How to build A Custom Ford 9-Inch Center Section with GearFX Driveline

10 min read

How to build A Custom Ford 9-Inch Center Section with GearFX Driveline

10 min read

Building a rearend and/or setting up a ring & pinion is one of those things that a lot of hot rodders leave to the professionals. Getting the pinion depth and gear pattern correct with all the preload adjustments, shims and what not, can be tricky, and in our case it’s always just been easier to pay someone that knows what they’re doing to accomplish it, and then stick it in the car after the fact. Think of it like painting—if you’ve tried to paint a car then you know what a tremendous pain in the neck it can be, and oftentimes the finished product turns out to be less than expected, even after all that work.

We went to GearFX’s shop in Mooresvile, North Carolina—right in the hot seat of NASCAR country—and got the full scoop on how they build a rearend. Shop Operations Manager Jeff “Fuzzy” Horton ran us through the entire process and said, “If it’s a manual transmission or a rear gear, we’ll tackle it” but also pointed out that the Ford 9-inch rear is the company’s bread and butter, representing a big chunk of the business at GearFX. “We’ve built 8.8s, rears for C5 and C6 Corvettes, Tremec transmissions, and did the rear gears for the Mazda Cup race cars, Spec Miatas primarily.” He also pointed out a few custom NASCAR 4-speed boxes used in various top levels of the game.

Horton said, “Building a 9-inch gear really isn’t all that difficult and a lot of guys can do it, but there are things that we’ve learned over the years of building championship-winning NASCAR drivelines that we apply to all of our street gears as well. We strive to ensure that anything that leaves here is top-notch and you won’t have to deal with any noise. We’re essentially blueprinting the gears.”

For this installation, we had GearFX set up a 9-inch center section with a Tru-Trac differential. Follow along below and let’s take a look at the process.

For more information on GEAR FX Services and Products, CLICK HERE.

GearFX Nodular Iron Case

This nodular iron gear case is very popular when using a 9-inch rearend. GearFX uses new cases that come from original Ford molds.

GearFX pilot bushing pinion

The first step is pressing on the pinon’s pilot bushing. All Timken bearings are used in a GearFX setup, as well as ARP hardware. All good stuff right there, and if you’ve ever played with ARP fasteners, you know they’re like jewelry.

GearFX Ring Gear press

With the pinion and gear assembled, attention turns to the ring gear, which is a tight fit that needs to be pressed on. The ring gear is usually heated up in the steam cleaner to increase the clearances, and then pressed on using two or three dowel pins made of ring gear bolts that have had their heads removed. See those little studs? Those are the headless bolts. They make it easier to line the gear up, and are replaced with ARP bolts during final assembly.

GearFX ring gear ARP bolts

Again, GearFX only uses ARP fasteners in their rearend setups, including the ring gear bolts.

GearFX torque to spec

Shop Foreman Rob Knipp torquing the ring gear bolts to spec.

GearFX safety wire

The ring gear bolts are also safety-wired in place. This is typical race car stuff that most street guys don’t do, another advantage to having GearFX set a rear up for you.

GearFX truetrac unit

With the ring gear, bearings, and safety-wired ARP bolts in place, this is a complete Truetrac rear differential setup ready for assembly into the whole package.

GearFX pinion seal and slinger

This is the pinion seal that also holds an oil slinger. It’s a thin metal washer that is used to “sling” the oil and keep it off the back of the seal.

GearFX pinion bearing gets oil

The pinion bearing gets a light coal of oil before being pressed into place.

GearFX pressing on pinion bearing

The pinion bearing is installed into place with a hydraulic press.

GearFX complete ring and pinion

Here is the fully assembled pinion gear and ring gear with differential ready to go. Now they are ready to be mated together.

GearFX pinion yoke tool

This handy bench-mounted tool holds the pinion yoke in place so that the nut can be tightened into place.

GearFX Pinion retainer

Installing the pinion retainer.

GearFX dial indicator/pinion depth

This dial indicator is used to measure pinion depth, which is set to the manufacturer’s specs.

GearFX metal shims

Metal shims are used to help set pinion depth.

GearFX pinion yoke

The pinion yoke is always a NASCAR 1350 series billet unit.

GearFX setting the gear pattern

With the pinion in place, the ring gear and diff are placed into the housing to set the gear pattern. Pattern is important and is a major factor in how much noise (and wear) you get with the overall gear setup.

GearFX retainer bolts torqued

The differential retainer bolts are torqued in place and then the backlash is checked to make sure it’s in spec.

GearFX dyno run

With the center section ready to go, the last step is to run it on GearFX’s run-in dyno, which most of their competitors don’t have. The dyno runs the gears in and checks for noise and other issues, and every gear setup is run on the dyno before it ever leaves the door.

GearFX build certificate

Every GearFX rear gets this build certificate that lists off the specs and clearances, as well as the people responsible for assembling it. This is handy reference material to have in your toolbox that provides a little more faith that it was all done correctly and by talented people.

For more information on GEAR FX Services and Products, CLICK HERE.


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