The speedo in the W210 is electronic and thus there is no mechanical speedo cable. There will be a few bundles of wires hooked to the back. I don't know for sure on the W210, but I believe there should be enough slack to disconnect them after you slide the cluster out a bit. Maybe someone who has personally pulled a W210 cluster can chime in from experience.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record