The boost valve assembly is activated by torque signal pressure from the pressure control solenoid and reverse pressure to aid in adjusting line pressure at the pressure regulator valve. This boost valve is continuously oscillating in the sleeve, which leads to wear and hydraulic leakage. When wear occurs, critical oil pressure is allowed to cross leak between the circuits or leak to exhaust. These leaks can result in either no line rise or an unwanted increase in line pressure. Sonnax offers a replacement boost valve assembly 72754-01K that restores hydraulic integrity and properly controlled line rise. The sleeve is manufactured from highly wear resistant aluminum, and the valve from anodized aluminum. Tight tolerances on the sleeve and valve maintain an ideal fit that prevents leakage.

Symptoms:

Delayed Reverse
Harsh shifts
High line pressure
Low line pressure
No Reverse
Soft shifts

Cause:

A worn boost valve sleeve allowing torque signal and/or reverse pressure to cross leak or exhaust can cause these complaints.

Correction:

This replacement boost valve assembly restores hydraulic integrity to the circuits and properly controls line rise.

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72854-03K

94741

TCC Regulator kit 4T80E

Part #

72854-03K

Reference #

94741

Extra information

TCC Regulator kit 4T80E

Sleeve
Valve
Springs (3)
Washer
O-Ringed End Plug

Symptoms:

Code 39, 741
Overheated converter
TCC apply & release concerns

Cause:

Continuous oscillation of the converter regulator valve in the cast-aluminum bore causes bore wear, which results in apply oil leakage.

Correction:

The Sonnax kit provides more support for the valve during oscillation and restores hydraulic integrity.

Required tool

72854-TL2

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72854-01K

94741 / S94741FK

AFL Sleeve kit 4T80E

Part #

72854-01K

Reference #

94741 / S94741FK

Extra information

AFL Sleeve kit 4T80E

Sleeve
Valve
Regulating Spring
Retaining Spring
Sleeve Retaining Clip

Symptoms:

2nd Gear starts
Band failure
Clutch failure
Harsh shifts
No 4th
Soft shifts & poor line rise
Solenoid codes
Wrong gear starts

Cause:

Actuator feed limit bore wear results in low pressure at shift and EPC solenoids.

Correction:

This wear-resistant sleeve and hard anodized valve refurbish the bore to prevent AFL leakage while providing greater durability and thermal expansion properties.

Required tool:

72854-TL

NOTE: Sonnax reamer tool kit 72854-TL must be used to oversize the existing bore.

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72871-01

94932A

Accumulator Piston 4T80E 2-3

Part #

72871-01

Reference #

94932A

Extra information

Accumulator Piston 4T80E 2-3

1994 & later

Increased bore length for more piston-to-pin support.
Machined from high-quality aluminum.
More durable than OE replacements.
Piston accepts standard OE or replacement seals.

Symptoms:

2-3 Soft
3rd Clutch distress
4-3 Kickdown
Damage from broken spring
Worn accumulator piston pin bore

Cause:

Normal wear and uneven loading from spring.

Correction:

Install the Sonnax replacement piston with increased bore length for more piston-to-pin support and greater durability

NOTE: This piston should not be used in a first-design 2-3 accumulator found in '93 models. These units do NOT have the second bumper spring on the top portion of the accumulator piston. If the large spring is broken, replace with GM part number 8684827

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72872-01

94937A

Accumulator Piston 4T80E 3-4

Part #

72872-01

Reference #

94937A

Extra information

Accumulator Piston 4T80E 3-4

The piston bore in 4T80-E units is prone to wear, either through normal operation or uneven loading from the spring. The Sonnax replacement piston 72871-01 provides more piston-to-pin support and greater durability than OE replacements.