Here at Motobilt we get technical questions all the time from simple questions to in-depth discussions. One question that comes up often is how much differential fluid should be purchased to fill up a diff. Well the general rule of thumb is to fill your diff up until the fluid starts to run out the fill hole. This does not estimate how much gear oil you should purchase. Since Motobilt is in the business manufacturing 1000’s of heavy duty diff covers every month we get asked all the time how much should be purchased. We put together this capacity chart to help answer the question. With the after market covers we make you may find that they hold slightly more than the factory specs listed below.