is supplied to all four wheels. The differential, however, is open. This means that if one wheel loses traction it will spin due to it being the path of least resistance. An open diff. also allows us to drive normally, making turns where the outside wheel spins faster than the inside. When you lock the differential, drive is supplied to all four wheels equally REgardless of slippage. This makes everyday driving difficult and you will notice it kind of "hopping" around turns on pavement.
That's my very basic understanding, sorry if I'm off.

 

[MUSKYMAN]

Ok ...follow me here guys.

a differential is designed to split TORQUE 50/50 to either output shaft. Yes a open diff ALWAYS SPLITS THE TORQUE 50/50.

so if one side has little or no traction the other side is limited to only transfer that amount of torque.

Lets look at a standard 2wd to understand this.

say you have a 2wd pickup and one rear wheel is on ice and the other side is on dry pavement.

when the driver steps on the gas the torque is divided between the two sides 50/50. because the tire on ice can say only apply a very small amount of torque before it breaks loose and spins then that same very small amount of torque is applied to the tire with the traction and that small amount of torque being applied to both tires is what propels the truck forward. thats why it is called 2wd both tires are getting equal torque.

the age old concept of open diffs really only being one wheel drive is INCORRECT. both wheels are are actually driving or propeling the truck forward.

 

[MUSKYMAN]

now the locker part.

when you lock a CDL you know allow up to 100% of the torque to be applied to either side of the differential.

now you have the same 2wd truck and it has lifted one tire off the ground.

because the truck has a locker now 100% of the torque will be applied to the tire on the ground and propel the truck forward.

--------------------------------

the secret to understanding this is to remove land rover and disco and CDL and all the other distractions and just think about it in a simple 2wd application. Once you understand that then you can expand it to 2 differentials and then three.

having a complete understanding of these concepts will make you a better off roader.

 

[Swift]

Ok ...follow me here guys.

a differential is designed to split TORQUE 50/50 to either output shaft. Yes a open diff ALWAYS SPLITS THE TORQUE 50/50.

so if one side has little or no traction the other side is limited to only transfer that amount of torque.

Lets look at a standard 2wd to understand this.

say you have a 2wd pickup and one rear wheel is on ice and the other side is on dry pavement.

when the driver steps on the gas the torque is divided between the two sides 50/50. because the tire on ice can say only apply a very small amount of torque before it breaks loose and spins then that same very small amount of torque is applied to the tire with the traction and that small amount of torque being applied to both tires is what propels the truck forward. thats why it is called 2wd both tires are getting equal torque.

the age old concept of open diffs really only being one wheel drive is INCORRECT. both wheels are are actually driving or propeling the truck forward.

Right, so this is completely wrong.

A differential is designed to distribute power to the wheels that need it (i.e. turning a corner where the 4 wheels of your car need to turn at different speeds). A permanent 4WD system requires a centre differential as the front and rear axles need to spin at different rates in different situations. They are not designed to distribute power 50-50......UNLESS YOU LOCK THE DIFF. If you lock any differential, it sends equal power to both sides of the differential. In a centre diff, it distributes power equally to the front and rear propshafts. In the case of front or rear diff locks it equally distributes power to the left and right axles.

If you don't believe me, try this at home.....get a Discovery 1, make sure the centre diff lock is unlocked, and jack up one wheel only, leaving the other 3 on the ground. Get into your Discovery 1, start it up and gently accelerate. THE CAR WILL NOT MOVE. That is due to open differentials. Trust me, I've done it before to show people the difference between open diffs and centre diff lock. If the diff did distribute power 50-50 as the poster above suggests you would drive off the jack and into the nearest wall! If you engage the centre diff lock, the car will drive straight off the diff and probable damage something.

This example doesn't work with Disco 2 onwards as traction control will make the car drive away.

 

[garrett]

What a mess. Lots of questionable information going on. Maybe it't not being explained very well. ???

Easy solution. Grab a copy of Jim Allen's "Four Wheelers Bible" and have a read through. It explains the funtion(s) quite well.

In short the CDL physically connects the FRONT and REAR axles.

I will take a segment directly from his book, which just about every good driving school will reiterate.

"Full time systems continuously supply torque to the front and rear axles, but because front and rear wheel speeds differ in turns, a differential device is needed to allow the front and rear driveshafts to turn at different speeds. In most 4x4s this center differential can be locked when a true 50/50 torque split is needed in rough terrain."

Power flows like water........following the path of least resistance.

With the CDL LOCKED and you spin a wheel in the back you are GUARANTEED that a wheel in the front will spin. They are now physically connected and the front and rear are turning at the same speed. Nothing can change that unless you UNLOCK the CDL. I can tell when a student has the CDL locked or unlocked by just watching him drive slowly on limited traction terrain.

 

[ratboy]

What a mess. Lots of questionable information going on. Maybe it't not being explained very well. ???

correct.
maybe we should start again.