A new world record! I took over four hours to fill a differential today.
I have been tidying up many loose ends the past few weeks. The kind of loose ends that make for very dull reading, e.g. “crimped six lugs onto the wires for the right rear tail lights”, today I was preparing to “close out” the rear in preparation for putting the car on the ground. The last item on the list was to fill the axle. This is normally a very simple job: pull a fill plug, pump oil in until it starts coming out the plug, the put the plug back in. About ten minutes on a very slow day. But today, I found the fill plug on my axle was galled, and the 3/8″ socket fitting was completely rounded.
No amount of verbal incantations, large hammers or penetrating oil would budge the plug, and the only solutions I could think of beyond that required me to remove the housing which would have cost me days. I found a differential cover that features both a drain plug and a fill plug (T/A Performance Girdle thanks to Aria for the detailed measurements!), but it is too deep to clear the panhard rod.
After an hours or so of staring at it, dreading the though of pulling the axle again, I realized I had the answer in my Oxy-Acetylene rig. I will modify the existing cover with a fill plug, and a drain plug for convenience.
The cover material is too thin to hold a reasonable number of threads, and there is very little clearance between the cover and the moving internal parts. So I need to material to make the housing thicker where I wanted to get a reasonable number of threads, and allow the bolt to seal without intruding into the volume of the differential.
I dug through my parts box and found a 1/2″ 13 bolt and nut the look like a good size for a filler plug. I drilled a half inch hole at the same level as the filler plug in the housing and welded the bolt to the cover. I shortened the plug bolt to be flush with the inside of the cover, and thus, fill problem solved. The drain plug will allow me to change the differential fluid without having to crack the cover, which practically requires pulling the panhard rod to renew the gasket and sealant.