Posted September 23, 2019 by NAPA Solutions Know How

How to Replace a Toyota Diff Cover

Toyota trucks may be legendary for their off road trail toughness and reliability, but their solid axles have a weak spot that often sends owners to salvage yards and online forums in search of answers. Underneath 4Runner, FJ Cruiser, Tacoma and Tundra vehicles, the cap that covers the differential is made of thin-gauge stamped steel, which lets rust eat away at it faster than other areas.

The first sign of Toyota diff cover failure is typically a wet spot on the outside of the cover, or a small drip on the ground under the axle. Left to corrode further, the axle loses fluid, or water gets into the housing, mixing with the gear lube. If you spend a lot of time wheeling in mud or deep water, then the problem is obvious.

Fixing it hasn’t always been simple.

These covers are welded in place, not bolted on like other trucks, so they’re tough to replace by themselves. In the past, you’d have to get a whole new axle from the dealership, replace the axle with a rust-free salvage part, or fabricate a replacement Toyota diff cover by hand.

We’ve seen these homemade differential cover patches. They aren’t easy or pretty. And if you live in a rust-prone area, odds are salvaged axles near you will also be rusted. That means you have to source an axle from outside your region, which can get pricey. That’s why our NAPA Solutions partners designed replacement differential covers for Toyota trucks. They’re made of heavier stamped steel for greater rust resistance, and are pre-primed.

Installing this Toyota diff cover still requires cutting off the old cover and welding on the new one. Below we show you how to do that.

SAFETY WARNING: Please use caution when performing this service. Always support the vehicle securely before beginning work. Eye and hand protection should be worn at all times. Work only in a well-lit, well-ventilated workspace. This procedure is only to demonstrate how the replacement part is installed. Follow factory-approved workshop manual for all removal, installation and other assembly procedures. If in doubt, visit your local NAPA AutoCare location.

Step 1

Remove the axle unit from the vehicle, following the workshop manual. After removing the axle shafts and differential, drain the gear lube.

Step 2

Carefully cut through the original Toyota diff cover using an electric or pneumatic cutoff wheel, around the circumference of the cover. — Carefully cut through the original differential cover using an electric or pneumatic cutoff wheel, around the circumference of the cover.

Step 3

Use an angle grinder to clean up the mating surface where the new cover will be installed.

Step 4

Carefully position the new Toyota diff cover in place, being sure to orient it correctly. Using an appropriate welder, tack the new cap in position initially. — Carefully position the new cover in place, being sure to orient it correctly. Using an appropriate welder, tack the new cap in position initially.

Step 5

Run a continuous bead weld around the circumference of the new cover, making sure there are no gaps in the weld.

Step 6

Once cool, degrease the work with a pre-paint solvent. Apply self-etching primer, and finish with a coat of chassis paint to prevent future corrosion.

Check out all the drivetrain parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to replace a Toyota diff cover, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.