Planting Blown-Coyote Power With A Robust Rearend

It’s been well documented that the Coyote engine really responds to forced induction. Even on low boost, just bolting a blower up to Ford’s modular 5.0-liter mill can really transform the way that DOHC V8 behaves. But as the horsepower goes up, so does the stress on all of the components that grunt gets sent to.

With an L&R short-block, a VMP Performance Gen2R supercharger, JBA long-tube headers, cat-less mid-pipes, Comp Cams Stage 2 camshafts, forged pistons and connecting rods, Boss 302 cylinder heads and a few other goodies, this 2013 Mustang GT is putting down about 800 horsepower to the wheels, a combination that puts this pony in the nines at the drag strip on competition rubber.

Ordering a custom-fabricated M9 allows Moser to tailor your rearend to your exact needs and requirements. You can narrow or widen the rear and choose from standard 3 or 3.250 DOM, seamless steel axle tubes. Moser also offers chromoly options for the tubes when needed, and you can also request larger spline counts of 31- to 40-spline for the custom Moser axles. The engineering outfit also offers options from standard differentials to upgrade units ranging from Detroit Locker Truetrac all the way up to the Wavetrac units that offer lifetime warranties even when used in a motorsports environment.

But now that it’s putting out more than twice the power that it offered in stock form and it’s getting all that grunt to the pavement through those gummy Mickey Thompson drag radials, it’s clear that the stock rear end is being asked to put up with abuse that Ford never designed it for.

In the interest of not scattering rearend components into the staging lane the next time we line up at the lights, we’re turning to Moser Engineering for a custom 9-inch rearend that’ll be future proofed to 1,000 rear-wheel horsepower. Here we’ll discuss the particulars of the new rear with the experts at Moser, and go over how to correctly spec out a custom assembly for a specific application, talk differential lubrication with the folks from Driven Racing Oils, and upgrade the rear suspension with an anti-roll bar kit from BMR Suspension.

A Robust Rearend

While increased strength might be the most obvious reason to swap out the OEM rearend for an aftermarket piece, the benefits aren’t limited to just beefed-up durability. Still, stock rearend failures are often what initially sends enthusiasts Moser’s way.

There are a few reasons for switching to a fabricated 9-inch from a factory housing. — Jeff Anderson, Moser Engineering

“There are a few reasons for switching to a fabricated 9-inch from a factory housing,” Moser Engineering’s Jeff Anderson explained. “Usually this housing swap change is needed because you are having either ring gear or axle failures. When it comes to ring gear failure this is usually related to the design differences between the two. The most commonly quoted reasons for the strength difference comes down to the size of the 9-inch gear and also the location of the pinion gear to the ring gear. With it being lower it improves tooth contact and adds strength at only a slight loss of efficiency. You also have the case size and bearing size adding to the internal support of the pinion support itself giving the 9-inch even more of a strength advantage.”

Moser's built-to-order fabricated 9-inch rearend packages include new housing, custom alloy axles (28-, 31-, 33-, or 35-spline), bearings, studs and heavy-duty retainer plates. Moser also offers a number of options for both drum and disc brake setups, and the company says that most custom orders have a two-day turnaround from start to finish.

The most important thing to consider first is your intended use for this vehicle. — Jeff Anderson, Moser Engineering

But Moser’s design approach also makes other considerations for performance and motorsport use that stock units typically don’t, resulting in not only improved efficiency and longevity, but ease of use as well.

“The Moser M9 housing itself features a geometric design to distribute load forces evenly to the face plate and the axle tubes,” Jeff added. “The M9 fabricated is not assembled from individual triangles but from a single, laser-cut piece of steel that is then shaped on a press to allow a perfect geometric alignment that could never be matched by welding individual pieces together. This allows a direct transmission of load forces through the housing to the face plate. We also add Internal bulkhead style gussets so that the tubes and housing are rock solid, as well as oversized fill and drain plugs also allow ease in maintenance for any serious racer. And when comparing equal size splines on the axles, you can actually lower the weight of the rear when going to a fabricated M9 design over the stock unit.”

Since we knew the stock brakes would be coming off, we took the opportunity to upgrade the rears with Moser’s Dynamic Rear Drag Brake Kit. The setup includes black anodized four-piston calipers made from 6061 T6 billet aluminum along with two-piece, keyed, slotted, and cross-drilled rotors, and all the ancillary pieces required to make the swap.

Of course choosing the proper specs for your application when ordering a custom rearend is particularly important if you want to get the most out of this modification, and Jeff offered some advice in that regard as well.

“The most important thing to consider first is your intended use for this vehicle,” he said. “Is it a street cruiser, a road course racer, a strip-only car, or a little of everything? You will also need to think about the differential, wheels and tires you’re going to run and also brake options. With that information you can then put together a plan for the spline count needed along with bolt pattern and stud size. You also want to consider the axle bearings you should use, along with any ABS options you may need to retain, then you look at the carrier or differential options and case type from aluminum to nodular depending on your needs, gear ratio and type of gear, and finally the yoke size.”

The Moser M9 housings are made from 1/8-inch-thick, laser-cut mild steel, which is fabricated from one triangulated piece of metal and combined with a 3/8-inch thick faceplate. The M9 comes standard with internal gussets and bulkheads. Custom-machined fill and drain bungs are also standard.

It may seem like a lot of info to put together into an effective plan, but Jeff is quick to point out that the experts at Moser — who’re racers and street-rod enthusiasts themselves – are just a phone call away if you need some assistance with zeroing in on the most ideal setup for your application.

Smart Lubrication

The Right Stuff

Using the wrong oil in your differential can lead to excess heat, which in turn can cause premature wear and a shorter service life overall, so it’s important to pair up your fancy new differential with a gear oil designed for the job.

When it comes to high-demand applications like these, the oil used can have a profound effect on performance, which is why we’re using gear oil from Driven Racing Oils for our new Moser rearend.

“Gear oils utilize a completely different chemistry than motor oil, and that is because the sliding loads in a rear gear are much higher than in any engine,” says Driven’s Lake Speed Jr. “As a result, the level and type of extreme pressure additives must be tailored to the needs of a differential. This is especially true of a hypoid-style rear gear. Because NASCAR has mandated Ford 9-inch hypoid style rear gears for decades, we have over a million race miles of experience with hypoid gears.”

He says that most applications can run a 75W-90 synthetic after the gears are broken-in, and just like your engine, you should be using a break-in gear oil to break-in any new differential or manual transmission.

“After break-in, a 75W-90 is good up to about 1,000 horsepower. A 75W-110 is good up to 1,500 horsepower and a 75W-140 is good beyond that,” he added.

With that experience under its belt, Driven has been able to hone in on the specific lubrication attributes that are best suited to the demands asked of the rearend assembly in a performance setting, especially those using the hypoid-style gears with an offset pinion gear. These arrangements allow for larger, more durable gears that run quieter.

“The key lies in balancing traction and extreme-pressure/anti-wear protection,” Lake explained. “While hypoid gears need a lot of extreme pressure and anti-wear additives, these additives can actually increase friction, which can cause a whole other set of problems, so the formulator must balance the needs to reduce friction and provide excellent wear protection. Friction and wear are not two sides of the same coin — just because you reduce wear does not mean you reduce friction and vice versa.”

Planting The Power

While we’re in the process of swapping out the stock rearend for the Moser unit we’re also upgrading the rear suspension with an Xtreme anti-roll bar kit from BMR, as the stock sway bar can no longer be used with the new rearend without additional legwork. Along with being compatible with the new differential hardware, the BMR bar (PN XSB011) features some design improvements over the stock piece that should help keep the rear suspension in check during hard launches.

“The BMR XSB011 replaces the stock sway bar with an anti-roll bar that’s better suited to this kind of performance application,” BMR’s Mustang suspension specialist Kelly Aiken said. “It also eliminates the need to purchase and install additional components like our sway bar relocation kit (PN SRK001), and the XSB011 is unique in that it is the only S97 anti-roll bar of its kind with Delrin bushings, which are much stiffer than a poly bushing and typically last a lifetime.”

Available in black hammertone or red powdercoat and manufactured from heavy-wall 1.375-inch DOM tubing, BMR's Xtreme Anti-Roll Bar kit was designed with drag racers in mind. The bushings are CNC-machined form solid Delrin, which reduces deflection versus OEM rubber bushings as well as polyurethane bushings, delivering more body roll control for better traction and more consistent launches, and the bar's hollow design adds strength without piling on a lot of extra weight.

Offering more than a 400-percent increase in stiffness compared to the OEM bar, the BMR bar also helps plant the power more effectively by eliminating the body roll that the S197 three-links suffer from.

So essentially what the BMR anti-roll bar will do is keep the suspension consistent side to side. — Kelly Aiken, BMR Suspension

“The S197 three-link has a tendency to roll more than most, as the single upper third link acts as a pivot point for body to roll over the axle,” Kelly said. “When the body rolls back towards the passenger side, this causes the force to the tires to contradict its natural tendency. The driver side wheel has the most force applied initially, which causes the car to come up on that side and rolls the weight over to the passenger side.”

This motion causes the rear passenger side suspension to compress, which actually takes force away from the tire in this scenario. On the driver side when the body rises it is planting the tire, but if it rolls too much, it will unload and shock the suspension.

If you plan on running slicks at an NHRA track, you’re going to need a driveshaft loop like this one from BMR. With ambitions to get into the eights in the quarter mile, it made sense to add one now while we were working with rearend and associated hardware.

“So essentially what the BMR anti-roll bar will do is keep the suspension consistent side to side,” Kelly added. “This ensures that the driver-side tire plants smoothly and does not over extend, and the passenger side will not squat as much, which takes away force and unplants the tire.”


With the new rearend assembled, the car up on the lift, and the rear wheels removed we got to work removing the old components. Since we opted to use Moser’s Performance Dynamic Rear Drag Brake Kit we wouldn’t need to transfer over any components from the old rearend to the new one, so all of that hardware was removed as one piece.

The removal process was made easier by virtue of the fact that we would be replacing brakes as well, so the entire assembly could be uninstalled as one piece. The new Moser rear is the first piece of the puzzle to go back in, and once it's installed we can move on to the new big brake kit.

Since the driveshaft came out for the rearend swap, we opted to fortify this as well, replacing the stock unit with a beefier piece from JE Reel, along with a driveshaft loop from BMR. First the new Moser rearend needed to be installed though, followed by the new brakes.

Providing both improved aesthetics and enhanced stopping ability, the Moser Performance Dynamic Rear Drag Brake Kit pairs up nicely with the sharp looking M9 housing.

With the brakes installed on the new rear, we hooked up the new driveshaft as well as the new driveshaft loop.

With the M9 in and the brake kit bolted up, the JE Reel driveshaft and the BMR driveshaft loop were installed next.

Next we turned our attention to the installation of the BMR anti-roll bar kit. To open up more room to work, we removed the mufflers.

The BMR anti-roll bar features three different positions so that drivers can adjust the bar to best suit their setup, and provides up to a 4,090-percent increase is sway bar rate over stock sway bar depending on year and model. Installation of the particular bar we used requires welding the end-link tabs to the axle-tube housings.

All in, this setup should not only provide much more strength and durability than the stock rearend, it should also yield improved e.t.’s by more effectively putting the power to the ground and offer more consistency in its performance overall.

Ready to step up your rearend game? Moser Engineering, BMR Suspension, and Driven Racing Oil have the stuff you need to lower those e.t.’s while ensuring that you won’t be “that guy” with the detonated differential at your next drag night. Stay tuned…

Article Sources

About the author

Bradley Iger

Lover of noisy cars, noisy music, and noisy bulldogs, Brad can often be found flogging something expensive along the twisting tarmac of the Angeles Forest.
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