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Trunk Lock Cylinder Repair
 
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Pelican Technical Article:

Trunk Lock Cylinder Repair

Tom Morr

Time:

1 hour1 hr

Tab:

$455

Talent:

**

Tools:

T9, T30 Torx drivers, 7mm open-end wrench, small flatblade screwdriver

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Replacement lock tumbler assembly

Hot Tip:

Mark screw locations so that components can be re- assembled in their previous locations

Performance Gain:

Trunk locks and opens as intended

Complementary Modification:

Adjust the latch if the trunk doesn't pop open easily when the button is pushed

Pre-facelift (built before 2/1/2000) R170 SLKs have their trunk locking cylinders between their license plates and right taillights. (The later cars have theirs above the license plate.)

Trunk locks on both variants are part of the central pneumatic locking system. Pre-facelift locks also interface with the Vario roof. So, the lock mechanism can malfunction pneumatically, electrically, and/or mechanically.

The trunk lock assembly is an expensive part (#170-750-01-91-MBZ) and worth attempting to repair before ordering a replacement. In the best-case scenario, something is loose between the lock assembly's socket and the lock rod that connects the cylinder to the trunk latch.

The lock assembly removes easily. Installation can be more challenging. The lock rod must be seated properly in the sockets on both the lock and the latch. The latch might need to be unbolted and moved upward to verify proper ball/socket engagement. Mark the positions of the three bolts prior to removing the latch. The latch won't catch and release on the striker if it isn't reinstalled in the correct position.

If the trunk lid won't pop open using the lock cylinder, open the trunk from the front using the Vario roof switch. Make sure that the lock rod is seated correctly in the latch's socket (remove the handle recess for access) and twist the rod clockwise to hopefully release the latch. Then adjust the latch's mounting position until it engages and disengages properly. Please refer to the latch-removal article for further details.

Lock rod access is improved by removing the handle recess (red arrow).
Figure 1

Lock rod access is improved by removing the handle recess (red arrow). A screw with a T9 Torx head (purple arrow) holds it in the trunk.

Two bolts with T30 Torx heads (red arrows) secure the lock assembly to the trunk lid.
Figure 2

Two bolts with T30 Torx heads (red arrows) secure the lock assembly to the trunk lid. Consider marking the bolts' locations on the mounting slots so that the lock can be reinstalled in the same position.

With the lock assembly unbolted, it can be pivoted out of the lock rod (blue arrow).
Figure 3

With the lock assembly unbolted, it can be pivoted out of the lock rod (blue arrow). The pneumatic line (yellow arrow) is gently pulled out of its fitting (red arrow). The recommended method is with a 7mm open-end wrench. Finally, the electrical connection is unplugged (purple arrow).

The lock cylinder is a complete unit.
Figure 4

The lock cylinder is a complete unit. The trim bezel is even part of the assembly.

The lock assembly can be disassembled by unhooking the tang (purple arrow) with a small flatblade screwdriver.
Figure 5

The lock assembly can be disassembled by unhooking the tang (purple arrow) with a small flatblade screwdriver. Then the halves slide apart while depressing a couple tabs.

The socket (red arrow) clips into the rear half of the assembly.
Figure 6

The socket (red arrow) clips into the rear half of the assembly. Pushing on the lock rod can easily poke the socket into the housing.

The return spring (red arrow) slots into the housing and socket.
Figure 7

The return spring (red arrow) slots into the housing and socket.

Before reinstalling the lock, verify that the key turns the socket and that the return spring kicks the key back to its initial position.
Figure 8

Before reinstalling the lock, verify that the key turns the socket and that the return spring kicks the key back to its initial position.

The lock rod's balls and pins must seat in the sockets on both the lock assembly and the latch.
Figure 9

The lock rod's balls and pins must seat in the sockets on both the lock assembly and the latch. Otherwise, the key and push button won't open the trunk lid properly. The rest of the installation reverses the disassembly.

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Page last updated: Fri 12/9/2016 02:25:50 AM