Ford F-150 9.75 Inch Rear Differential Cover 697-734

A rusted, pitted or rock-dented rear cover on a Ford 9.75 axle is one of the most common reasons an F-150 starts leaving gear oil spots in the driveway. This is a ribbed, black textured cast replacement cover for the 12-bolt Ford 9.75 rear, cross-referenced to Ford BL3Z-4033-A and Dorman 697-734, and it ships with a set of cover bolts. It fits the 1997-2021 F-150, the early Expedition and Navigator, the Lincoln Blackwood and Mark LT, the E-150 and the Transit.

What the rear cover does on a Ford 9.75

On the 9.75, the cover is the back wall of the gear oil reservoir. It seals the open rear of the carrier housing, shields the ring gear from road debris, and gives the gear oil a surface to wash against and shed heat. Because the 9.75 is a C-clip axle, the cover is also your access panel: you pull it to reach the pinion shaft lock bolt and remove the C-clips before an axle shaft or wheel bearing job. That means the cover comes off far more often than most owners expect, and every time it does, a rusty or warped flange makes the next seal harder to get right.

Symptoms of a bad 9.75 differential cover

• Gear oil seeping from the lower edge of the cover or around individual bolt holes.
• Heavy scale and pitting on the flange that keeps RTV from bonding.
• A dent from a rock or rut that has pushed the cover in toward the ring gear; in bad cases you may hear scraping.
• Stripped or rust-seized cover bolts that break on removal.
• Low gear oil level found at a service, which can lead to the bearing whine the 9.75 is known for when it runs low on cooked oil.

How to confirm the leak is the cover

Clean the area with brake cleaner, drive a few miles, and look again. Oil that starts at the cover flange is a cover or sealant problem. Oil coming from the pinion seal at the front of the housing, or out at the axle ends near the brakes, is a different repair, and on 2011-and-up trucks axle-end leaks are common. Our differential cover leak guide explains gasket versus RTV, and the Ford 9.75 rear axle guide covers the other leak points and bearing noise.

Fitment

Listed fitment is the 1997-2021 F-150, 1997-2001 Expedition, 1998-2001 Lincoln Navigator, 2002 Lincoln Blackwood, 2006-2008 Lincoln Mark LT, 2003-2007 E-150 and 2015-2020 Transit 150, 250 and 350 HD with the 9.75 rear axle. Ford's current number for this cover is BL3Z-4033-C, which supersedes BL3Z-4033-A and F75Z-4033-AA, and Ford's catalog notes list it for 9.75 ring gear applications. Not every truck on that list has a 9.75. Many F-150s use the Ford 8.8, which has a 10-bolt cover, so count your cover bolts: 12 means 9.75. Check the axle tag or send us your year and VIN if you want us to confirm. Browse our other axle and transmission hard parts.

Install notes

• Drain the axle, remove the old cover, and scrape every trace of old sealant off the housing flange. Do not let debris fall into the gears.
• Clean both mating surfaces with brake cleaner until they are dry and oil-free.
• Lay a continuous bead of gear-oil-resistant RTV on the cover, running inside the bolt holes, and install within the sealant's working time.
• Run the bolts in snug, then tighten them evenly in a crisscross pattern to the torque in your service manual.
• Let the RTV cure per the tube, then fill with the gear oil grade Ford lists for your axle, adding friction modifier for a limited-slip unless your oil already contains it.

If the oil came out dark and full of metal, plan on more than a cover. For 2011-and-up axles, the Ford 9.75 master bearing kit covers carrier and pinion bearings; earlier trucks use the 2000-2010 Ford 9.75 overhaul kit. Worn spider gears can be replaced with a 34-spline 9.75 spider gear set, and a 9.75 Detroit Truetrac is the upgrade for one-wheel peel.

How do I know if my F-150 has the 9.75 or the 8.8 axle?

Count the cover bolts. The Ford 9.75 uses a 12-bolt cover and the 8.8 uses 10. The axle tag on the housing and your VIN build data will also tell you.

Does this cover fit both 1997-2010 and 2011-and-up 9.75 axles?

Yes, the listing covers 1997-2021 F-150. Ford redesigned the 9.75 internals for 2011, but both versions use a 12-bolt cover. Internal parts like bearing kits are not interchangeable between those generations.

Do I need a gasket?

Install it with a continuous bead of gear-oil-resistant RTV run inside the bolt holes on clean, dry surfaces. Let the RTV cure fully before filling and driving.

Are bolts included?

Yes, the cover comes with a set of cover bolts. Replacing old bolts is a good idea if the originals are rusted or stretched.

What gear oil should I use after installing it?

Use the grade Ford lists for your axle, and add friction modifier if you have a limited-slip unless the oil you buy already contains it.

My cover is leaking but so is the area near the brakes. Will a new cover fix that?

No. Oil at the axle ends is an axle seal or wheel bearing issue, common on 2011-and-up 9.75 trucks. A new cover only fixes leaks that start at the cover flange.