9 Inch Ford Rear Axle Information

Many people swap Ford 9 inch rear ends into their muscle cars, Hot Rods and drag cars because they're readily available, strong from the factory and can be strengthened easily. The center section of the 9 inch rear end is removable allowing you to swap gears or differentials on a bench. Nine inch Ford rear ends came in many widths and configurations. Depending on the application, the rear end may be heavier duty, be made of high performance materials or have a locking differential. Axles came in 28 or 31 spline versions from the factory. Typically the more splines the better up to a point. You'll commonly see 9" race axles with 33 or 35 splines. The differential spline count has to match the axle spline count. Gear ratios varied based on the engine, transmission and vehicle type. Center sections, or 3rd members, are completely removable and were generally made of cast iron. High performance 3rd members were made of nodular iron and hold together better than standard cases. These types are hard to find and command more money. You can usually nearly buy a new high performance case for what you have in a good original nodular iron case.

9 Inch Ford rear differential

Most 9" rear differentials will be the open type. To recognize a Locking 9" differential, look for a metal tag on one of the bolts that holds the center section to the housing. There is a gear ratio stamped on the tag. For example: The tag will say: 350 for 3.50:1 ring and pinion gear ratio. If there is an "L" in between, you should have a locking or limited slip differential. A gear ratio with a locking or limited slip differential would look like this on the metal tag: 3L50. Sometimes the period is on the tag as in 3.50, depending on the year and model.

There's nothing to guarantee that it is the stock differential if you're buying used. It's best to verify for sure.

How to recognize 9" Ford housing centers

• 57 - no dimples, flat center band up the center of the rear cover, bottom drain plug
• 58-59 - two dimples on back of housing, flat center band, some had drain holes
• 60-67 - two dimples, flat center band, oil level hole in back cover
• 63-77 Lincoln, LTD, Thunderbirds had 9.375 inch centers, housings were cut away at the gasket surface for ring gear clearance, one curved rib at the front top portion of differential. Strong, but no gear options.

9" Ford Axle Facts

• 28 spline axles cannot be shortened because they're tapered (except 69-73 Mustang and Cougars).
• 72 and earlier 31 spline axles have the ability to be shortened
• 73 and later 9" (big cars) have a 5-on-5 bolt circle and the axles cannot be shortened

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