Building a Muscle Pak Rearend With Moser Engineering
As untold numbers of hot rodders have found out the hard way over the decades, producing additional power and reliably putting it to the ground is very much a package deal. In that, we mean you can’t simply pour all your hard-earned cash into the engine and ignore what’s connected to it. Well, not unless you enjoy fixing transmissions, tossing driveshafts, and dumping rear ends on the pavement, anyway.
Because we all want to go fast (after all that’s why you’re here reading this), aftermarket rear end housing upgrades are a common item on the enthusiast checklist. But say, unlike a drag racer who will piece together his own high-end, fabricated race housing, you’re looking for the simplicity of a complete aftermarket housing that will handle the rigors of your daily driving and some light dragstrip action without breaking your piggy bank?
Moser’s Muscle Pak rear ends take the hard work out of building a housing so that you can spend more time enjoying your ride and less time under it.
Listed below are just some of the features of the six different Muscle Pak rear-ends that Moser offers. Across the board, these housings come with OEM mounting provisions, axle bearings, stock wheel studs, retainer plates, a differential set up with Timken bearings, and 11-inch drum brakes with an E-brake. Every Muscle Pak housing is sent partially assembled for shipping purposes, but is a complete housing with only minimal grunt work involved. To learn more about each housing and the myriad of vehicles for which they mount as a direct bolt-in, visit moserengineering,.com.
Based on the popular Ford 9-inch utilized by drag racers, features Moser’s new 9-inch Hot Rod housing, 31-spline bolt-in axles, axle bearings, Superlight nodular case, nodular Daytona pinion support, Track-Loc Posi, ring and pinion, 1310 series pinion yoke.
Featuring a fabricated housing like that of Moser’s higher-end drag racing rear-ends, the M9 package includes all of the same great features of the 9-Inch above, but with the strength and rigidity that a fabricated housing offers.
Moser’s 12-bolt Muscle Pak for a wide range of 1955 and later Chevrolet pickups and muscle cars sports 30-spline bolt-in axles, Moser’s new 12-bolt casting from the best nodular steel, 3-inch DOM seamless tubing, 1310 series yoke, and more.
Based on the original Dana 60 housing, the Moser 60 features 35-spline bolt-in axles, a 5 x 4-1/2 bolt pattern, 1350 series cast pinion yoke, chrome cover, and flat pinion snubber.
For A, B, and E-Body Mopars, the 8.75 Muscle Pak rear-end includes a new 8-3/4-inch stamped housing with 30-spline bolt-in axles, a nodular iron 489 case, and an Auburn Posi.
Also for the classic Mopar vehicles, the MO 875 features Moser’s new MO875 fabricated housing, 30-spline bolt-in axles, 5 x 4-1/2-inch bolt pattern, nodular iron 489 case, and an Auburn Posi.
When purchasing your Muscle Pak housing, Moser offers your choice of a range of gear ratios and several knurl, screw-in, or knurl/disc brake stud options (only two of which come at an extra cost). The optional upgrades, as previously mentioned, include such features as True-Trac Posi’s, a WAVETRAC (35-spline only), Detroit Lockers, Aluminum cases, upgraded Moser Economy or Performance Drag Brake Kits, a long list of Wilwood Dynalite and Dynapro rear brake kits, spools, and more. Many of these upgrades are dependent upon the particular housing and not available on every unit, so be sure to check out the Moser Engineering print or online catalog for a complete listing of options.
Optioning Out Your Muscle Pak
As mentioned above, each Moser Muscle Pak housing comes with its own distinct list of options catered to the specific style of housing and the application for which you plan to install it. To view the product pages for each Muscle Pak housing, simply click over to the Complete/Asssembled Housing section on the Moser Engineering website, where you’ll find the Muscle Paks, along with various other product offerings from Moser.
As our example spotlight, we’ll take a look at the 9-inch version. As you navigate to the product page, the first option you’ll come to is the shipping arrangement. Keep in mind, this is no small package being carried to the door by the UPS man; we’re talking freight here. From there, you’ll locate the year, make, and model of your vehicle, before moving on down to select your desired gear ratio and your stud type/measurements.
Then comes the fun part where you get to make your Muscle Pak your own with a number of different options. First are the Miscellaneous Upgrades, consisting of thins such as upgraded Nodular Iron Cases, Truetrac’s, Detroit Lockers, WAVETRAC’s, and spools. As we move down to the next section, we see brake upgrades, of which there are many. In essence, you have your choice between Moser’s own line of drag brake kits, and Wilwood’s Forged Dynalite, Dynapro Low-Profile, forged Dynalite Pro Series, and Dynalite Drag brake kits. There are 23 brake packages listed, and if by chance you already have a set of brakes, you can opt out on ordering them entirely.
In the section that follows, space s provided for you to enter a custom width and pinion offset if you so desire to have the housing prepared to your specifications.
Finally, we come to the Powder Coating options, where the look of the underside of your vehicle takes shape. Moser offers 12 color options on the nine-inch Muscle Pak, including such colors as Flat Black, Semi-gloss Black, Flat Red, Gloss Red, Gloss Orange, and others. Or, like the brake kits, you can opt to save and paint the housing yourself.
Assembling a Moser 60 Muscle Pak
Today, with the help of the expert staff at Moser Engineering, we’re going to walk you through the complete assembly of one of their Moser 60 Muscle Pak’s, intended for A, B, and E-Body Mopar vehicles such as the Duster, Dart, Barracuda, Demon, Belvederes, Superbirds, Road Runners, and other classic Chrysler iron.
Muscle Pak housings come standard with drum brakes and a Posi, but this particular buildup is set to utilize an optional spool and Wilwood brakes. It also features a welded and braced four-link bracket setup.
Backlash is the minute space that must exist between the contact areas of the ring gear and pinion. When the differential is spun, there’s a specific amount of space that it will turn before actually contacting the ring gear, and this is essential for a couple of reasons. Too little backlash will cause the pinion to jam into the ring gear and produce friction and heat that will lock the axles up. Too much backlash, however, will set the ring and pinion teeth too far apart and ultimately chip the edges of the teeth off under hard driving conditions.
Because the Moser 60 housing is assembled from the rear, our build process begins with the assembly of the pinion, which has the bearing pressed on and is then set down into the housing.
From there, we assemble the spool and ring gear, which are easily bolted together using an impact following the application of some Loctite. Simple to assemble, but not quite as quick and easy to set up properly.
Backlash is achieved using one or more thin shims that are placed on one end of the spool to arrive at the proper offset in relation to the pinion. This creates some headache for anyone performing the assembly, as you must install the bearings, drop the spool into the housing, measure how far off you are, pull it out and remove the bearing, add or remove shims, rinse and repeat. In this particular case, the housing had already been assembled once and the desired 0.010″ to 0.020″ backlash determined, so we missed out on the fun part. Backlash is also achieved with shims on the pinion shaft that alters its depth in the housing.
Fear not, however, as Moser utilizes “dummy” or “setup” bearings that slide on and off rather than being pressed on for determining backlash so that the bearings you receive are fresh and only press-fit once. For final bearing assembly, the bearings are heated up so they slide right on and then are pressed. In the Moser 60 and 12-bolt housings, the shims are on the outside of the bearing races, eliminating some of these steps.
With the measuring out of the way and the bearings pressed, the pinion set in place, and the spool and ring gear set in the housing. The caps that hold the spool in place are torqued, the yoke installed and torqued, and we’re ready to move on to installing the rear cover.
Moser offers both street and performance covers dependent upon the horsepower range for these Moser 60 housings; the performance cover is what you see here. These covers feature pre-load bolts that are torqued from the outside to just seven in/lbs to essentially “back up” the carrier caps as the pinion tries to force the spool and ring gear out the back under load.
This customer requested his Moser 60 have a centered Pinion rather than a standard half-inch offset, meaning the axles won’t be of the same length. The longer of the two axles goes into the passenger side of the housing and the shorter on the drivers side.
Before sliding the axles into the housing, we must install the Wilwood brake caliper brackets to the axle. These slide over the bearings and install quickly and easily. From here, the axle seals are tapped into place, followed by the axles with the e-brake assembly installed. Once the axles are in, the axle and brake assembly is bolted up to the housing flange. Finally, the brake rotors and brake calipers are installed and the brake and e-brake lines connected to bring our assembly to a close.
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