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Symptoms:

  • High line pressure in Drive
  • Low line rise in Reverse
  • Soft shift & low accumulator pressure

Cause:

Wear of the accumulator control bore and valve spool causes low accumulator pressure that results in soft shifts.

Correction:

Ream the valve bore and install the Sonnax oversized valve, matched spring and oversized end plug.

4L80-E, 4L85-E

Oversized Accumulator Control Valve Kit
Part No. 34994-22K


You need this if... View Instructions

The 4L80-E accumulator control valve controls shift firmness by managing accumulator back pressure. Wear at the valve or bore can lead to multiple symptoms, the most common being reduced line pressure in reverse, elevated line pressure in drive, and soft or harsh upshifts depending on location and magnitude of wear. When valve/bore wear allows cross-leakage of torque signal/boost oil to exhaust to the sump, line pressure drops causing soft shifts. Alternatively, when bore wear allows drive oil to enter the torque signal passage, line pressure increases and shift feel hardens.

  • Upgrade '91-'96 4L80-E accumulator control valve to '97-later calibration
  • Restore OE accumulator control valve response in '97-later units
  • Valve
  • Spring
  • End Plug

February 21, 2013

GM 4L80-E Vacuum Test Guide

Topics: Vacuum Testing Vacuum Test Guides Transmission GM 4L80-E Transmission

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September 30, 2005

Anatomy of a Transmission: Oil Flow in the Pump-PR-Converter-Cooler Lube Circuits

Gregg Nader

Topics: Diagnostics And Theory Transmission

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  • 34994 22k combo
  • 34994 22k

You need this if...

A vacuum test fails to yield the indicated 14 or 18 in-hg or greater, depending on the port tested as shown, or if visual wear is detected.

  • 34994 22k test