Diff lockers - why?

[lindamc]

I am wondering why people need to add diff lockers on their vehicles when by changing the gears to high lock or low lock this locks the diff? Is this not locking all the diffs, maybe just the centre one or something? Obviously my 4wd training course didnt all sink in. My car is a prado with fulltime 4wd, front, back and centre diff.

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[D4D]

Prado only locks centre diff. Diff locks front and rear allow greater traction when you lift a wheel or one wheel is spinning as it drives both wheels with a 50:50 power split.

[edz]

G,Day Lindamc, Front and rear diff locks are a similar idear in principle to the central diff lock youre saying about ..
Oon an all wheel drive the tourqe / power is fed aprox 60 / 40 or 70 / 30 % in a front to rear bias , when you hit the center diff lock button etc it locks up the center diff to send 50 % power / tourqe to the front / rear diff, but you are only actually driving one wheel at at each end of the truck at the same time  ..
With front rear diff locks when you lock the diff it drives both wheels on each axle at the same speed as they are now joined by a solid conection between them .

[ozbogwam]

Diff locks lock both wheels on the same differential so that they both receive equal power. A differential by its very nature disperses power unevenly to each wheel so that when you are turning a corner you don't scrub your inner wheel when turning.

In an off road situation this uneven distribution of power causes problem as the wheel with the least resistance, which can be the wheel that is in the air or spinning in mud or sand, gets all the power. This leaves you stuck. With the diff locks on both tyres get all the power helping you through the ibstacle

[Diesel Power]

By hitting the centre diff lock that will send equal amount of torque to your front an

d rear diff.
Then you need diff locks to send equal torque to left and right side as Toyota LSDs are junk (they slip too much).

So when you lock your centre diff and FnR lockers you will have an equal 25% drive to all wheels.
Regards
Angus.

[Jason B]

Some 4wds have a centre diff that locks drive front and rear. Most have a limited slip diff in the rear, that lock up automatically when needed however they never fully lock up hence the name limited slip also, Toyota limited slip diffs are crap. The front diffs in most 4wds is an open diff so that you can still steer easily around corners etc.

Diff locks physically lock drive in the diff from side to side so that the axels on each side of the diff are traveling at the same speed all of the time. If you have a locker both front and rear you have a sensational amount of grip available as all 4 wheels have drive no matter what. Without them I'm a normal set up the wheels with the least amount of grip will spin and you don't go iny where in the worst of case.

Lockers can only be use in slippery conditions as the wheels need the ability to slip, otherwise you will break things like axels and cv joints. You also essentially need to be traveling straight as the different wheel speeds if going around corners etc can also place load on components and break them.

The negative with lockers in my opinion is that the rear limited slip diff must be replaced with an open diff when a locker is fitted. So the auto style is lost and you must engage the locker.

Hope that helps a bit.

Jas

[Bigsteve]

Hi Linda

On your prado there are three diffs, front, rear and central.  When in normal High mode all three diffs are open and equal torque is supplied to all wheels.  If one wheel lifts then you lose drive. When you go into High Lock or Low Lock the center the Center diff only is locked.  This means the front and rear diffs turn at the same rate and of one wheel is lifted (say front) power is still sent to the rear diff.

When two wheels loose traction on the front and rear then even with the Center diff locked you'll loose drive as all the toque is sent to the wheels spinning.

A rear or front diff locker will keep both the wheels turning at the same rate even if one has no traction.

On Prados there is a rear limited slip diff which should keep some torque going to both wheels when one is spinning, but these are notoriously bad and don't work well.  If looking at one in a prado I'd start with a rear e-locker so not to stress the front cv's and not having to worry about compressors and leaking seals.  Having said that I don't have lockers and haven't needed them, just drive appropriately for the conditions. Not to say I won't get them at some point, but if building up a 4wd there are other items I would look at first.

S


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[lindamc]

Thank you guys,  you have helped me see how it works. now to decide if i need them or not ... i cant imagine i would get my self in to many situations of not having wheels on the ground , more likely to get stuck in sand but i would have jules trax things to help out and a shovel .
So do you guys use these front and rear locks much and if not are u still glad you have them?

[oldmate]

Thank you guys,  you have helped me see how it works. now to decide if i need them or not ... i cant imagine i would get my self in to many situations of not having wheels on the ground , more likely to get stuck in sand but i would have jules trax things to help out and a shovel .
So do you guys use these front and rear locks much and if not are u still glad you have them?

I would spend a few years learning how to drive your 4wd in situations without diff locks. It will teach you how to pick smarter lines through obstacles or to go around them. Diff locks are great but can get you into more problems than they get you out of sometimes.
No the last time I needed my diff lock was well over 12 moths ago, having said that on my last 5 camping trips I haven't even put it in 4wd.

 

[rodw]

In an AWD vehicle the front and rear axles can travel different distances because  of turns etc so a centre diff allows for this. If this problem was ignored, the drive line would bind up on bitumen and shafts would snap! When you lock the centre diff, it is like engaging 4WD and locking the hubs in a vehicle with part time 4WD.

So without centre Diffs and ignoring all the fancy electronic offroad features creeping in to vehicles today, the axle diff will basically send all torque to the wheel with the least load. So if you put one wheel in the air, it will spin and forward motion ceases. Now in a 4WD, With a bit of luck, the other axle might still be driving so you keep moving.

If you have axle diff locks, engaging them will lock the axle so that if one wheel turns, the other must also turn.

Having axle diff locks means you need less momentum to get over an obstacle so lower revs and more torque. You don't have to hit an obstacle hard enough to bounce over the low/no traction bits. This then permits a much more controlled approach that is less likely to damage the track or the vehicle.

Electronic traction control on an open diff attempts to do the same thing by sensing a slipping wheel on an axle and applying the brakes to that wheel only. This evens up the torque on both sides of the axle so forward motion starts again.

One point worth noting that most 4wd's including the Prado have rear limited slip Diffs. These require a higher torque differential across  the axle before slippage occurs. Installing a locker replaces the LSD with an open diff so you may find yourself engaging the rear diff lock wher you could just drive on previously.

Diff locks are not usually needed on sand as the idea is to make sure you don't spin a wheel and dig in. Crossing the axles up and getting a front and back wheel spinning is not that hard to do. If possible approach an obstacle square on so both wheels have grip.

[Patr80l]

Without repeating what has already been said; 99% of us never get into a situation where you'd need axle diff locks.
My understanding of what they do is not 50:50 power distribution etc.   What they do is force all wheels to turn together, whether that have grip or not.   That means that if three wheels have no traction, the one with grip will use 100% of the power.    Without a lock, the differential allows the wheel without grip to spin while the others don't turn.

[MadMarv]

all depends on the type of traveling you want to do ... for me its high on my wish list .. just under the winch .. but then I want to do more solo traveling ... the old maxtrax or similar are probably a cheaper option and never go astray in your recovery kit either.

[lindamc]

Ok thanks guys it must be frustrating trying to teach a female about these things but you have all done very well. So i will leave the vehicle without lockers for now and just concentrate on never having less than 3 wheels on the ground , picking a good line to drive and not being silly.

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[rodw]

Without repeating what has already been said; 99% of us never get into a situation where you'd need axle diff locks.

I agree for touring this holds true as we tend not to take risks a long way from home. I will say it was nice when in the Flinders Ranges to slip the lockers in and gently climb up to a lookout with a Telstra  repeater tower  on it.

Ok thanks guys it must be frustrating trying to teach a female about these things but you have all done very well. So i will leave the vehicle without lockers for now and just concentrate on never having less than 3 wheels on the ground , picking a good line to drive and not being silly.

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A good approach. When we talk about picking a line, a large part of it is to ignore the track surface and keep the axles as level as possible by just focussing on the wheel tracks you will take. The fact that you might be 4 foot off the ground under the vehicle then does not matter unless you fall in the hole!

[duggie]

For the average person going camping/four wheel driving diff locks are just bragging rights. Until you go to the extreme out and away camping spots with a lot of very rough tracks or extremely steep climbs your diff locks will very rarely if never be used. For the price you will spend on fitting the diff locks you could buy the better off road tyres and a bloody good winch and have a fair amount of change left over .  I class diff locks as a want not a need.

In saying this I do have my GQ Nissan Patrol fitted with a front diff lock, this was fitted because I was going on a trip to the tip of Cape York as a recovery vehicle, I need to be able to get power to all four wheels to assist those who needed to be recovered. Since that trip I have only engaged my locker once and that was only to ensure that the locker was still working.

Experience in four wheel driving will allow you to be able to get where you want to go with out the need for lockers.

cheers duggie

[DannyG]

I've never engaged my lockers and I've done most of the iconic hard core Tassie 4wd tracks and quite a few on the big island.

Oh and the reason I've never used them is because I can't afford them, I haven't got any But I do drive a Patrol

[time]

Have a read here (http://auto.howstuffworks.com/differential.htm), it explains diffs and and their various iterations well.

[alnjan]

Sometimes diagrams help explain or only confuse more. 

http://www.lcool.org/technical/diffs/diffs.html

This example is talking about the 80 Series Land Cruiser but the Prado's run a system with the same basics.

Hope this helps

[GeoffA]

......with diff locks you can get REALLY stuck........

[alnjan]

Or more fun




Diff locks can be an expensive outlay but really you can do a lot of 4wding with ever needing diff locks.  My advice for anyone curious about getting diff locks is to full understand what they do and more so when you would need them and are you really going to be driving anything that requires you using diff locks. 

[Bird]

I would spend a few years learning how to drive your 4wd in situations without diff locks. It will teach you how to pick smarter lines through obstacles or to go around them. Diff locks are great but can get you into more problems than they get you out of sometimes.
No the last time I needed my diff lock was well over 12 moths ago, having said that on my last 5 camping trips I haven't even put it in 4wd.

 

Great advice.. 99% of people buy lockers cause they are told by the store they need them, or they hear that Tuff truck people use them.. more or less it makes them feel hardcore for no reason.

[KingBilly]

Hi Linda, some great replies above but what it all boils down to, is what sort of driving do you intend to do?  If you want to get into adventurous challenges on mountain tracks or go to 4X4 parks and test your skills, in similar circumstances to the above example, diff locks may be an advantage.  Obviously there are other examples where diff locks may help but they are often only a one-off, or a once in a vehicle's lifetime, type of experience.

If you just intend to take a dirt road, be it the Plenty Highway or CSR, to your favourite camp spot, diff locks would, in 99.9% of examples, not be needed.  Some of the roads to the Cape are a possible exception but can be driven safely with a winch and travelling with support.

I agree with oldmate, take your time getting to know your vehicle.  Take your time working out what you want to do with it.  Then make a decision.

KB

[alnjan]

I agree 100% KB.  I enjoy the harder 4wding so my vehicles are twin locked.  In saying that Diff Locks are not the be all and end all.  They do get you out of a lot of situations but before diff locks I make sure I have a winch.  A far more useful piece of kit that will safe you and your travelling partners and can also help to clear fallen obstacles that otherwise can stop your plans.   

[lindamc]

Do i want to be in a situation like your picture KB??    nooooooooooooo
I enjoy moderate 4wding, exploring, not extreme. Way to scary for me.


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[D4D]

Keep in mind even a simple track can turn pear shaped in an instant, you could find yourself in a situation like the Hilux above quite easily. Slippery up hill track, lose traction or miss a gear, slide backwards and drop into a rut. Diff locks can be a great traction aid to keep/get you out of strife. This is where knowing what your vehicle is capable of is required and this comes from practice. In your case I'd probably fit tyres and suspension before diff locks.