96-04 Mercedes SLK 230 320 R170 Convertible Top Hydraulic Cylinder O-ring Seals

The Mercedes R170 SLK-Class (SLK230, SLK320, etc., 1996–2004) uses a hydraulic system with five cylinders to operate the retractable hardtop:

• Front lock cylinder (center, near windshield header): Often part A1708000072 or similar (170800072 / 170800072)
• Left main lift cylinder (driver side, trunk area): Commonly A1708000572 (170800572)
• Right main lift cylinder (passenger side, trunk area): Commonly A1708000672 (170800672)
• Left trunk/tonneau lid cylinder: Often A1708000272 or similar (170800272)
• Right trunk/tonneau lid cylinder: Often A1708000372 or similar (170800372)

hese are the OEM cylinder part numbers. Leaks usually come from the rod seal (U-cup or similar) at the gland end, plus O-rings at ports/fittings and sometimes piston seals.

Replacing the O-rings (and full seals) is a common DIY rebuild to fix external leaks without buying new cylinders (which cost $200–$500+ each rebuilt). Many owners use our O-ring kits that replace the rod seal with an O-ring + backup, plus port O-rings.

Warnings Before Starting

• Use Mercedes/Pentosin CHF 11S hydraulic fluid (or exact equivalent)—do NOT use ATF or brake fluid.
• Support the hardtop and tonneau mechanically (props, straps) to prevent crushing injury or damage.
• Work clean: Dirt kills seals fast.
• If piston rods are scored/pitted or bores corroded, seals won't last—consider professional rebuild (e.g., Top Hydraulics) or replacement.
• Bleeding air after is critical; incomplete bleed causes erratic operation.

Tools Needed

• Basic hand tools (sockets, screwdrivers, pliers, 8–10mm wrenches)
• Pick set or small hook tool (for old seals)
• Clean rags, drain pan
• Hydraulic fluid, turkey baster/syringe for filling
• Optional: Cylinder vise/holder, snap-ring pliers if applicable

General Steps for O-Ring/Seal Replacement on R170 Cylinders

The process is similar across cylinders, but main lifts and trunk ones are trickier to remove. Our kit use O-rings to replace the U-cup rod seal that commonly fail.

1. Preparation
• Park level, battery disconnected.
• Manually position/open the top as far as possible for access (use emergency release cables if needed; trunk lid may need propping).
• Drain reservoir if low (under trunk panel).
2. Remove the Cylinder
• Remove trunk panels, carpet, or side trim to access (main lifts are in rear trunk wells; front lock under header; tonneau near hinges).
• Disconnect hydraulic lines (catch fluid; label hoses—most use banjo bolts or quick-connects with O-rings).
• Remove mounting pins/clips (clevis pins with circlips or roll pins—tap out carefully).
• Extract cylinder (main lifts may require tilting top or removing links; tonneau ones near exhaust/muffler).
3. Disassemble and Replace Seals/O-Rings
• Clean exterior.
• Extend rod fully, drain fluid.
• Remove gland/nut or retaining clip at rod end (some are threaded, others snap-ring or pressed plug).
• For many R170 kits: Drill small access holes if needed (some cylinders have a pressed plug—drill carefully to extract old seal without damaging bore).
• Use pick/hook to remove old rod seal (U-cup), backup ring, O-rings on gland.
• Clean bore/rod thoroughly (no scratches!).
• Install new seals from kit:
• Reassemble gland/cap securely.
4. Reinstall
• Reverse removal.
• Reconnect lines (torque banjos gently; check for cross-threading).
• Refit pins/clips (may need gentle persuasion on main lifts).
5. Bleed and Test
• Refill reservoir (under rear seat/trunk area).
• Cycle top multiple times (engine running helps pump pressure).
• Bleed air: Operate fully up/down 10–20 times; top off fluid.
• Check for leaks at ports/seals.
• Test in warm/cold conditions.

Key Resources

• Top Hydraulics DIY Videos (highly recommended—detailed, step-by-step for R170):
• "Mercedes R170 SLK - How To Replace The Convertible Top Hydraulic System" series (multiple chapters on YouTube, covering all cylinders).
• Specific main lift removal: Search "R170 main lift cylinders Top Hydraulics".
• Pelican Parts Tech Article: "Mercedes-Benz SLK 230 Vario Roof Hydraulic Cylinder ID and Replacement" — Great for cylinder locations and basic removal.
• PDF Guide: Download "R170 SLK-Class Cylinder Removal" from tophydraulics.com (free, detailed photos/steps).
• Forums: SLKWorld.com and Benzworld.org — Search "R170 hydraulic rebuild" or "SLK cylinder O-ring kit" for user photos/tips.