Which speedo cable? The one for the EGR/O2 sensor box (you know, the one that trips every 30k miles) should unscrew. I'm pretty sure the other one (the one from the tranny to the speedometer) just pulls out after you break off the tamper plug. For sure the cable basically just gets plugged back in with nothing keeping it in place. I found it easiest to stick my legs up on the door sill and stick my head under the dash with a flashlight to guide me. If you don't feel anything on the cable in question (save for a spring) you should just give it a good tug. If you're more daring you can just pull the cluster until it detaches. If you break something, the parts are cheap *bfg*.

- alex

'85 244 Turbo ~144k miles