One of the least-understood and most-commonly misdiagnosed complaints/problems with manually shifted transmissions and transfer cases is synchronization.
In a transmission we have a sequence of events that must take place in a precisely timed manner to get a smooth, effortless, clash-free shift. Let’s follow these events to understand the theory of operation and with that knowledge find the solutions that will fix and prevent further shift problems.
Manual-shift transmissions have been manufactured with synchronized gear train for decades. The early designs were three-speed transmissions with 2nd and 3rd gears synchronized, and as transmission design progressed, four-, five- and six-speed transmissions were developed. At this point all forward speeds were commonly synchronized, and as the purchase costs of the vehicles increased and customers became more demanding, reverse was synchronized in most late-model vehicles. Synchronizers remain the most-misunderstood components in manual transmissions and transfer cases and therefore cause a great number of diagnostic headaches and comebacks.