1958 9 inch rear end fill hole

[JamesDockree]

Hi guys, I need some help.....

I have a 9 inch rear end on my 1958 ford fairlane. I want to top up the gear oil in the rear diff but I can't find the fill hole anywhere. I can see the drain plug but no fill hole.

On the drivers side there is a flat on the side of the housing and this looks like where the fill hole should be.

I realize there must be a fill hole somewhere but I just can't find it.

Any help much appreciated, thanks, James

[Ford Only]

I have never seen a drain plug on a early Ford 9" rear end, are you sure that there is not a plug where you say the flat spot is, sometimes the flush type plug that is used gets filled up with crud and is hard to see or possibly what you are calling the drain plug maybe the fill hole.

[JamesDockree]

See attached photo, the flat has nothing there.

The drain plug is right at the bottom of the diff so I assume this can only be the drain hole?

[Ford Only]

That is strange, did you check the housing I have seen fill holes in the housing on the back side of the rear end but never in the early 9" rear ends.
There has to be a place to fill it somewhere, I guess it is possible that someone installed a later rear end without the filler plug and put oil in through the vent on top of the axle.
Strange things happen with these old cars.

[1959retractable]

I agree with Ford Only. It is likely someone installed a differential gear assembly that has no fill hole and that they installed it in your differential housing with no fill hole. I have seen this before and it's annoying. There are kits where you can drill and tap your own plug but you have to guess where to put it and then deal with shavings in the rear end. I know one guy who removed an axle and poured gear oil in there. Unfortunately, most people end up having to get a differential gear assembly with a drain plug in it and install that in their differential housing. Sorry to be the bearer of bad news. If you Google Ford 9" Fill Plug Kit you will find some weld-in kits.

I have seen fill plugs use a square drive from a ratchet (both 3/8" and 1/2"), allen wrench plugs and hex head plugs requiring a socket. Many differentials were switched out over the years. My '59 has an allen wrench fill plug. Not sure if that's original or not but I prefer the 1/2" ratchet plug.