NIVAS FROM OZ AND AROUND THE WORLD
Traction Enhancing Differentials for a Lada Niva
"A very flexible rear suspension is key to the Niva's offroad performance, but sometimes you need more"
Why do you need a traction enhancing differential?
The Lada Niva is quite a capable offroad machine, two key contributors to its sucess offroad is its inherently low weight and a very flexible rear suspension.
What makes the flexible rear suspension important?
Well the answer lies inside the differential housings and how a standard differential operates. If you have a frank conversation with an owner of a Lada Niva, a Land Rover Discovery 1 or a Jeep Wrangler you will likely come away with a sense that there is an unwritten understanding among owners of those vehicles of what is key to making an offroad vehicle. It is a subtley, the design of those vehicles, is somewhat unassuming but their appearance hides their true capbility. It comes out when you go 4WDing (Four Wheel Driving or offroading) with other brands of 4wd, they can even be heavily modified , look like they will go well offroad and seem to be matched or outclassed by a relatively lightly modified Niva.
If you own a niva, you already know what I am talking about, its written on the faces of the other drivers who are shocked at how the Niva just casually walked up an obstacle when they had to blast up the same obstacle after 5 attempts, or worse couldnt get up. Well the trick that the lada, Land Rover and Jeep vehicles have in common is that they have very supple and flexible suspensions for their class (we will go into suspension design more in Making the most of your Niva Suspension). It makes common sense that the more wheels you can keep in contact with the ground the more traction you will have. But what if despite your secret ultra flexy niva suspension, you just cant keep all the wheels on the ground or perhaps you just drove into a deep muddy pit and one or more tyres just simply cant find traction.
It is at this point you could use the assistance a traction enhancing differential can provide to help keep your vehicle on the move. There are a myriad of designs and they can have many different names , Limited Slip Differentials, LSD's, Limo's, ATB's, Torsens, Powerloks, Posi's, Lockers, AirLockers, Diff Locks to name a few. They are not all the same and each type of differential has some specific advantages and disadvantages to offer a driver both on and off the road.
From the factory the Niva comes with a conventional differential in the front and rear axle, the same type as found in the vast majority of cars on the road today. It is actually a very good engineering solution. Cars when they turn the corner have a little problem to solve, their wheels travelling the closest to the inside of a turn travel less distance than the wheels on the outside of a turn. This difference in distance travelled means we either scrub the tyres as we make a turn or we come up with an engineering solution. It just so happens that the conventional diff is very good at allowing for wheels to rotate at different rates which helps to turn corners without scrubbing tyres, but importantly (for the vast majority of on road users) it applys torque evenly across the two wheels of an axle. This even torque (turning force) distribution provides very predictable handling under normal driving conditions. This may make it seem like a normal differential is the perfect power transmission solution, however there are some downsides. The biggest downside is simple, while it splits torque evenly, the maximum amount of torque able to be supplied across an axle is limited to the amount of torque able to be applied to any one wheel. In other words, the most tractive force you can get from the axle is the lowest traction available from either of the two wheels on the same axle. We are going to call this the "golden rule".
Conventional Differential
Scenario: One wheel on a low traction surface and one wheel on firm ground.
To keep the example simple we are going to assume that our vehicle is set to be RWD only, hence the big red X where the transfer case/centre diff would be in the diagrams, meaning no drive to the front wheels. We can explore the impact of the centre diff and having locked or unlocked later on, but for now lets keep 4wd out of the discussion for clarity. Also I have included some relative force numbers (N), they are not meant to be representative of real world figures, they are intedended to be purely for simple demonstration of the principles at work.
The way a conventional diff design works is both its greatest asset and its own worst enemy. A conventional diff works by applying the driving torque (turning force) evenly across both wheels. Its golden rule is that neither wheel can have more turning force applied than the other. On the street, this is a good feature as the handling will be predictable and tyre wear even etc. The problem is the rule still applies. In the case of lifting a wheel off the ground, the wheel in the air doesnt need much turning force to spin freely. And by the golden rule of conventional diffs it means the diff will only apply the same force it takes to spin the wheel in the air and that usually isnt enough to keep the car moving forward so you become stuck, or it simply fails to proceed and spins the wheel in the air.
The same applies in a low traction situation like greasy mud or clay. In this example the vehicle is a rear wheel drive only and if the amount of traction of the wheel in the mud is insufficient to keep the vehicle moving forward, then the maxmium force applied on the good high traction side will be limited to that available on muddy side, even though one of the wheels is on the high traction side of the axle and could take a signifcant amount of tractive force, the humble conventional diff sticks to its golden rule and leaves you stranded. In this example the car simply would spin the tire in the mud, the driver would take their foot off the accelerator to prevent the wheels or engine from over spinning, and therfore limit the torque applied. The end result is the car does not move forward.
Offroad Rating: 1/5
Onroad Rating: 5/5
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Benefits:
-Smooth torque delivery and predictable handling under onroad conditions
-Factory Fitted
-Simple mechanism
-Low wear on tyres and driveline
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Disadvantages:
-Relatively weak 2 satellite gear design in Niva
-Poor torque transfer characteristics under low traction conditions
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Niva specific application:
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Approx Price: AUD$100 + Shipping
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Limited Slip Differentials
Disc (Or Plate Clutch Style) Limited Slip Differential (LSD)
Our little example above highlighted the main shortcoming of the conventional diff in low traction situations. The Limited slip style differential is the next step up from a conventional diff and tries to improve on the split of driving force across the axle. It comes in many different styles and designs, some use use viscous liquids, others use clutch packs to increase friction across the differential and some designs use gear packs to bias (or send more) torque across the differential. The aim of each of the designs is he same, that is to increase the amount of torque that can be applied across a differential in the event of uneven traction conditions. With a disc type limited slip Differential the amount of torque that can be applied to the good traction side wheel can be increased beyond the limit of the low traction side.
As promising as that concept sounds there is a compromise involved, At first it seems that we have solved the problem, we can just tighten up the clutch inside the limited slip diff so that it is locked and we will have full turning force available on either wheel. As good as that sounds, remember we have to turn corners and our wheels need to turn at different rates when on the tarmac. So we cant just bind up the clutch, the designer of the LSD needs to soften the locking effect to prevent odd handling and rapid tyre wear. Often in the case of a clutch pack (Disc) LSD the biasing effect is intentionally limited in order to not to introduce undesired handling problems. With a traditional disc based LSD, the "tighter" the diff is setup in order to improve torque transfer, the less freely the LSD allows the wheels to move at different speeds. This introduces handling changes, indeed in a high performnce RWD road or race car this tighter hadling effect would be considered desirable.
The benefits to an offroad vehicle are less straight forward. If we return to our example, the LSD could increase the force applied to the wheel with good traction to the point where the vehicle keeps moving forward in some situations, but remember we said that often the LSD is setup with a limited amount of biasing power in order to keep tyre wear and handling within limits, if the vehicle now nudged up against an obstalce such as a rock, that slight increase in force applied to the good traction side might not still be enough to keep the vehcle moving forward.
Offroad Rating: 2/5
Onroad Rating: 4/5 **depends on preload setup
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Benefits:
-Can provide better traction than a conventional differential under slippery conditions
-Relatively inexpensive
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Disadvantages:
-Not recommended for front axle applications
-Requires special oil with anti chatter additives
-Preload (grip effect) in some models can fade with use or wear
-Can affect on-road handling, especially with high preload models
-Accelerated tyre wear compared to a standard diff
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Niva specific application:
Val Racing
http://www.val-racing.ru/catalog/samoblokiruyuschiecya-differencial/blockross/DIF-2101
Approx Price: AUD$300 + Shipping
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Torsen Style (Gear) Limited Slip Differential
Remember how we said there were many different designs of Traction enhancing differentials out there. The Gear driven LSD is one such design and lets see what happens when we bring it into our example scenario from above. These diffs are marketed under different names, torsen, gleason, quaife, ATB (Automatic Torque biasing), true trac to name a few. Each has slightly different operating designs but all share a common operating principle and that is to use gears to apply and multply torque across the differential. The engineers designed a fixed bias (transfer) ratio into the differential which normally varies somewhere between 2.5 and 4.5:1. This ratio is the effective mechanical advantage that the diff can apply across the differential. In our example in stead of applying the equivalent of the least traction wheels force with a gear LSD up to 4.5 times the force could be available to keep the vehicle moving. This is often a very handy amount of force in many circumstances, but again there is a limit to its effectiveness as a torque transfer device. Think of a situation where the amount of traction on the wheel with low grip to be really low indeed, 4.5 times of almost nothing is still almost nothing and so the vehicle may once again fail to proceed even though we have a wheel on a potentially high traction surface.
It is really the same as if we were to lift one wheel off the ground you would effective have zero torque available to multiply and again the vehicle not move forward. The very low traction or wheel in the air scenario is the primary downside of the Gear based diff. A trick with the Gear based LSD in these circumstances is to apply the handbrake, a word of warning here is that for vehicles with transmission or tail shaft handbrakes this trick wont work, anyway apply a couple of notches or very lightly apply the brake pedal. This creates a resistance to allow some torque to apply against the low traction wheel and gives something for the LSD gear work their multiplying magic against. It can be very effective at generating usable torque. The real magic is that whatever the brakes are loading up are usually applied evenly, but the multiplier effect of the gears inside the LSD will put 2.5 - 4.5 times to the other wheel, this is usually more than enough to keep the vehicle moving. The down side to this technique is having to left foot brake while balancing the accelerator and clutch in demanding offroad situations and is definitely easier with very low range gearing, a torquey motor, or auto transmission. These simply make it more forgiving to drive, think of the scenario where you are on a steep rocky climb and you need to very quickly balance the clutch pedal, brakes and accelerator pedals in order to start moving, certainly possible, but probably a bit too entertaining and not everyone's idea of a great days driving. One other thing is that if you crank up the breaking effect really high and keep driving more torque through, that multiplier effect can in certain situations increase the torque beyond the rating of axle shafts, CV joints etc causing them to fail, even more than a straight locked axle situation. So just be careful about using too much braking if you have really low gearing or a powerful engine and a gear based LSD.
Offroad Rating: 3.5/5
Onroad Rating: 4/5
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Benefits:
-Can provide significantly better traction than a conventional differential under slippery conditions
-Smooth operation and engagement of traction enhancement
-Traction improvement is automatic unless wheel lifts off the ground
-Does not need special diff oils
-Relatively inexpensive
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Disadvantages:
-There is a strong self centre effect when installed in the front axle. Vehicle feels like it wants to track straighter around bends especially with high preload models.
-Requires driver to use a Brake Modulation technique or hand brake application when the wheels are lifted off the ground.
-Preload in some models can fade with wear
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Niva specific application:
Val Racing
http://www.val-racing.ru/catalog/samoblokiruyuschiecya-differencial/blockross/blok_2101_2123
Approx Price: AUD$250 + Shipping
Full Locking Differentials
When you get into situations where you have two diagonal wheels of the ground and your trying to climb up an obstacle or cant use momentum to safely get you through it is hard to beat the performance and convenience of having a fully locking differential on hand.
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Better still is having a fully locking differential in both the front and rear axles. In the video to the left, which was filmed when we ran the killy loop shakedown test run for project "Yuri". If you fast forward to 1min 30sec you will see the prime sort of obstacle where fully locking differentials make a real difference. Despite being "Cross axled" meaning a diagonally opposed wheel on each axle, which would see a conventional differential stopped, the niva was able to keep driving forward.
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It is under these circumstances of very low traction or lifting wheels off the ground that a true locking differential becomes a worthy asset in your offroad tool set. The Locking differentials fall into two broad categories, manual locking and automatic locking. Lets have a look at each one and how they have different benefits in different situations
Automatic Locking Differentials and Lunchbox Lockers
Automatic Locking Differentials come in a variety of designs. Lets start with the Lunchbox Locker.
What is a Lunchbox Locker?
This type of traction enhancing device uses a set of dog clutches. A dog clutch is avery positive sort of engagement, it has mating "Teeth" that mesh together in very much an on or off sort of fashion. They have the advantage of being mechanically simple, easy to produce and because they have many teeth tend to be quite strong in their engagement. The "Lunchbox Locker" is so called because the parts they come with in the box would fit in your lunchbox. Their key feature is that they usually are made to fit inside the stock conventional diff carrier. this keeps the cost down and also means that it is usually possible for a reasonably mechanically savvy DIY (Do it yourselfer) to setup a lunchbox lock at home. Because it uses the standard carrier it may be possible to install the locker parts without having to reset up the gearing. The fact is with a Niva you basically do have to reset the backlash and re-set up the gears so if your not familiar with setting up a differential then id recommend to talk a specialist anyway. It is still a lot easier than having to reset pinion depths and pressing bearings on and off from a full diff carrier change. The lunchbox style is very inexpensive compared to other traction enhancing devices and has the added advantage of being automatic.
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See the Locker install page for further information.
The Lunchbox locker isnt the only design of automatic locker and others such as the Detroit brand of lockers offer an auto locking mechanism. They replace the standard diff carrier entirely and tend to be built much stronger than the standard carrier would allow. This also makes them much more expensive than a lunchbox locker and require more technical expertise to install properly.
The main advantage of the various auto locker designs is that they don't wait for driver input to lock up which can be very handy in unfamiliar offroad conditions as maximum traction is potenital always available. In fact these designs are really an auto unlocker, it is actually locked most of the time until a wheel wishes to run faster than the other, the mechanism allow the wheel to ratchet freely as long as it travels faster than the carriers rotation. This means in a turn the outside wheel will ratchet freely while the car drives off the inside wheel. The lunchbox lockers can also audibly click as they ratchet on turns, it is hard to hear inside the car but can be clearly heard from outside, this is a normal part of their operation.
This driving the inside wheel on turns can introduce some handling quirks as most drivers aren't use to the inside wheel being the driving wheel around a corner, this has a tendency to "straighten" the car up or move to the outside of the turn if you apply plenty of throttle, lucky for the average niva driver there isnt a lot of power available to cause too much change. Generally the effect is not dangerous, but it is there and the driver needs to be aware of the behaviour. Another handling quirk with auto lockers is that under very light throttle coasting around a corner, the locker can switch driving sides back and forth creating a lurching, this is quite noticeable , not exactly comfortable and may result in some puzzled looks from passengers and can be avoided by not lightly coasting around a corner. Avoiding cornering with a neutral coasting throttle with either decelerating or accelerating lightly will prevent it from happening. The auto lockers can give random loud bangs from time to time. There is usually alot of backlash in the design and you can get some noise on sharp take offs. Another source of bangs is when the dog clutches lock into place rapidly after a sharp corner, doesnt happen all the time and is a normal part of operating one.
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One final consideration is the fact that because the autolocker is always ready for duty and there is no way to switch them off, there are certain situations where it would be nice to turn them off. These situations usually involve having the auto locker fitted in the front axle. Firstly, i can not say this enough, dont try to run an auto locker in your niva as a constant 4x4 or all wheel drive vehicle. The un-even loads that change from throttle application and turning corners makes the steering and handling very unpredictable. I can say this conclusively from prior experience and we installed a part time conversion kit into "Yuri" before installing the front auto locker. When you install a part time kit you can run the transfer 2wd and this actually deactivates the front locker and you cant notice that there is one installed on the front during normal driving. As soon as you put it into all wheel drive or lock the centre diff the steering effect is immediately noticeable. As an example when i broke the rear diff on yuri attempting the Steve's Ridge Trail we had to limp home on the locked front diff and it was not a pleasant experience driving that onroad.
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Offroad Rating: 4.5/5 (would be nice to be able to turn off the locker sometimes)
Onroad Rating: 3/5
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Benefits:
-100% lock up traction available without thinking about it.
-Allows differential action on road so tyre wear can be ok
-Often cheaper than a manual locking differential and other LSD systems
-Stronger than standard diff carrier (in full carrier models)
-Increase strength of differential (compared to niva 2 gear design)
-no special oils and lubricants required, use standard diff oil
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Disadvantages:
-Steering ability reduced when all wheel drive or centre diff lock is engaged.
-Steering much heavier when all wheel drive or centre diff lock is engaged.
-Off Camber low traction conditions can result in vehicle sliding sideways rather than driving forward.
-Can be noisy with high backlash and occasional harsh engagement
-Some odd handling quirks in certain situations - changed driving style can help
-Makes a clicking ratchet sound on turns hard to hear inside car but clear outside.
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Niva specific application:
Manual Locking Differentials and Selectable Lockers
Manual Locking Differentials allow the driver to pick when they want 100% locked traction or conventional diff behaviour. By design these differentials need an input from the driver in order to activate and there are a variety of actuation methods. these include:
Compressed Air Locker:
This type of system comes complete with switches, solenoid valves and onboard compressor - The locker is activated by a switch on the dashboard which allows compressed air to run from a small accumulator tank into the differential. Commonly a piston mechanism is activated by the compressed air and locks one of the side gears to the diff carrier. You will probably find references in competing marketing materials of other diff manufacturers about compressor reliability and the vulnerability of compressed air lines under the car. The truth is it is quite rare for a failure to occur, but I admit I have been 4wding with a another vehicle that suffered from a damaged air line when a stick flicked up and severed the line. The lockers could not be engaged as a result and made for a lot of winching. But in many years of running Air Lockers on my previous vehicles in rough terrain I never had an issue with airline damage. On the plus side, depending on the compressor model it can be used to re-inflate your tyres.
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E-Locker or Electric Locker:
An electric solenoid is used to engage and disengage the locker mechanism, this has the advantage of not requiring additional valves or compressors. Eaton E-Lockaers are an example of using electrically actuated locker technology
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Cable or mechanical Locker:
A bowden style cable is used to activate the locker. A lever is fitted inside the cabin and the cabin transmits the position of the lever to the locker mechanism. Having a simple mechanical cable linkage can be viewed as an advantage in some ways, howeer the cables can still go out adjustment and the cables are still open to trail damage causing improper engagement.
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Offroad Rating: 4.5/5 (Sometimes it would be nice to have the traction automatically)
Onroad Rating: 5/5 ** Unlocked
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Benefits:
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100% lock up traction when you want it. you can decide when its needed or not.
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Conventional Differential when its turned off so handling and tyre wear are normal when its not engaged.
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Solid (Spool) Locked when engaged can give great precision in technically difficult offroad situations
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No special oils and lubricants required, use standard diff oil
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Disadvantages:
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Steering ability compromised when engaged. Vehicle wants to track straight
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Off Camber low traction conditions can result in vehicle sliding sideways rather than driving forward when engaged
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Need to plan your activation of the locker in advance for optimum results
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Expensive and can often need epxensive compressors and valves
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Actuation systems such as cables, wires or air lines can be damaged on the trail
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Niva specific application:
Pro Track Air Locker
http://protrack.gr/proionta/lada/52-niva/91-air-locker-niva.html
Approx Price: AUD$1000 + Shipping
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