I'm wanting to install 31 spline axles in my 99' Grand Marquis LS. All the axles I've found online say for 2005 and newer. Are there axles out of something else that will fit my 99' properly? If nothing else could a whole rear end axle assembly out of a 05' fit under a 99'? I'm taking out the factory diff/ gears and replacing it with a limited slip diff with 3.73 gears, plus other upgrades.

 

Hello, 'Steel, and welcome to the Mercury Forums --
That's a pretty ambitious project for a 20-year-old, 4-door, 2-ton sedan -- and such a gear change is of very limited benefit.
You are GUARANTEED to DECREASE Engine and Transmission life, use MUCH more fuel, and endure a LOUDER overall sound, both inside and outside.
But hey, I'm sure you have your reasons for wanting to do those mods -- and if you DO them, please let us know how it all works out.
On The 95 MERC, I left the stock 2.73 gears in there -- and beefed up the rear-end by installing a Cast Aluminum Differential Cover -- which has jack-bolts to allow pre-loading of the axle bearings -- strengthens the entire axle housing, as well as the differential carrier.
LubeLocker Gasket and Royal Purple 75-W-90 Gear Oil -- quiet, cool-running, and NO leaks !


8.8" Cast Aluminum Differential Cover, LubeLocker Gasket, Royal Purple 75W90 Gear Oil