A Chevy 12-Bolt Moser Upgrade You Can Do In Your Driveway

If you’ve been following along with my C10 Cheyenne upgrades, then you know I’m in the process of building a cool street truck that can hold its own at any cruise night, and be a reliable daily driver. In my opinion, I have the appearance upgrades handled and now it’s time to focus on some performance enhancements. This month, my update is accomplished with the help of Moser Engineering.

From the factory, the Cheyenne was equipped with an anemic 350ci engine, Turbo 350 transmission, and a 12-bolt rearend with 2.76 gears. While the combination does offer great drivability on the highway, there isn’t much fun to be had when traveling from red light to red light. Knowing the immediate effect a gear swap can offer, I decided to start by doing something with the rearend of the truck as the first step to my performance goal. Sure, a gear swap can definitely deliver huge grins while driving around town, but go too steep with gear selection (numerically high), and highway cruising will needlessly suffer. I need the Cheyenne to have the best of both worlds, so moderation is the order of the day.

All Moser rearends are assembled using brand-new components. There's no worry about anything being remanufactured, refurbished, or rebuilt. The Muscle Pak rears come completely pre-assembled and ready to install under your car or truck.

Just A Little Steeper

To that end, I gave serious thought to a set of 3.73 gears for the upgrade. While some might question the choice as being a little “steep,” I feel the choice will make a nice compromise for fun around town. But, I know what you’re thinking — those gears might not be the best choice for highway driving with the Turbo 350. You are correct. But, those gears will be a great match-up with the planned overdrive transmission upgrade when it is completed.

Our 12-bolt housings are completely new and manufactured from Moser-owned casting boxes – Jeff Anderson, Moser Engineering

Having a complete plan outlined before any parts are ordered is a great idea. At first, I thought about rebuilding the factory rearend. But, when I priced the new differential (gotta have a posi), bearings, gears, seals, gaskets, and axles, I learned a complete Moser Muscle Pak rearend was definitely a viable option.

That being said, if I were to rebuild the factory rear, I “could” reuse the housing, axles, and drum brakes. But, I plan to add disc brakes to the truck eventually, so in actuality, the housing and the axles would be the only thing I would keep. There is a peace of mind in knowing the Moser unit is all new.

The C-Clip Eliminator kit gets rid of the C-clips in your GM 10- and 12-bolt rearend. When using a C-clip, if the axle breaks, the wheel and axle can come out from under the car. With the C-clip eliminator, the wheel and tire cannot escape from under the car. They make any 10- and 12-bolt rear much safer. You can use C-clip eliminators with drum brakes or nearly any factory or aftermarket disc-brake setup.

The Moser built-to-order 12-bolt Muscle Pak is a complete unit ready to slide under almost any vehicle, and getting a new casting seems like a no-brainer. “Our 12-bolt housings are completely new and manufactured from Moser-owned casting boxes,” says Jeff Anderson, Moser’s marketing director. “Moser only uses U.S.-made steel, forged in U.S. plants, using Moser-designed dies and tooling. You feel the sense of devotion to the U.S. and patriotic pride when you talk to the people at Moser.” In fact, the company’s founder, Greg Moser, used a team of engineers to develop the proprietary material that the company still uses today.

12-bolt

Open the crate and you find a complete 12-bolt. All Moser 12-bolt housings are designed and manufactured in the USA. The package includes the housing with OE-located mounting provisions, seamless steel tubing (3-inch O.D., 1/4-inch-thick wall), custom-alloy 30-spline bolt-in axles, differential, new brakes, brake lines, brake line clamps, and emergency brake cables. Find the options you want and the vehicle you have on the Moser Engineering website and make your choices.

A Complete Package

When you are ready to order a Muscle Pak rear, you’ll find Moser offers a wide range of gear ratios, axles, differentials, and even several wheel-stud options. Also, although I chose to include an Eaton posi in my build, other options include; Detroit Locker TrueTrac, WAVETRAC (35-spline only), Auburn differential, or a spool.

The Moser Muscle Pak is a direct replacement. However, since I chose to upgrade to rear disc brakes, modifications needed to be made. For starters, the hard lines between the calipers and the factory rubber line needed to be made.

Brakes are another consideration I needed to… well… consider. While the factory drum brakes did technically work, adding a set of rear discs was something I planned to do in the future anyway, so why not order them now. Disc-brake options come in the form of economy units, Wilwood binders, or Moser-spec drag-race parts. If you wish to stick with drum brakes, that is also an option. You can even opt-out of ordering brakes entirely. In my case, this isn’t a race truck, so the economy binders were chosen.

The economy disc brake kit is in fact, designed around ’79 through ‘84 Cadillac Eldorado calipers. These calipers incorporate an emergency brake, which is a must-have in my opinion. The E-brake on these calipers does require the brakes to be bled in a certain sequence, or you will never get the air out of the system.

In short, the E-brake must be adjusted before any fluid is introduced into the caliper. If they are adjusted with fluid in them, it forces an air pocket into the piston of the caliper. This is because the piston is further back in the housing than the bleeder. All I can say is follow the instructions. If you decide to forego the reading part, there is a process involved to remedy the spongy pedal feel you will get for doing things incorrectly. It’s also a lot messier to fix once brake fluid has been introduced.

12-bolt upgrade

The economy disc brakes are designed around ’79 through ‘84 Cadillac Eldorado calipers, which incorporate an emergency brake. There is no reason not to have an E-brake.

It seems axles are usually the first thing in a rearend that seems to break. Muscle Pak axles come in a variety of spline counts, and the choice is yours. You can also utilize the OE-style C-clip retaining method or the recommended “bolt-in” retainer that eliminates the axle C-clip. Moser’s technical crew recommend the bolt-in axles, because of the additional safety factor the parts deliver. (i.e. if you break an axle, you won’t lose your wheel.)

12-bolt upgrade

The E-brake cables can run to each cable bracket on each side of the truck. Simply cut the cable and cable housing to length and attach to the factory frame brackets.

“Our development team has tested the bolt-in axle retainer with most types of brakes and brake backing plates to ensure there are no fitment issues. A T-bolt kit for axle mounting comes with the built-to-order package,” Jeff affirms.

When it comes to connecting the rear to your driveshaft, fitment options continue to abound. There are multiple pinion-yokes available. Most GM cars and trucks use a 1310-series yoke. But, if you want to add a little strength — and I did — a 1350-series is available. If you want a really trick piece, Moser even offers a 1350-series yoke in billet aluminum.

 

I don't know about you guys, but I don't have a way to install the swage ends required for the E-brake cables. The top image shows the E-brake connection kit that came with the rearend. I modified the cable kit and made it work. I made the new cables a little long and modified the supplied cable-clamping piece to create two individual pieces. When I find a local shop that can install the swage ends, I'll have it done.

For a standard upgrade on a vehicle that isn’t destined for track use and launching on slicks with huge horsepower, the 1310 yoke is sufficient and should fit the OE driveshaft without a problem. “If you’re throwing a lot of horsepower at the rearend and have tires with serious grip, you might want to consider the 1350-series yoke,” Jeff states.

Finally, you have even more options when choosing the rearend finish. The standard option delivers an unpainted rearend for those wanting to save a few pennies and paint the housing themselves. But, several powdercoating colors are available as well. The Moser Muscle Pak I spec’d for my truck was ordered in a matte-black finish. In actuality, I like the look of the matte housing with the silver-hued bolts showing.

Although I happened to be doing the install in a C10 pickup, the premise will be the same whether you’re working on a Chevelle, Nova, Camaro, or Impala. You can easily do this in your driveway over the course of a relaxing Saturday.

Out With The Old…

As you can imagine, swapping the rear is a really straightforward process. In an afternoon, the Cheyenne received a bullet-proof Moser rearend that I couldn’t wait to test out, and test I did. I don’t have to tell you that swapping from a 2.76 to a 3.73 rearend gear definitely makes the truck a blast to drive around town. In fact, I might even get myself into some trouble. Although engine RPM is understandably higher than before (2,800 rpm at 60 mph), tire smoke now comes much easier when leaving from a dead stop. AS expected, the transmission also shifts through the gears much sooner than before. But, that’s to be expected, as the engine RPM climb much quicker than before.

But, the real benefit of the gear swap will be realized when the TCI-built 700R4 is finally stabbed into place. That’s when I will be able to fully enjoy the benefits of both the steeper gears when leaving from a dead stop and the pleasure of being able to cruise the highway with the help of the overdrive transmission. There is no doubt in my mind the truck will be a blast, I guarantee it.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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