Limited Slip defined...
#1
03-01-2010, 10:52 AM
Limited Slip defined...
For those who have an "Open Differential" you are basically stuck, pardon the pun. If you are in a situation where one wheel has traction and the other does not, for example on ice, torque inherently takes the path of least resistance causing the tire on ice to spin and the tire with traction to sit there motionless.
Sometimes a bit of light pressure applied to the brake or some creative use of the emergency brake can transfer enough torque to the wheel with traction, but most times, you are just stuck!
As everyone knows, the Dodge OE LSDs are crap. Even if it doesn't "explode" and take out the carrier, it doesn't work worth a damn, so I am only going to look at aftermarket differentials here.
Enter the Limited Slip Differential: Basically a LSD achieves the same result as applying the brake does in an open diff, except it does it more efficiently. There are primarily two different ways a LSD achieves this, either using a series of clutches (Auburn LSD) or gears (Eaton/Detroit TruTrac).
The amount of braking or torque applied to the wheel with traction is measured as the Bias Ratio. The lower this ratio, the closer to an open differential you will have (open diffs have a bias ratio of 1:1) meaning the better the characteristics on dry pavement, especially when going around turns. The higher this bias ratio, the better the differential will "lock", but you will have adverse effects such as ratcheting around turns, poorer gas mileage, etc, if this is too high. So a balance between the two is needed. At around 2:1, this is ideal for a primarily street machine who just wants extra traction in snowy and icy conditions. The "ratcheting effect" and any other negative effects are minimized, if even noticeable at all.
For maximum traction without going to a true locker or spool (neither of which are very "streetable"), LSDs are available with a bias ratio of up to about 4:1, great for traction, but the negative aspects of a LSD will be very pronounced on the street.
Most of us IFS 4x4 owners choose either the Auburn Gear or Eaton/Detroit TruTrac. The Auburn, available in the Performance Series with a 2.5:1 bias or the Pro Series with a 3.5:1 bias. These are clutch type utilizing dual tapered cones with a set of preload springs. Advantage is cost, and an almost instant but progressive locking effect. Most "track" guys opt for this type as "lock-ups" off the line are instant. Disadvantages are that the clutches will wear over time, although with average use, performance does not usually begin to degrade till around 100k miles. Also a special "friction modifier" is required to be added to the differential lubricant and synthetic lubes are NOT recommended for optimal performance.
The TruTrac is a gear driven unit, with a bias of about 3:1. It's advantage is that it does not require a special "friction modifier" additive, synthetics are fine and it does not wear over time. Disadvantage is it's relatively high cost and it does not "lock-up" as fast as some of the higher end clutch type LSDs.
Sometimes a bit of light pressure applied to the brake or some creative use of the emergency brake can transfer enough torque to the wheel with traction, but most times, you are just stuck!
As everyone knows, the Dodge OE LSDs are crap. Even if it doesn't "explode" and take out the carrier, it doesn't work worth a damn, so I am only going to look at aftermarket differentials here.
Enter the Limited Slip Differential: Basically a LSD achieves the same result as applying the brake does in an open diff, except it does it more efficiently. There are primarily two different ways a LSD achieves this, either using a series of clutches (Auburn LSD) or gears (Eaton/Detroit TruTrac).
The amount of braking or torque applied to the wheel with traction is measured as the Bias Ratio. The lower this ratio, the closer to an open differential you will have (open diffs have a bias ratio of 1:1) meaning the better the characteristics on dry pavement, especially when going around turns. The higher this bias ratio, the better the differential will "lock", but you will have adverse effects such as ratcheting around turns, poorer gas mileage, etc, if this is too high. So a balance between the two is needed. At around 2:1, this is ideal for a primarily street machine who just wants extra traction in snowy and icy conditions. The "ratcheting effect" and any other negative effects are minimized, if even noticeable at all.
For maximum traction without going to a true locker or spool (neither of which are very "streetable"), LSDs are available with a bias ratio of up to about 4:1, great for traction, but the negative aspects of a LSD will be very pronounced on the street.
Most of us IFS 4x4 owners choose either the Auburn Gear or Eaton/Detroit TruTrac. The Auburn, available in the Performance Series with a 2.5:1 bias or the Pro Series with a 3.5:1 bias. These are clutch type utilizing dual tapered cones with a set of preload springs. Advantage is cost, and an almost instant but progressive locking effect. Most "track" guys opt for this type as "lock-ups" off the line are instant. Disadvantages are that the clutches will wear over time, although with average use, performance does not usually begin to degrade till around 100k miles. Also a special "friction modifier" is required to be added to the differential lubricant and synthetic lubes are NOT recommended for optimal performance.
The TruTrac is a gear driven unit, with a bias of about 3:1. It's advantage is that it does not require a special "friction modifier" additive, synthetics are fine and it does not wear over time. Disadvantage is it's relatively high cost and it does not "lock-up" as fast as some of the higher end clutch type LSDs.
Last edited by HammerZ71; 03-02-2010 at 08:20 AM.