An Engineer Discusses GM's Valve Body Issues: Is a New Repair Sufficient for HD Owners?

      GM-DESIGN

      The most significant automotive news and reviews, without the nonsense

      Our complimentary daily newsletter brings you the most important stories each weekday.

      If you’re among the numerous customers awaiting a replacement valve body for the 10-speed Allison transmission in your GM heavy-duty truck, there may finally be some positive developments. The company announced in August that it has new replacement parts and a revised repair procedure for its HD lineup, which should help alleviate the backlog of owners seeking transmission repairs.

      The downside? It might only be a temporary solution.

      To provide some context, GM’s version of the 10-speed transmission, co-developed with Ford Motor Company, is utilized in nearly all rear-wheel-drive models sold by GM, ranging from the Allison variant in heavy-duty trucks to the lighter version in the Cadillac CT4 and CT5 sedans. That amounts to a significant number of gearboxes. Over the past two years, GM has recalled virtually all of them (at least through ’22) due to valve body problems that caused some customers' rear axles to lock while the vehicles were in motion.

      However, the recall was not the end of the issue. When GM initiated the campaign, it had not fully identified or resolved the underlying mechanical problem. The “remedy” associated with the recall was essentially a stopgap that puts the truck into limp mode when a failure occurs, preventing the lock-up but still leaving customers with a compromised vehicle.

      In early August, GM finally made progress by releasing a revised valve body and updated repair procedure for its gas-powered pickups, introducing new replacement parts into the pipeline and simplifying matters for those customers encountering the issue for the first time.

      Around the same time GM was rolling out the third-generation valve body redesign, a customer waiting for a new valve body for his 2023 Chevrolet Silverado 3500 HD informed us of another affected group: heavy-duty truck owners. Upon reviewing GM’s updated procedure, it became clear that it excludes every diesel-engine truck, both light- and heavy-duty. The common factor? Torque, and a substantial amount of it.

      These heavier-duty transmissions use a different valve body, and at the time, GM had not made one available. The tipster was Robert Shafto, and just a week after his alert, GM issued an updated service bulletin, which was forwarded to us by another reader.

      Whether this repair truly resolves the problem or not, its mere existence is encouraging, as GM refrained from distributing the new procedure to its dealerships until it had the necessary parts available. As we learned last month, the actual failure is seldom the primary concern for GM owners; rather, the lengthy waits for replacement parts are the biggest headache. Shafto went without his truck for two months, and based on emails we received after our initial report, he was not alone nor was he the most extreme case.

      “Availability of replacement parts for the ten-speed transmission valve body for both light- and heavy-duty diesel engine pickups is improving,” stated Bill Grotz, Global Public Policy and Regulatory Communications Senior Manager at General Motors. “Additionally, we expect a recently launched valve body service repair process for the 2021-2024 Silverado and Sierra 2500/3500 HDs will aid customers and enhance valve body availability.”

      “We apologize for any delays experienced by our customers and are actively working to deliver parts and facilitate necessary repairs as soon as possible,” Grotz added.

      That same week, Shafto received his truck back. It remains unclear whether it was repaired according to the most recent service guidance—Shafto has been in discussions with GM’s customer care agents to clarify this—but he is, once again, in possession of his truck.

      Regarding the fix itself? Not everyone is convinced it will solve the issue permanently. Shortly after our article ran, several sources reached out, suggesting that I consult Nate Valentin from NextGen Drivetrain for his perspective on the situation.

      NextGen specializes in enhancing factory drivetrains for high-power users. Valentin is an independent transmission engineer and the chief designer of everything that NextGen manufactures. His transmissions come with a lifetime warranty without any questions, and understandably, NextGen’s upgrades come at a premium.

      In his own words, “Whatever they cost, they ****ing cost.”

      Chevrolet

      “We have around 150 different inventions; all of them were designed by me,” Valentin shared. “Approximately a quarter of these are specifically for General Motors and the Ford/GM 10-speed,” he said. “I understand more about this valve body than anyone at General Motors or Ford,” he asserted with total conviction.

      “I have redesigned every iteration of this valve body. The non-shift by wire models, all of them, the diesel, the gas; I have reengineered all of them personally. Our version is currently the most sought-after upgrade kit on the market for all of them,” he stated. “I don’t mean to appear boastful, but the point I’m making is there is no more