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| The Cusco RS diff uses 10 discs on each side of the pressure ring. This is a lot of discs and the diff can provide a lot of lock if needed. The discs are grooved to allow free flow of lubrication in between them to help assure long life. We WPC treated our discs before installation. If you haven't heard about WPC treatment yet, it is a Japanese process where the surface is bombarded by microscopic super hard particles at very high speeds. This creates a very hard and slippery surface with good wear properties. When done to differential clutches, the result is a very smooth and quiet diff that also runs cooler. Mechanical limited slips are known to chatter and clunk a lot in street driving and WPC treatment eliminates most of this. WPC treatment also makes the diff smoother in operation which helps put the power down better. Finally, WPC treated discs last over twice as long. |
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| Before putting the clutches in the case, we lubed them up with Motul 75/140 competition synthetic gear oil. |
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| To help our car get traction on corner exit, for our tire size and type (Nitto NT05 285/35-18) we want to reduce our total amount of lock. On most diffs this is done by deactivating clutch packs. This trick can be done on all Salisbury clutch type limited slips, not just Cuscos. The clutches are deactivated by pairing drive clutches and driven clutches together, rendering them not in use. You can see here that we have put two drive and two driven clutches together. This reduces the total amount of lock by 20 percent. We could deactivate two more sets of clutches per side which would reduce lock by 40 percent. We would only do this on a light low powered car with narrow tires like perhaps an FR-S used in grip driving. Deactivating clutches reduces both the initial torque and the total amount of lock and delays the onset of full lock. Just what you need for more grip on corner exit. |
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| The clutch pack is placed in the diff case. |
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| Then the pressure ring. |
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| Then the side gear. On a Nissan you have to be careful as the two side gears have different splines between the right side and left side. On most other LSD diffs you have to buy special stub shafts for a Nissan because the stock diff has different side gears and most aftermarket LSD's have the same side gear on both sides. The Cusco diff uses different side gears just like the OEM Nissan diff saving you the expense of having to buy special stub shafts. However if you mix them up, you will have to take everything apart and start over. Don't ask us how we know this! |
6 comments
Thank you for your really excellent explanation of how these components work.
One question: Gear type differentials (Torsen), appear to me to offer perfect distribution of power at all time. They are strong and require essentially no maintenance or replacement of parts.
What is the advantage of the Salisbury clutch type that you chose?
If the car was to be used exclusively on the street, would you have made the same choice?
They work better, torsens are really not that great.
Great write up, what lock rate was selected 60%, 80% or 100% for your build?
A youtube channel mentioned cusco recommended to leave it at 100% and only mess with the spring preload because with lower lock up rates the disc tend to run hotter. is this true?
Hey Mike – would you be able to do a detailed article on LSD tuning in all aspects?
1) Initial Breakaway torque
2) Ramp angles
3) Belleville thicknesses and spring rates
4) Different clutch plate treatments and surfaces
5) Different clutch plate materials (steel/carbon)
6) Tuning with different oils and additives
From the rabbit hole that i’ve gone down, it seems that most people only focus on the initial breakaway torque and that’s it. But having different spring rate bellevilles (cone washers) or stacking these washers also effect the LSD and how it behaves and reacts.
For example, the ATS carbon LSD needs ~250ftlb breakaway torque, but yet it doesn’t cause the wheels to skip/chatter in the parking lot. But a metal LSD with 80ftlb breakaway torque can skip/chatter with small steering input.
Something as simple as removing one of the belleville/cone washers and replacing it with a spacer and setting the same breakaway torque. How will that effect the LSD and driving?
Cheers, Mike
We did a few already, a couple of youtube video too. search is your friend.
We have several, use the search function. Videos too on youtube. We have never tuned an ATS diff before except for drifting and we didn’t like it and ended up going back to a spool.