4L60 final lock up not staying locked up

Subzilla

Subzilla

Test Driver
Joined
Jun 13, 2011
Location
Triad - Mt. Pleasant, Concord & Georgeville
2003 Tahoe 4L60 goes in and out of final lock up on the highway. No consistent pattern. Can stay unlocked from 2 minutes to 10 minutes no matter the “pull” on the transmission. Shifts perfect otherwise. 205k miles. Been doing this for the last couple of years.
 
Subzilla said:
2003 Tahoe 4L60 goes in and out of final lock up on the highway. No consistent pattern. Can stay unlocked from 2 minutes to 10 minutes no matter the “pull” on the transmission. Shifts perfect otherwise. 205k miles. Been doing this for the last couple of years.
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I have 1 that goes in and out of lockup constantly around 45, but never an issue like that at highway speeds.

Is your brake switch being activated? Make sure your brake lights aren't coming on, or stick your foot under the pedal and pull it up when it's acting up.
 
Common tc lockup failure is either the solenoid or the lockup spring in the valve body, both require a lot of disassembly. If it’s in the valve body, some people put stiffer spring, some shim the spring to just make it firm, or sonnax makes a kit that requires reaming the valve body but is supposed to eliminate the problem

Or the lockup o ring on the input shaft as stated above
 
Given the mileage of this transmission, I will probably just wait until it needs a rebuild and not try to tear it apart and replace parts that may or may not fix it. I’ll still check the brake light switch. The trans shifts fine otherwise….it’s just one of those unfixed things that nags at me when I see it happening. Thanks for the responses.
 
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