El Diablo Squarebody Gets A New MusclePak Rearend From Moser

El Diablo Squarebody Gets A New MusclePak Rearend From Moser

Welcome to the latest chapter of our mischievous 1984 Chevy Squarebody project, appropriately christened El Diablo. We’ve created several other articles chronicling the build as it transforms from an underpowered grocery store schooner to a beefed-up muscle truck. Now that we’ve updated the suspension with Aldan American coil overs and Performance Online tubular suspension components, completed the $100 junkyard LS swap, and installed Dakota Digital Gauges, it’s time to tackle the rearend.

The shortcomings of the factory differential were exposed after we installed our mighty, high-revving GM LS V8. While testing the Edelbrock Pro Flo 4 fuel system, it became apparent during freeway cruising, the economy rear gears were not suited for high-speed driving or even the random stoplight-to-stoplight Grand Prix.

To remedy the situation, we called up our friends at Moser Engineering and ordered a MusclePak GM 12 Bolt with an Eaton TrueTrac differential with 35-spline axles, and 3.55 gears. While we were at it, we upgraded to Wilwood BlackOut brakes to match the Performance Online brake master cylinder we ordered. We tackled the installation of the rearend at Performance Online in Corona, California while they were performing a whole host of additional upgrades that we’ll cover in a future article.

To get a better idea of all the benefits of our new rearend, we talked with the folks over at Moser and they gave us the 4-1-1 on their MusclePak complete rearend package.  “We all know how a build can come screeching to a halt when you’re trying to combine parts from multiple vendors. A missed shipment can be a real pain, so we created MusclePak, a complete rearend system built by us under one roof,” says Jeff Anderson, Marketing Director of Moser Engineering.

“The Muscle Pak is completely assembled and is available in several different combinations. You can select from a Chevrolet-style 12-bolt, M88 (Ford 8.8), Moser 60 (Dana 60), M0875 (Mopar Fabricated 8-3/4), Mopar 8-3/4-inch stamped housing, 9-inch HD Stamped housing and the M9 (Ford fabricated 9-inch.) Or, customize a build to your specifications.”

“From there, build your setup almost any way you want from the ground up. Whether bare bones, ready to race, or somewhere in between, all are easily achieved. Choose your finishes, gearing, splines, and brakes. After you create the rearend of your dreams, our techs get to work assembling your tailor-made MusclePak hardware and ship it out to you in three to five business days.”

Moser Engineering has been leading the competition since 1986 and continues to provide segment-busting products. They pride themselves on their ability to supply quality America-made products, at an affordable price with unmatched turnaround times.

With those formalities out of the way, follow along as we take you through installing our MusclePak rearend from start to finish.  The installation was a breeze because our rearend came to us as a finished assembly. We just had to remove our ancient OEM hardware, position the new system, and bolt it in. It may sound too good to be true, but the MusclePak was just that easy to install.

Our MusclePak 12-Bolt arrived in a crate fully assembled and ready to bolt into El Diablo. When Moser says it is a complete system, they mean it!

We promptly loaded the trick new rearend in the bed of El Diablo to take to our friends at Performance Online for installation.

As soon as we got to Performance Online we put El Diablo on the lift to see what we were working with. The factory rearend was tired to say the least. The leaf springs were clapped out, and the differential had certainly seen better days. The nicest parts on it were the Aldan double-adjustable shocks we recently installed.

Randy, our host and POL’s shop manager, made quick work of removing the factory rearend.

The leaf springs that El Diablo was sporting were well beyond their expiration date, resulting in an uneven ride height. We elected to replace them with new leaf springs, pictured here (P/N: 731014,) and new hangars and shackles. With new stout components, it was now going to be easy to get our ride height straightened out.

With the MusclePak on the rearend jack, there really wasn’t any prep work to be completed. It arrives ready to install.

Randy stands back to admire the quality craftsmanship of the MusclePak before bolting it to the leaf springs and driveshaft.

With some new U-bolts and a few swings of the socket wrench, El Diablo’s fresh rearend was in its new forever home.

With the MusclePak supported by the leaf springs, we bolted the Aldan American shocks back in place.

Nearing the end of the install, Randy bolted the driveshaft to the pinion yoke and filled the rearend with Lucas Oil Gear Oil.

Fortunately, the MusclePak came with stainless braided brake lines already plumbed and connected to the caliper, so all Randy had to do was bend some steel line and connect it to the factory line that was affixed to the top of the original rearend.

Driving Impressions

The change in driving characteristics was immediately apparent on our first test drive. We’re not sure what the factory granny gears were in the original rearend, but the 3.55:1 gears certainly woke this little red devil up.

We especially liked the quality and the “no hassle” aspect that Moser brought to our project. Although not a project for a newbie, the simplicity of the MusclePak sub-assembly was amazing and made the installation hiccup-free.

Our 1984 C10 Chevy Truck is a testament to the resilience of GM’s 1973-1987 Squarebody trucks. It’s amazing how easily they take to modern components. Moser’s MusclePak looks like it was born with the truck, albeit with way better components than anything GM offered in the ’80s. In the meantime, we’ll be putting miles on El Diablo and enjoying the ride. Stay tuned to Street Muscle for more updates to our 1984 Chevy Squarebody, El Diablo.

What we’ve sacrificed in fuel economy, we’ve more than made up for in terms of fun and speed. This is hot-rodding, after all. We can’t wait to get this thing out in the twisties. The other additions we made at POL will certainly aid with that as well. More on that in the next installment of El Diablo’s transformation.

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About the author

Dave Cruikshank

Dave Cruikshank is a lifelong car enthusiast and an Editor at Power Automedia. A zealous car geek since birth, he digs lead sleds, curvy fiberglass, kustoms and street rods. He currently owns a '95 Corvette, '76 Cadillac Seville, '99 LS1 Trans Am and big old Ford Van.
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