GM recognized the 4L60E's sun shell as a weak link and slightly upgraded it for the stock 4L65s. FLT goes several steps further, modifying the legendary "Beast" sun shell to accept a Torrington roller bearing in place of the stock thrust bearing. | 
This cracked OEM sun shell was well on its way to failure, ultimately resulting in the loss of all gears except First. With a Beast sun shell, this sort of failure is eliminated. | 
Modified to accept the Torrington roller bearing, FLT's modified sun shell will spin effortlessly. This reduction in friction frees up power and increases durability. |
The 4L60E's four pinion planetary gears are upgraded to a pair of new genuine GM five pinion parts. FLT has found GM planetaries to be the best available and avoids the inconsistent quality of used and imported parts. | 
On the left is a used pump housing showing signs of wear on the machined surfaces. FLT machines the pump surfaces to ensure a leak-free parallel surface. | 
On the top are the OEM sprag and low roller clutch; underneath are Borg-Warner parts FLT upgrades, too. |
This close-up of the Borg-Warner sprag (left) shows its double cages and the larger cross-sectional area than the OEM sprag. | 
In FLT's experience, failure of the 3-4 clutch is the most common clutch failure. FLT addresses that by upgrading to an eight-clutch pack over the 4L60E's six-clutch pack. | 
For my blown 5.3L '01 4x4 applicataion, the Level 5's cryo-treated output shaft is plenty strong. Now for the guys who are combining power adders like getting stroked and blown, a stronger shaft is in order: FLT now offers a forged 4340 version to prevent unexpected shaft failure. |
In blown applications using a vacuum modulater, a blower bypass check valve must be used to prevent boost pressure from entering the vacuum circuit. | | |