We all like to keep our vehicles in good mechanical condition, and one of the easiest ways to keep our cars running their best is to service the vital fluids at the proper intervals. The lubricants in the engines, transmissions, differentials, and hydraulic systems of our Mopars can be subjected to extreme pressure, and can break down after months of lubricating the vital parts of our cars. The fluids are also essential to cooling the moving parts of the drivetrain, and suspend dirt, particles, and shavings caused by normal and aggressive driving. For these reasons, changing the fluids in our Mopars is an important part of routine maintenance.
Tired of being able to easily change your engine oil and transmission fluid but not the fluid in your differential? We've got a fix that will allow you to service your 8 3/4 Chrysler rear-end quickly and easily.
While changing the oil is pretty straightforward, and servicing the transmission just requires dropping the pan, changing the gear oil in an 8 3/4 differential is a different story entirely. The problem is, there's no drain plug or pan on the 8 3/4 rear end, no rear cover like the Dana 60, and no lines to disconnect like the braking or power steering system. So if you want to change the fluid in your 8 3/4 the choices are to use a pump like you'd use to change the oil in a boat engine to pump the fluid out, or to remove the heavy centersection entirely, drain the fluid, then re-seal and re-install the centersection. Since the pump never removes all the fluid and can leave heavy particles behind to contaminate the new oil, and removing the centersection is an arduous task, we've found that it is convenient and easy to add a drain plug to the 8 3/4 housing, allowing easy fluid changes.
Since we were at Inline Performance getting some suspension work done to our '71 Road Runner, we decided to install a drain-plug in the differential housing while the car was on the lift. This task is actually easier than you might think, requiring only a drill, a 21/64-inch drill bit, a 1/8-inch pipe tap, and a 1/8-pipe plug. We were lucky to have our car on a lift, but you can also perform this modification with your car on jackstands as long as the differential is high enough that you can get the drill under it. Drilling a smaller pilot hole will help you drill a straight hole, and remember to drill on the passenger side of the housing's center to avoid the ring gear. After drilling the hole, the oil will start draining so have a pan ready. The draining oil will remove most of the shavings created by the drill, and a magnet can be used to remove any additional metal. A 1/8-inch pipe tap is then used to thread the hole and a magnet can again be used to remove any shavings before installing the 1/8-inch pipe plug.
<strong>1</strong> The first step in this modification is to drill a 21/64-inch hole in the bottom of the rear end housing. Remember to drill on the passenger side at about the middle of the area on the bottom of the housing.
Since the 8 3/4 differential housing has a reinforcing ring where the centersection bolts in, the drain plug doesn't compromise the strength of the rear end at all. Best of all, having a drain plug makes future gear oil changes easier, and it only takes about an hour to make this helpful modification.
Editor's note: You may want to either use a socket head type plug, or be careful when you jack the rear of your car up after this "enhancement."
