Spicer as the manufacturer of the differential assembly provide a product based on specifications provided by a mechanical engineer from Rover. The engineers from Spicer will follow the specifications provided and not deviate from that. They provide a product for an agreed price as detailed within their contract. After receipt Rover are not entirely happy with the product, but Spicer have provided exactly what was asked for. So what does Rover do? To ask for an improved pinion extension case with additional ribs for stiffening is an expensive option, and as Peter no doubt correctly states, "no new money for an improved casting". So engineers being good at solving problems consider the degree of flexure that testing has revealed to be evident within the casting. One cheap and very effective way of reducing flexure whilst also reducing the resulting vibration is to provide a form of lamination. A piece of steel clamped to the pinion extension case will do the trick nicely. Its shape and thickness along with its material properties are all important. More material than necessary is waste of money, so remove what is not required meaning more pieces per sheet of unit area. I expect the location of the clamps is important else the assembly workers might well place them anywhere. Engineers will normally write an assembly specification which will stipulate the spacing and location relative to datum points for the clamps. The torque will also have been specified. In this way it is a controlled process that will deliver a required outcome.
