On the 4.7 gears, the stock case must be machined or ground to provide clearance for the cluster gear. You can grind the necessary clearance; however, it is recommended to machine the case for this clearance.
If your not sure about this grinding or the machining process, we now offer a new heavy duty front Toyota housing. Our new Toyota HD housing can be used as a crawler box with stock Toyota gears or with our low gear sets. It can also be used as a new front housing for the lower gear sets listed above. This housing will save you time and money. When installing our low gears into a stock Toyota housing, grinding & machining on the stock case is required. Our housing has been engineered with additional clearance for our gear sets. Thus, hours of grinding & expensive machining labor are eliminated. This housing is made from 356-T6 heat-treated aluminum alloy with an average thickness of .550”. A “stock” housing is die cast aluminum and only has an average wall thickness of .200”.