Fluid change

[bran3b]

I have a TKO and 9" locker, so far I have about 5 miles on the car. When should I replace the gear fluids, and should I go to a synthetic fluid? I am using the "recommended" fluids for both now, but have you guys found something better?

Thanks for any help,
Bran

[Jack21]

There are several threads on just this subject. Opinions, as you might expect, are many and varied. I used standard 5W30 in the engine for break in, then switched to Castrol Syntec 10W30. The T-5 box needs ATF, so I used synthetic ATF right out of the box. The diff got filled with Mobil1 synthetic diff oil + Ford friction modifier. With the locker, you can eliminate the friction modifier.

Have been using the synthetics for about 10 years now on other cars. The stuff just seems to work better, make parts last longer, stay cleaner, not form sludge from high temp coking, crank and roll easier in the winter. Can't say that any one brand of synthetic is better than another. Marketing hype is marketing hype. Read the independent test results for comparison. Can say that synthetics are an improvement over petroleum based lubricants from personal experience.

[justa6]

I've also got a new Tremec. I called their "Tech" line and asked them what was the best fluid to put in their trans. They said GM Synchromesh Trans fluid. So I went to a Chevy dealer and bought enough to fill the trans. We then took the car to Run and Gun the next day. The trans was stiff and wouldn't "Power shift". I hoped that it was "breaking in". It has and now it shifts great and I have not missed a power shift at the drags since we brought it back home in late Sept. I'm very happy with the trans.

Regards,