Get It In Gear Part 2: Installing A Moser Muscle Pak Rearend

A few weeks ago, we reached out to Moser Engineering and spoke to them about upgrading the rear end in our turbo Silverado project. While we were looking at ordering a Moser 12-bolt Muscle Pak, after talking to Shane St Meyers, sales and tech at Moser Engineering, we quickly realized that we were going to need a beefier rear axle to take the punishment that we plan to dish out. Shane says, “For what you guys are doing with that kind of power potential in a heavy vehicle, I recommend the M9 Fabricated 9-inch.” 

With the weight of the truck and the amount of power we want to make in the future, it made sense to go with the Moser M9 Muscle Pak unit. Not only would this setup be overbuilt for our power goals, but it would also save us money and headaches in the long run.

If you’re not familiar with the Muscle Pak line from Moser, allow us to fill you in with the details.

The Muscle Pak is completely assembled when it shows up at your door, 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 8-¾-inch stamped housing, 9-inch HD Stamped housing, or the M9 (Ford Fabricated 9-inch) which we ordered.

 

All of the components that Moser uses in the Muscle Pak series are newly manufactured items that aren’t refurbished or rebuilt. These packages come standard with a made-in-the-USA housing, OEM mounting provisions, seamless steel tubing, custom alloy bolt-in 31-spline axles, bearings, wheel studs, seals, heavy-duty retainer plates, new housing ends, Trac-loc clutch-type posi, 1310-series pinion yoke, ring & pinion, Timken bearings, new drum brakes, brake lines, clamps, and an emergency brake with cables. Another great feature about the Muscle Pak line is they can be tailored to fit your needs. 

In the case of our M9 replacement axle, we had a few upgrades added to ensure the strength of the unit to make sure it would take the abuse that we will eventually dish out. Right off the bat, you will notice that the M9 is powder-coated red for a long-lasting, durable finish. Moser also added a back brace to the housing to add rigidity. Another option that’s pretty obvious is the addition of the Wilwood DynaPro Low-Profile series disc brakes. We opted for these brakes over the standard drums for several reasons. The Wilwoods are designed for street use, offer incredible stopping power, awesome looks, and, most importantly, they clear our Bogart Racing Wheels bead-locks. 

While we made a few changes that are noticeable at a glance, we also made some that are not so obvious. Weight and power tend to stress components, and we wanted to make sure everything would hold up. With Shane’s help, we were able to identify what upgrades were needed for the Silverado. 

Our first modification on our M9 order was the axle selection. Instead of the standard 31-spline units, we stepped up to the more robust 35-spline axles. We also upgraded the posi unit to a 35-spline Wavetrac, which is rated at 1,000 horsepower and carries a lifetime warranty. 

Speaking of warranties, Moser covers its 35-spline axles from breakage for up to 10 years when used for drag racing applications, too. Per Shane’s recommendation, we also beefed up the u-joint selection and opted for the stronger 1350 u-joint in place of the 1310 that comes standard with the Muscle Pak. Other changes on our M9 included narrowing the axle 1.5-inches per side, 3.50 ring & pinion gear, and we located both shock mounts to the rear of the axle for better shock placement. 

After we finalized the order, even with all of the changes, the new custom-built rear end showed up to our doorstep within a week. Talk about service! The unit was crated up in a wooden box that kept the axle safe during shipping. 

Excited to see what was on the inside of the package, we grabbed a prybar and unveiled the beastly Moser M9. The rear end is almost too nice to hide under the bed of our Silverado. However, we knew that it had to be done, and we wanted to see if the unit would bolt into the truck like the factory piece. For this process, I recruited my 19-year-old son and told him to get to work. Chase Havins has worked on some projects before, but is not an experienced mechanic. We figured this would be a good test to see how difficult it would be for the average person to install the Muscle Pak.

Armed with four jack stands, a jack, and a few hand tools, Chase went to work. The first order of business was to remove the factory rear end. Chase made quick work of this process. He started off by securing the truck on the jack stands and then removed the tires and wheels. Next, he unbolted the shocks, brake lines, e-brake cables, u-bolts, and Cal-Trac bars. At this point in the disassembly process, two people make the procedure easier and safer. I jumped in to help as he unbolted the leaf springs and lowered the rear to the ground. It took a little over an hour to get the OEM unit out of the truck and on the ground. 

When you set the two axles side-by-side, the differences are apparent. The factory rear is old, dirty, and small in comparison to the Moser M9. But a question remains: would the Moser bolt-in like the factory one?

We grabbed the M9 and placed it on carpet dolly to help us move it around easier. After we had it in position, we jacked it up and put it on the jack stands. We raised the leaf springs and bolted them to the truck’s rear hangers. As we lowered the M9 down on the leafs, the pad location was perfect and lined up just like the factory. We used the existing U-bolts and hardware to secure the rearend to the springs and the traction bars. In less than an hour, we had the shiny new axle in place. We went ahead and test-fitted the factory driveshaft, knowing that we would need a different u-joint. As we expected, the factory U-joint would not bolt into place. Summit Racing offers 1310 to 1350 conversions if you want to use the factory shaft. We have no intention of sticking with the weak OEM unit and will be upgrading ours for a stronger one. Another thing to note, if we would have put the shocks in the factory location, they would have simply bolted-in. Since we changed the mounting location on the passenger’s side by swapping it to the rear, we will need to modify the upper mount on the truck to accept the new position. But, we plan on removing the bed at a later date to make that process easier. 

After we checked the nuts and bolts, Chase decided to tackle the e-brake cables. This process took a little ingenuity and time, as well. With the Muscle-Pak assembly, Moser includes a Lokar e-brake kit to use with the Wilwood brakes. When used with a Lokar handbrake, the entire system bolts together easily. Since the Silverado was already equipped with an e-brake pedal, it only made sense for us to utilize what we had and tie back into the factory design. 

The first order of business was to remove anything that we didn’t need, and the factory e-brake bracket was in the way. With this piece removed, Chase had a straight shot to the factory cable, which unfortunately wasn’t long enough. The fix for this delima was to remove one of the cables from the old rearend and somehow attach it. Another problem was the spacing of the new cables. They needed to be moved out about an inch off the frame. Chase used a piece of angle iron cut to length and welded it to the frame, but not before drilling and tapping holes for the Lokar bracket. 

With everything in place, Chase routed and then marked the cable housing before cutting them to size. He then did the same with the cables after running them back through the housings. The pair of cables are joined through a brass piece that is provided by Lokar. This part attaches to the vehicle’s e-brake cable. Since the factory cable was not long enough, Chase drilled a hole through the pin and inserted the cable from the old axle. He cut it to length, added a collar, welded it to the end of the cable, and inserted it in the factory clamp. With a few adjustments to get the tension right, he was done with the e-brake and ready to move to the brake lines. 

Moser did a really nice job on the brake lines coming off the Wilwood brakes. However, you will not be able to use your factory brake lines. Instead, we headed to the auto parts store and purchased two 3/16-inch lines to build a set. For this process, you will need a tubing bender, tube cutter, and a double flaring tool. Since Chase didn’t have any experience in this department, I helped him out. We measured, cut, and flared each line and then attached them to the factory bulkhead using the original bracket. With the brake lines installed, we are now ready to bleed the brakes.

The installation of the Muscle-Pak rear end is straightforward and can easily be performed over a weekend’s time with hand tools. Moser has done its homework on these kits and it’s nice to know that you are getting a quality product with your hard-earned money. Ironically, the most challenging part for us was hooking up the e-brake up to the factory pedal in the Silverado, which took longer to execute than installing the M9. And while we still have a few more custom things to do before cruising around the block, we are well on the way to a bulletproof driveline thanks to the bolt-in M9 Muscle-Pak rear axle from Moser.

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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