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04 PST 4x4 F250- 75-140syn in rear axle, OK to use same in front axle? Couldn't find anything by searching. Also How much friction modifier to add? service book says 8oz in one place and 4oz in another. Just in rear axle? in looking up parts, there are always references to which type of axle is in the vehicle, both front and rear. Dana, Spicer, traction lok. How do you tell which that you have?
 

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Rear axle in a F250 is a Sterling 10.5. If you had a F250 single wheel, it would be a Sterling 10.5. If you had a F350 dually, it would be a Dana 80. Your front axle is a Dana (60, I think) A considerable number of synthetic 75W140s come pre-loaded with friction modifier. Make sure yours doesn't before adding any. If you do, add half the bottle and go do some figure 8s in a parking lot. If you get any chirping, then add the other half.

You can put 75W140 in the front axle, but there is really no reason to. The front axle doesn't get the same continuous loads the rear does.
 

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diff fluid

Valvoline synthetic fluid has the friction modifier in it. no need for additional.
 
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