I have had a slow leak from my rear axle seal and I think I am going to replace it today.
I have a 1996 F150, 4X4, A/T
Is this a big job?
Does anyone have any suggestions or tips?
Also, when I replace the oil, what is the best oil and do I have to also use an additive to the oil? (Something to do with slip something??????)
Sorry for sounding completely clueless.

 

If you have an LS diff the recommendation is to add a bottle of friction modifier when refilling, this is available from Ford. Knowing how these diffs are built and how little added traction they provide over an open diff I'd try it out without the modifier first just to see if it behaves abnormally. If you notice any ueven grabbyness from the rear end when rounding tight corners the modifier will smooth this out, but in any event there is no danger of damaging the diff if you don't add the modifier.

The side axle has to be removed to change the axle seal, and to do that you have to remove the pinion shaft and axle C-clip from the diff. The pinion shaft is secured with a single lock bolt and it is also recommended that this be replaced when the axle is serviced.


P.S. Since you are going into the diff now would be the time to restack the clutch packs and improve the performance of the factory LS diff. As delivered the clutch packs are stacked with two metal plates between each pair of friction plates, and as you can imagine placing two metal plates together in an oil bath isn't a recipe for exceptional grip. Simply changing the stack sequence to alternating metal and friction disks vastly improves the differentials performance. To do this you will need extra friction disks which you could salvage from another diff or you could buy a clutch pack rebuild kit. To change the clutch packs you simply spin the spider gears out of the diff after you have removed the pinion shaft and S spring, the clutch disks are then easily removed. The pic below is for a factory LS diff in which you can clearly see the disk stack sequence I was referring to. With the modified stack sequence you will end up with 4 friction and 3 metal disks per side.

 

So are you saying I also should replace the pinion shaft too?