Install Differential Drain Plug Drain Fluid

Installing A Drain-Plug In The Differential Housing - An Easy Rear-End Mod For Your 8 3/4

An easy rear-end mod for your 8 3/4

By Dave Young

Tired of being able to easily...

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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.

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.

Install Differential Drain Plug Drill Hole

1 The first step in this...

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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.

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."

2 When the drill bit breaks... read full caption 2 When the drill bit breaks through the housing, the oil will begin to drain, taking the metal shavings with it. A magnet can then be used to ensure all the metal is removed from the differential housing.	3 If you don't have the proper... read full caption 3 If you don't have the proper drill bit or 1/8-inch pipe tap, you can pick them up at the local auto parts or hardware store. Don't forget to get a metal pipe plug while you're there. Be careful while tapping the hole as the tap is tapered and will cut larger diameter threads the deeper you go. The tap should be backed out frequently to remove shavings and a magnet can then be used to ensure all metal is out of the housing.	4 Pipe plugs don't need excessive... read full caption 4 Pipe plugs don't need excessive torque to seal properly, especially if wrapped with Teflon tape. For added protection, a magnetic plug can be installed. 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."
5 Now the proper amount of... read full caption 5 Now the proper amount of the appropriate gear oil and Sure Grip additive (if needed) can be added...	6 ...and the fill plug can... read full caption 6 ...and the fill plug can be reinstalled.	7 Of course the last step... read full caption 7 Of course the last step in this modification is to drive your car. Gotta check to make sure it doesn't leak! Knowing that you can now easily change all of the vital fluids, including the gear oil in your 8 3/4 rear end, makes maintenance not seem so troubling.