Spontaneous gear disengagement indicates wear or damage to the synchronizer clutch teeth and gear rings.
Synchronizers of I and II, as well as III and IV gears are identical in design, so they are repaired using the same techniques.
You will need a screwdriver.
1. Before disassembling, mark the position of the coupling relative to the hub.
2. Pry it up with a screwdriver.
3. ...and remove the two springs.
Note: The second spring is not visible in the photo, as it is located on the back side of the synchronizer.
4. Using a screwdriver, pry...
5. ... remove three crackers from the hub grooves.
6. ...and remove the coupling from the hub.
7. Inspect the synchronizer parts. The springs should not have any signs of wear where they contact the crackers.
8. The crackers should not be deformed, and the locking protrusions of the crackers should not be significantly worn.
9. On the ends of the coupling splines.
10. ...and the blocking rings should not have any chipping or creasing.
11. The hub should not have any nicks in the splines or signs of wear.
12. When installing the locking ring on the cone of the corresponding gear, the gap between the ends of the ring and gear rims must be at least 1 mm, otherwise replace the locking ring.
13. Assemble the synchronizer in the reverse order of disassembly, installing the coupling on the hub in accordance with the marks applied before disassembly.
(The article is based on data from the website «ChevyMan»)