How to Weld a Rear Differential
Welding the rear differential on an automobile has been popular for quite some time in both the drag racing and the off-road community. Welding the spider gears essentially locks both wheels together so that they always turn at exactly the same rate and with the same amount of torque. This greatly increases traction, which is why racers and trail drivers alike make the modification to their differentials.
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Instructions
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Remove the differential cover. Depending on the make and model of your vehicle, the rear differential cover will have anywhere from 10 to 14 bolts. These must be removed and set aside. Even with the bolts removed, the cover will likely want to stay on the housing, especially if RTV silicone was used. Gently pry the edges with a flat-head screwdriver to loosen the seal. Make sure you have an oil drain pan under it because when the cover comes off the oil will come out. Once the cover is off, scrape the gasket surface on both the housing and the cover clean with the flat-head screwdriver.
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Clean out the housing well. When you begin welding, you do not want any oil in the area at all. Use a strong solvent and a clean rag to clear all the gear oil and other debris out of the housing and gear set, and let the entire area dry well before attempting to weld. Try to use a quality rag that will not leave fuzz or material inside the housing because it could cause a fire once the welding begins.
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3
Weld the spider gears. The two very large gears inside the differential housing are the ring and pinion (drive) gears, and they won't be welded. The four smaller gears, known as spider gears, are what allows each axle to spin independently of the other one for turning corners. Weld them together thoroughly and slowly to ensure that the fusion does not break when power is applied. When the spider gears are welded to each other positively, both axles will be forced to spin at the same rate, creating a "locker" of sorts. Sometimes this modification is called a Lincoln Locker because it is accomplished using a welder instead of installing a locking differential unit. Clean out the housing again so that slag and bits of metal do not remain.
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Reinstall the differential cover and add fluid. After the welded spider gears have cooled completely, put on a new gasket and replace the differential cover onto the housing using the original bolts. Then remove the gear oil fill plug (usually toward the center of the differential cover) and slowly pump in oil until it begins to seep out the hole. Replace the plug at that time. Now the differential is locked together, and traction in the rear of the vehicle has effectively doubled.
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