GM 6T40 & 6T70 3-5-R Clutch Drum Repair
General Motors’ 6-speed automatic transmission was designed for front-wheel-drive and all-wheel-drive applications, particularly in compact and mid-size passenger vehicles. It has been widely used in models from Chevrolet and Opel, among others. Common issues with these transmissions include clutch drum failures and control module faults. Read our article about 6T40 common fault codes here!
If the transmission fluid has not been changed since the vehicle left the factory, we recommend performing a complete fluid exchange using a flushing method.
3-5-R Clutch Pack Waved Plate Failure
Whether dealing with an early or later version of the 6T40/45/50 or 6T70/75 transmission, the 3-5-R clutch pack design is a well-known weak point. Simply installing an updated OE waved plate does not always guarantee long-term reliability. A structurally improved solution can help break the cycle of repeated failures, reduce warranty returns, and provide a more dependable result during a rebuild.
When the 3-5-R clutch pack waved plate breaks, it often damages the drum splines. This can lead to the need for an expensive drum or housing replacement. Even if the plate has not yet failed, leaving the original design in place poses a risk — which is why it is almost always addressed during transmission overhaul work.
What Causes the Plate to Break?
Inspection of failed plates shows that cracks almost always originate at the corner of a tooth. These sharp corners create structural stress concentration points where loads accumulate over time. A plate that appears visually intact may already contain hairline cracks, indicating that a more serious failure is imminent.
A Structural Solution to the Problem
With more than 40 years of experience, Sonnax designs, develops, and manufactures high-quality aftermarket components for the automotive industry. To address this issue, Sonnax offers 3-5-R drum saver kits for the 6T40/6T45 transmission (144555K) and the 6T70 transmission (124555K). The waved plate included in these kits is still shot-peened to improve durability, but the most significant improvement lies in its redesigned structure: the teeth — which act as crack initiation points — have been completely eliminated.
Because the redesigned plate has no teeth, it requires a different method of positioning inside the drum. For this purpose, the kit includes a precisely machined, cup-shaped steel plate. This heavy-duty component securely retains the waved plate in place on the drum. The thickness of the steel plate matches that of the bottom steel plate in the clutch pack (which is replaced by the kit component), ensuring correct clutch clearance without additional adjustments. An added benefit is improved heat dissipation, contributing to greater overall durability..