February 21, 2013
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Vehicles with '95-later GM 4L80-E and 4L85-E transmissions commonly exhibit wear in the Reverse checkball sleeve located in the 3-4 shift valve bore. This issue is caused by normal movement of the checkball within the sleeve over time. As wear progresses, sealing function of checkball becomes compromised and results in loss of apply pressure to direct clutches. Consequences of this pressure loss are slipping or no 3rd, 4th, and Reverse gears, burnt direct clutches, and ratio codes.
Installing Sonnax Reverse checkball sleeve 34200-38 restores the hydraulic integrity of this circuit to reestablish normal shift operation and performance.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg., or if wear is visually detected.