differential

[brushwolf]

That is a really good point to remember. Have not encountered it myself, but if I do then welding a fill bung on the housing prior to axle assembly would seem to be the way to go.

[Rancher]

Put the car on a rotisserie...flip it over...fill the diff via the drain plug...flip it back...drive on. 

Just kidding...my mind is a bit warped today...okay...EVERY day...but I had to it out today! 

Thinking about that a bit...
Actually a diff could be filled via the drain plug.
If a clear hose was temporarily "plumbed" to the drain hole even the correct fill level could be determined before quickly swapping in the drain plug.

That's not too different from how today's transmissions without  filler-tube are topped off.

[gasman826]

I just dug out all my 9" spare parts to see if I could assemble a complete carrier.  The empty carrier I found had no fill plug.  It drilled easy on the drill press and tapped it 1/2" tapered pipe.  Problem solved.  The other means of filling would require measuring the fluid.  A pint over full is good but too much and the axle seals will likely fail.   

[mustang6984]

And I was just being a smart-a$$...LOL!!!

[Rancher]

So was Goodyear when he accidentally developed pasteurized rubber. 

But through-the-drain fill would work and with accurate level check.

Of course Gasman's drill and tap is the pro way.

[Ford Blue blood]

I did exactly that (drill and tap) when installing a 3.00 in my Ranch Wagon.  Worked perfect and never leaked.  Never did do a "stress test" as tires and parts cost too much......

[alltin33]

The center (section is the differential ) on a 57  housing is not 9 inch opening for the ring and pinion it is 8 3/4  . Most openings are for 9 inch ring and pinion in later years so  later housings that are notched from factory  mine was not and it is original from factory 57  28 tooth splined axles I used a 1970 mustang center (differential) section with 2.75  connected to c4 I also had to notch the housing half a penny size top and bottom so the ring gear and the gasket so it would clear the housing . As far as the depth of the pumpkin it  is 3/16 in back clearance for the ring gear  and used the same factory axles 28 spline and the differential.  And one thing the that Ford forgot do was no drain plug on later Fords my 57 has one so that being said I always put one in the housing one of many street rods I've   done  so much easier  to do when your doing  your project.  Lot easier than pulling the center section and axles to change the gear oil  It took a great  friend and thinking to get installation  done and figure it out why the ring gear would not clear the  opening housing and LOTS  of measuring .

[Ford Blue blood]

I have not noticed the "notch".  I just put a mid 70s 2.75 in my 58 Pacer.  The paper gasket had no notch and the 70s center section slid home the first try. 

I have discovered that later Lincolns and Bird 9" rears were in fact 9 3/8".  They will fit into the original 9" housing with a notch and bolt up.  Their most common ratio, 2.75.

[alltin33]

If you look up gear ratios in  mustangs in the 70s  2.75 with  a c4   was factory common as for driving great highway cruising ratio. In fact youtube has pictorial showing them notching a housing with no structural integrity . The lip of the housing is 1/4 " thick and your right about the gasket  I had to notch it.  Hope this helps the next person on this site.   

[lalessi1]

I had the ring and pinion changed on my car by a friend who owns a gear shop. He put in a 3.25 ring and pinion in my car with 31 spline axles. If I remember right he had to notch the housing. The 3.89 gear came right out.