* Worn Fifth Gear Synchronizer: This is the most common cause. The synchronizer's job is to match the speed of the gears before they mesh. Wear and tear (especially with aggressive driving or neglect) leads to it failing to properly synchronize, causing the gear to slip or jump out.
* Worn Fifth Gear Dog Ring or Gear Teeth: These are the components that actually engage to create the gear ratio. If the teeth are worn, chipped, or damaged, they won't mesh properly, resulting in the gear popping out.
* Worn Shift Fork: This component moves the shift collar to engage the gear. If it's bent, worn, or broken, it won't properly engage fifth gear.
* Bent or Worn Shift Rail: The shift rail guides the shift fork. Damage here can prevent the gear from engaging completely.
* Loose or Worn Shift Linkage: This is the system that connects the shifter in the cabin to the transmission. Slack or wear can cause imprecise shifting, leading to gears not engaging fully. This is less likely to specifically affect *only* fifth gear, but it's worth checking.
* Low Transmission Fluid: While less likely to cause the gear to *jump* out, low fluid can lead to poor lubrication and ultimately contribute to wear and exacerbate existing problems. Check your fluid level and condition (look for discoloration or metallic particles).
* Improper Adjustment: Although less common, the transmission's internal adjustment might be slightly off, causing imperfect engagement.
What to do:
1. Check the transmission fluid: This is the easiest and cheapest first step. Low or dirty fluid can point to bigger issues.
2. Get a professional diagnosis: Pinpointing the exact cause requires a mechanic to inspect the transmission. They will likely need to open it up to check the condition of the gears and synchronizers. A simple visual inspection might not suffice.
Ignoring the problem will almost certainly lead to more extensive, and more expensive, damage. The longer you wait, the more likely the damage will extend beyond just the fifth gear components. You risk complete transmission failure.
