On a 14 bolt FF or a rockwell, you can get by with welding the spyder gears to the axle gears only, but on the little stuff, you need to weld the side gears to the carrier. If doing it in the car, you will hardly get a good weld because you can not get the parts clean and oil free. For best results, remove the carrier, remove the ring gear, carrier bearings, clean thuroughly with solvent, then flush with carb cleaner or de-natured alcohol. Do not use Brake parts cleaners, as they normally contain chemicals that leave a residue which is corrosive when heated. After air drying, preheat carrier throughout to about 400 degrees, weld the axle gears to the carrier with "Super Missle Weld" rod made by Welco with the least amperage possible to minimize inevitable warpage. If you want, 7018 will work. Weld in short beads ballanced across from each other. Maintain preheat temp. When fully welded, post heat at 400 degrees till temp stabilizes throughout, then allow to cool slowly (overnite), as in a box or can full of floor dry or cat litter. After cool, have face of carrier where ring gear bolts up trued up on a lathe, clean slag and spatter out, then reassemble rear axle. Backlash will need to be adjusted.
Standard MIG wire is for mild steel, not properly compatable with the steel used for the gears or the carrier, although many a rear has been welded with MIG. If you must weld in the car, be sure to ground directly to the carrier itself, so the current doesn't pass through the bearings.
For more discussion of this topis you can see Welding Teck at
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