On both the main drive (3rd) gear and the second speed gear there is a synchronizing energizer spring.
The two ears on the inside of the synchronizing cone pass over these springs forcing the cone into the brass synchronizer when shifting into gear.
I have for years put a .010" shim under the energizing spring to make it harder for the cone to pass over the spring.
The spring also gets worn with use so I move it one tooth over (more later).
The shims I use I cut from a paint thinner can. The shims are 1/8" wide x 4 1/2" long x .010" thick.
The spring has a slight offset on one end. To remove the spring from its groove I carefully lift the offset end out of the groove and rest it on the teeth next to the groove. I then work around the gear lifting the spring and sliding it on to the gear. Care must be used as to not distort the spring.
Next I lay the shim in the groove with the ends opposite the ends of the spring.
Next I carefully slide the spring back into place over the shim.
The Shop Manual states "It will be noticed that upon examining these springs that one of the ends is slightly offset. Each spring must be assembled in its groove in the clutch gear and the second sped gear with the offset or locking end between the third and fourth teeth of either of the two banks of teeth on these gears".
Factory spring position
As I mentioned these springs wear over time so I move the offset end one tooth so it ends between the forth and fifth teeth.
1/8" x 4 1/2" x .010" shim
Spring out of groove. Also note offset end