Can an auto locker actually be a disadvantage in certain circumstances?

You didn't mention if you were talking front or rear.
I had an auto locker in the front of my last hilux without issue for 200,000kms. The steering in 4wd definitely has a heavier 'return to centre' feeling, but nothing that you don't get used to in 10 minutes.
The turning circle of the vehicle when in 4wd was also marginally bigger - again never an issue.
The benefits however are amazing (any style locker).

Buy either style with confidence.

Mine was a 'lokka' from 4wd systems and I'd say it would be the best improvement for $600 odd that anyone could do to a fourby.

The ARB dealer was right in saying that in some instances an auto locker can be a disadvantage but is possibly overstating the problem to make a sale. Likewise the problem with leaking seals was very minor & just led to a little oil blowback in the airline. This was mainly an installation problem from what I've been told & nothing to be too concerned about.
Autolockers by there design will stay locked in slippery conditions so can lead to some understeer which may happen when you least want it to. This can often be minimised by simply backing off the power momentarily. Also some vehicles handle poorly on sealed roads when they are fitted to the front axle. So annoying was it for a friend with a shorty Cruiser that he would pull up every time he hit the main road & take the hubs out.
Personally I like the ability of the ARB locker to have it IN or OUT when I want it to be while others like the fact autolockers still work on main roads in wet slippery conditions.
Cheers Craig........

Moose,

The auto locker that you talk about is really an "un locker".
The diff is locked all the time. When the vehicle is driven in a straight line this is not a problem for the diff.
When the vehicle is driven around a corner, a wheel on the same axle has to go slower than the outside wheel.
With an open diff this is not a problem and a open diff is designed to work like this.
If the diff is locked and the vehicle is driven around a corner one of two things have to happen.
The inside wheel has to slip on the road surface or if the wheels can not slip one of two thing can happen. The vehicle will not turn or the axle/ diff will snap.

The auto locker will allow a wheel on the same axle to go slower around a corner by ratcheting. The locker will unlock mechanically to allow the wheel to travel at a different speed.
If there is not enough traction for the inside wheel to make the diff ratchet the vehicle will tend to go straight and will not turn.

On the rear wheels you can get away with it but on the front wheels, with the vehicle in 4WD, it can be very dangerous.

Wayne

Moose,

This link might also help.

Diff

Wayne

Following on from what Wayne said - it is true that the auto lockers are actually more correctly referred to as auto UNlockers because they are usually locked and only unlock when they need to.

When do they need to unlock?
It's when one wheel is road driven faster than the other* - usually when you go around a corner and the outside wheel takes a wider/longer arc (it needs to turn faster to complete the longer arc in the same amount of time as it takes the inside wheel to complete a smaller arc). This means that the inside wheel is doing all the driving while the outside wheel is just rolling along (being driven by the road) - this is what causes the self-centering when fitted to the front axle.

Since the diff is unlocked by the outside wheel being 'road driven', you need some grip/traction on the outside wheel in order for the diff to unlock. In very low traction situations (greasy mud/clay or snow) sometimes the diff does not unlock. If this is on the front axle, it makes steering very difficult (or impossible) - this is what the salesman was referring to.

However, in the rear axle (which is where you said you'd want it), it can cause worse problems (assuming you're driving a part-time 4WD - the effect will be less in a full-time 4WD). Going around a corner will unlock the diff and all drive (engine power) will be going to the inside wheel. However, at higher speeds, turning a corner shifts more of the vehicle weight onto the outside wheel (as the vehicle leans around the corner) and OFF the inside wheels. If you're accelerating around a slippery corner, this can cause the inside wheel (which is doing all the driving) to lose traction and spin. As it spins, the speed of the inside wheel 'catches up' to the speed of the outside wheel which then locks the diff again - locking a spinning wheel to a non-spinning wheel can be enough to break traction on the outside wheel also, and if that happens while you're cornering, you'll very likely end up in a spin.

I've heard it said that the ideal set-up would be an auto locker in the front (so you don't have to switch it off for steering) and an electronic locker (or air locker) in the rear.

* This poses an interesting question: what happens if you're descending a hill under engine braking and one wheel loses traction? Does the other wheel just free-wheel down the hill?

auto-locker, even a premier set of tyres can esily be not a benefit....
like in getting you into places you have the potential you can't get out of....

I had a Detroit for 8 years in the rear of a 2door Range Rover.

In that time I had a couple of occasions where it was a disadvantage.

Going up a steep slippery hill with a hairpin half way up. The car tended to plough forward and not turn in as both rears remained locked.

Ditto in the Nissan Trials, the turning circle is larger with both rears driving on slippery clay, which made me miss a couple of "gates' .

However with an ARB , exactly the same would occur unless you unlocked the diff and then you would not have the traction benefit.

My objections ( which caused me to fit a Maxidrive to my next Rangie) were more about the civility on road. My locker was an interim sof-locker which was not as smooth as the latest ones .

When you accelerated say in second gear around a sweeping curve, as you changed gear the car would move inwards as the load came off.

Turning a right angle turn in a shopping centre could cause a chorus of clanks and bangs unless you made sure to accelerate through, and this can be difficult.

Sometimes when taking off from lights on a very slight curve, the splines would sit on top of each other and fall into mesh with an almighty "bang"

You do not say which car but sometimes you will need upgraded axles as axles are generally not designed to take full torque through one wheel.
Regards Philip A

I had a Detroit Locker in the back of a red prado I used to have and I now have airlockers in the hzj 105 I currently own. The Detroit was not bad, but it was a PITA in some places, like navigating tight car parks etc. Also, I did find on very slippery red clay roads it was difficult to keep the vehicle in a straight line with Detroit compared to using the Airlocker.

I much prefer the Airlockers to the Detroit locker.

I can't comment on the TJM airlockers as I have not used them.

The only general comment is to ensure that you get your locker fitted and setup by a diff specialist. Also, in the case of a 105 series it is a good opportunity to go to a solid pinion spacer to strengthen the diffs, but they have to be fitted by someone who really knows what they are doing.

what type of vehicle doyou have? TJM seem to be more reliable and arb still do have seal problems.if you have a nissan shim the rear ,if toyota a detroit can be better than a air locker in a lot of situations,they are a lot better now than a few years ago.

Thanks guys. Most educational. Good to hear from those that have actually used them. Sounds like the air locker may be the better option for me - but gee they are expensive (wouldn't worry some, but lots of $ for me).

One thing that is missed in this whole conversation - lockers, manual or auto have the propensity of getting you DEEPER into trouble, making it that much harder harder to get out. Automatic lockers will do that automatically (bad pun intended), manuals you have a choice.

I had a manual vacuum operated lock in my Rangie - I rarely used it, effective as it was. I think on one memorable occasion I was carting a whole bunch of people up a knarly hill, deep ruts and washouts. The Rangie spun a wheel, so I engaged the locker. Yep - my progress up the hill resumed - until I slid sideways into a rut and damaged the sill and door. I got myself out with much bellowing (6 litres will do that) and the use of the locker, but it reinforced the message that lockers drive you further into trouble it not used judiciously...

Brings to mind a conversation I had with a locker specialist in Sydney when I was thinking about putting autos in my Rangie. There is a track:wheelbase formula that is used to see if lockers can be used. Apparently the older Rangies (mine was a two door) have a short wheelbase and wide track and thus auto lockers would not work well in them... This may well change with modern lockers.

viz

Don't blame a poor old diff lock for picking the wrong line.
Perhaps a camry would keep you safer from getting stuck.

Like gbc, I have had a 4WD Systems Lokka in the front of my Hilux for years and would never be without one. I have driven the car in mountains, mud and outback sand and noticed only the most minor of disadvantages. If there are any major ones then I am still trying to find them.

I did initially think about putting one in the rear but so far I have not seen the need for it. The combination of manually selected 4wd with a front locker and the stock lsd rear diff has always taken me everywhere I want to go without any problems.

It is often said these things are locked all the time and only unlock when going around corners. That is correct but there is a little more to it. When going forward, the wheel with the shortest distance to travel is always driven by drive shaft applied torque while the wheel with longest distance is driven by road applied torque. That is pretty much all the time because two wheels on the same axle will rarely turn at exactly the same speed, even in a straight line on a freeway. The moment a wheel has a longer distance to travel, the unlocking process will commence. It may only partially unlock before a change in vehicle direction or road surface causes the other one to turn faster. The unlocking process will then start on that wheel. This process is constantly changing depending on road surface, direction and even tyre diameter.

This is why you can drive around a city or bush track all day with a auto locker in the rear but you can't do it with an air locker engaged. The problems described by Timbo are very real but a sensible driver will soon eliminate them by the correct driving technique.

Regarding the operation up and down hills: the 4wd Systems type operates in both directions. Other types may do the same but I am not sure. Drive comes from the diff carrier cross shaft pushing into the oval shaped hole in the two cam gears. Half of the hole is in each gear, there is a gap of about .150" to .170" between them and they are held apart by tiny springs and pins. The hole is the same shape front and rear. The driving teeth on these gears are in constant mesh with matching teeth on the driven gears on the ends of the axles. The cam gears can't move out any further but they can slide in towards the centre of the diff allowing the teeth to ratchet over each other.

The moment you drive forward, the cross shaft presses hard into the front end of the two halves of the cam hole. This action tries to spread the cam gears further apart. It can't do that because they are already in full contact with the gears on the axle. The result is the gears are held together with so much pressure they can't possibly separate so the diff is locked. This continues until one wheel is driven ahead of the other by road torque. Its half of the cam hole will now come off the cross shaft freeing the pressure on the teeth and they will start to ratchet over each other. The diff is now unlocked.

This will continue with the inside wheel i.e the one with the shortest distance to travel, doing the driving until it looses traction. The cross shaft will instantly apply pressure to the teeth on the other side, pressing them firmly, and that wheel will take over driving. The diff will now be locked and both wheels will be turning at the same speed although the one that lost traction will just be rolling over the loose or muddy surface without assisting.

When you back off downhill, the cross shaft is now pulled back into the rear end of the cam hole. The cam gear on the wheel with the longest distance to travel will now be the one in firm contact with the shaft, that is it will be the one that wants to roll forward but the shaft will be pulling it back. Its teeth will now be the ones with firm pressure on them so they will stay firmly locked. The inside wheel, if it has a shorter distance to travel, will unlock the same way a wheel turning faster does and its teeth will ratchet over each other only it will be in the opposite direction.