Project EJ Civic, Building the Drivetrain


The M Factory diff is available as a one way and a 1.5 way diff.  The one way diff only locks under acceleration and the 1.5 way locks full on acceleration and partially on deceleration.  On the advice of several of our friends that run this diff successfully on Honda Challenge racers, we speced our diff as a one way.  Our NASA racing friends reported that the 1.5 way diff tended to contribute to understeer on turn in.

The M Factory differential case is made of strong forged steel.  This greatly helps durability and overall strength.  This could be an issue if you have a strong turbo engine.

The standard setting for the M Factory diff is 60 percent lock under full lock.  M Factory did a few custom tuning steps on our differential to make it a little quieter and smoother to improve streetablity.  The first thing they did was to reduce the initial break away torque.  The M Factory diff allows a lot of adjustment here as it uses coil springs to preload the clutch plates which controls initial breakaway torque.

The M Factory LSD has 4 pinion gears, twice as many as the stock diff.  The ends of the pinion shaft have a cam shape that engages the diff’s pressure rings.  The cam shape influences the lock up characteristics of the diff.

Typically most LSD’s use cone springs which are like huge washers with a slight conicity to them to apply preload to the plates.  The disadvantage to cone springs is that they have very little travel and as the clutches wear and get thinner, the preload falls off greatly.  Coil springs have much more constant tension over their range of travel and a much greater travel so the LSD will have more consistent action over the life of the clutches.

The initial lock up torque is controlled by these coil springs.  The initial lock up torque can be adjusted by the tension and number of springs.  M Factory reduced our initial lock up torque to decrease its contribution to understeer under turn in.  Notice that only about half of the spring spaces are being used.  This tuneabilty is a good feature

After talking to M Factory about our cars end use as mostly a dally driver, They decreased the initial breakaway torque by removing some of the springs and by machining another set of pinion shaft ramps with a more shallow slope in make the differential locking ramp more gradual.  This will make the car turn in better when the throttle is off and make lock less aggressive so the car won’t tend to push out to understeer as much with the throttle on.  These are better with lower powered cars and smaller tires.

The pinion shaft cams sit in these slots.  The shape of the slots control the locking characteristics of the diff.  Our diff is a one way diff so the slot is flat on one side.  This means that the pressure rings can only wedge on the clutches in the acceleration direction.


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