Dealing with a malfunctioning convertible top on your 2007 Mercedes SL550 can be frustrating. A common issue, especially in older models, is a leaking hydraulic cylinder. One owner recently encountered this problem and reached out for guidance on diagnosing and repairing a leak in their SL550’s convertible top system. They had already identified a leaking front top cylinder and were in the process of replacing it, but were facing challenges tracing hydraulic lines, identifying the correct lines at the pump, bleeding the system, and dealing with a partially opened trunk. This guide addresses these common issues and provides expert advice for DIY repair.
Tracing Hydraulic Lines in Your SL550 Convertible Top System
Tracing hydraulic lines in a Mercedes SL550 convertible top system can be tricky, as they are often tightly routed and concealed. The owner in question had removed the headliner and was struggling to follow the lines back towards the pump in the trunk. Here are a few tips to help:
- Patience is Key: Hydraulic lines are often bundled and secured, so take your time and avoid forcing anything.
- Gentle Manipulation: Try gently wiggling or rotating lines from both ends (headliner and trunk) to see if you can identify movement at the other end. This can help you trace their path.
- Visual Aids (If Possible): While a complete diagram might be hard to find for specific line routing, try searching online forums or Mercedes repair manuals for general diagrams of the SL convertible top hydraulic system. These can give you a general idea of line pathways.
- Avoid Cutting Lines Prematurely: Cutting lines should be a last resort. If possible, try to identify the correct lines before cutting. However, in some cases, carefully cutting the old lines to ease removal and guide the new lines can be a practical approach, as long as you are meticulous and take precautions against pinching the new lines during installation and operation. Ensure you meticulously note which line goes where before cutting.
Identifying Top Latch Cylinder Lines at the Pump Manifold
Identifying the specific hydraulic lines at the pump manifold that correspond to the top latch cylinder is crucial, especially if you’re considering replacing lines or need to disconnect them. Without a specific diagram, here’s how you can approach it:
- Visual Inspection at the Cylinder: Before disconnecting anything, carefully examine the hydraulic lines connected to the old top cylinder. Note their colors or any markings if present.
- Trace Back Visually (If Possible): Attempt to visually follow the lines from the cylinder back towards the trunk area as far as possible. This might give you a general area to focus on at the pump manifold.
- Process of Elimination (Cautiously): If visual tracing is impossible, and you must disconnect lines at the pump to replace the cylinder, proceed with caution. Typically, hydraulic systems use pairs of lines for each cylinder (one for extension, one for retraction). If you have to disconnect lines at the pump without knowing exactly which are for the top latch cylinder, label each line clearly as you disconnect it. You can then try to identify them by process of elimination, but this is risky and not recommended unless absolutely necessary. It’s always better to try and trace or find a diagram first.
Bleeding Air from the SL550 Convertible Top Hydraulic System
Air in the hydraulic lines can cause erratic operation or complete failure of the convertible top system. Bleeding the system after replacing a cylinder is essential. Here’s a general approach, keeping in mind that specific Mercedes procedures should always be prioritized if available:
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Locate the Hydraulic Pump Reservoir: You’ve already found the reservoir and filled it, which is a good first step.
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Identify Bleed Point (If Any): Some systems have bleed screws, but as you noted, your pump might not have a dedicated bleed port. The allen key port on top could potentially serve as a fill/bleed point.
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Gentle Operation: With the reservoir filled to the correct level, and the new cylinder installed, try gently operating the convertible top mechanism in small increments. This can help circulate fluid and push air bubbles back to the reservoir.
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Check Fluid Level Regularly: As you cycle the system, air will be purged, and the fluid level in the reservoir might drop. Keep checking and topping off the fluid as needed.
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Listen for Noises: Gurgling or sputtering noises from the pump or cylinders can indicate air in the system. Continue cycling the system until these noises subside.
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Manual Bleeding (If Necessary and No Bleed Screw): If there’s no bleed screw, and gentle cycling doesn’t purge the air, you might need to slightly loosen a hydraulic line fitting at the highest point in the system (often at the cylinder itself) while operating the pump briefly. Exercise extreme caution when doing this, as hydraulic fluid is under high pressure. Loosen the fitting just enough to allow air to escape, then retighten immediately. This should only be done with extreme care and if you are comfortable working with hydraulic systems. It’s generally safer to repeat the gentle cycling and reservoir top-off method multiple times.
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Professional Bleeding: If you are uncomfortable with any of these bleeding procedures, or if the system continues to malfunction after bleeding attempts, it’s best to consult a Mercedes-Benz specialist or a qualified mechanic experienced in convertible top hydraulic systems. Improper bleeding can damage the system.
Resolving a Partially Opened Trunk Lid
A trunk lid that is stuck partially open, as you described, is a common consequence of hydraulic system issues in convertibles. Here’s how to address it:
- Locate Trunk Hydraulic Cylinder/Struts: Identify the hydraulic cylinder(s) or struts that control the trunk lid’s opening and closing. These are usually located in the trunk hinges or near the trunk lid supports.
- Manual Release Valve (If Present): Some hydraulic systems have a manual release valve, often located on the pump or near the hydraulic cylinders. Check your owner’s manual or search online for the location of a manual release valve for your SL550’s convertible top system. Releasing this valve might relieve hydraulic pressure and allow you to manually close the trunk.
- Careful Manual Override: If there’s no manual release, and as a last resort, you can try to carefully and gently push down on the trunk lid while someone else operates the convertible top switch in the “close” direction (or attempts to manually trigger the trunk closing mechanism if you can identify it). Be extremely cautious not to force anything or damage the mechanism. You are trying to assist the hydraulic system, not overpower it.
- Check Hydraulic Lines to Trunk Cylinder: Examine the hydraulic lines going to the trunk cylinder for any kinks, leaks, or damage. A problem with these lines could be preventing the trunk from closing.
Important Safety Advice: Working with hydraulic systems involves potential risks due to high pressure fluid. Always exercise caution, wear eye protection, and if you are not comfortable with any step of the process, seek professional assistance. Incorrect repairs can lead to further damage and costly repairs.
By following these steps and proceeding methodically, you should be able to diagnose and address common issues with your 2007 Mercedes Sl550 Convertible top hydraulic system and get your top operating smoothly again. Remember to always prioritize safety and seek professional help when needed.
