The primary design function of the OE end plug is to prevent critical pressure loss by capping the bore. OE end plugs rely entirely on small clearances between the end plug and bore to confine hydraulic fluid under fluctuating pressure. End plugs are often tasked with a secondary role functioning as a spring stop or valve stop. The repetitious and varying actions of fluid pressure, spring motion and valve impact cause wear at the end plug and bore mating surface, and can distort the shape of the end plug. This allows critical oil pressure to escape and prevent proper valve function. In the 55-50SN, 55-51SN locations, this results in loss of SLT (throttle) pressure, and drive/line pressure at various bores. The results are the various driveability complaints noted, as well as related burnt clutches and bands.
The end plugs in Sonnax O-ringed end plug kit 59947-21K have small clearances to mechanically block the bore and include an O-ring seal to provide a positive seal with worn bores to prevent future leakage.

Prevents loss of critical pressure
Sonnax kit services five different bores, can be used in other bore locations as applicable
Drop-in Zip Valve™ parts install quickly and easily



O-Ringed End Plugs for AW55-50SN


Valve
Location
Diameter


End Plugs included in Kit 59947-21K
Forward Clutch Control
Front Control VB
9mm

2nd Coast Clutch Control
Front Control VB
9mm

Neutral Relay
Front Control VB
9mm

M1 Shift
Middle Control VB
9mm

3rd Gear Band Release
Middle Control VB
11mm


Learn More About Zip Valve™ Drop-In Repairs

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