I've got a 66 Mercury M-100 with a 300 I6 in it.

I am going to be upgrading the rear diff. for the 521 that is going into it. Looking to grab a Ford 9" out of a 73-79 F150 4x4 and use it as the base for 33 spline strange axles and a spool.

Is the 9" that is in my truck right now the same width as the diff. that I am looking for? If not, what are the width differences? Does anyone have accurate measurements?

Thanks,

Derek

 

The width of the rear frame rails increased in 1973 from 33 1/2" to 37 1/2."

The 1973 and later housing is wider, as are the rear springs.

Some 1973/79 9's have 28 spline axle shafts, some have 31 spline axleshafts.

1957/67 9's have 28 spline axleshafts as do some 1968/72 axleshafts.

Some 1968/72 9's have a Heavy Duty 9" rear axle, with a 9 3/8" ring gear...and 31 spline axleshafts.

There is no parts catalog listing for 33 spline axleshafts...for any year F100 or F150 9 inch.

 

What is the specific reason for wanting the '79 housing? I would assume to upgrade from small axle bearing to large axle bearing? I have one under my Jeep from a 78/79 I can get the flange to flange widths for you.

 

Thanks for the information. Obviously there were no 33 spline units from the factory, hence the noted upgrade to 33 spline Strange axles.

Where could I find a big bearing Ford 9" that is the same width as the factory unit under my truck?

 

Mainly bearing size. 73-79 actually, but that is out the window now.

Thanks for your input.

 

The bearings in the 66 rear are the same big bearing diameter as the 79.

They are big bearing old pattern on the 66 and big bearing new pattern on the 79. Small bearing is used in fairlanes and some other intermediate an smaller cars. Never used on nine inch housings in trucks.

Here is a big bearing new style housing end


The old style are flat on top and rounded on the bottom.

Garbz

 

D8AZ1225B (replaced C1SZ1225A & C1SZ1225B) .. Large 9" Axle Bearing.

Fits: All 1961/73 F100 (except 1968/72's with 9 3/8" ring gear) / Some 1974/83 F100 / Some 1975/86 F150.

Fits: 1961/76 Thunderbird (except 1966/72 with 9 3/8" ring gear) / 1974/79 Lincoln / 1974/76 Continental Mark IV / 1961/78 Ford/Merc full sized Station Wagons & Police Cruisers / Misc other FoMoCo Passenger Cars.

Note: Some 1974/86 F100/150's & 1974/79 Passenger Cars have a 9" with an axle bearing/seal combo: D4AZ1225A .. Axle Bearing & Seal Assy / D4AZ1177A .. Axle Seal (only).

1974/86 F100/150 & 1974/79 Passenger Cars: There's no way to tell what bearing/seal these vehicles have. You either need the rear axle ID tag code (when decoded, the info is known), or...

You have to pull the axleshaft to find out what type of bearing is present...a first class PITA!