August 16, 2019

The Curious Case of the Missing 6R140 Forged Billet Cover

Torque converter rebuilders are frequently reporting that their customers are asking for a “heavy-duty” Ford 6R140 torque converter with a forged billet cover. While the 6R140 comes in both gasoline and diesel powered variants, it’s usually the hard-working diesel Super Duty trucks that have been modified for increased power output that find their way into a local transmission shop for diagnosis and repair. It’s those transmission shops (and the enthusiast owners of these trucks) that want — and are willing to pay for — a heavy-duty converter.

Important Note

There are options out there where some companies have gone to the effort and expense of making a forged cover and have it be integral with the design. The point being made here is that:

  • It’s really expensive to do that.

  • It’s overkill unless you are dealing with extreme power applications.

In the vast majority of the applications showing up in shops today, the Sonnax Smart-Tech® converter clutch kit FD-CP-20K is a great alternative that upgrades the converter clutch without the expense of a forged cover. Yet you end up with a converter that’s heavy duty where it counts. It’s FORGED ON THE INSIDE.

As the premier full line supplier of torque converter components to the aftermarket, converter builders look to Sonnax for a wide variety of products — including a large selection of forged billet front covers. For those of you who have dealt with the 6R140 transmission and/or converter, you know the “supersized” nature of the unit. It’s large! But Sonnax does NOT offer a forged cover for the 6R140. Really? The converter alone, completely dry, weighs in at somewhere around 70 pounds. Transmission shops and diesel enthusiasts are all surely saying, “Boy, if there ever was a converter that needed a billet cover, this has to be it!”So if the demand is there, why doesn’t Sonnax offer a forged billet cover for the Ford 6R140? As noted, Sonnax offers forged billet covers for a wide variety of units: Ford E4OD/4R100, 5R110, Chrysler 47/48RE, 68RFE, GM 4L60, 4L80, 6L80, Allison and more. If Sonnax can make forged billet covers for those applications, then why not the 6R140? Well, that seems like a case for the Torque Converter Detective.

In all of the lock-up applications where Sonnax currently offers a forged billet cover, all of the associated converter clutches move toward the engine block and ride up against the inside surface of the cover (Figure 1).

Figure 1 – 6L90 Converter
6L90 ConverterIn a typical lock-up converter, all of the associated converter clutches move toward the engine block and ride up against the inside surface of the cover.

Sonnax forged covers typically offer a much more rigid, flat and durable surface for the friction material to ride against – that’s the main reason you need a forged cover to begin with! By eliminating the thin, flexible, stamped OE cover, you are adding real-world clutch capacity and durability to the unit. But in the 6R140 converter, the clutch DOES NOT engage the front cover. When a 6R140 converter clutch applies, it does the opposite and moves away (Figure 2) from the engine block and engages a stamped steel backing plate that is not a part of the front cover assembly. The captive clutch surface never touches the front cover!

Figure 2 – 6R140 Converter
6R140 ConverterWhen a 6R140 converter clutch applies, it moves away from the engine block and engages a stamped steel backing plate that is not a part of the front cover assembly.

So, unless you would go to the considerable effort and expense to reroute hydraulic circuitry in the 6R140 to change the way the TCC functions, an expensive billet cover would get you no benefit. While it might look nice to the inquiring transmission shop or truck owner, a billet cover on a 6R140 converter would be like a shiny new hubcap on a crappy old wheel. It might look nice, but it would have no functional value. And, unlike a hubcap, you don’t even see a forged billet torque converter cover once it’s installed in the vehicle.

So, the next question for the Torque Converter Detective: If a forged billet cover is of no value in this application, how can the 6R140 converter be effectively and intelligently upgraded? The answer: the Sonnax Smart-Tech® converter clutch kit FD-CP-20K.

When converter rebuilders use the Sonnax Smart-Tech® converter clutch kit to rebuild a 6R140 torque converter, you end up with a converter that, from the outside, looks the same as a stock OE unit. However, while the converter doesn’t have the outward appearance of a heavy-duty forged unit, it does contain significant upgrades.

By using the FD-CP-20K, you get a converter that:

  • ... is FORGED ON THE INSIDE! The stamped OE backing plate is discarded and replaced with a forged billet backing plate (Figure 3). This forged piece provides the same rigidity and flatness that promotes the same converter performance and durability that you get with all of the other forged billet covers that Sonnax offers.
Figure 3
Removing the 6R40 Stamped OE Backing Plate
  • … is set up with a precise amount of clutch release clearance. When welding in the forged reaction plate, torque converter builders can easily and exactly set clutch release clearance – no guess work (Figure 4)!
Figure 4
Machine at the Stop on The Sonnax Forged Backing Plate
  • … eliminates the problematic riveted OE leaf springs that fracture and cause lock-up codes and failures. Sonnax replaces the leaf springs with coil springs, which serve to eliminate clutch drag and guarantee a consistent clutch release when commanded (Figures 5A & 5B).
Figure 5A – OE Leaf SpringsFigure 5B – FD-CP-20K Coil Springs
6R140 OE Leaf SpringSonnax FD-CP-20K Coil Springs
  • … utilizes forged clutch drive lugs – not the soft stamped OE clutch lugs (Figure 6).
Figure 6
Sonnax FD-CP-20K Drive Lugs
  • … boasts a new BorgWarner dual-sided, segmented OE clutch plate – the most recent updated design with hardened drive lugs.
  • … eliminates all the weak points of the OE design, without the added expense and complexity of an unnecessary forged front cover.
  • … is upgraded with premium-quality Sonnax engineered components. It’s FORGED ON THE INSIDE.

Whenever there is an exception to a general rule, it can be difficult to educate people on the unique circumstances that cause the exception. The transmission aftermarket has long identified “heavy-duty” remanufactured converters by the presence of a forged billet cover.

In the Curious Case of the Missing Billet Cover, the Torque Converter Detective believes it is worth the time and effort to educate your customer as to how this converter works, and why a forged billet cover would not indicate any upgrade at all. Remember, based on the hydraulics of this particular unit, a forged billet cover is just overkill. On your next 6R140, ask your converter builder if their converter is FORGED ON THE INSIDE. If not, tell them about the Sonnax Smart-Tech® converter clutch kit FD-CP-20K. It can save everyone some hard-earned cash and keep a hard-working late model gas or diesel Super Duty on the road.

Thanks for your feedback!

Related Units


Related Parts

While Sonnax makes every effort to ensure the accuracy of technical articles at time of publication, we assume no liability for inaccuracies or for information which may become outdated or obsolete over time.