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Any moving part can potentially cause vibration. This involves rotating parts and assemblies, which need to be carefully balanced. Thankfully Datsun balanced all parts to a high degree of precision right at the factory. It also includes non-rotating parts subject to swaying such as body panels which can vibrate at certain frequencies such as responding to road undulations.
Wheel and Tire
Wheel balance Tire with broken belts
Move the rear tires to the front just to eliminate balance or damaged tires. Look for missing wheel weights. Inspect all lugnuts for proper installation (not on backwards) and loose nuts.
* broken steel belts in tire? * bent wheel? (Hit? ) * wheel spacers issues? ( cheap ones give problems ... ) * etc ...
Driveshaft
U-joints. When they go bad the unwanted clearance allows the heavy driveshaft to go off center, ever so slightly, thus allowing it to wobble and vibrate.
This is often a problem when lowering the car as it puts the u-joints at a higher angle (which is not bad, but will make a problem more noticeable).
You can't tell by shaking the driveshaft unless they are so extremely worn they are about to break.
I jack up car and go under there and with both hands rotate 1 wheel back and forth and look at the u-joints for slop. When they are moderately worn you can see it.
To fully test them you go by rotation and turning force: Rotate them back and forth and round 360 degrees by hand. They should be:
- Not loose, but have a slight drag
- Absolutely smooth with no clicks or binding spots
If they are really bad you can tell without disassembling. Block the wheels, put in neutral and grab each shaft and flange and see if you can move the joint rotation-wise. Good u-joints won't let the part move.
... but you won't be able to inspect fully (the drag/rotation part). You will be able to tell if one is grossly worn out. If you don't find anything, then take the shafts off and inspect each one individually.