How to Install Bevel Gears

What You'll Need
Three Eighths Inch Socket Wrench
Oil Pan
Jack and Jack stands
4-Inch Gear Puller
One and an Eighth-Inch Socket
Breaker Bar
Gear Oil
Backlash Measurement Tool
Friction Modifier

Bevel gears are cone-shaped gears that allow a machine to smoothly and quietly transfer power from one gear to another. By changing the sizes of these gears, one can also use them to manipulate the mechanical advantage of a machine. This means that by mating two bevel gears with differing diameters and numbers of teeth, one  can change the speed or torque produced by a driveshaft  as well as the amount of power required to turn it. Unlike spur gears where the only mounting concern is the center distance and the alignment of the shaft, bevel gears must be mounted in perfect sync with each other. To learn how to install the bevel gears on the backend of a vehicle read the steps below. It is important to note that this article describes the method for removing the gears on a Ford because the mechanisms may be different on other vehicles. Also, this article assumes that the rear wheels and their brake mechanisms have already been removed. 

Step 1 – Jack Up the Vehicle

Before jacking up the car, make sure it is in park so that the wheels cannot roll and place chocks behind the back tires. Next, place a jack directly under the chassis or frame where jack will be able to press against a flat, non-bendable surface, and jack the car off the ground. Insert a jack stand and then repeat the process on the opposite side.

Step 2 – Open the Gearbox

Place an oil pan beneath the gearbox to catch any oil that may spill out from the gearbox when it is cracked open. Then, using a three eighths of an inch socket wrench, remove all of the bolts securing the gearbox cover except for the topmost one. Then, use a mallet to tap a screwdriver in-between the gearbox cover and the rest of the gearbox and pry the cover outward. This will break the seal within and cause the lubricant inside to pour out into the oil pan below. Once all the fluid has rushed out, remove the final bolt in the cover and remove it. It may be wise to use a rag to sop up any lubricant that may remain within.

Step 3 – Remove the Driveshaft

A twelve millimeter socket wrench will be required to disconnect the bolts holding the driveshaft to the gearbox. Use a marker or white out to mark where the driveshaft bracket meets the gearbox flange so that it may be properly aligned during reassembly. Use a mallet to knock the driveshaft loose if necessary.

Step 4 – Remove the Pinion Nut

Use a one and an eight inch socket and a breaker bar to twist and loosen the pinion nut which is located within the area from which the driveshaft was removed. The flange that sat between the pinion nut and the driveshaft can then be removed with a four inch gear puller.

Step 5 – Remove the Center Pin

Use a three eighths inch wrench to loosen the bolts near the bevel gears that hold the axels in place. Then, slide the axels inward just a bit and remove the C-clips that prevent the axels from sliding away from the car. Pull the axles away from the bevel gears and us a three quarters of an inch socket with a breaker bar to remove the bolts securing the clamps around the bevel gears. At this point the old bevel gears should slide right out (including the pinion bevel gear). If desired, this would be a good time to replace the seals and bearings.

Step 6 – Slide the New Bevel Gears into Place

Bolt the new bevel gear to the differential and then reinsert it, as well as the pinion bevel gear, into the gearbox. Once the gears are in place, use a backlash measurement tool to check the gear mesh. Add or remove shims to the pinion gear as necessary until the gears are perfectly aligned. Paint can be applied to the teeth of one of the gears so that when the two are turned, one can see where the teeth are hitting on the opposite gear. Once the gear mesh is correctly aligned, use an arbor press to connect the pinion gear to the shims and a new bearing if desired; then reassemble things in the reverse order that they were taken apart. Apply Loctite to the bolts as they are reinserted.

Step 7 – Fill the Fluids

Finally, once the gearbox has been completely reassembled, fill it with gear oil and add a friction modifier.