Drift Engineering
Time at the track helps redesign a failure-prone BMW rear differential cover
REAR DIFFERENTIAL COVER | OE FIX CASE STUDY | DOWNLOAD PDF
Race on Sunday, sell on Monday.
It’s one of the oldest strategies in the auto business, usually focused on luring people to buy shiny new machinery.
But motorsport’s also a valuable tool in product development. Racing, after all, is essentially an accelerated testing program that forces design weaknesses to the surface far faster than in real-world use.
Fortunately, Dorman’s assembled a world-class team of automotive experts, some of whom have spent their lives pushing vehicles to their limits. In other words, we have a lot of people who are good at breaking their cars.
Matt Petty’s one of the best. Matt manages the Dorman Proving Grounds Garage, our dedicated facility where our teams of engineers and product designers test their innovations in real world vehicles. But when he isn’t helping developing solutions to people’s automotive repair problems, he’s creating problems for his own cars, enjoying one of the most extreme activities you can put a car through: drift racing.
In the early 2000s, Matt helped bring the movement to America, establishing it as a legitimate form of motorsport. If you’ve ever witnessed a crowd cheering uncontrollably as two cars slide their way around a track just inches from each other, fully sideways with smoke streaming off their tires in a steady cloud, you can thank Matt and his friends for that spectacle.
“Drifting is all about running the car at its limits,” he said. “Transitions happen fast and put a lot of stress on the driveline.”
The best drift cars are light, powerful and rear-wheel drive, like Nissan Z and BMW 3-series vehicles, both of which Matt owns. In fact, it was his BMW that inspired one of Dorman’s OE FIX solutions.
“I was running my 3-series at the track and the differential cover broke at the bushing mount,” he said. “I replaced it with a new factory diff cover, and a couple weeks later I broke the new part in the same place. I‘m not that hard on the car, so I knew I couldn’t be the only one having this issue.”
“Drifting is all about running the car at its limits. Transitions happen fast and put a lot of stress on the driveline.”
Matt Petty, Dorman Proving Grounds Manager
Matt shared his problem with Dorman’s ideation team who learned it wasn’t just high-performance drivers breaking their diff covers. The failure was common enough that BMW dealers kept replacement covers in stock. Further investigation showed this part was breaking at a similar rate on both stock and modified vehicles.
Fortunately, Dorman’s assembled a world-class team of automotive experts, some of whom have spent their lives pushing vehicles to their limits. In other words, we have a lot of people who are good at breaking their cars.
To get to the heart of the problem, Dorman engineers started with a new original equipment part and went to work performing a design failure mode effects analysis (DFMEA). The original part was made of magnesium, which flows into its casting dies more readily than aluminum. It’s also slightly softer, which is easier on the manufacturing tooling, but more fragile under load.
Dorman’s team redesigned the differential cover with stronger gussets and additional material for greater strength. They also switched from magnesium to die-cast aluminum. The resulting Dorman OE Fix part proved to be 30 percent stronger in lab testing.
But the true test was at the track. Matt installed the redesigned diff cover on his drift car, and put an end to the cycle of failures with the old diff cover.
Based on discoveries from researching the original problem, Dorman’s product planners chose to release the OE FIX differential cover without bushings pre-installed, as they normally would do
“We found a lot of owners that had this problem were using firmer polyurethane bushings,” says Steve Butcher, Product Manager for Dorman’s Undercar unit. “This way we keep the cost down, and let owners choose the bushings that fit their own needs, giving them the freedom to fix their cars as they choose.”
“The resulting Dorman OE Fix part proved to be 30% stronger in lab testing”
Problem:
The original equipment differential cover breaks at the bushing mounting points.
FIX:
Dorman’s redesigned differential cover uses thicker gussets and stronger aluminum material for greater strength.
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