4L60, 4L60-E, 4L65-E, 4L70-E Heavy Duty 3-4 Clutch Backing Plate Kit Sonnax Part Number 74140-01K
Requires ‘91-later 3-4 apply ring stamped with number “7”, measuring 3.671–3.682" in height.
A thin, weak backing plate is the leading cause of 3-4 clutch distortion and burnup – a pervasive problem in listed GM transmissions.
Even the thickest OE backing plate flexes during clutch apply, allowing heat to build up unevenly, causing problems in daily drivers and mid-level street/strip vehicles alike.
Other aftermarket solutions typically employ a thinner backing plate, and thinner steels which ultimately exacerbate the problem.
Sonnax heavy duty 3-4 clutch backing plate kit 74140-01K significantly reduces backing plate flex for increased 3-4 clutch durability. It features a significantly thicker and stiffer backing plate, used together with a thinner (yet stiffer) apply plate.
Designed for use with GM high energy clutch pack with seven .067" frictions and six .095" steels, this kit can be used to upgrade OE 700-R4 and 4L60-E five-friction or six-friction clutch packs to seven frictions, or to improve stock, seven-friction clutch packs in 4L65-E and 4L70-E units by reducing backing plate flex.
- Backing plate is significantly thicker and stiffer than OE for added durability
- Drop-in, mid-level upgrade for daily drivers and mild street/strip applications
- Backing Plate
- Apply Plate