This video is part three of a three part series on the overhaul of the GM 8L90 transmission. In this video, I cover the valve body in depth. Not only do I disassemble, inspect, and identify all the valves, but I also cover the additions and improvements found from Sonnax and Transgo. I cover what they changed with their components and how it will likely change the operation of the transmission.

Here are the other videos in this series:

8L90 Overhaul - part one covers disassembly:    • General Motors 8l90 Overhaul Part One...  
8L90 Overhaul - part two covers assembly, including clutch and gearset assembly and measurements:    • General Motors 8l90 Overhaul Part Two...  

8L90 Hydraulics theory and operation:    • General Motors 8L90 hydraulic operation  
8L90 Electrical theory and operation:    • General Motors 8L90 electrical theory...  
8L90 Torque Converter:    • General Motors 8L90 torque converter ...  
8L90 Rebuilding Particulars:
8L90 Modifications and Tuning:

Special thanks to Precision International, TransGo, and Sonnax for providing me with product to use in these videos. Also thanks to KB Cores and AA Midwest for providing me with a few 8L90 cores at a good price!

Video Contents:
0:00 Intro
1:25 solenoid ID
7:59 solenoid accumulators
10:24 shift kit overview
11:12 Torque converter feed limit valve
16:47 clutch regulator valves
22:54 Vacuum testing lower VB
26:21 Sonnax accumulator kit
27:57 Transgo Accumulator Kit
30:07 Sonnax zip kit
33:32 Upper valve body disassembly
33:58 Oil pump
37:06 pressure regulator valve
38:33 exhaust backfill
40:24 pressure regulator valve operation
42:08 vacuum testing upper valve body
45:46 isolator valves
53:36 oil pump assembly
56:03 pump priming