* Rear Main Seal of the Transmission: While unlikely to leak directly *at* the driveshaft, a failing rear main seal on the transmission can cause leakage that migrates along the transmission housing and drips down near the driveshaft. This is the most probable culprit if the leak is near the transmission's connection to the driveshaft.
* Output Shaft Seal (Transmission to Driveshaft): This seal is located where the transmission output shaft enters the transfer case (or directly into the driveshaft if it's a single-stick setup). A damaged seal here will leak transmission fluid.
* Transfer Case Seal (if applicable): If your Jeep has a transfer case (almost certainly), there are seals where the output shaft of the transmission enters the transfer case and where the output shaft of the transfer case connects to the driveshaft. Leaks here will appear near the driveshaft.
* Driveshaft U-Joint Seals: While less common, worn U-joint seals can leak grease, but not transmission fluid. If it's thick, dark grease, it's likely this and not your transmission.
To Diagnose and Fix:
1. Clean the Area Thoroughly: Use a degreaser and pressure washer (carefully!) to remove all dirt and grime from the area around the suspected leak. This will allow you to pinpoint the source accurately after a test drive.
2. Inspect Visually: Carefully examine the area where the transmission connects to the transfer case (if present) and the driveshaft. Look for any signs of fluid leakage around the seals mentioned above.
3. Test Drive (short): After cleaning, drive the Jeep for a short distance to allow any new leaks to appear.
4. Identify the Source: Once the clean area is marked with new fluid, you can accurately pinpoint the source.
5. Repair: The repair will depend on the source of the leak. This will almost certainly require some mechanical skills and possibly specialized tools. Options include:
* Replacing the Seal: This is often the solution. You'll need to remove the driveshaft, likely the transfer case (if applicable), and replace the failing seal(s). This is a moderately challenging job requiring mechanical knowledge and tools.
* Replacing the Rear Main Seal (Transmission): More complex and usually requires transmission removal, depending on the Wrangler model.
Important Considerations:
* Transmission Fluid Type: Use the correct type and amount of transmission fluid specified in your Jeep's owner's manual. Using the wrong fluid can damage the transmission.
* Professional Help: If you're not comfortable working on your Jeep yourself, take it to a qualified mechanic specializing in Jeeps or manual transmissions. Improper repair can lead to further damage.
* Safety: Remember to support the vehicle properly when working underneath it.
Before attempting any repairs yourself, consult a repair manual specific to your 1991 Jeep Wrangler model. These manuals provide detailed instructions and diagrams. A poorly executed repair can lead to far more expensive problems.
