For many custom builds, there are certain components that many feel need to remain true to their heritage. For instance, it’s sacrilegious to some people if you put anything other than a Ford engine in a Ford, a Chevy in a Chevy, and so on. Debates on this topic span forums the world over, often times leading to heated discussions because it’s such a sore subject for some diehards and purists.

But one major component seems to fly under the radar of that diabolical cross-breeding faux pas, and it doesn’t get near the amount of attention as the engine swaps that cross over to the dark side. For our latest build with Moser Engineering, we crossed that threshold with our Control Freak Suspensions four-link kit for a purpose-built rearend that utilized components we felt would be best for the type of driving we do. After all, our goal with Project Track Attack is to get faster at the track, one upgrade at a time.

We’ve done builds with Moser before that were direct replacements, such as our Mopar 8-3/4-inch rearend that replaced our factory original unit with no alterations necessary. This build is the polar opposite, and although our Moser M9 Fabricated rearend is going in a Mopar, the only thing that stays true to Mopar is the wheel bolt pattern.

When we decided to upgrade our suspension to a four-link setup with QA1 double-adjustable coilovers, we took it a step further than just welding on some brackets. Although it took a little bit of back-and-forth shipping to complete the build, this project highlights what Moser Engineering can do for your custom build – by putting together a custom rearend built to your specifications.

Building The Perfect Beast

The goal for this build was to allow us to keep our cruiser attitude for the several thousand miles per year that our Plymouth sees, but also to lay it all on the line when this dual-purpose musclecar transforms into Project Track Attack a few times each year.

As with any car that sees occasional track time, many components need to lean more towards the track time aspect because of the abuse the car sees there. While we didn’t have any particular issues with our Moser-built 8.75 replacement rearend, we had to start from scratch with this unit because we had a few other changes we were making to the overall stance.

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The goal for this build was to fit 18x10.5-inch Weld Racing S76 wheels and 315/30R18 Falken Azenis tires inside the rear wheelhouse. This meant we had to make some changes to the rearend housing width, also.

We went full bore with this build, having previously mini-tubbed the rear to accommodate 10.5-inch wide Weld Racing wheels and Falken Azenis 315/40R18 tires. The wheels and tires are nearly twice as wide as what originally came on the car. With the added space from mini-tubs, it gave us a little extra room for fat tires, and we needed to narrow the axle housing, too.

None of this happened all at once, as we set up a plan and laid out all of our goals for this custom build with Moser, and made sure that we checked everything twice. The great news is that however custom your project is, Moser Engineering can work with you to achieve your goals, whether it’s a stock replacement or a full custom build that throws out all the stops.

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We couldn't help but to slide the Weld Wheels and fat Falken Azenis tires up under the car on the lift to see how it would look. We liked it!

Setting Up The Build

Our first step in the process was to get on the line with Moser Engineering and lay out a plan of attack. We had to give them the details: we needed the unit two inches narrower than the stock width housing, we wanted to add some flexibility and strength with a Ford 9-inch differential, and although the typical Green bearings on our Mopar build weren’t giving us any problems, we decided that it was time to step up to a tapered wheel bearing that was better suited for road racing with the Big Ford (Set 20 Torino) bearing.

We talked with Moser’s Jeff Anderson, and decided that Moser’s fabricated M9 would be a good canvas with which to build our perfect beast of a rearend. While Moser can accommodate a stamped steel housing for that factory look, such as on our Mopar replacement, the fabricated M9 (for Ford 9-inch applications) was going to provide more strength for our open track days.

Anderson said, “Basically the triangulated and geometric shape lends itself to better vectoring of the load forces thru the housing itself as a support structure for the tubes, axles and the center section compared to an OEM, or even aftermarket, stamped housings.”

This was enough to get the process started, so they fabricated the center section, installed the tubes, and sent us the bare housing so we could tack on the suspension brackets and send the unit back to Moser for final welding. Anderson stated that a competent welder could do the finish welding, but it’s recommended to have a jig so that everything can be kept aligned properly.

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The M9 benefits from a triangulated cover design and gussets for added torsional strength.

He went on to explain that fabricated housings tend to use a bulkhead design to lock the axle tubes to the housing and the faceplate that the center section mounts to. “It is nearly impossible to have an accurate and reliably strong bulkhead in a stamped housing and this is the key to the strength in this design,” he said.

You might see the fabricated housings more in drag racing applications, because the forces that you’re fighting against are the rearward and downward flexing that happens during the launch. Anderson said, “Tying the surfaces of the housing to the tubes is really simple and one of the best things you can do for any fabricated or stamped housing.”

Our future plans call for much more power under the hood, and we have already acquired fatter tires in the rear that are going to provide much better traction, so a reinforced housing was part of our plan with this build.

Putting The Pieces Together

Installing coilover shocks and the Control Freak rear suspension kit meant getting completely rid of the leaf springs, and installing brackets and braces that are a part of the Control Freak kit. All of the necessary templates are provided in the kit, and the unique thing about this conversion to a four-link setup is that none of the components mount to the outside of the rear frame rail. That means that there is nothing to get in the way of wider tires, and it opened up an extra couple of inches, making plenty of room for our 12-inch wide Falken tires.

We started by pulling the old suspension entirely, removing the fuel tank, and putting brake lines and fuel lines aside to make room for some cutting and welding of brackets. There are a couple of brackets that need to be removed from the floor to make room for the new Panhard bar included with the kit, and a part of the rear frame rail needs to be trimmed per the template.

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The first step was to get the body-side brackets attached to the rear frame rails. Control Freak Suspensions did an incredible job on the fabrication of these brackets, and each was designed to have a positive-stop location, rather than requiring exact measurements. This forward link bracket lined up to the leaf spring hanger bracket, which didn't have to be removed.

The front link bracket is a solid, formed piece that is aligned to the frame rail and perimeter-welded in place. So it was time to break out our Millermatic 252 welder and get to work. We began by prepping the surface to remove dirt and surface rust, and using the bracket as a template and marking the mounting location.

A perimeter weld was necessary; this bracket is what the rear suspension bolts to and it needs to be a strong connection for the forward links. After that, we had to mark and cut the frame rail for the coilover shock supports, which mount directly to the underside of the frame rail. Control Freak includes the brackets and they’re even notched to help line them up to the car.

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The coilover shock supports move the shock mount from up in front of the fuel tank to the frame rails, so Control Freak Suspensions provides a solid, heavy gauge support with reinforcements that require a little cutting and perimeter welding. They even provide a solid metal template that allows you to mark your lines easily, unlike a paper template that invites potential errors.

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We broke out the Miller welder for the first time to weld the shock supports to the frame rail, not only was the finished welding solid and thorough, but the show was quite spectacular, too.

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You can see here that the control arm support lines up to existing points on the frame rail, providing a stop point for the bracket that assures proper alignment when it's welded into place. You can see the finish welding on the shock support, it's beefy, and strengthens the frame rail considerably.

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Top: The next step was to weld the rearend housing brackets into place, so lining up the housing and measuring twice was very important. We measured the distance to the leaf spring pad to the axle tube, and then measure side to side to center the housing.
Bottom: Be sure to use anti-seize compound on all rod end threads, and to lube the bushings prior to installation. Since the rearend needs to come back out and get finished at Moser Engineering, we didn't worry about setting pinion angle or alignment at this point.

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We attached the four links and tack welded the housing-side brackets, then set up the panhard bar and tacked that bracket into place. Anderson stated that we could do the finish welding before sending the housing back for completion, but they have a jig for the housing that ensures everything stays in place during the finish welding process.

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We shipped the housing back to Moser, and all the finish welding and the powdercoating was done. Sure, this bright red stands out underneath the car, and we like that. Moser also added the back brace to the housing after we attached our brackets; it was easier on us, and they were able to work around the four-link brackets.

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The next step was the assembly process, and the next non-stock component was the Ford 9-inch differential with an Eaton Detroit Truetrac limited slip.

As any Mopar owner will attest, gear choices and components are not as plentiful, and are not easy to find. We chose the Ford 9-inch because there are several gear ratios available all the way down to a 3.00:1, and rebuild parts/gaskets are plentiful and easy to find. With our past success with the Eaton Truetrac in the Plymouth, it was a no brainer to stick with what works.

There are several advantages to the Truetrac differential, and for a driver/part-time weekend warrior, it’s a great overall choice. There are no wearing parts in the Truetrac, and keeping fluid in the housing will allow the differential to do its job and should last for decades.

It’s very important to note that the Truetrac is a torsion-type differential and relies on friction to function, therefore, friction modifiers and synthetic gear lube is to be avoided. We went with Lucas gear lube, 80W/90 weight, which is fine for a driver like ours.

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Moser supplies all the necessary hardware for the differential. The studs for the 9-inch have a nylock nut on the inside, and we coated the threads with thread sealant to keep fluids inside. Thread locker isn't necessary on the stud; we threaded them in place and used a pair of nuts on the outside to hold the stud in place while we tightened the lock nut.

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If you haven't worked with these big Ford (Torino - set 20) bearings, you'll find that the bearing doesn't completely sit inside the housing, even with the flange. That is normal, and if using factory style rear brakes you'll notice that the OE-style bearing retainer does not sit flush with the housing end, so don't panic if you're in this boat, don't try pounding the axle in further.

With the suspension in place, and the rearend assembled, it was ready to go in the car and the only thing that kept us from driving the car was finishing the front suspension (a major component that needed to be completed, installing our Master Power rear disc brake kit, and acquiring a new, longer driveshaft.

We’ll follow up with the front suspension install from Control Freak Suspension, give you a quick update on how we converted our Mopar disc brake conversion to a Ford Torino-style rear brake setup using our Master Power disc brake kit, and explain our decision to reach out to QA1 for a carbon fiber driveshaft.

Take a look at how that rearend and those fat Falken Azenis tires and Weld Wheels look on this 1965 Plymouth, we definitely can’t wait to try this combination out at the track. The Control Freak rear suspension kit is a very well engineered kit that keeps everything inside the frame rails, and gives us added control over the way the car is going to handle. They have kits for Mopar A, B, and E body cars, as well as AMC and some Ford and GM products as well.

Working with Moser Engineering to put this entire package together was a breeze, and everything turned out exactly as we expected, and one call to Moser can get you on your way to a full-custom rearend, from flange to flange, and cover to yoke. Stay tuned for the rest of our suspension update, and finally our real test: out on the track.