[maccarron]

This is definitely a very subjective discussion, with valid points both ways.

To add another spanner, those of us with newer vehicles have traction control and stability control, surely this would be sufficient on a dust road in 4H?

I was also wondering about the potential max speed in 4HLc?

[Gerrit Loubser]

Roelf, I'm with you on making more use of 4H (instead of 4HLc) on dirt roads.

Here is what I have learnt from members on the forum:
4H engages the front wheels with 66% of the power going to the rear wheels. The centre diff is still open.

Roelf, the above statement is sort of true for the Gen 3 with the Super Select II transfer case (which has a planetary center diff), but not for the Gen 2 with Super Select (which has a conventional bevel gear diff).

I say sort of true, because the center diff is not an open diff, but has a viscous coupler turning into a viscous limited slip diff.

If a Gen 3 is running in 4H and has equal grip at both the front and real axle, then 66% of the torque will be transmitted via the rear wheels and the rest via the front axle (under these same conditions, the Gen 2 would split torque 50/50 front to rear).

The moment one of the axles starts to spin out, the viscous coupling starts to lock the front and rear propshafts together and the lock up torque increases as a non-linear function of the rotational speed difference between these two propshafts. This means that the torque split can vary away from the 66/34 split (or 50/50 in the case of the Gen 2)

4HLc changes the split to 50:50 rear:front and locks the centre diff

This is only true if there is equal grip at both axles. If this is not the case, the torque splits according to the grip avaible.

For my money: I do not believe that 4HLc will add any benefit (over 4H) on a normal dirt road. All you achieve is potential drivetrain windup. That is just my opinion and the way I prefer to drive my Pajeros

I agree. The viscous coupling is brilliant at controlling spin-out, but still prevents too much wind-up from occurring: Wind-up interferes with handling.

On the Gen 3, the fact that 4H mostly creates a rear wheel drive handling balance is also beneficial in terms of reducing on-the-limit understeer.

[Gerrit Loubser]

Is speed limited on 4Hlc?

No, there is no mechanical reason for the speed to be limited, but be aware that a locked center diff does interfere with the vehicle's handling balance and as the speed increases this might become more significant.

[Gerrit Loubser]

What additional wear would be incurred by keeping to 4H instead of 2H?

I can think of tyres,additional traction leads to more wear,if I'm correct,maybe even wear between front and rear?

Would any other part of the drivetrain be adversly affected?

The viscous coupling is subjected to additional wear in 4H compared to any other mode.

[SimonB]

Roelf, I'm with you on making more use of 4H (instead of 4HLc) on dirt roads.

Then why would the vehicle (IMO) feel considerably more sure footed? There is most definitely a difference in handling. For the record I never exceed 100km/h on dirt and I'm more comfortable in 4HLc

[HBannink]

4HLc changes the split to 50:50 rear:front and locks the centre diff

This is only true if there is equal grip at both axles. If this is not the case, the torque splits according to the grip avaible.

I do not agree with this statement, If the diff is locked the drive would be split equal to both axles regardless of the grip of each axle. If the front axle is on ice and r the rear on solid the drive would be equal on both axles resulting in spin on the front and the rear one pushing you on to the ice as well. In center diff open mode the result should be that the drive is transmitted to the front wheels and spin would result without the rear wheels turning.

A friend of mine broke a universal on the rear prop shaft and had no drive in 4h but when we locked the center diff he could drive home on front wheel drive only, the rear prop shaft was removed.

4 hlc does make the vehicle more stable on gravel and the loose surface of the road provides enough slip for the drive train not to wind up. The equal distribution of the drive to both axles not only make the traction in the drive direction more positive but aids in the stability of the vehicle. This is easy to test by doing a few swaying movements on a normal tar road and engaging 4h and then repeating it, on gravel this is even more so in 4hlc

[Gerrit Loubser]

Then why would the vehicle (IMO) feel considerably more sure footed? There is most definitely a difference in handling.

Not sure, Simon, but my Gen 3 certainly does not feel more stable in 4HLc than in 4H...

[SimonB]

Then why would the vehicle (IMO) feel considerably more sure footed? There is most definitely a difference in handling.

Not sure, Simon, but my Gen 3 certainly does not feel more stable in 4HLc than in 4H...

Perhaps something to do with the fact the Gen3 is IRS?

[Gerrit Loubser]

4HLc changes the split to 50:50 rear:front and locks the centre diff

This is only true if there is equal grip at both axles. If this is not the case, the torque splits according to the grip avaible.

I do not agree with this statement, If the diff is locked the drive would be split equal to both axles regardless of the grip of each axle. If the front axle is on ice and r the rear on solid the drive would be equal on both axles resulting in spin on the front and the rear one pushing you on to the ice as well. In center diff open mode the result should be that the drive is transmitted to the front wheels and spin would result without the rear wheels turning.

Henk, torque transfer in drivetrains is widely misunderstood and many motoring journalists and even so-called industry professionals perpetuate the misunderstanding by endlessly repeating the same erroneous information.

Have you heard the saying: "Don't confuse motion for action"? Wheels spinning don't necessarily mean drive torque being transferred. This is the root of the misunderstanding.

If the center diff is locked, it forces the front and rear propshafts to spin at the same speed, so in your example with the front wheels on ice (both having equal grip) and the rears on a high grip surface (both having equal grip) a locked center diff will ensure that all wheels rotate at the same rpm, but the lion's share of the tractive effort will come from the rears. The drive torque is directly proportional to the tractive effort and hence much, much more than 50% of the drive torque will be transmitted via the rear propshaft, if the center diff is locked...

The bottom line is that torque can not be "forced down the throat" of a shaft unless there is resistance to rotational motion to oppose the torque. These pieces of steel are stupid and don't know that people expect a certain percentage of the total torque to be transmitted through them. All they can do is obey the laws of nature, like every action requiring an equal, opposite reaction. If there is no grip, no resistance to rotation can be generated and hence no torque can be generated. If you hold a broomstick horizontally and grip it in the center and apply a rotational motion to it with your wrists, you will not experience any resistance and hence no torque will be transmitted by the broomstick. Now if I were to hold tightly onto one end of the broomstick while you try to rotate it again from the center, then the piece of broomstick between where you are trying to apply the rotating motion and where I am holding it will be subject to torque. If you apply enough torque to overcome my grip, the whole of the broomstick will rotate at the same speed, but only one half will transmit 100% of the torque. If Simon no grips the opposite end of the broomstick to where I am, then the other half of the broomstick will also experience torque. In the special case where Simon and I both grip the broomstick with equal reacting torque, then 50% of the torque will be transmitted by Simon's half of the broomstick and 50% by mine. The point is that the broomstick (which is like the two propshafts locked together by a center diff lock) can not control the torque distribution; that is controlled by the resistance to rotation.

A friend of mine broke a universal on the rear prop shaft and had no drive in 4h but when we locked the center diff he could drive home on front wheel drive only, the rear prop shaft was removed.

Exactly, so in this case 100% of the total drive torque was transmitted
via the front propshaft, not 50%...

For interest sake, note that he could have driven in 4H as well, because the viscous coupler would have seen to it that drive is transmitted via the front axle, but this is not recommended to do for any distance, because it is a sure fire way of seizing the viscous coupler...

4 hlc does make the vehicle more stable on gravel and the loose surface of the road provides enough slip for the drive train not to wind up.

The very fact that the wheels have to slip to release wind-up means that traction is broken due to wind-up. There is only so much grip available on a dirt road. This finite amount of grip has to propel/brake as well as generate latreral force to corner. I would rather not lose an additional bit of grip to release wind-up. Sure it won't make much of a difference unless one is on the limit, but who knows when one would need to take drastic evasive action.

Think about this: What kind of drivetrain configuration is used in rally cars such as the Lancer Evo and Subaru Impreza WRX? They do not run locked center differentials and they are designed to run on the limit on dirt roads. OK, the clever driver controlled center differential (DCCD) in the later model WRXs can actually lock the center diff, but if the automatic control system is left to its own devices (i.e. not overriden by the driver), it never locks the center diff 100% when lateral force is being generated (i.e. when cornering).

This is easy to test by doing a few swaying movements on a normal tar road and engaging 4h and then repeating it, on gravel this is even more so in 4hlc

Like I said, this is not my experience on my Gen3.

[4ePikanini]

I get what Gerrit says with torque bias in 4HLc.

In other words if the front wheels are operating on ice and the rears are on tar then almost all the power will go the rear wheels even though the fronts are turning at the same speed as the rears.

In my Gen2 the 4H feels best for me on dirt. It allows a little bit of a drift but keeps it in balance and it doesn't whip around. In essence just a little bit of oversteer but in 4Hlc I feel I get a bit of understeer which I suppose is a bit safer when really hammering it and if the driver is less skilled.