[Dr Fly]

Not quite sure i understand your problem. the rear diffs are linked all the way to the slipper shaft so its pretty easy to check.

If you hold both front wheels so that they dont turn, then try and move both of the rear wheels. If its too lose, the diff will slip meaning that the belts wont move as the diff is slipping, you can tell because the slipper nut and shaft sticking out the side does not rotate. If the diff is tight, the belts, slipper shaft and nut will all turn, or the belts may jump a tooth.

You can do exactly the same for the front, but turn the front wheels backwards if you are running the clicker.

The tlr guys recommend you do something slightly different to check the diff tension, which they posted on you tube, i dont really like the method as it assumes your diffs are all in good condition and well built, which may not always be true in my case.