Thread: How defender 4wd system works

Land Rover, constant four wheel drive, three diffs. Diff between front wheel, diff between back wheel, lockable diff between front and back wheels.

In an unlocked diff the power goes to the wheel with the least traction, so if one wheel is slipping, the opposite wheel is getting nothing. In the same way, the centre diff spreads power front and back. If you lose traction at the back all the power goes there and nothing to the front wheels.

A diff lock sets the power sent to whatever is at either side of it - left and right front wheel, or front and back axle - to a fixed percentage of the power.

So, with a diff lock if you lose traction on one side of the diff you still get power on the other side.

And the reason you don't have locked diffs all the time, is that diffs are there to allow the car to go around corners, where the wheels on the outside of the car travel further than the wheels on the inside of the corner. If you have a diff lock on the axle and locked, the tyres will be forced to slip and scrub.

Cheers
Simon

Bigmark,

Lets hope your not pulling my leg.

Your modern 4x4 has a number of electronic aids which I will not make a major part of this description.

Basic 4X4 as per Toyotas etc is what is referred to as a part-time 4x4. Most of the time only the rear wheels are driven and when the front wheels are engaged it is usually wihtout any differential action between frnt and back axles. Your part-time 4x4 has 2 diffs one on the front axle and one in the back.

Defenders and discos for that matter RR and freebies (I think) have constant four wheel drive, all four wheels are driven all the time. To allow for using 4x4 on surfaced roads and the fact that the rear wheels cut the corner and take a shorter path than the front whhels when going around corners a diff has to be used between the front and rear axles. Therefore LRs have three diffs. When on unmade roads and wheels can slip and lose traction the center diff can be locked splitting the drive 50:50 between front and rear axles the same as the part-time 4x4 with out a center diff.

Lockers, do you need them if your not doing rock climbs? some will say yes some will say no. Diffs work in such a way as to send the drive to the wheel with least resistance, when one wheel loses traction it spins and the other wheel with traction just stop rolling as all the drive is going into the spinning wheel. Now picture this, Defender with the center diff left open, one wheel on the back axle starts spinning the other back wheel stops as it still has traction, so all the drive going to the back axle is going to the spinning wheel. Now the center diff much like the rear diff will also send the drive to the axle that has lost traction so all the drive is now going to the back axle and your front wheels stop providing drive. You effectively have a one wheel drive and that one wheel is spinning due to loss of traction so your going nowhere. Lock the center diff and now you have a two wheel drive you need to have one wheel on each axle spinning before you stop putting drive into wheels that will propel you. Lock the rear diff and now you have a back axle where both wheels will turn at the same rate spinning or with traction so you will still have drive. So do you need a locker in your axles? You might be able to answer the question for yourself if I have got the message across.

One reason for loss of traction at a wheel is due to the wheel coming off the ground. The coil sprung LRs have very long suspension travel so it is not often that you lift wheels. Some will use this as a reason as to why you do not need lockers with LRs.

I have a rear locker in my defender and I don't do rock climbs so you can guess at to what my answer to your question on the need for lockers would be.

The others have given a good explanation of the differences. As to whether you "need" a locker, it depends on what you use your Landrover for. There is no doubt that a locking rear differential (and for that matter a front one as well) will extend the capability of the vehicle - but relatively few owners ever approach the limits of their vehicle's capability anyway, and usually the driver's limits are reached even earlier.

To complicate the matter a number of recent Landrovers are fitted with traction control, which provides some of the advantages of a locking differential, further extending the capabilities.

John

This is a good explanation of how 4wd works:

HowStuffWorks "A Basic System"

Have always wondered,why did LR not fit limitted-slip diffs in the D1 & older model countys&fenders.They dont need them these days because of the electronic traction aids,but they would have been handy in previous models.Reliability maybe?
Was watching my sons Navara on the weekend on some steep loose rocky slopes & the slipery diff was very helpful,in fact i doubt he would have climbed many of the hills without it.


ummm....maybe this should be in the tech chat area

On that note, what's the advantages, if any, of a LR's full-time 4wd as opposed to a part-time 4WD (like on a Pootrol)?

All things being equal, I assume they'd be much-of-a-muchness when front hubs and 4wd engaged on the Pootrol and centre-diff locked on the LR.