You shouldn't need to take the clamp-nut all ythe way off to collapse the sliding joint. If it's all the way off, it may actually prevent you from fully collapsing the joint. You may need to screw the nut partly back on to provide more collapse space. If, after fully collapsing the joint, you can't drop the center bearing low enough because of interference from the brake cable and exhaust, you'll need to disconnect the driveshaft at the differential. The 'U' joints aren't clipped in but are permanently pressed in and peened in place at the factory. You'll need to unbolt the rear end of the driveshaft from the differential.

Happy Motoring, Mark

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DrDKW