hi, ok I have a question about gears, I want to get 3.73's and i'm wondering if it matters what i get. Like if i buy used ones outta an old truck or old mustang that are factory ones or if i buy racing ones or what. And do i need 31 spline axels or will the stock setup support 3.73's
As long as they're for an 8.8 rear end they'll work fine. They can be used with either 28-spline or 31-spline axles, but the 28-spline axles will be fine for most applications. Some will tell you not to use used gears, but I've done it several times in the past, with no issues.
The used gears should be fine as long as they're out of a factory ford setup. I'm not sure I'd go for used aftermarket gears. All of the factory and FMS gears can be installed with your factory shims. I've seen 3 different guys running FMS gears pull out the trak-loc and put in a spool and all they did was change the ring gear. No indicators, no paste. Maybe they were just lucky. I'm sure there's got to be others out there that do it, too. I haven't used an indicator on any of the last 5 gear changes using FMS gears. Only paste to get an eye on the mesh. Reused the factory shims with the new gears and everything was fine. So far, so good. I don't know for sure how many miles these guys have accumulated, but I'd guess they're over 40k between the bunch of them.