How difficult/time consuming would it be to change the transmission mount and U Joint? How many joints and mounts will I need? I have jack stands and the like, and where is the mount located?
Sometimes a metallic "ping" (funny about the M1 clip, haven't heard that in "awhile," LOL) many times is slack in the joints, yoke/ driveline, and also play in the rear axle, especially a non-limited slip (Sure Grip.) Putting the trans from one direction to the other 'bangs' the slop out of the ring/ pinion and spider gears. IF that is what it is, could be considered "normal" on a somewhat worn drive train.
