1966 Ford Mustang Gets 9-inch Rear- Tough As Nails!
If You Plan To Thrash Your Street Machine, It Pays To Build In Some Strength. This 9-Inch Rear With Parts From Chassisworks, Currie, And Eaton Will Handle It!
From the May, 2009 issue of Popular Hot Rodding
By Liz Miles
Photography by Liz Miles
The basis for the 9-inch rearend...
The basis for the 9-inch rearend in Project Street Fighter is a Fab 9 housing from Chris Alston's Chassisworks. We got our housing from Chassisworks with a Wilwood 13-inch, four-piston brake system for the hardcore track work we plan on. The final part of the equation came from Currie: a set of 31-spline axles, an Eaton TrueTrac diff, and a Currie Sportsman 9-inch carrier will make this rear indestructible.
Those who have experience building or racing cars know that the weakest link of your drivetrain can cost you dearly. Many hobbyists start out with modest intentions and under-build their cars, only to find that what they really want is something indestructible and worry-free. For the kind of abuse these cars get, it's no wonder that some guys are constantly chasing down problems and making temporary bandage fixes. This is not something we intend on doing with project Street Fighter. Our '66 Mustang coupe is being built to race and to flog out on the street. Every part we're using needs to be able to withstand the tortures of power and traction.
Our original six-cylinder Mustang rearend was not going to last one night with the 427ci stroker Smeding powerplant we've got in store for it; we had to go bigger and better for all parts that are going to see this dynamo's prodigious torque. With plans to use Chris Alston's Chassisworks' G-Bar rear suspension system (eliminating the leaf spring setup), we would be using Chassisworks' 9-inch housing as well. It came with all the necessary bracketry to attach their new four-link suspension, making the conversion complete. We got the housing powdercoated satin black at AR Powdercoating in Anaheim, California, which you can read more about in my column (see "The Last Word," page 98). Powdercoating is durable, good looking, and fairly inexpensive, making it a favorite option.
The bombproof guts of a Ford 9-inch are what really make it one of the strongest rear ends out there. A GM 12-bolt may be lighter and take less power to operate, but when it comes to setup tolerances, it's hard to beat a 9-inch. Among the biggest checks in the "plus" column is the option of having one or more alternate carrier assemblies (or third members) with different gear ratios or differentials. These can be easily swapped track-side or in your garage in just an hour or two. When it comes to building and setting up a 9-inch rear, few outfits have more experience than the pros at Currie Enterprises, and that's where we went to help us get this rear end together.
The type of driving you intend to do with your project car determines the type of carrier and what gear ratio you want. For our application, we chose a Detroit TrueTrac posi. This posi doesn't use clutches like most, but rather a set of gears that seamlessly apply the power to both wheels under load. A smooth operation was very important to us, since we will be driving the car on the autocross and the road course. The Mustang will constantly undergo load changes--so the traction needs to be predictable, and the TrueTrac provides that in spades. We chose a 3.25:1 gear ratio to give us a little more speed in each gear. If your power is in the higher-rpm range, you may want to choose a numerically higher gear, such as 3.50:1 or 3.70:1, to get you into that power sooner. Currie uses gears by Midwest Motive in all their assemblies, and they have proven strong enough for the drag racers, rock crawlers, and road racers they service. To go along with the built-tough theme, we chose a 1330 yoke over its original 1310 model.
The last decision to make is what to use for rear brakes. Many cars can get away with drum brakes in the rear; for street driving and drag racing, there isn't much need for a ton of rear brake. In fact, that's the option editor Hunkins selected for his '68 Chevelle, which sees more dragstrip use than road course abuse. Our Mustang, however, will need some major braking back there. We chose a matching set of Wilwood's 13-inch rotors to go with our fronts, and four-piston Superlight calipers. These brakes are fitted with an internal parking brake drum, so you can still park on hills without worry.
With all the parts chosen, we needed to get it all together. The guys at Currie walked us through, step by step, on how to put together a rear end that is built to last. Currie's assembly experts, Rueben and Gonsalo, have built rear ends for over 15 years collectively, and they make it look so easy. Here's what you can expect to do when you assemble your indestructible 9-inch rear.
|WHERE THE MONEY WENT |
|Wilwood rear brake kit ||$1,701.95 |
|Chassisworks Fab 9 housing ||$1,139 |
|Currie 31-spline axle package ||$459.95 |
|Currie installation kit and hardware ||$124.95 |
|Powdercoat housing ||$20.74 |
|Midwest Motive 3.25:1 gearset ||$199.95 |
|Eaton TrueTrac posi ||$609.95 |
|Currie Sportsman 9-inch case ||$239.95 |
|Currie 1330 yoke ||$106.60 |
|3 quarts (non-synthetic) gear oil ||$27.98 |
|Total ||$4,631.02 |
Once you've selected a 9-inch...
Once you've selected a 9-inch housing, the first step is to measure for axles. For a reference measurement, Currie uses the third-member bolt just above the axle centerline as a reliable index point, and takes the measured length from there to the axle flange at the end of the tube.
The Fab 9 housing from Chassisworks...
The Fab 9 housing from Chassisworks doesn't come with the third- member bolts installed, so you'll need to thread these in from the rear. Some required a little bit of grinding to clear.
Currie will build your axles...
Currie will build your axles to the length you need, but you'll have the option of either installing them yourself, or having Currie set up and build the rearend for you ($223 total; $124 to set up the third member, and $99 to install the third member and axles in the housing). If you do it yourself, the first thing you'll do is press the studs in with a press. I've used a nut to pull them in, but I don't really recommend that unless you're in a pinch. You'll want to make sure to order studs that will fit your brakes and wheels before proceeding. These -inch studs are three inches long, were included in the Currie axle package, and will work fine on the Street Fighter Mustang.
Here we are at another hydraulic...
Here we are at another hydraulic press--get the feeling that one of these is kind of important for setting up a rear? This time, the bearings need to be pressed into the carrier. After the gear is bolted on and torqued to spec, you'll need to install the bearings with a hydraulic press. This procedure is included in Currie's setup charge.
The Currie pinion support...
The Currie pinion support comes with the bearing races already installed. We pressed the inner pinion bearing on with a solid spacer rather than a crush sleeve. The outer bearing is then slid on and the pinion nut installed to check for the correct pinion gear preload. When that is satisfactory, the yoke is removed to install the seal, and then is reinstalled.
Here, Rueben, the assemblyman...
Here, Rueben, the assemblyman at Currie, adjusts the side load on the bearings. He does this step all by feel. His accuracy will be tested when backlash is measured!
To check backlash, you install...
To check backlash, you install the caps over the bearing adjusters, and get them tight. While pushing in and out on the gear, read the dial to make sure it's within spec.
Since the backlash was within...
Since the backlash was within spec (way to go, Rueben!), he torqued the caps down and installed the lock clips that fit into holes on the adjuster. Also, now the pinion bolts can be torqued.
Before dropping the third...
Before dropping the third member onto the housing, apply a steady 1/8-inch bead of silicone sealant to the housing surface around the perimeter of the bolts, and then around each bolt. Currie uses a gasket on top of that with a second bead of sealant on it. We guided the third member down with a hoist, but if you don't have a hoist, have a friend help you--these things are heavy.
The final check for proper...
The final check for proper clearances and alignment is to paint the gears with a special lapping paint. We painted a section of the teeth on the ring gear and spun the pinion gear. The best way to do this is to use an impact gun on the pinion nut. Adjustments on the outer bearings and shim under the pinion can adjust this wear pattern.
The third member may need...
The third member may need some persuasion over the studs, so use a soft-faced mallet to force it down, then torque the bolts to spec in a star pattern, the same as with the wheels.
Our next step was to install...
Our next step was to install the brakes. There are four anchor bolts on each bearing housing end; they have a long head that rests up against the axle tube to keep them from spinning. The Wilwood backing plate and bracket slip over these studs. Note the brake shoes for the internal parking brake assembly.
When the axle bearings get...
When the axle bearings get pressed on, remember to keep the axle retainer trapped between the axle face and bearings. You don't want to redo that step! Slip the axle into the housing and guide the plate onto the studs.
Here is the tricky part: You...
Here is the tricky part: You will need to get the axle retainer nuts started, and you won't have any room to fit your finger and thumb around them. Once they are on, torque them to spec through the hole in the axle's face.
The last step is to slip the...
The last step is to slip the brake rotor over the axle, then the caliper onto the rotor. The black coating on the rotors will wear off rapidly where the pads contact them. The slots, holes, and hub will remain black, giving our brakes a pretty cool appearance once they're broken in.