Selecting a bulletproof rear end for your car may seem easy, but there are a lot of different builders, and hundreds of options from wild to mild. A name that has always been at the top of the list is Currie, and they have released a new fully fabricated 9-inch housing – the F9 – for hardcore drag racing applications. We got a first hand look at the F9 as they build one for our Project Grandma.
For our Project Grandma, a 1979 Malibu powered by a 1,000+ horsepower Edelbrock/Pat Musi Big Block Chevy, we knew that we were going to need something a little more than just a junk-yard 9 inch. 1,000+ hp and 3,400 lbs is an ugly combination, and a bullet proof fabricated 9-inch fit the bill.
Fabricated Housing (F9) vs. Stock-type Housing?
So you decide to use a 9-inch. Good start. However, over the years that the 9-inch was installed in passenger vehicle, there were over 20 different versions of rear end, with differences from as simple as suspension mounts to width and axle wall thickness. There are three different choices you typically have for a 9-inch build.
- Junkyard 9-inch housing
- Brand new “OE” style housing made by companies such as Currie
- Fully Fabricated 9-inch housing
Sure the price seems right, but you are going to get what you pay for.
Junkyard housings are a bad idea unless your idea of a car is a Dirt Track Street Stock bomber like our sister website OneDirt.com runs. They are of unknown quality, specifications, and condition. Even if you find a good one, the reconditioning required probably means new axle tubes, and then at that level, you’re better of with a new “OE” style re-manufactured housing. The new OE-style housing a great start, and the foundation of MANY rear end builds even down to 7-second applications.
Then why a fabricated housing such as the F9?
There are really four primary advantages to an F9 Fabricated housing such as the Currie Housing:
- Strength – made from premium materials, the F9 can be built to be bulletproof right from the get-go without having to modify an OE housing. Depending on your application Currie can add bracing to the rear end to handle 1,500+ hp applications or even greater.
- Customization/Flexibility – since the Currie F9 is made from scratch, you can customize almost anything on the rear end in the original build stages – from shock brackets, suspension mounts, wheelie bar brackets, etc. You can also do this to some degree with an OE-housing but there you are really modifying an already produced housing.
- Precision – All Currie rear ends are made precisely, but the nature of a fabricated housing allows Currie to get their specifications, clearances, and measurements down to .001 of an inch. Unlike a cast or forged housing, this is fabricated precisely and double-checked every single step of the way.
- Cost is Comparable – If the F9 was 3X the price, or even double, it’s value would be less. But it’s only slightly more expensive than a comparable OE-style housing.
Currie’s F9 Fabricated Rear End: A Look Inside
Currie has been making and modifying Ford 9-inches for over 30 years, and now they have taken that experience and applied it to their new offering the F9, Currie’s first fabricated 9-inch rear end.
The F9 incorporates the best qualities of all the different version of the 9, and blends them into one complete package. We spoke with Brain Shephard of Currie to get all the juicy facts on the F9. “The F9 was designed to be strong, versatile and affordable,” says Shepard, “We bended our knowledge of everything from drag racing, hot street cars, Jeeps and off-road desert racing to make a rear end that could survive anywhere, under any conditions.”
So let’s take a look at each components of this bullet proof rear end, and finally – walk you through an installation on our Project G-Body “Grandma.”
The F9 Housing
Starting off with the housing. Currie begins with 3/16-inch thick Hi-Form steel for the center section.
“We wanted to make the center section out of one piece of steel to help prevent leaks,” says Shephard, “If we couldn’t make it work, we were not going to build this rear end.” The flat steel is then bent, pressed and massaged into the armadillo shape seen here. Then the team really gets to work, starting with the welding.
Currie adds in strength anywhere they can fit a welding torch. The 3rd member mounting face is made from the same Hi-Form steel as the rest of the center section and then welded on with studs installed. Gussets are added inside of the center section and welded along the inside of the mounting face. The drain hole and a magnet to catch any metal flakes are added at this step as well.
Then the center is taken over to a jig that assists one of Currie’s welders in installing the axle tubes. He grabs two 3-inch or 3.25-inch axle tubes, depending on the order, and places them in the jig as well. The axle tube is flat cut on one side so that it matches up with the bulkhead that is welded inside the center section on each end. When installed, the axle tube keys in to the bulkhead adding strength and a resistance against rotating.
The housing ends are also welded on at this stage as well.
In addition, you can see that we added a back brace to our housing, needed because of the fact that our Malibu is going to be making well over 1,000 horsepower. While it might not seem like much, this back brace was custom sized to ensure it would not conflict with any of the rear suspension and provides even more holding power to our already sound rear end.
“Because this housing is already so strong, we really didn’t have to put a huge heavy back brace on this rear end” Shepard told us, “You can have the strength with plenty of room for your other components, such as suspension and gas tank.”
The axles are first cut, then cleaned up before sent off to the next step of the process. While this is going on, on the other side of the building, workers are busy machining the axles for our rear end. It all starts in the cutting shop. Currie cuts the axle down to size and cleans up the cuts before sending it over to have the splines cut.
We choose to go with Currie’s Extreme Axel that are 40-spline. “These axles are made from heat treated forged alloy that is sized to accept the 45 mm drag race bearing,” says Shepard, “This bearing has smaller roller balls that cut down the amount of resistance or friction on the axles turning.”
That means more power to the ground.
A large press helps get the bearing down the length of the axle, resting it just behind the hub.
Here Currie uses one of their many CNC machines to cut the splines into the axles. We ordered ours in a 40 spline version to really make sure it could handle all the hard launches we could come up with.
Finally, Currie installed a set of 5/8-inch wheel studs in a five on four-and-three-quarter pattern to match our Billet Specialties Street Lite wheels. “These studs are the Cadillac of wheel studs,” explained Shepard, “These are the same studs the Pro Stock guys are running.”
The final component needed to begin building our rear end was the 3rd member. Currie started with their a brand new 9-Plus Nodular Iron Race Case. As the name implies, this piece is cast from extra-strength nodular iron, Currie precision machines these cases to original O.E.M. specifications.
This means it is a “brand new” manufactured unit, not a salvage yard rebuild.
Inside the Race Case, Currie installed a set of 3.89 Pro Gears. We installed a 40-spline Currie 4340 Steel Spool to work with out monster sized axles. On the front, we opted for a bullet proof Strange 1350 yoke – the standard sized yoke for drag racing. Keep in mind that this is a track only car, so installing the Pro Gears would not be a problem.They are too soft for street use.
“Our Pro Gears are strong, but are not heat treated and designed to flex. This provides a cushion for the hard launches you are going to submit this car to,” explained Shepard, “A heat treated hardened gear would have no give to it, and break under the torque stress. I wouldn’t recommend a Pro Gear for street use, but on the track, it’s the best way to go.”
Now that all the individual components of our rear end were completed, it was time to move them all over to the assembly section and put it all together. Again, the housing was placed in a jig to assist the builder in assembly. First up was the housing and it was cleaned for one final time.
As you can see in the photo above, this is one of the strong points of the F9 (or any 9-inch). With it’s ability to remove the entire 3rd member, should we want to change gears, all we have to do is quickly swap the 3rd member out with a different one or pull it out and change the gears on the bench.
Next the 40-spline Currie Extreme Axles were slid in on each side and bolted down with the necessary four bolts on each side.
Install Time: Project Grandma gets the F9
Back in the powerTV Garage, we prepped the Currie F9 for install into our G-Body. While the rear end was out of the car, we took the easy approach to putting the brakes on. Like the front of the Malibu, we went with Aerospace Components Brakes. These brakes were designed to fit the Torino style ends that our rear end was built with.
Mounting these was as simple as holding up the bracket and wrenching down the bolts. The calipers were no different. Once we slid the large cross drilled and slotted rotor up on the wheel studs and the brake pads were inside the caliper, we secured it to the bracket with the necessary two bolts per side of the car.
A set of large jack stand were used to help support the rear end while there were no shocks installed. After lifting it on to our trusty transmission jack, we were able to maneuver the assembled rear end up into the wheel wells and hook up the TRZ suspension and QA1 shocks.
Then came the best part, we lowered the car to the ground and crawled around checking for any issues.. We were glad to see that our measurements were spot on and both tires were able to be mounted to the car without any chassis interference. Heck, the car was even able to roll around the shop for the first time in months!
Now our driveline is going to be ready to take the punishment of the Edelbrock/Musi 555ci that when we open the bottle on, will be making over 1,000 horsepower. Currie’s F9 rear end might be the newest kid on the block as far as fabricated housings go, but look for this rear end to make a name for itself as being both strong, durable and reasonably priced. And most importantly, give Currie a call or e-mail if you have any questions. Nobody can walk you through better the advantages of a F9 vs. a standard Currie “9” than the company themselves!