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  • 2-4 Band burned
  • 3-4 Clutch burned
  • Burnt Low/Reverse clutch
  • 3-2 Bind-up
  • Delayed Reverse


Wear of the bore plug in the forward and reverse abuse valve bores can allow valuable oil pressure to exhaust.


This increased diameter plug restores proper clearance in the valve body and requires no tools for installation.

4L60-E, 4L65-E, 4L70-E

Forward & Reverse Abuse Bore Plug
Part No. 77754-21

Fits in either of two locations

View Instructions

The bore plug in 4L60-E units is held loosely in place with a coiled spring pin, allowing the opposing spring and oil pressure forces to stroke it within the bore.

This constant oscillation causes the plug to wear and allows PR oil at the low overrun valve and 3-4 clutch oil at the 3-2 downshift valve to exhaust at the abuse valves. This excessive oil loss can result in delayed apply of the low/reverse clutch and a tie-up of the 3-4 clutch and 2-4 band. Sonnax forward and reverse abuse bore plug 77754-21 resolves these problems.

This plug is used in two locations in the valve body: to separate the forward abuse and low overrun valves, and to separate the reverse abuse and 3-2 downshift valves.

  • The Sonnax plug has an increased diameter to restore proper valve body clearance in the circuits
  • The plug has a smaller retaining pin hole to reduce plug movement that results in wear
  • No tooling is required for this bore plug

January 21, 2013

GM 4L60-E Vacuum Test Guide

Topics: Vacuum Testing Vacuum Test Guides Transmission GM 4L60-E Transmission

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  • 77754 21 combo
  • 77754 21