Dialing In Efficiency With Mark Williams’ New 4-Inch Bore Gear Case


Back in the 1960s, Mark Williams Enterprises made a name for itself as a chassis shop, building cars for a variety of racing classes and racking up national event wins in the process. As the years went on and the company expanded their operations, they began to see a need for higher quality driveline components than what were readily available to most builders.

By the mid-1970s the company had a forged steel axle of their own design in the marketplace, and by the end of the decade they’d become one of the most trusted manufacturers of motorsport-caliber drive line components, which would go on to see use in various racing disciplines.


If you’re working with serious horsepower that goes well beyond factory spec, it’s a good idea to start looking into an aftermarket gear case. In comparison to a factory piece, Mark Williams cases are built with significantly higher quality materials to help fight deflection and flex, which offers benefits ranging from less parasitic power loss to improved longevity and reliability.

These days, Mark Williams Enterprises conducts their design and manufacturing out of a 32,000 square-foot facility in Louisville, Colorado, where they have the notable distinction of being the only company in the industry who can produce both induction-hardened and thru-hardened axles in-house.

The company’s latest offering is their new 4-inch bore gear case for use with 10-inch ring gears that fit Ford 9-inch housings. This new design allows for a bearing race that is much thicker than the 3.812-inch bearing race that fits into a factory-style third member, in turn allowing for higher power applications without the need to make drastic design changes in order to get everything to work together. We got the lowdown from the folks at Mark Williams Enterprises about the features and details of this new case, along with some insight about how to choose related components with consideration toward strength, efficiency, and cost.

A Bigger Bearing For Improved Strength

As is often the case when optimizing an existing design, some of the biggest hurdles involve finding ways to make it better while simultaneously retaining the core design features so that it still plays nice with the rest of the hardware around it. “The challenge here was to fit a 4-inch bearing into a factory-style third member without redesigning the whole system,” says Andrew Dickson of Mark Williams Enterprises. “The larger bearings are needed to allow for large spline axles, but there’s little room to fit bearings that large into standard caps.”

A look at the new 4-inch angular contact adjuster bearings. While the ones pictured are steel balls, a ceramic option is also available, which offers efficiency benefits from reduced friction.

Their engineers clearly got the problem figured out though, as the bearing race of the new 4-inch case is substantially thicker than the 3.812-inch bearing race, which in turn adds a lot of strength to the bearing. “This allows for higher power applications, and a ceramic bearing upgrade option as well,” Dickson adds.

Mark Williams offers all of the related components as individual parts, or customers can opt to order them as a fully assembled third member. “Most customers order their third member assembled from the factory,” Dickson points out. “This is the best way to ensure that you have the right combination of options.”


Third members are complicated devices and the forces applied to them are tremendous, particularly in high performance applications. While Mark Williams offers their components separately, they say most of their customers wisely opt to get a fully assembled unit rather than piecemealing it together on their own. This not only ensures you get the right combination of parts, but that they’re assembled to Mark Williams’ exacting specifications, as well.

Mark Williams Third Member Options

Builders have a number of different features and options they can add to their assemblies as needed. Those options include:

  • Different carrier bearing sizes, including 4-, 3.812-, 3.250- and 3.062-inch
  • Steel caps, aluminum caps and Thu-Bolt designs
  • Aluminum spools, steel spools as well as lockers, posi’s etc.
  • Dual ball bearing pinion supports, taper/taper bearings and ball/taper
  • 9-, 9.5- and 10-inch gears
  • Pro and Street gears
  • Gear lightening
  • Nodular iron, light weight aluminum and through bolt aluminum cases
  • Large and small pinions
  • Various axle splines
  • Supra-Fin Polishing
  • Shot Peening
Selecting those components on your own can be a tricky proposition for the uninitiated, and understanding the resulting effects of different ring gear sizes can be a dark art in and of itself.

“It can be a little confusing because, while we call the gears 9-inch, 9.5-inch and 10-inch, they are all designed to fit into a 9-inch, Ford-style third member,” Dickson says. “To make things even more confusing, the 9.5- and 10-inch gears measure smaller than 9.5-inch and 10-inch. The reason is because the gears are made on 9.5- and 10-inch patterns, and then the outsides are trimmed down. This works because the area that’s cut away doesn’t contact the pinion gear, so there’s no strength loss.”

Understanding how the different forces interact with one another, and how mechanical leverage fits into the equation, is a fundamental element of the process as well. Andrew offers a mental image that provides some insight into how these parts work in unison.

“The best way to think of the larger gears is to imagine the gear as a big torque wrench. A larger gear is like having a longer wrench — it takes less pressure to generate the same amount of torque. This means that the stresses on the teeth and pressure between the two gears are smaller than they are in a smaller diameter gear. Less stress and pressure translate to longer life. Less pressure also reduces friction between the two gears.”


Significant differences separate street gears from those designed for motorsport applications. OEM gears used in street cars are made from materials like 8620 steel, which is heat treated for longevity. That’s a good approach for long-term durability, but it’s not an ideal design for racing use and high-shock loads applied on the drag strip. Pro Gears like this one use 9310 for its high fatigue strength despite its relative material softness, the latter of which allows the gear to more effectively absorb the shock when launching off the line.

But are there some situations where smaller 9-inch gears are actually more efficient than larger alternatives? Dickson explains that while it’s uncommon, it’s not unheard of. “In general, the larger gears will be both stronger and more efficient than a smaller gear. Every gear ratio has its own efficiency ratings, and there are some exceptions where a smaller diameter gear can be rated more efficient than a larger gear, but it’s only when there are different tooth counts between the two gears being compared, which is very rare.”

The question of whether or not to use the larger gear typically comes down to whether a particular build requires the additional strength provided by the larger gear, since that usually equates to added expense, as larger gears are more expensive due to the fact that they’re produced in smaller quantities.

The rearend housing itself is a prime area for reducing friction -- a slight misalignment of the pinion ring gear, spool, axle, bearing, or housing end can have detrimental effects on performance. Use of a modular alloy housing, where all tolerances are tightly maintained, assures proper component alignment and optimum efficiency.

Reducing Friction For Greater Efficiency

MW also has a new double ball pinion support available for their cases. Offered in both large and small pinion for 9-, 9.5-, or 10-inch gears, this option further improves efficiency by reducing friction. “Most pinion supports currently offered have either two tapered bearings or a ball bearing and tapered combination,” Dickson points out.

“Our new design allows us to run an angular contact ball bearing in both the front and rear of the support. The key benefit is that these ball bearings have much less friction and are in turn much more efficient than the tapered bearings.”

In the realm of gears, friction is the enemy of efficiency. Utilizing a surface treatment on the ring and pinion gears will cut down on friction and also improve the service life of the gear set. Micro-polishing techniques like Mark Williams' Supra-Fin process help to reduce friction between the gears, in turn requiring less energy to spin and creating less wear during operation.

And for those looking to take that idea a step further, they can opt to upgrade to ceramic bearings, as well, in turn reducing friction even more and bolstering efficiency that much more.

Not sure what you need? Your best bet is to jump on the phone with a Mark Williams representative so they can help you figure out exactly what you need. “It’s worth the 20 minutes on the phone to make sure that you get the right parts the first time,” Dickson wisely points out. “We have a very knowledgeable staff that will make sure that you get the right combination for your application and budget.”

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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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