7 Reasons Why A Moser Muscle Pak Is The Perfect Rearend Upgrade

Horsepower numbers found in cars and trucks today have skyrocketed as technology has provided incredible efficiency and performance for our engines. Who would have thought cars today would eclipse 1,000 horsepower and still be very drivable on the street? It wasn’t the engineers who designed your classic muscle car or late-model ride with a 10-bolt or even a 12-bolt differential when they were new. If they had, you can bet they would have put a lot more thought into the rearend trying to get all that performance to the ground. Thankfully, there is the Moser Muscle Pak to make up for all those engineers’ short-sightedness.

The knowledgeable staff at Moser Engineering have many years of experience building durable differentials and rearend assemblies, and they’ve combined all they have learned into a convenient, comprehensive, and stout offering they call the Muscle Pak. One of the benefits of the Moser Muscle Pak assembly is it gives the enthusiast a variety of options to build just the right rear for their application.

Moser Muscle Pak

The beauty of Moser’s Muscle Pak is that it is a complete swap. Everything including the brakes, lines, and E-brake cables is included in the kit. You can also choose a variety of upgrades when ordering.

When ordering a Muscle Pak on Moser’s website, customers can see and specify each option via drop-down menus. If you prefer to speak to someone, a quick call to one of Moser’s sales staff will get you everything you need. As a bonus of working on the website, the price of each rearend updates with every choice, showing a running total at the bottom of the page.

All Muscle Pak rearends are assembled to order from brand-new parts and castings. You’ll be able to choose the specific housing, gear ratio, axle, differential, and brake upgrades, as well as the color (or lack) of the housing. The entire assembly is built-to-order and nothing is reconditioned or remanufactured. As if that wasn’t enough, one of the greatest benefits of ordering a Moser Muscle Pak is they are designed as a complete, ready-to-bolt-in assembly.

The Muscle Pak rearend assembly from Moser Engineering has much more to offer the automotive enthusiast than the OEM’s engineers could have ever envisioned. Here are seven benefits of every Moser Muscle Pak assembly and why one of these stout performers is the perfect replacement for that aging, outdated rearend in your ride.

12 bolt, Dana 60, and Fab9 rear end

Moser offers several beefy housings to handle just about any level of horsepower your car’s engine can produce.

#7You Have Options!

We all enjoy options, and when ordering a Moser Muscle Pak, you have a variety of housing designs to choose from to suit your application. Moser offers Muscle Pak assemblies in various configurations including a Chevrolet 12-bolt, Dana 60 (Moser M60), a Ford-style 9-Inch or M9 Fabricated (9-inch), an 8.8 (Moser M88), a Mopar 8 3/4-inch, and a Fabricated 8 3/4-inch housing.

Moser only uses U.S.-made steel, forged in U.S. plants, using Moser-designed dies and tooling. – Jeff Anderson, Moser Engineering

Every Moser Muscle Pak cast housing is newly manufactured using Moser-owned casting boxes. Each Muscle Pak includes seamless, 3-inch O.D steel tubing and is manufactured with the necessary OEM-located mounting provisions for easy installation into the vehicle it is designed for. No matter who originally manufactured your muscle car or truck, or how much horsepower you intend on making, there’s a Moser Muscle Pak option to get all that power to the pavement.

Assembling a GM 12 bolt

Moser builds each rear to order, so you can choose from a variety of options including the gear ratio, axle spline count, and even alter the width of the housing if you wish.

# 6 – You Can Pick Your Numbers!

Enthusiasts have been using calculators and math for decades as a proven way to go faster. Thankfully, the mathletes at Moser Engineering have done most of the heavy lifting so far as number-crunching is concerned, but you will need to tell them a few digits to get your rearend spec’d out properly. During the ordering process, you’ll have the option to choose your gearing (ranging from 3.00:1 to 4.86:1), the necessary bolt pattern and stud size, as well as the number of splines for the axles. Then, the Moser team will set to work, quickly assembling your new rearend to your specifications.

Wavetrac differential

Moser offers several differential options in the Muscle Pak, including this Wavetrac unit, as well as a Truetrac, and Detroit Locker unit. Moser offers a 31-, 33-, or 35-spline axle for specific differentials, or you could opt for a 40-spline spool.

# 5Beefing Up The Center Section

When choosing the internals for your center section, there are many options to increase the capacity of your Muscle Pak. Additional bracing can be ordered on most Muscle Pak assemblies to increase rigidity and a variety of differentials are offered, including Auburn, Truetrac, Yukon, Wavetrac, and even a spool if necessary.

When filling the center section of your rearend, you can choose to strengthen the differential with upgraded housings, a variety of posi units, and axles specific to your application, as well as opt for bolt-in axles to get rid of the C-clips that retain each axle.

As a safety bonus, Moser Muscle Pak assemblies can utilize bolt-in axles to eliminate the “C-clip” style axle retainers. Axles can be upgraded to 35-spines and gun-drilled for certain applications, as well as Moser’s PRO-flange and lightening holes for drag race-only applications.

A Moser axle achieves added strength thanks to an in-house induction heat treatment that improves the metal’s torsional strength. As part of the final inspection, Moser uses a Magnaflux process to ensure the structural integrity of the necessary parts.

The base Muscle Pak comes with drum brakes but you can upgrade to Wilwood disc brakes ranging from the "Economy" set to full-on drag race units to suit your application.

#4Brake Upgrades

All Muscle Pak assemblies come standard with drum brakes. From there, customers can choose from numerous offerings to upgrade to disc brakes. Moser offers Wilwood disc brakes as an upgrade to each Muscle Pak. There is also an “Economy” disc brake kit which consists of a single-piston caliper and an 11-inch rotor. From there, several other disc brake upgrades are available to suit the application. Each brake upgrade, and its cost, are listed as you fill out the order form.

Whether using the OEM mounting surfaces or upgrading to a full-on pro-touring chassis, Moser can custom-build your Muscle Pak to be a bolt-in application.

#3Suspension Upgrades

The beauty of the Muscle Pak rearend assembly is that it is a bolt-in application with all the necessary mounting points for your particular application. But that doesn’t mean you’re limited to factory-designed applications. When filling out the order form, you can custom-tailor your rearend’s build by choosing any suspension upgrades desired, such as additional sway bar mounts, adjustable control arm mounts (where applicable), and even mounts for highly-adjustable coilover shocks. Moser even offers single- and double-adjustable coil-over shocks with the kit, making this a single-source upgrade!

Muscle Pak in Moser Red

Adding color to your Muscle Pak is another option when ordering. You can choose from a variety of colors and the powder-coating will not only make your rear look great, but its durable finish will protect it from the elements.


All Muscle Pak rearends are shipped as a bare finish, but Moser gives you the option to add some color before the assembly gets assembled. Moser can powder-coat the housing in a variety of flat, semi-gloss, or glossy colors, including black, red, silver, Chevy orange, and even a silver-sparkle finish if you desire.

Moser Muscle Pak crate

When you receive your Moser Muscle Pak, everything will be included in the crate.

#1Everything Comes Shipped To Your Door!

For many enthusiasts, this is the number one reason a Moser Muscle Pak is the perfect replacement for their aging rearend. Everything is shipped to your door in a sturdy crate. Everything you need to complete the upgrade is included in the kit, and the entire rearend can be swapped out in a weekend. The Moser Muscle Pak comes standard with a made-in-the-USA housing featuring OEM (or specified) mounting provisions, new drum brakes, brake lines, clamps, and an emergency brake with cables.

Over the years, our cars have likely gained much more horsepower than their designers had ever imagined, putting more strain on the OEM differential in the process. Combine that with the numerous miles they’ve endured over the past several decades and it becomes obvious they could use a rebuild. When it comes time to wash away all that wear and tear, a bolt-in replacement such as the Moser Muscle Pak brings many upgrades and benefits and makes perfect sense.

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About the author

Andy Bolig

Andy has been intrigued by mechanical things all of his life and enjoys tinkering with cars of all makes and ages. Finding value in style points, he can appreciate cars of all power and performance levels. Andy is an avid railfan and gets his “high” by flying radio-controlled model airplanes when time permits. He keeps his feet firmly grounded by working on his two street rods and his supercharged C4 Corvette. Whether planes, trains, motorcycles, or automobiles, Andy has immersed himself in a world driven by internal combustion.
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