1985 Bobcat 743 Skid Steer Rear Main Seal Problem: Diagnosis and Solutions

[MikePhua]

Introduction
The 1985 Bobcat 743 skid steer is a popular piece of equipment used in construction, landscaping, and other heavy-duty tasks. However, one common issue that owners of this model face is a rear main seal failure, which can lead to oil leakage and potentially serious engine problems if left unresolved. This article outlines the symptoms of a rear main seal issue, potential causes, and solutions to help fix the problem.
Symptoms of Rear Main Seal Failure

1. Oil Leakage
   The most obvious symptom of a rear main seal problem is oil leakage. If the rear main seal is damaged, engine oil will leak out from the back of the engine. You may notice oil puddles under the skid steer or oil stains around the bellhousing area.
   • Location of Leak:
     • The oil will typically pool around the rear of the engine, near the bellhousing.
       
     • In some cases, you may see oil dripping from the skid steer’s transmission area.
       
2. Oil Pressure Drop
   A rear main seal that’s compromised may also cause a drop in oil pressure, which can affect the overall performance of the engine.
   • Symptoms:
     • Inconsistent or low oil pressure readings on the gauge.
       
     • Potential engine performance issues due to lack of proper lubrication.
       
3. Burning Oil Smell
   If the oil is leaking onto hot engine components, such as the exhaust manifold, it may burn off, producing a strong burning oil smell.
   • Warning Sign:
     • If you notice a burning smell, it could be an indication that oil is leaking onto hot engine parts, creating potential safety hazards.
       

Possible Causes of Rear Main Seal Failure

1. Wear and Tear
   Over time, the rear main seal can simply wear out, especially in older models like the 1985 Bobcat 743. This is a natural result of constant engine operation and heat cycles that can degrade the rubber or material used in the seal.
   
2. Improper Installation
   If the rear main seal was not installed properly during manufacturing or a previous repair, it could cause improper sealing and eventual leakage. A poorly seated seal can lead to oil seepage and other related issues.
   
3. Excessive Crankshaft Endplay
   Excessive endplay (lateral movement) in the crankshaft can put pressure on the rear main seal, causing it to wear prematurely or fail. This could be caused by worn bearings or other internal engine issues.
   
4. Contamination
   Dirt, debris, or other contaminants can damage the rear main seal, preventing it from making a proper seal and allowing oil to leak.
   

Step-by-Step Diagnosis and Solution

1. Confirm Oil Leak Location
   Before jumping to conclusions, make sure the rear main seal is the actual source of the oil leak. Clean the engine area thoroughly to remove any old oil and dirt. Once cleaned, run the skid steer and observe the engine for signs of fresh oil leaks, especially around the bellhousing and rear engine area.
   
2. Check Oil Pressure
   If the rear main seal is leaking, it’s important to check the oil pressure to ensure it’s within safe operating limits. A drop in pressure can indicate that the oil is not circulating properly, leading to potential engine damage.
   
3. Remove the Transmission
   To access the rear main seal, you will need to remove the transmission. This involves detaching the skid steer’s driveline and unbolting the transmission from the engine. Ensure that you have a lifting device and a helper to safely handle the heavy components.
   
4. Replace the Rear Main Seal
   Once the transmission is removed, the rear main seal can be accessed. Carefully remove the old seal, being mindful not to damage the surrounding surfaces. Clean the area thoroughly before installing the new rear main seal. Be sure to install the seal correctly, ensuring it is seated properly and without damage.
   • Tip: Use a small amount of engine oil or grease to lubricate the new seal before installation to ensure it fits smoothly onto the crankshaft.
     
5. Check Crankshaft Endplay
   Before installing the new seal, check the crankshaft endplay to ensure there is no excessive lateral movement. If there is, you may need to replace the crankshaft bearings or address other engine issues.
   
6. Reassemble and Test
   After replacing the rear main seal, reassemble the skid steer by reinstalling the transmission and reattaching the driveline. Once everything is back in place, check the oil levels and start the engine to ensure the leak has been fixed. Monitor the engine for any further signs of oil leakage or pressure issues.
   

Preventive Measures

1. Regular Maintenance
   To prevent rear main seal failure and other engine issues, follow the regular maintenance schedule outlined in the operator’s manual. Regular oil changes and inspections can help detect potential problems before they become serious.
   
2. Check for Leaks Regularly
   Keep an eye on the skid steer for any signs of oil leakage, especially around the rear of the engine and bellhousing area. Early detection of oil leaks can help prevent larger issues.
   
3. Address Engine Wear Early
   If you notice any unusual sounds, vibrations, or performance issues with the engine, address them as soon as possible. Excessive crankshaft endplay and bearing wear can lead to rear main seal failure if left unchecked.
   

Conclusion
Rear main seal failure is a common issue in older machines like the 1985 Bobcat 743 skid steer. If left unaddressed, it can lead to serious engine problems and costly repairs. By identifying the symptoms, diagnosing the issue, and following the proper steps to replace the rear main seal, you can restore your skid steer’s functionality and prevent further damage. Regular maintenance and timely repairs are essential to keep your Bobcat 743 running efficiently and extend its service life.