How to tell if trac-loc needs to be serviced??

It probably does that from the torque produced by the gearbox. When you floor it, both wheels are getting the power, and the driveshaft is spinning as hard as it can clockwise (when viewed from the rear of the vehicle), and so pushes down on the driver's side tyre, giving it more traction than the other side.

When you turn, the weight being forced to the outside wheel, as well as the fact that the outside wheel has to travel further give the outer wheel (driver's side turning right, and passenger side turning left) more tractive ability.

Now, when you turn left, the torque from the DS cancels out the weight shift and the extra distance travelled, giving both tyres approximately the same amount of grip, making them both spin.

When you turn right, the tractive forces (DS torque, weight shift, and extra distance travelled) combine to make one tyre have significantly more tractive ability than the other. The inner tyre will spin faster, and match the speed of the grippier outside tyre, and with less distance to travel, make it skid.

There is a tool at ford that bolts on in place of the wheel that allows you to center a torque wrench over the axle shaft (you should be able to come up with an idea for doing this). I think the spec is something like it has to take at least 40 # of torque to break the wheel free with the other wheel locked up such as on the ground so it can't turn.

A Torsen diff.

Route666 said:

A Torsen diff.

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Now those rears are cool! I have one of them factory installed in my new Miata 6-speed.

PoliceInterceptor said:

http://www.tractech.com/Products.htm

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Cool Website!