Ford 8.8 vs Ford 9-Inch
Rear End Differences

The Ford 9-inch has a reputation that borders on religion, and the 8.8 gets treated like the cheap replacement. That is not fair to the 8.8. It went under millions of Mustangs, F-150s, Explorers and Crown Vics, and a built 8.8 handles more than most street cars will ever throw at it. The 9-inch is still the better rear end for a serious drag car. The question is whether you are building one.

Side-by-Side Comparison

Which Vehicles Got Each Rear End

• Ford 9-inch: Ford and Mercury cars and light trucks from 1957 into the mid 1980s, including Galaxies, Fairlanes, Torinos, muscle-era Mustangs, early Broncos and F-100 and F-150 pickups.
• Ford 8.8: arrived in the early 1980s and replaced the 9-inch. Fox-body V8 Mustangs and every solid-axle Mustang after, F-150s that did not get the 9.75, solid-axle Explorers and Rangers, Crown Victoria, Grand Marquis and Town Car. Later versions show up as the IRS rear in Explorers and newer Mustangs, and as the reverse-rotation front in 2009-and-later F-150 4x4s.

Telling them apart takes two seconds. An 8.8 has a 10-bolt rear cover. A 9-inch has a smooth rear housing with no cover and a ring of nuts on the front where the third member bolts in. For 8.8 wear patterns, see our Ford 8.8 problems and rebuild guide; the Ford 9-inch problems guide covers the other side.

Pinion Support Is Why the 9-Inch Wins

The 9-inch's real advantage is not the extra 0.2 inch of ring gear. It is the pilot bearing. The 9-inch pinion rides in a pinion support with two tapered bearings behind the gear head and a straight roller bearing in front of it. Under a hard launch the pinion wants to climb out of the ring gear. On a 9-inch, the pilot bearing holds it in mesh. On an 8.8, the pinion is overhung on its two bearings and can deflect, which is how 8.8 teeth get chipped on drag radials.

The 9-inch also runs a deep hypoid offset, which puts more of each tooth in contact. That same offset is why it loses a little more power: the teeth slide more, make more heat and want a good 75W-140 on a hard-run car. Expect a few percent difference, which matters to a class racer and to nobody commuting.

Not all 9-inch parts are equal. A nodular iron case, usually marked with an N, is the one to build. The Daytona pinion support uses a bigger front pinion bearing and is the upgrade for big power. The master overhaul kit for the Daytona 9-inch and Daytona pinion support ($358.89) covers that setup.

Axles: Splines and C-Clips

The 8.8's other weak point is the c-clip. The axle is held in by a clip on the inner end, so if an axle snaps, the outer half and the wheel can slide out of the housing. That is why many tracks require c-clip eliminators past a certain speed. Check your track's rulebook. Early 8.8s ran 28-spline axles; later Mustang, Explorer and F-150 units mostly went to 31. If you have 28-spline shafts and real power, 31-spline axles and a matching carrier are the first upgrade.

The 9-inch uses bearing-retained axles. The bearing is pressed on the shaft and bolted to the housing end, so a broken axle stays put. Stock shafts are 28 or 31 spline, and 35-spline axles with a 35-spline locker are the standard drag combination.

Gear Availability and Cost

Both rear ends have more gear ratios than you will ever need, and the prices are closer than people think. An 8.8 set runs from the Motive Gear 3.73 ($252.99) and Revolution 3.55 ($272.99) up to the Yukon 4.11 ($458.46) and Yukon 4.56 ($524.94). On the 9-inch, the Revolution 3.50 ($292.99) or Yukon 3.50 ($503.36) are typical street and strip picks.

The real cost gap is setup. Any 8.8 regear is a careful job of pinion depth, preload and backlash inside the housing. On a 9-inch you can set up a spare third member on the bench and bolt it in. A rotating 9-inch assembly stand ($140.99) makes that easy. Our backlash and pinion depth guide covers both, and the gear ratio guide helps you pick.

Street, Strip and Truck Use

• Daily driver or towing truck: 8.8. Lower loss, cheap parts, and the factory Traction-Lok rebuilds for well under $200.
• Street Mustang on a street tire: 8.8 with 31-spline axles, a fresh limited slip and the right ratio.
• Bracket car on a drag radial or slick: a built 8.8 with a c-clip eliminator works into the 10s for many cars; past that, the 9-inch is cheaper insurance.
• Pro builds and frequent ratio changes: 9-inch with a nodular case, Daytona support and 35-spline axles.

What It Costs: Rebuild the 8.8 vs Swap to a 9-Inch

Fill either one with quality gear oil from our fluids section, and add friction modifier if it has a clutch-type limited slip.

Parts and Tools for the Job

For the transmission side of the same build, CoreTransmissionParts.com carries rebuild parts.

FAQ

Is a Ford 9-inch stronger than a Ford 8.8?

In built form, yes. The 9-inch has a slightly bigger ring gear, a pinion supported on both sides of the gear head, and bearing-retained axles that can go to 35 splines. A stock 8.8 with 31-spline axles is plenty for most street cars and trucks, but the 9-inch has more headroom once you add sticky tires, a hard launch or a lot of power.

Why does the 9-inch lose more power than an 8.8?

The 9-inch has a very deep hypoid pinion offset. That offset gives the teeth more contact and strength, but it also makes them slide against each other more, which turns a little more power into heat. The difference is a few percent at most and only matters to racers counting every tenth or every mile per gallon.

Are 8.8 and 9-inch gears interchangeable?

No. The ring gear, pinion, carrier and bearings are all different. On a 9-inch the gears and carrier live in a removable third member, so many racers keep a spare third member set up with a second ratio and swap the whole assembly.

Should I rebuild my 8.8 or swap to a 9-inch?

Rebuild the 8.8 for nearly every street car, truck and mild bracket car. A regear, a good limited slip or locker, 31-spline axles and a c-clip eliminator cost far less than a 9-inch swap. Swap to a 9-inch when you are making serious power on a sticky tire, need quick ratio changes at the track, or are building an older Ford that came with one.