What is the typical cause of a grinding noise when trying to shift into a higher gear?

A grinding noise when attempting to shift into a higher gear can often be attributed to worn blocking rings. These components are crucial for smooth gear engagement. The blocking rings serve to synchronize the speeds of the gears and the main shaft during a shift. If they are worn out, they may not effectively match these speeds, leading to a grinding sensation or noise as the gears clash instead of meshing cleanly. This issue is particularly prominent in manual transmissions, where synchronizers are essential for smooth operation.

The other options, while they may contribute to shifting issues, would typically present different symptoms. For example, excessive clutch wear can result in slipping or difficulty in disengaging the clutch, which may prevent shifting altogether rather than specifically causing grinding. Improper gear oil viscosity can cause various operational problems but does not directly lead to a grinding noise. Similarly, poor linkage adjustment may lead to difficulty in selecting gears or misalignment, but it would not necessarily cause grinding sounds if the synchronizer mechanisms are functioning correctly.