Why upgrade the input drum?
The 4L60E transmission input drum is a common source of failure when it develops a pressure leak from the area where the input shaft is pressed into the drum. There are a couple of high performance options you can go with depending on your budget and engine horsepower output.
Sonnax Smart Tech Input drum
The OEM 4L60 input housing flexes under load, causing heat buildup and the common 3-4 clutch burnup. Sonnax’s Smart-Tech input housing kit solves this with a stronger anchored backing plate and a taller, higher-capacity clutch pack. The kit allows either eight .067″ frictions with seven .095″ steels or nine .062″ frictions with eight .077″ steels for maximum 3-4 clutch capacity. Built from the newest upgraded GM housings, it features thicker material and improved spline specs for better durability and shaft retention. The reinforced housing and custom backing plate prevent flexing, blowout, and heat-related distortion.
A high-strength 300M steel input shaft eliminates the undercut failure point found in OE shafts.
Overall, the Smart-Tech design dramatically increases clutch durability, prevents 3-4 burnup, and improves long-term transmission reliability.
You can purchase just the housing and use an OEM input shaft, or include their heavy duty input shaft. This is the most expensive option, but well worth it.
4L79 Input drums
The upgraded 3-4 clutch system delivers extreme rigidity and a massive increase in clutch surface area, unmatched by any other setup.
A machined input housing with a threaded 6061 billet aluminum end cap improves heat dissipation and durability under heavy load.
The 4L79 kit includes 8 custom larger-diameter frictions, 8 steels, and a thick apply plate designed for superior cooling and strength.
Increased steel mass further aids in shedding heat, making the kit ideal for 600+ hp or any heavy-duty long-life build.
The 4L78 version uses OEM-sized frictions and steels but maintains the same rigid construction and is safe for 600 hp and under.
Both kits include the billet cap, apply plate, steels, frictions, and set screws, requiring no special parts to install.
The 4L75 drum uses snap-ring retention and seven larger custom frictions with matching plates, offering a strong upgrade without special parts needed.
You can purchase just the housing and use an OEM input shaft, or include their heavy duty/reinforced input shaft.
