Under the cone spring is one of the two clutch packs. Half the clutch packs are tabbed to the differential case, the other half are splined to drive the side gears which are also splined to the axles. 

The resistance in movement that the clutches make between the case and the side gears is the lock preventing one wheel from running away and free spinning. 


Here is a close look at the clutches. The case driven clutches are tabbed on the outside while the side gear driven clutches are splined to be driven on the inside diameter. 

To reduce the total amount of lock, individual clutches can be deactivated by pairing the case clutches or side gear driven clutches. It is pretty rare that you would even want to do this though with an OS Giken diff given the other tuning options.

Note the grooves on the clutch plates. These allow for a good flow of gear oil to keep the plates cool and lubricated. This not only assures for long clutch life but also helps keep clutch chattering and racheting to a minimum. OS Giken diffs are among the smoothest and quietest clutch type LSD differential on the market. 


At the center of the OS Giken diff are the pressure rings, spider gears, and cross shafts. They are all contained within this assembly. This is the heart of the diff where a lot of the tuning magic takes place.

A cool thing about the OS Giken diff is that it has 4 spider gears and two cross shafts. Stock differentials typicaly only have one cross shaft and two gears, which tend to break. The OS Giken diff is literally twice as strong in this regard. 


The center assembly has two halves. In the center are the cross shafts that the spider gears spin on. 

On the ends of the of the cross shafts are cams.  When one wheel starts to spin faster than the other, the side gears put a torque on the spider gears which transfers the torque to the cross shafts. The cross shafts cams then spread the pressure rings apart which puts more clamping force on the clutch packs, increasing the amount of lock that the differential has.

Several factors affect the locking characteristics of the differential. The first is the shape of the windows that the cross shaft cams ride in. If the windows are a symmetrical diamond shape, the locking force is close to equal on acceleration and coast, this is called a 2-way differential. The diff will lock close to equally on acceleration and deceleration. This is great in applications where you want to use the gas or brake to rotate the car, like drifting or rally.  

If one pressure ring is like half of a diamond and the other a flatter diamond or even a half circle, the differential is a 1.5-way. This means that the differential locks harder on acceleration than deceleration. The 1.5-way is the best all around for an RWD car, but generally looks up too hard on deceleration and causes understeer on turn in for FWD and the front of AWD cars.

On our diff, the pressure ring windows are diamond shaped on the acceleration side of the cross shaft cam and flat on the deceleration side. This gives a positive lock under power and way less lock on deceleration. This is called a one-way differential. This setup usually works best on an FWD or the front of an AWD car. 

The shape of the windows has a lot to do with the locking characteristics. Triangularly shaped ramps on the windows will lock sooner and harder while flatter shaped ramps will lock softer and later.

The next tuning factor is the shape of the cams.  The cams shape affect how the cams will engage with the pressure ring windows and control how much wedging action they will have.  A pointy cam shape will lock harder and sooner while a rounded shape will lock softer and later.

What shape your windows and cams have are determined by OS Giken for your anticipated use. For instance, a drift diff will have diamond-shaped windows and a cam that is pointy on both sides for maximum lock on acceleration and deceleration. An FWD diff like ours will have a window that is diamond shaped on the acceleration side for maximum lock and flat on the deceleration side for minimal lock. The cross shaft cams will be pointy on the acceleration side and flat with rounded corners on the deceleration side for a very slight locking effect.

The final tuning factor for an OS Giken diff is the pressure ring springs. These springs are placed in between the pressure ring halves and counter the wedging action of the cross shaft cams. These control how quickly the locking action comes in. OS Giken has 3 weights of springs from soft to hard. A soft spring allows for faster lock up and is something like you would use in a drift car, while a hard spring causes the lock to come in more gradually like you would in slippery conditions or in a FWD car. 



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Wednesday, February 14, 2018 8:15 AM
I know some clutch type LSDs require special fluids. Is there any hard set rule on what fluid (or additive) and which LSD? Or is this more of a manufacturer spec kind of thing?
Mike Kojima
Mike Kojimalink
Wednesday, February 14, 2018 10:11 AM
Most LSD manufactures have there own lube. I tend to use whats good for the transmission and use something like Redline friction modifier if the diff chatters. I have found that OS Giken diffs are generally pretty quiet.
Thursday, February 15, 2018 1:37 PM
I've looked for a front did like this for a 2017 WRX, does anybody know of one? I looked through giken's website and didn't see anything.
Mike Kojima
Mike Kojimalink
Thursday, February 15, 2018 1:46 PM
I would try calling them
Thursday, February 15, 2018 3:47 PM
Great article! Did you have to replace the pilot bearing fork with a new one? That was something that failed on my GS-R.
Mike Kojima
Mike Kojimalink
Thursday, February 15, 2018 5:13 PM
no, the old one was ok.
Saturday, February 17, 2018 10:49 AM
Hey Mike, I have 2003 Acura CL comes with factory lsd. I believe it is a Mfactory 1-way helical. I use my car for autocross and track. Only aftermarket lsd I've seen is Cusco RS. Would you recommend that over factory? 1-way I'm assuming for fwd?
Sunday, February 18, 2018 3:41 AM
"When one wheel starts to spin faster than the other, the side gears put a torque on the spider gears which transfers the torque to the cross shafts. The cross shafts cams then spread the pressure rings apart which puts more clamping force on the clutch packs[...]"

First part is all wrong, locking have nothing to do with wheel slip, quite the opposite. It should be: "When torque is applied to the insides of diff through ring gear, pressure rings are spread apart because they encounter resistance from cross shaft cams which are connected to wheels through spider and ring gears. That spreading action increase clamping load on clutch packs, increasing the amount of lock that the differential has."
In short the more traction and torque the more clamping force the diff have.

At last i would like to point out that you should put Loctite inside hole, not on the bolt when bolting flywheel.
Monday, February 19, 2018 4:04 PM
@Feluke, You both are right and wrong. Mike is missing a few words but has the principle correct. You are missing one major thing that is required for a clutch diff to work, traction/road resistance. Which once you add it you will get right back to what Mike is saying. Mike saying "when one starts to spin faster.." is in the right direction just a little misleading.

The diff cannot lock without traction. If you free spin a diff, since there is no load on the spider gear/cross shaft, the diff will not add any additional breakaway torque other than what is in the clutch preload. As soon as you add load, to even one side of the diff is when the cross shaft will wedge on the hub and start to add additional force on the clutch packs. This will then try to lock the front wheels. What you need to take into consideration is what is more, traction on the inside wheel over total clutch load or if the clutch load is greater than the available traction. If traction is greater than the diff breakaway, the diff will differentiate(desirable). If the dynamic breakaway torque is greater than traction you will get wheel slip(undesirable). You will see this when looking at wheel speed data. with the steering wheel turned and off or part throttle you will see wheel speed differential, as soon as your diff settings come into effect you will see wheel lock up(to the diff) and front wheel speeds will equalize even though the steering wheel is still turned. When and where this happens will really determine how much your diff is hurting or helping you.

@Mike, I have practiced more decel ramp than a 1 way(maybe 60:40 or 70:30), less clutch preload/initial breakaway torque and a really slow/delayed lock timing. I have found a lot better drive ability due to the low initial preload. The added decel allows for a good wedge to help rotation. This is similar to what you are trying to achieve with more preload and zero lock/ramp angle. Once mid corner and part throttle comes you will have a lighter diff preload to help the target wheel slip differential mid corner. Once to exit you will have the delayed lock timing and still a good lock. Too much lock too early and once locked you are loosing traction on the inside wheel since it is spinning faster than road speed. Then you just hope you don't over power the outside wheel and start to push.
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