Thread: LSD Ramp Angle vs Adding clutches

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LSD Ramp Angle vs Adding clutches

So I have a very good understanding of the way an LSD works and the way you can add lock but unfortunately I don't have the experience of knowing how different setups feel, nor do I have the funds to build different diffs and try them out.

So for those who have been in the game for a while can you tell me, if you as a driver can tell the difference between adding clutches to an LSD (done properely with the correct pre-load maintained) and decreasing the ramp angle to achieve the same effective lock? Is one method less clunky than the other, is one more progressive etc?

BRENDAN - Put a SOHC in it!

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-Adding clutches by itself doesn't make much difference for a given preload, more clutch for same preload = less wear

So adding ramps vs % lock

-Adding ramp = open diff into curves and high % lock on acceleration

-Adding % lock = the high % lock is kept thru a turn (and this is why welded diff are crappy)

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Here's how I understand it. Adding clutches isn't simply increasing the area, which wouldn't change the lock (as Friction force=Normal Force x Coefficient of Friction, that is Friction is independent of area) but because you are stacking them they you are doubling the number of friction surfaces as each clutch receives the same normal force regardless of the number of clutches so adding clutches should add lock. Therefore with the same pre-load the diffs should theoretically perform the same but I am asking about transients and other properties.

BRENDAN - Put a SOHC in it!

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Originally Posted by Bwaterman

Here's how I understand it. Adding clutches isn't simply increasing the area, which wouldn't change the lock (as Friction force=Normal Force x Coefficient of Friction, that is Friction is independent of area) but because you are stacking them they you are doubling the number of friction surfaces as each clutch receives the same normal force regardless of the number of clutches so adding clutches should add lock. Therefore with the same pre-load the diffs should theoretically perform the same but I am asking about transients and other properties.

I didnt word it correctly sorry, for a given breakaway torque more clutches = same way. But if I remember correctly preload is adjusted according to breakaway torque so in the end what I said would apply. It just that for the bmw diff messing with clutch numbers usualy tighten up assembly and increase breakaway torque. You could machine the carrier a little and use 5 clutches vs using 4 at same breakaway torque to help with wear tho.

ZHP is offline" />

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What you're really talking about here is the difference between static lock and dynamic lock. Jim Blanton discusses this a little on his web site here. Be sure to mouse over static lock and dynamic lock "links" and read the associated popups.

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Think of it as surface area vs. pressure. I don't think you can achieve a certain level of total lock just by changing one of the ramp angles. That's like saying instead of bigger brakes I can just press the brake pedal much harder Friction versus pressure is not exactly a linear. You are going to add at least one disc, which is a no brainer as you have to disassemble the diff to machine the ramp.

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Originally Posted by gisqc

I didnt word it correctly sorry, for a given breakaway torque more clutches = same way. But if I remember correctly preload is adjusted according to breakaway torque so in the end what I said would apply. It just that for the bmw diff messing with clutch numbers usualy tighten up assembly and increase breakaway torque. You could machine the carrier a little and use 5 clutches vs using 4 at same breakaway torque to help with wear tho.

Yeah what I'm saying is that after you add clutches and then adjust the diff to retain stock breakaway torque, the %lock under load caused by the spider gear shafts riding up the ramp is proportional to the number of clutches. More clutches=more lock, that's why you can tune OS Giken and KAAZ clutches for less dynamic lock by deactivating clutches.

Originally Posted by yokoseiki

Think of it as surface area vs. pressure. I don't think you can achieve a certain level of total lock just by changing one of the ramp angles. That's like saying instead of bigger brakes I can just press the brake pedal much harder Friction versus pressure is not exactly a linear. You are going to add at least one disc, which is a no brainer as you have to disassemble the diff to machine the ramp.

You can change the locking force by changing the ramp angles, its pretty common knowledge for diff tuning, its just a case of working out the trig. For a 45deg ramp the amount of force applied in the clutch tangential direction by the spider gear shafts is the same as the force applied in the normal direction to the clutches. If you consider a 30deg ramp then the clutches will receive 1.73 ( tan(60) ) times as much force as the spider gear shafts apply due to the decreased angle.

What I'm trying to ask here is for the really experienced guys, if achieving the same dynamic lock will feel different depending on the method that it is achieved by. So does a 2-clutch diff with 26.56 degree ramps (50% lock) feel any different to a 4 clutch diff with 45 degree ramps (50% lock)? Obviously increasing the number of clutches increases the life of them but I'm mainly concerned with feel and drive-ability for the purpose of this discussion

Last edited by Bwaterman; 06-03-2012 at 09:54 AM .

BRENDAN - Put a SOHC in it!