* Worn synchronizers: Synchronizers are components within the transmission that match the speeds of the gears before engagement. Wear, particularly on the cones and rings, prevents smooth engagement and can cause gears to pop out, especially under high-RPM stress where the speed difference between the input shaft and the gear is greater. This is a very common cause in high-mileage vehicles.
* Worn shift forks: These are the components that physically move the gears into place. Wear or bending can lead to imprecise gear selection and popping out of gear.
* Worn or damaged gear teeth: If the gear teeth are worn, damaged, or broken, they won't mesh properly, leading to slipping and popping out of gear, especially under high loads and RPMs. This is often accompanied by grinding noises.
* Low transmission fluid or incorrect fluid: Insufficient transmission fluid leads to insufficient lubrication, causing increased wear and potentially causing the gears to slip and pop out. Using the wrong type of fluid can also lead to similar issues.
* Loose or worn shift linkage: The linkage connecting the shifter to the transmission can become loose, worn, or bent over time. This can result in imprecise shifting and gears that don't fully engage. This often manifests as difficulty getting into gear, as well as popping out.
* Bent or damaged shift rail: Internal to the transmission, the shift rail guides the shift forks. Damage or bending can prevent proper gear selection.
* Worn clutch: While less directly related to the gear popping out, a worn clutch can cause slippage at high RPM, which can indirectly contribute to the feeling of gears popping out. You might notice other clutch-related symptoms as well.
The rattling sound is likely a symptom of the above problems. It's often caused by worn components within the transmission thrashing around due to insufficient engagement or damage.
Troubleshooting:
It's difficult to diagnose the exact cause without physically inspecting the transmission. However, start by checking:
1. Transmission fluid level and condition: Check the fluid level and look at its color and smell. Dark, burnt, or smelling fluid indicates a problem requiring attention.
2. Shift linkage: Inspect the linkage for looseness, wear, or bends.
If you're not mechanically inclined, taking the vehicle to a qualified mechanic is strongly recommended. Transmission repair can be complex and expensive. Ignoring the problem will likely lead to further damage and a more costly repair.
