Goldrush is correct, this is a 1981-83 t/case, or Type 1-B t/case (
t/case Bible).
The difference between what we call "Run Quiet" and "Noisy" t/cases is related to how the low range gears are designed. The rest of the t/case is unrelated to this difference. To summarize as simply as possible, pre 1984 t/cases have a simple gear-to-gear mesh, but 1984-95 have thin gear plates that are mounted adjacent to and with a preloaded fit on both the idler gear and low speed gear. These thin plates have exactly one tooth less than the main gear they are installed directly onto. Therefore, as the neighboring gear spins around and meshes with this gear+thin gear plate combo, the thin plates have a higher angular velocity (fewer teeth = higher gear ratio = higher rotational speed) which works against the preloaded fit resulting in a gear mesh that has zero free-play. Zero free-play equals zero gear chatter equals "run quiet" design.
Things to note are that run quiet gears are theoretically weaker because each gear is cut to a thinner width in order to make up room for each thin gear plate. So noisy gears are wider and therefore stronger (assuming they are made from the same material and annealing process).
Because the run quiet design is only used on the low range gear components, it mainly only affects low range operation, however, even in high range the low range components are still rotating so gear chatter can occur in high range as well.
When we invented the 4.70:1 ratio in 1995/96, we decided to not include the run quiet design because we wanted to maximize strength. Moreover, customers who desire such a low ratio probably have larger than stock tires which are also more noisy than stock and will drone out any additional gear chatter noise from our gear sets.
Regards,
BigMike
