Rear Diff and Axle Shaft Upgrades
 

I have a turbo’d 99 Miata with 275 whp, 5 speed, and 4.3 rear diff gearing. The 5 speed, rear diff, and axle shafts have 265k miles on them. I picked a 6-speed from a junkyard last week and now I’m trying to decide on what to do with the rear diff. I’m still undecided on what gears I want, 3.3 or 3.63 gears.



I image that I’ll need to replace my axle shafts sooner or later. I’m wondering if I should upgrade to a MSM diff and axles since I'm already here? How often do you all break stock axles at this power level?



Also, does a 265k mile torsion still have a lot of life left or should I get one with less miles?

Thanks!

When you swap FGR change the bearings/seals and set backlash in your diff and you'll be fine.

Most folks that break axles in these cars are at torque levels that would have already killed the 6 speed. That being said - Driveshaft shop does offer axle upgrades.