How to Identify an S-10 Rear Endby Floyd Drake III
The Chevrolet S-10 pickup truck, one of the first compact models manufactured by a domestic auto maker, was equipped with three different rear-differentials, or rear ends. According to Chevy High Performance, the 7.5-inch was standard until 1993, when the previously optional 7.625-inch became standard. 1995 and newer S-trucks equipped with the high-output V6 were equipped with the 8.5-inch rear end. Although these rear end units are similar in appearance, the 8.5-inch has visual differences, however, the 7.5 and 7.625 differences are internal and driveshaft splines must be counted.
Look under the rear of the vehicle. The rear end is centrally located between the rear wheels. On the back of the unit, count the number of bolts holding the inspection plate cover to the rear end housing. All three units have 10 bolts, as they are all variations of the GM Corporate 10-Bolt.
Match the shape of the differential cover on the back of the rear end housing to the gasket shape chart found on Roadkill Customs Differential Identification page. The 8.5-inch inspection cover gasket shape is rounder than the squarish 7.5 and 7.62-inch. Also, the original inspection plate on the 7.5-inch rear end has a drain plug on the lower passenger side; the 8.5-inch does not.
Remove the differential input shaft to count the number of splines. The input shaft enters the unit from the transmission and must be removed, as the differences between the 7.5-inch and 7.625-inch differentials are internal. According to S10 Planet, the 7.5-inch shaft has 26 splines, or grooves, while the 7.625 has 28 splines.
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