How to Tell the Difference Between an 8.8 and a 7.5 Rear Endby Robert Bayly
The venerable Ford 9-inch rear axle was phased out during the late 1970s and the mid-1980s. The 7.5-inch rear axle came out in 1979 and is found in four- and six-cylinder cars. The 8.8-inch rear axle came out in 1986 and is found in trucks and V-8 cars. The 7.5- and 8.8-inch axles both have rear differential plate covers and look very similar. Normally you can identify the axle by the axle tag attached to one of the differential cover bolts, but if the axle does not have the tag, there's an easy way to identify these axles.
Locate the axle tag. It is attached to the rear differential cover by one of the bolts, usually the top middle one. If you have to raise the rear of the vehicle to see the differential cover, lift the rear with the jack and support it with jack stands.
Note the three sets of numbers across the bottom of the tag. The middle number will be "7.5" or "8.8." This is the size of the rear axle. If there is no tag on the differential, you can visually identify the axle another way.
Place a drain pan under the differential.
Remove the bolts that secure the differential cover. Remove the differential cover. Catch the gear oil in the drain pan. Note the shape of the differential cover gasket. The top and bottom of the 7.5-inch gasket are straight with rounded sides. The 8.8-inch gasket has flat sides, top and bottom, with rounded corners.
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