Cummins Diesel converter plagued by failures


Member Howard Johnson, of the Torque Converter Company in Salt Lake City, Utah, notified the TCRA of a continuous problem inherent to the non-lockup Cummins Diesel converter, Dacco part number 590. This converter has created multiple problems for Johnson, and most likely many rebuilders have experienced his frustration.

One problem surrounding the diesel converter is the pilot. It appears the pilot, which is welded on during manufacturing, may develop stress cracks and cause converter leakage. Many have experienced this problem, and are asking other members if they have reason for the fracture or a cure/repair that will resolve this issue. Some rebuilders machine away the OEM weld and reweld the pilot to the cover, only to have it return within a few thousand miles.

It has been suggested that converter ballooning, poor alignment and excessive high-torque conditions may contribute to this failure. Although these scenarios are realistic, it has yet to be proven that one or more are causing the failure. Some companies install a type of anti-ballooning plate to the cover, welded in place, which may or may not solve the condition.

If any reader has experienced this problem and knows of a solution for the cracking weld, please contact

An additional issue frequently encountered by rebuilders is turbine/turbine hub failure. One of the largest problems plaguing this converter is complete turbine explosion caused by excessive turbine distortion. The turbine hub completely separates from the turbine in a twisting motion, literally ripping it apart.

Sonnax Industries carries a turbine stiffener ring which easily welds in place and prevents the inevitable catastrophe. This plate normally requires no machining or modifications; however, you do need to check for proper turbine to front cover clearance. On occasion, an additional shim will be required to obtain the needed clearance.

Found in issue November 2005