4L80E 4L85E Sonnax Sure Cure Valve Body Kit SC-4L80E

This is the Sonnax Sure Cure kit (part number SC-4L80E), a single package that bundles Sonnax's individual drop-in valve and spring fixes for the GM 4L80E and 4L85E into one master reconditioning kit. Instead of chasing one worn circuit at a time, you address the whole valve body and pump during a rebuild. It fits the 4L80E and 4L85E (RPO MT1 and MN8) used behind big-block gas and diesel engines in GM 2500 and 3500 trucks and vans, Suburbans, and Hummer H1, 1991 and up.

These transmissions wear at predictable spots in the aluminum valve body and pump, and that wear is what shows up as low or unstable line pressure, burnt clutches, torque converter shudder, TCC slip codes, and shifts that go soft, delayed, or harsh. The kit targets those wear points, including the pressure regulator and boost circuit that sets line pressure and the torque converter clutch regulator and apply circuit that controls lockup. Restoring the clearance in those bores brings pressures and shift feel back to where they should be rather than masking the problem with an additive or a higher-pressure spring alone.

Use it on the bench during an overhaul or a valve body service: the kit installs with the transmission apart, follows the included step-by-step instructions, and is meant to be done once so the rebuild does not come back with the same soft-shift or converter-shudder complaint. One rebuilder running a 4L80E in a Chevrolet 3500 reported firmer, better shifting after 1,000 miles with the Sonnax parts installed alongside a shift kit.

Kit weighs about 1 lb and ships from the USA with handling in 1-2 business days.