Okay my front driver is leaking a little oil from driveshaft seal,where do you add oill at,this is on a 2001 IH 9400.This axle was rebuilt not to long ago,before I purchased it,its seeping. What kinda oil goes in the axle?Also what something like this cost to have seal replaced?

 

Replacing seals isn't that expensive. If it's already leaking, it's time to get it in. Waiting is only risking more problems. Just the cleanup from a blown seal will hurt your pocketbook, as the oil usually coats the brakes pretty good.

As far as where to add oil, I believe those hubs are a sealed system (although I could be wrong), in which case you can't add oil like you can to a trailer hub.

 

Check the vent on top of the axle housing. A clogged vent can allow pressure to build up inside the housing and cause an otherwise good seal to leak.

To add oil, use the plug on the rear side of the axle housing (it's located about halfway between the bottom and top). Some have a square headed pipe plug, and some have a plug with a recessed square drive which you can use a 1/2 inch drive breaker bar to loosen.

Remove the plug and fill the housing so the lube is up to the filler hole.

Most rears today use 75W90 synthetic gear lube.

After you've filled it, replace the plug and tighten it.

(and BTW, get the seal fixed ASAP).

A blown seal on the driveshaft yoke will spray gear lube all over the underside of the truck, which is messy, and an invitation for a closer look in the event of a DOT inspection.

 

Apparently I am confused. I thought he was talking about an axle hub. My bad.