Cross Axle Diff Locks
Every single Land Rover I have owned during the past 30 years, I've always wanted to have some form of axle lockers fitted to it but never got around to it, mainly due to the expense. This time, I've bitten the bullet.
Why Fit A Locker?
As good as a standard Defender is, most people who use them off tarmac (whether for P&P or Green Laning) will at some point look at improving their vehicles off road ability. This may be something as simple as changing the tyres, or something more involved such as lifts and changing the suspension to give amazing articulation. As well as being my laning truck, my Defender is also my daily drive and the vehicle of choice for family days out, weekends away etc etc, so whatever changes I make to it for off road use, can't have a detrimental effect on it as a road going vehicle. Changing to bigger, more aggressive tyres will impact both on the gearing and noise of the vehicle and quite possibly the road holding in the wet, so for this reason, more aggressive tyres than those currently fitted has been ruled out.
Changing to +1 or +2 inch longer shocks will improve the suspension droop without impacting on the compression. While this is an improvement, it's not a massive difference to the standard setup (which is pretty good anyway). To go much larger with springs and shocks would involve quite a bit of work to do properly. Brake pipework extended, castor angles corrected and wide angle props fitted to stop the prop binding at extreme angles. Shock mountings also need to be moved higher otherwise the shock will run out of upwards movement long before the axle hits the bump stops, so while you're gaining in droop, you lose in compression. Ultimately, even the best suspension will still have its limits and while you may still have all four wheels on the ground, without any weight on the downward wheel (springs will have dislocated at this point) it's not going to be doing a fat lot traction wise and you can still get cross axled as the open diff feeds power along the line of least resistance. The only sure fire way of preventing this is to lock that diff up. The video below demonstrates this rather well.
Changing to +1 or +2 inch longer shocks will improve the suspension droop without impacting on the compression. While this is an improvement, it's not a massive difference to the standard setup (which is pretty good anyway). To go much larger with springs and shocks would involve quite a bit of work to do properly. Brake pipework extended, castor angles corrected and wide angle props fitted to stop the prop binding at extreme angles. Shock mountings also need to be moved higher otherwise the shock will run out of upwards movement long before the axle hits the bump stops, so while you're gaining in droop, you lose in compression. Ultimately, even the best suspension will still have its limits and while you may still have all four wheels on the ground, without any weight on the downward wheel (springs will have dislocated at this point) it's not going to be doing a fat lot traction wise and you can still get cross axled as the open diff feeds power along the line of least resistance. The only sure fire way of preventing this is to lock that diff up. The video below demonstrates this rather well.
Lockers, But Which One?
There are many different lockers on the market (including Limited Slip Diffs and Torque Biasing Diffs which while not true lockers in the strictest sense, are worth considering) so it's worth looking at all options and variations to see what suits you best. Before looking at the various manufacturers, you need to decide whether you want a manual/selectable locker or an automatic one. This is just a brief overview rather than an in depth technical appraisal. More in depth information can be found on the various manufacturers or distributors sites.
Automatic lockers
Automatic lockers lock and unlock automatically with no direct input from the driver. Some automatic locking differential designs ensure that engine power is always transmitted to both wheels, regardless of traction conditions, and will "unlock" only when one wheel is required to spin faster than the other during cornering. These would be more correctly termed "automatic unlocking" differentials, since their at rest position is locked. They will never allow either wheel to spin slower than the differential carrier or axle as a whole, but will permit a wheel to be over-driven faster than the carrier speed. The most common example of this type would be the famous "Detroit Locker," also known as the "Detroit No-Spin," which replaces the entire differential carrier assembly.
- Pros: Automatic action, no driver interaction necessary, no stopping for (dis-) engagement necessary
- Cons: Increased tyre wear and can have a noticeable impact on driving behavior. During cornering, the automatic locker can cause heavy understeer which transitions instantly to power oversteer when traction is exceeded.
Reading various forums and message boards (especially Ozzie and SA boards where lockers seem far more commonplace than in the UK), opinion seems split as to how much an auto locker (or unlocker) affects the on road behaviour of the vehicle. Originally I was planning on fitting an auto locker but there is no clear consensus of opinion as to whether or not it affects the road going behavior of the vehicle and to what degree. Some brands are also known for clunking and banging when turning on tarmac. Some, not all.
Torque biasing limited slip diffs are also an option if something with an automatic action is preferred. These are a good compromise between a standard differential and a locking differential because they operate more smoothly, and they do direct some extra torque to the wheel with the most traction compared to a standard differential, but they are not capable of 100% lockup. Ashcrofts do their own ATB which has had some very good reviews.
Torque biasing limited slip diffs are also an option if something with an automatic action is preferred. These are a good compromise between a standard differential and a locking differential because they operate more smoothly, and they do direct some extra torque to the wheel with the most traction compared to a standard differential, but they are not capable of 100% lockup. Ashcrofts do their own ATB which has had some very good reviews.
Selectable Lockers
As the name suggests, selectable lockers allow the driver to lock and unlock the differential at will from the driver's seat. There are a number of different manual lockers available but probably the three best known ones in the UK are KAM, ARB, and the Ashcroft Locker.
Looking at the KAM Locker first, this is controlled electrically via a heavy duty solenoid located inside the diff pan. A cable runs from the solenoid to an illuminated rocker switch in the cab that engages the diff lock. KAM have a very good reputation but to fit this locker requires some welding and modification to be carried out to the axle case to accommodate the solenoid.
ARB have been producing lockers and various other 4x4 goodies for quite some time and is usually the first name that springs to most peoples minds when talking about lockers. ARB lockers are pneumatic and are operated via an onboard air compressor bought separately. Generally speaking, ARB lockers have a good reputation and work well.
Ashcrofts have been around for quite a while but it's only relatively recently they have introduced a locker of their own into the market. Very similar to the ARB in terms of operation, Ashcrofts have seemingly taken the best features of the ARB's while eliminating the weaknesses to produce a very strong, reliable locker. Happily, it also retails for less than the ARB too.
Looking at the KAM Locker first, this is controlled electrically via a heavy duty solenoid located inside the diff pan. A cable runs from the solenoid to an illuminated rocker switch in the cab that engages the diff lock. KAM have a very good reputation but to fit this locker requires some welding and modification to be carried out to the axle case to accommodate the solenoid.
ARB have been producing lockers and various other 4x4 goodies for quite some time and is usually the first name that springs to most peoples minds when talking about lockers. ARB lockers are pneumatic and are operated via an onboard air compressor bought separately. Generally speaking, ARB lockers have a good reputation and work well.
Ashcrofts have been around for quite a while but it's only relatively recently they have introduced a locker of their own into the market. Very similar to the ARB in terms of operation, Ashcrofts have seemingly taken the best features of the ARB's while eliminating the weaknesses to produce a very strong, reliable locker. Happily, it also retails for less than the ARB too.
Make Your Mind Up Time.
Originally I was looking at an autolocker (unlocker) mainly on the grounds of price but as I wasn't 100% certain it wouldn't effect the road behavior of the vehicle (short wheelbase vehicles seem to be more affected than the 110 when used in the front), I discounted it as an option simply because should I find I'm not happy with the on road behavior, it could be an expensive mistake to make. While a LSD or ATB do seem to be fairly seamless and transparent in operation, they don't provide 100% lockup. Had my Defender had Traction Control (these diffs work very well in conjunction with TC) I may have given them a shot but since it doesn't, ultimately they aren't as effective as a full on locker. For these reasons, I chose a selectable locker.
KAM have a good reputation but having to get the axle case cut and welded was a negative point for me. I also didn't know of anyone personally who had one fitted. ARB are very popular and widely available but I can't see any reason why anyone would choose an ARB over an Ashcroft locker. The Ashcroft is both stronger and cheaper than the ARB and operates in the same manner. I've yet to see or hear of a negative opinion of these lockers. As airlockers go, it's the obvious choice in my opinion.
While I chose the Ashcroft locker, that's not to say there's anything wrong with any of the other choices mentioned. You pay your money and make your choice as to what fits your needs best and for me, thats the Ashcroft locker.
KAM have a good reputation but having to get the axle case cut and welded was a negative point for me. I also didn't know of anyone personally who had one fitted. ARB are very popular and widely available but I can't see any reason why anyone would choose an ARB over an Ashcroft locker. The Ashcroft is both stronger and cheaper than the ARB and operates in the same manner. I've yet to see or hear of a negative opinion of these lockers. As airlockers go, it's the obvious choice in my opinion.
While I chose the Ashcroft locker, that's not to say there's anything wrong with any of the other choices mentioned. You pay your money and make your choice as to what fits your needs best and for me, thats the Ashcroft locker.
Price
While costing less than the equivalent ARB unit, that's not to say the Ashcroft is cheap. A fully built up diff with an Ashcroft locker installed is £745.00 (inclusive) from Crown Diffs at the time of purchase. Not cheap but to all intents and purposes this is a new, 4 pin diff so not bad either considering the price of a standard open diff from Land Rover. To this, you will also need to add the price of a compressor. The compact compressor which is capable of running twin lockers is around £150.00, the next size up is around £100.00 more. If you want to inflate your tyres then the larger one is the one to go for (add around £30.00 for the inflation kit). I opted for the smaller, cheaper compressor as for an extra £130.00 all in for the larger unit, I can live without that option.
Drivetrain
There are two schools of thought as to whether or not the drive train should be upgraded or not when fitting a locker. There is an argument that it is advisable to keep the 1/2 shafts standard. By doing this, the 1/2 shafts are the weak point which are relatively easy and cheap to replace and save other, more expensive components. I can see the logic behind this. The counter argument is to make everything as strong as possible. I know of three people that have been running standard shafts with rear ARB's and Ashcroft lockers for the past 18 months without any issues. Figuring that if the 1/2 shafts are coping, then there is very little stress being transferred to the gearbox I decided to go the upgrade route. Time will no doubt tell if this was the correct choice or not but given the amount of time a locker is actually engaged (on a recent eight hour laning trip I engaged the locker four times. Total time engaged in eight hours, under a minute) I'm expecting the gearbox to holdup. If you do uprate the 1/2 shafts (Ashcrofts in my case), then it is advisable to change the drive flanges also, as these will wear prematurely when used with the much harder Ashcroft shafts. If fitting a front locker then you should also change the CV's. With the standard items, using the front locker in anything than a straight line will see these go bang in very short order. This is the reason that currently I'm only running a rear locker, the front will go in when I can afford to uprate the front axle. The Ashcroft CV's are around £500.00 a pair
The Verdict
Typically, since having the locker installed I've found myself with very little time recently to actually test it out. I have managed to get out on one occasion however and drive some lanes that I know well. Although I have driven these lanes many times with open diffs in the past, the locker did make itself apparent. Where before you had to consider your line, choose your gear carefully or need a little bit of momentum to clear something, with the locker engaged these no longer become quite such important considerations and the Defender will happily trundle along and over the same obstacles on Antistall with no fuss or drama, feeling like it is being pushed by an invisible force. Even purposely getting it cross axled going uphill with open diffs didn't phase it, engaging the locker saw it simply drive up and out from a standing start. Kinder on the vehicle, kinder on the lanes.
Is it worth it?
As I said previously, lockers aren't cheap. For a built up locker, compressor, Ashcroft shafts and drive flanges, you're looking at around £1300.00 in parts. To this you can add fitting if you don't do it yourself or have a mate who can. This is for a rear locker, if you're adding a front one then you need to budget for CV's too which are around £500.00 at the moment I believe for the Ashcroft ones. For front and rear lockers you're probably looking at £3000.00 +, when taking into account consumables, uprated drive train etc. As a mate pointed out, you could buy another cheap Defender for this kind of money for laning, P&P, etc. This is very true but you also have to factor in tax, insurance, maintenance, etc for a second vehicle and while it may save damage to the main vehicle, it's not going to be anymore capable unless you start modding that one too. Is it worth it? Thats for the individual to decide, for some people yes, for others possibly not. For me, I want the most capable vehicle I can get without compromising on road driving. Lockers do that superbly so for me, the answer is yes. Some of you reading this may consider fitting a locker or ATB yourself, others may decide it's simply isn't worth it. No problem, I accept we all have our own, sometimes different opinions and as I neither sell or fit lockers for a living, have nothing to gain or lose either way what anyone else decides. I'm simply putting down my own experience and rationale for doing so and hopefully some may find it interesting and/or informative.
If you have any comments or questions on this, or any other topic on here that requires a reply then please email [email protected]
If you have any comments or questions on this, or any other topic on here that requires a reply then please email [email protected]