Most Likely Causes:
* Transmission Issues: This is the most common cause. Problems could include:
* Broken or worn clutch (manual transmission): The clutch might be engaging properly for reverse but not for forward gears.
* Damaged or malfunctioning transmission components (automatic or manual): This could be anything from worn gears or clutches to a failing torque converter (automatic) or a selector mechanism problem. Internal transmission damage often requires professional diagnosis and repair.
* Low transmission fluid (automatic): Low fluid can cause slipping and prevent forward motion. Check the fluid level and condition (color, smell).
* Transmission control module (TCM) problems (automatic): The TCM is the computer that controls the automatic transmission. A faulty TCM can cause various shifting issues.
* Driveshaft Problems:
* Broken or disconnected driveshaft: A driveshaft connects the transmission to the wheels. A broken or disconnected driveshaft will prevent forward motion.
* Driveshaft U-joint issues: Worn U-joints can cause vibrations and prevent power transfer in certain gears.
* Differential Problems:
* Internal differential problems: A problem within the differential can prevent forward motion while reverse may still work. This is less common.
* Wheel-related Issues (Less Likely):
* Wheel bearing failure: While less likely to only affect forward motion, a severely damaged bearing could affect one wheel enough to prevent forward movement.
Troubleshooting Steps:
1. Check Transmission Fluid (Automatic): This is the easiest first step. Check the level and condition of the transmission fluid. Low or burnt fluid indicates a problem.
2. Listen for Unusual Noises: When attempting to drive forward, listen carefully for any grinding, whining, or banging noises. These noises can give clues to the location of the problem.
3. Check for Obvious Mechanical Damage: Visually inspect the driveshaft, U-joints, and surrounding components for any signs of damage, leaks, or disconnections.
4. Check the Shift Linkage (Manual): If it's a manual, make sure the shift linkage is properly adjusted and not binding.
What NOT to Do:
* Keep trying to drive: Forcing the car could cause further damage.
* Attempt major repairs yourself unless you have significant mechanical experience: Transmission and drivetrain repairs are complex and require specialized tools and knowledge.
Next Steps:
If you've checked these things and the problem persists, it's crucial to have the car inspected by a qualified mechanic. They have the diagnostic tools and expertise to pinpoint the exact cause and recommend the appropriate repairs. Describing the symptoms (reverses but won't drive forward) will help them focus their diagnosis.
