Help...9" Ford Rear end with Currie Trac Lok

[brgarris]

I have a ford 9" rear end with a currie trac loc differential. The guy that build my rear end put 75W90 Mobil 1 synthethc limited slip differential fluid in the rear end. After talking to Currie today they recommend using non-synthetic 85W140 gear oil (3 quarts w/4 oz of LS adder).

What are the cons for running the 75W90 synthetic fluid as I have done for about 150 miles? I have noticed that my rear end housing does get slightly warm to the touch and I have a small amount of fluid try to come out of my vent. I did not know if the synthetic oil would expand more under heat vs. non-synthetic oils or if it has more of a tendency to foam???

I plan to drain the synthetic fluid and replace with the recommended 3 quarts of 85W140 and 4 ounces of limited slip adder. Will this possible cure my venting issue? FYI...if you are looking at the 3rd member my vent is located at the 2 o'clock position. I have threaded a barbed fitting into the housing and ran a hose with filter approximately 8" above the rear end.

Have I damage the differential with the synthetic fluid?

Thanks!!!

[bryant]

you havent damaged it.
in my experience, synthetic takes about 15,000 miles of heavy loads for a gear set to be damaged.
it shouldnt cause the leaking out of the vent, thats usually due to over filling.
should be filled to the bottom of the fill plug hole in the side of the thirdmember, or to the bottom of the axle tubes.

[brgarris]

Thanks for the response....this weekend I drained the synthetic fluid and put 85W140 Lucas gear oil in the rear end with 4 oz. Of the ford friction adder. While under the car I modified my vent line to ensure it had no places where it had a dead loop in it. So far so good...no leaks wihese Two changes.