Limited Slip Axle
#2
11-11-2009, 09:00 PM
More Turbo
Chock the front wheels.
What you can do is jack up the rear axle, being careful that it is securely resting on jack stands. The tires can stay on the vehicle, and shouldn't need to be raised more than a couple of inches off the ground.
With the transmission in neutral and the parking brake released, grab one rear tire rotate it. Observe the other rear tire. Is it rotating the SAME direction? A properly function limited slip should rotate the other tire in the same direction.
An open differential will rotate the other tire in the OPPOSITE direction.
You can get an idea of the "break away" torque of your limited slip differential with the following technique:
Let one of the rear tires down securely on the ground, leaving the other tire still suspended a couple of inches in the air.
With the transmission still in neutral and the parking brake released, attempt to rotate the lifted tire. You should be able to rotate it, however, it will likely be difficult to turn. The harder the tire is to turn, the "tighter" (and more effective) your limited slip is set up.
There is a factory "spec" for testing these units, but I do not have it. It involves using a torque wrench, I believe, applying pressure to one of the lug nuts, and observing the torque measurement when the wheel begins to turn. Like I said, I don't have any specifics per Ford, but I think it's pretty low- like 25l lb-ft.
The OEM limited slips are pretty weak, and reach break-away torque easily in such a heavy vehicle. You can try draining the fluid in your rear differential, and refilling it with the specified fluid LEAVING OUT the friction modifier specified by Ford. Drive in some figure-eights on hard pavement. If chattering develops from the rear axle, add the friction modifier 1oz at a time until the chattering stops.
Hope this helps.
What you can do is jack up the rear axle, being careful that it is securely resting on jack stands. The tires can stay on the vehicle, and shouldn't need to be raised more than a couple of inches off the ground.
With the transmission in neutral and the parking brake released, grab one rear tire rotate it. Observe the other rear tire. Is it rotating the SAME direction? A properly function limited slip should rotate the other tire in the same direction.
An open differential will rotate the other tire in the OPPOSITE direction.
You can get an idea of the "break away" torque of your limited slip differential with the following technique:
Let one of the rear tires down securely on the ground, leaving the other tire still suspended a couple of inches in the air.
With the transmission still in neutral and the parking brake released, attempt to rotate the lifted tire. You should be able to rotate it, however, it will likely be difficult to turn. The harder the tire is to turn, the "tighter" (and more effective) your limited slip is set up.
There is a factory "spec" for testing these units, but I do not have it. It involves using a torque wrench, I believe, applying pressure to one of the lug nuts, and observing the torque measurement when the wheel begins to turn. Like I said, I don't have any specifics per Ford, but I think it's pretty low- like 25l lb-ft.
The OEM limited slips are pretty weak, and reach break-away torque easily in such a heavy vehicle. You can try draining the fluid in your rear differential, and refilling it with the specified fluid LEAVING OUT the friction modifier specified by Ford. Drive in some figure-eights on hard pavement. If chattering develops from the rear axle, add the friction modifier 1oz at a time until the chattering stops.
Hope this helps.
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