I'm asuming that I would need to replace the factory gear oil when I put new gears in. Should I replace it with Redline oil...royal purple...mobile 1...suggestions??? and what is this Ford friction reducer I see on Stangsuspension.com that they recommend when changing out the gears...something I shold get as well?

 

Yeah, you need to change the diff. fluid when you do a gear swap. I used Mobil 1...and Posi-trak as an additive. I'm assuming it is the same as the friction reducer...it quiets the gears. If you don't put any in there will be clicking and clunking in your rear end.

 

definitely change the rear end lube when you change the gears. and you need to add the 4 oz. bottle of Ford friction modifier for the posi unit to keep the clutches and all quiet too. I would skip the synthetics and go with a good regular petroleum based differential oil instead. That's the recommendation I got from Strange engineering when I bought my new rear as that's what US gear told them is best for the gears.

 

Ford says though if you don't use synthetic then your a bad boy

 

that may be true for a stock 8.8 but when you pay over $3,500 for a complete pro built 9" with spool, etc. like I did from Strange and you specifically ask the tech rep what lube to use and he says the company that makes their gears has done extensive R&D on this and they recommend regular petroleum based gear oils, you can bet you *** I'm going to follow their recommendation! LOL