Manual vs Auto Hubs, 2H vs 4H vs 4L

[iandvl]

A couple of recent questions on the WhatsApp group got me thinking that a lot of stuff we take for granted are probably not general knowledge - especially to new Patrol owners. And so I thought I'd write this post.

Please note: I don't consider myself an expert, these are just my approaches in terms of things as well as some little things I've learnt driving my Patrol over the years.

2H and Sealed Roads

Firstly, as pointed out by Mr. Connan on the WhatsApp group during this conversation, it is not good for your Patrol to engage 4x4 on surfaces with good traction (ie: tar roads etc). There are exceptions to this - on a trip to Lesotho a few years ago, I did have 4x4 engaged on tar but that was only because the tar road was iced over. As in totally iced over.

Hubs - General

It is perfectly fine locking your hubs when travelling in 2H on tar road. In fact, if your 4x4 system is not regularly used, the owners manual actually recommends doing this occasionally to keep the front diff and drive lines lubed.

Hubs - Manual

If you've got manual hubs, these do need to be locked when you're in 4x4 or otherwise you're technically still going to be in 4x2. I remember a new Patrol owner with a Patrol pickup battling to get up the first tame incline at Piesangkloof during a NORC outing a few years ago. His hubs were unlocked. He idled up once we pointed this out and locked them.

Hubs - Auto

Autohubs are a different kettle of fish. They lock when the front drive train turns and they unlock themselves again when the front drive train turns in the opposite direction. Because of this, I always lock mine in specific circumstances.

1: When I'm driving obstacles.
2: When I'm going to be regularly alternating between gravel and tar roads.

The reason for point 1 is that it can be quite unnerving should a hub unlock itself in an obstacle.
The reason for point 2 is that I can shift between 2H and 4H on the fly (up until 50km/h) without needing to reverse to disengage the hubs.

Please note that your vehicle has to be completely stationary in order to shift to 4L.

2H vs 4H vs 4L

1: 2H on tar.
2: 2H or 4H on dirt roads, tracks and sand depending on conditions.
3: 4L on sand, mud, water crossings, obstacles etc. etc. etc.

Speed

There is no answer for this - this will depend totally on the conditions of the track / road, the driver etc.

Summary

That is it in a nutshell. If I've missed anything, or anybody else has anything to contribute to this thread, please comment.

[Peter Connan]

As far as Patrols up to and including the Y61 goes, the above is correct and pretty complete.

One or two additions:
There does exist another option on hubs, being the so-called drive flange or solid drive flange. To my knowledge these ware never fitted to officially-supplied Y60 and/or Y61's in SA, but they do exist and I have a set for my Y60.
This to my mind proves that driving around with your manual or auto hubs locked all the time will not cause damage (as long as you use the short lever correctly). It may cause increased fuel consumption. Some (not Patrol-specific) documentation I have read claim up to 10%, but the best fuel consumption I ever got with mine was with the hubs locked.

There may be one other drawback as well. The factory hubs (mostly the auto hub but the manual hub as well) are generally the most fragile component of the entire drivetrain. Now while I don't necessarily like down-rating the system, if a breakage must occur the hub is a nice place for it to occur as it is very easy to replace and a smallish component too, so easy to have a spare handy. The drive flange is a lot stronger, which means the next-weakest component in the drivetrain is going to be the thing that breaks. This is probably the Birfield, which is a much bigger job to replace and it takes up a lot more space too, if you wanted to carry a spare.

The other addition is another reason to manually lock the auto hubs in rough terrain: If the hub un-locks should you lift a wheel or lose traction for some other reason, that hub might un-lock, and when traction is re-gained, it could be subject to a lot of torque while partially locked (IE in the process of either un-locking or re-locking), which means less surface are in contact. Thus breakages are more likely.

[Peter Connan]

Additionally, I would like to add some information on the systems fitted to other vehicles, and how their operation might differ from that of the Patrol.
Unfortunately I stopped paying much attention about 10 years ago, and I am not too clued up about the latest systems.

In brief, the Patrol is what is known as a part-time 4 wheel drive. This means that, in normal use the rear wheels are driven. When 4x4 is selected, the front axle is connected. There is no mechanism to allow the front prop-shaft to turn at a different speed to the rear propshaft once 4x4 is engaged.

The other options I am aware of are full-time 4 wheel drive, hybrid systems which contain elements of both the above and "all wheel drive".

In a full-time 4 wheel drive, there is a third differential in the transfer case. Both axles are permanently connected, but the differential allows the front and rear propshaft to turn at different speeds. In most such vehicles, this third differential can be locked. When it is locked, such a vehicle will behave in exactly the same way as a part-time 4WD in which 4WD is engaged. Some however don't have a locker on the centre diff (some of the Landy Discos for example), and some others have a limited-slip mechanism and a selectable locker on this diff (like the early Fortuners).

The hybrid system found most often here in SA is Mitsubishi's "Super Select". this allows rear-wheel drive, four wheel drive with an open centre differential and four wheel drive with a locked centre differential. Some Jeeps also have hybrid systems.

The primary difference between a full-time 4WD and a part-time 4WD is in how the car behaves in the "lowest" setting (IE the setting the manual recommends for normal driving).
A part-time 4WD will behave like a rear-wheel drive vehicle.
In off-road situations, this means that if one rear wheel loses traction, the vehicle will lose momentum. But the front wheels do not contribute to tractive effort, they only provide steering and braking.
In a full-time 4WD in a similar situation, if any of the four wheels lose traction, the vehicle will lose momentum.
However, the above is as far as I am concerned really not of any importance. There are tools in the box for coping with that in all these vehicles, and most of them work well enough (with the possible exception of the traction control in those Discos mentioned above).

The real difference is in how these vehicles behave when pushed somewhat beyond the traction limits on the road.
A part-time 4WD can (at least theoretically) be pushed into oversteer. A full-time 4WD will typically understeer relentlessly.
Which is better depends partially the skill of the driver and partially on the situation.
A vehicle which is plowing straight on will probably not roll over. But once it is understeering, the driver has few options to exercise control over the vehicle.
A rear-wheel-drive offers far more options to a skilled driver, but get it wrong and there's a good chance the vehicle will roll.

All-wheel drive systems are different.
The basic all-wheel drive system is a front-wheel-drive vehicle which has some mechanism to transfer some drive to the rear axle. They typically don't have low-range gearing, and the connection to the rear propshaft is typically not a physical solid connection. It can be a fluid coupling (in the earliest ones, being the Audi Quattros, this was a viscous coupling) or some type of electronically-controlled clutch setup (like a Haldex clutch).
In some cases the driver can ask the system politely to do something, but there is no mechanism through which he can persuade the front and rear axles to turn at the same speed.
In other words, these systems are reactive in nature. They will detect slip, and then send power to the slower axle. Thus, a little bit of momentum is always lost before the system reacts. Whether or not that is important will depend mostly on how fast the system reacts (which is why the newer systems are almost always superior to the older ones) but also on the driver. For those of us who were taught "as slow as possible", it's more difficult to adapt. those who like momentum will have less of an issue.
Also note that these systems are highly variable in implementation. For example the all-wheel-drive Porche 911's (and the Ferrari all-wheel-drive systems) are rear-wheel drive based, and I believe some now have a center differential which is controlled by a Haldex clutch.

Some examples of each:
Part-time 4WD:
Patrol.
Most 4x4 bakkies.
Land Cruiser 70-series sold here (in some other markets they are available in full-time 4WD).
Jeep Wranglers?
Series Land-rovers (the ones with leaf springs).
Current Toyota Fortuners

Hybrid systems:
Mitsubishi Pajero, Pajero Sport and some Tritons.
Note that all the above vehicles have a transfer case, and in almost all situations, this transfer case will have a set of low range gears. This is crucial for most forms of technical off-roading.

Full-time 4WD:
Land River Defender (the coil-spring ones).
Land rover Discovery
Range Rovers (the bigger ones at least, not the Velars as far as I know)
First-model Toyota Fortuners.
Most of the Land Cruiser station wagons (IE 80, 100 and 105-series).
Some 70-series Land Cruisers sold in other markets
Mercedes Gelandewagen.

All-wheel drives:
Most modern smaller SUV's.
A whole host of road cars and sports cars, such as Audi Quattros, pretty much all Subarus (there were some part-time models right in the beginning but they were never sold here that I know of), VW Syncros, etc ad infinitum.

[Peter Connan]

One more vehicle to discuss: the Y62 Patrol
Note that this is based on Internet research and not personal experience.

It is my understanding that the Y62 is a bit of a hybrid.
Mechanically it is a part-time 4x4, but instead of having a manually-activated dog clutch to engage drive to the front axle like the earlier Patrols, it has an electronically-controlled multi-plate clutch setup.
So in terms of actually driving it, there is no two-wheel-drive-only mode, and the vehicle is actually sold as a full-time 4wd.

So normally power is sent to the rear wheels, but when the TCS measures slippage on the rear wheels, power is sent to the front axle.
There is a mode to lock the clutch so that the axle speeds are the same, in which the vehicle will behave the same as a part-time 4WD when in 4WD, or a 3-diff full-time 4WD with the centre diff locked.

[Peter Connan]

And while I am boring you all to tears, there is one more subject I want to discuss:
The terminology, or more correctly, the usage of the word "lockers".

Many novices seem to believe that locking hubs are synonymous with an axle locker. This is very much not the case.
The technically correct name for locking hubs is actually free-wheeling hubs, and while I try hard not to get too caught up in the weeds on terminology, it is important to understand what each of these items do, and what effect that has on vehicle performance.

The purpose of free-wheeling hubs is (with the transfer case in 2 High) to allow the side-shafts, the differential and the front propshaft to stay stationary while the vehicle is driving. Thus you don't need to expend energy (fuel) to rotate these components.
The connection is made and/or broken inside the hub. The operation of free-wheeling hubs does not affect the diff at all, except if one hub is locked and the other one is un-locked (this should never be done, not even to prank your buddy, as it can cause serious damage to the front diff).

A "locker" is more correctly called a differential lock. The purpose of this is to force the two shafts exiting the differential to turn at the same speed. It only works on the diff it is installed in. Many people seem to think the centre diff lock on a Land Rover or an 80-series Cruiser has the same effect as a rear axle locker on a real 4x4, but it doesn't. A part-time 4WD with one locking diff is superior to a full-time 4WD with one locking diff, beacuse on the part-time 4WD that locking diff will probably be the rear axle diff (although possibly it could be the front axle diff), while on a full-time 4WD that locking diff will be the centre diff (which is not present on the part-time 4WD). To be equivalent to a part-time 4WD with one locking diff, a full-time 4WD needs two locking diffs. And so on.