1. Mechanical Issues:
* Viscous Coupling Failure: The most common culprit in older Subarus. The viscous coupling is a fluid-filled unit that transfers power to the rear wheels when needed. If it fails, it can either constantly send power to the rear (resulting in poor fuel economy and potential drivetrain strain) or fail to send power at all (resulting in front-wheel-drive only). This often manifests as a lack of rear wheel drive in slippery conditions. A failed viscous coupling will often have fluid leaks.
* Rear Differential Problems: A damaged or broken rear differential will prevent power from reaching the rear wheels. This could be due to worn gears, a broken axle, or a lack of differential fluid.
* Drive Shaft Problems: A broken or severely damaged driveshaft (either the center or the rear) will prevent power from being transmitted to the rear wheels. Look for obvious damage like bent shafts or broken u-joints.
* Transfer Case Issues: Less common but possible. Problems within the transfer case itself can interrupt power to the rear.
* Wheel Bearings (Rear): While not directly related to the AWD system, severely damaged rear wheel bearings can prevent the wheels from turning, making it seem like AWD is not working.
2. Electrical Issues (Less Likely, but Possible on some models with electronic controls):
* Wiring Problems: While 1995 models were mostly mechanically controlled, there might be some electrical components involved in the AWD system. Damaged wiring or connectors could prevent proper operation. This is less likely than mechanical issues.
* Sensors: Modern AWD systems use sensors to detect wheel slip, and a malfunctioning sensor could cause the system to not engage properly. This is less likely in a 1995 Legacy but possible.
3. Fluid Related:
* Low Differential Fluid (Rear): Lack of fluid in the rear differential will severely damage the components, rendering the AWD system inoperable.
* Low Viscous Coupling Fluid (If applicable): As above, this is crucial for the viscous coupling's function.
Troubleshooting Steps:
1. Check all fluids: Inspect the levels of differential fluid (front and rear) and viscous coupling fluid (if equipped).
2. Listen for unusual noises: Grinding, whining, or clicking sounds from the rear differential or transfer case point to mechanical problems.
3. Check for leaks: Look for any fluid leaks around the rear differential, viscous coupling, or driveshafts.
4. Test on a slippery surface: Try driving on a low-traction surface (snow, ice, or loose gravel). If the rear wheels don't spin or help with traction, it's a strong indicator of an AWD issue.
5. Visual Inspection: Examine driveshafts and related components for visible damage.
Important Note: Diagnosing AWD problems can be complex. If you're not comfortable working on your car yourself, take it to a qualified mechanic specializing in Subaru vehicles, as misdiagnosis could lead to further damage.
