The self-leveling suspension (SLS) system on your 1984 Mercedes-Benz 500SEC (or similar W126 coupe) is a marvel of engineering, providing a smooth and controlled ride. However, the heart of this system, the hydraulic pump, is prone to wear and tear over time. A failing SLS pump can lead to a bouncy ride, rear suspension sag, and ultimately, damage to other components. Rebuilding your SLS pump is a cost-effective alternative to replacement and, with the right tools and information, a project you can tackle at home.
Why Bother Rebuilding? Is It Worth It?
Let's face it, rebuilding anything can seem daunting. But when it comes to your 500SEC's SLS pump, there are compelling reasons to consider it.
- Cost Savings: A new SLS pump can be a significant expense. Rebuilding, on the other hand, involves replacing only the worn parts, significantly reducing the overall cost. You're essentially giving your existing pump a new lease on life.
- Preserving Originality: For many classic car enthusiasts, maintaining the original components is a priority. Rebuilding allows you to keep the original pump, preserving the car's authenticity. This is especially important for a meticulously maintained 500SEC.
- Understanding Your Car: The act of rebuilding gives you a deeper understanding of how your car's systems work. This knowledge can be invaluable for future maintenance and troubleshooting. You'll become intimately familiar with the pump's inner workings.
- It's Doable! While it requires patience and attention to detail, rebuilding an SLS pump is a manageable task for the average DIY mechanic with some basic tools and a good guide.
Getting Ready: Tools and Parts
Before diving in, make sure you have everything you need. This will save you time and frustration later.
Tools:
- Socket set (metric)
- Wrenches (metric)
- Torque wrench
- Pliers
- Screwdrivers (Phillips and flathead)
- Bench vise
- Soft jaws for the vise (to protect the pump housing)
- Clean rags
- Parts cleaner
- Small containers to keep track of parts
- Camera (for documenting the disassembly process - highly recommended!)
- Hydraulic fluid (specifically designed for SLS systems - Pentosin CHF 11S is usually recommended. Double-check your car's specific requirements!)
Parts:
- SLS pump rebuild kit: This kit should include all the necessary seals, o-rings, and sometimes a new piston. Be sure to order a kit specific to your pump type. A good kit will revitalize the pump and prevent future leaks.
- (Optional) Check valve: If the check valve is showing signs of wear or leakage, consider replacing it during the rebuild. This valve is critical for maintaining pressure in the system.
Important Safety Note: Always disconnect the negative battery terminal before working on any electrical or hydraulic components. Hydraulic fluid can be harmful, so wear gloves and eye protection. Work in a well-ventilated area.
Step-by-Step Rebuild: Let's Get Our Hands Dirty
Okay, time to get to work. Remember to take your time and don't rush. A careful and methodical approach will ensure a successful rebuild.
- Removal: Start by carefully removing the SLS pump from the engine. This usually involves disconnecting the hydraulic lines, electrical connector (if applicable), and unbolting the pump from its mounting bracket. Document the hose connections with photos before disconnecting them! This will save you headaches during reassembly.
- Cleaning: Thoroughly clean the exterior of the pump with parts cleaner. This will prevent dirt and debris from entering the internal components during disassembly. A clean workspace is essential.
- Disassembly: This is where the documentation comes in handy. Take photos of each step as you disassemble the pump. Pay close attention to the order and orientation of the parts.
- Secure the pump in the vise using the soft jaws.
- Carefully remove the cover plate, usually held in place by bolts.
- Remove the internal components, such as the piston, springs, and valves.
- Inspect all parts for wear and damage. Pay particular attention to the piston, cylinder walls, and seals.
- Cleaning and Inspection (Again!): Clean all the internal components with parts cleaner. Remove any old seals or o-rings. Inspect the cylinder bore for scoring or damage. Minor imperfections can often be polished out, but significant damage may indicate the need for a replacement pump.
- Reassembly: Now for the fun part - putting everything back together!
- Install the new seals and o-rings from the rebuild kit. Lubricate the seals with fresh hydraulic fluid before installation. This will help them seat properly and prevent damage during assembly.
- Carefully reassemble the internal components in the reverse order of disassembly. Refer to your photos and any diagrams included in the rebuild kit.
- Tighten the cover plate bolts to the manufacturer's specified torque. Use a torque wrench to avoid over-tightening.
- Testing (Bench Test): Before reinstalling the pump in the car, it's a good idea to bench test it. This involves connecting the pump to a power source (if applicable) and manually turning the pump shaft to check for proper operation and leaks. You can use a small amount of hydraulic fluid to prime the pump. This step is optional, but it can save you time and effort in the long run.
- Reinstallation: Carefully reinstall the rebuilt pump in the car. Reconnect the hydraulic lines and electrical connector (if applicable). Tighten all bolts to the manufacturer's specified torque.
- Bleeding the System: After reinstalling the pump, you'll need to bleed the SLS system to remove any air bubbles. This usually involves raising and lowering the rear suspension several times while checking the fluid level in the reservoir. Refer to your car's service manual for the specific bleeding procedure.
- Final Check: Once the system is bled, check for any leaks. Monitor the fluid level in the reservoir and observe the rear suspension for proper operation.
Common Pitfalls to Avoid
Rebuilding an SLS pump isn't rocket science, but there are a few common mistakes that can lead to problems.
- Forgetting to document the disassembly process: This is the most common mistake. Take plenty of photos!
- Using the wrong hydraulic fluid: Using the wrong fluid can damage the seals and other components. Always use the fluid specified by Mercedes-Benz for your car's SLS system.
- Over-tightening bolts: Over-tightening can strip threads or crack the pump housing. Use a torque wrench and follow the manufacturer's specifications.
- Contaminating the internal components: Keep everything clean! Dirt and debris can damage the pump and cause it to fail prematurely.
- Rushing the process: Take your time and be methodical. Rushing can lead to mistakes.
Frequently Asked Questions
- How long does it take to rebuild an SLS pump? The rebuild can take anywhere from 3-6 hours, depending on your experience and the complexity of the pump.
- What if I can't find a rebuild kit for my specific pump? Contact a specialist Mercedes-Benz parts supplier. They may be able to source a kit or individual seals.
- How do I know if my SLS pump is failing? Common symptoms include a bouncy ride, rear suspension sag, and a whining noise from the pump.
- Can I drive my car with a failing SLS pump? It's not recommended. A failing pump can damage other components and compromise the car's handling.
- What if I'm not comfortable rebuilding the pump myself? Take your car to a qualified mechanic specializing in Mercedes-Benz vehicles.
Conclusion
Rebuilding your 1984 500SEC's SLS pump is a worthwhile project that can save you money and keep your car riding smoothly. By following these steps and taking your time, you can successfully restore your pump and enjoy the benefits of a properly functioning self-leveling suspension.