1963 DeVille rear differential overhaul

[chbaxter1]

The differential gears and bearing are in good condition, but the unit is leaking oil. What needs to be replaced.

[Poncholover]

The oil!
 

Actually, there are only 3 places: The pinion seal, the gasket & the axle vent. The pinion seal replacement is rather technique sensitive as it affects bearing & gear life so a pro should be consulted.
Also, should the vent be plugged, it can leak front the gaskets & seals as a result.

[Chopper1942]

If it is wet at the front of the diff where the driveshaft attaches, you have a pinion seal leaking. A DIYer can replace it with a little patience and the proper tools. You need an inch pound torque wrench and the tools to remove the pinion flange nut, pinion flange, and pinion seal.

Today many techs want to short cut and rip out the seal and slap in a new one and not do it correctly.

If this is not done properly, you can have a noisy diff or ruin the pinion bearings.

In the past, I have posted the procedure necessary to remove and install a pionion seal. Check past posts for the info.

If you don't have the tools, don't attempt it. I would find a good repair shop, print off the procedure, take it to them, and ask that they follow the procedure. Measuring the pinion turning torque before disassembly and during tightening the pinion nut is critical. Removing the rear wheels and drums/rotors must be done to get the correct pinion turning torque reading. Don't use an impact to remove or install the pinion nut.

[Dave CLC#16900]

Wheel bearings should be replaced if you are taking it apart in my opinion too.  They can leak as well, normally seen coming from the back of the backing plate.

When I first put my '56 Seville back on the road after a 9 year outside nap in Chandler Arizona, I put about 10 miles on it before the RH rear wheel bearing walked out of housing during a low speed turn....  It had dried up.

[dadscad]

I agree with Dave, replacing the wheel bearings is good insurance. Years ago,  I had issues with new National brand bearings with defective seals causing oil leaks. I bought SKF bearings to replace the new installed National brand and the SKF solved the problem.