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spiGini

4l80e shift issue - FIXED!

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First post here in a long time but just recently picked up a 2005 GMC 2500HD 6.0 with 183k miles and 4l80e transmission.  Vehicle is really clean but have come up with a transmission issue.  When cold the transmission shifts into OD on the highway no issues.  When the transmission gets up to operating temp it will not shift into OD, it sits at 3k rpm at 70mph.   I did a stall speed test and it comes up to 2400rpm (believe stock is 2600) unsure if that is a real issue only 200rpm difference so don't believe it is the TC.  When cold or warm the transmission shifts smooth as anything just when warm will hang 3rd.  Checked fluid and it looks clean, not burned and full.  Wondering if its worth changing the fluid/filter/shift solenoids and go from that point or just bring it to a shop.  Not sure if the wrong fluid was used and if that would even cause the shifting issue when warm or if it is just the TC that needs to be replaced.

 

Thanks!

Edited by spiGini

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Just an update since nobody responded.  Little more information on my issue which starts when the trans temp reaches above 150 degrees.  Below 150 degrees the transmission has no issues shifting into 4th or 4th gear lock up.  Above 150 degrees it will not shift into 4th but has no issues shifting 1-3.  My thought was the fluid was getting thinner but didn't know what or where it was going wrong.  Dropped the pan and checked all of the solenoids and everything was in spec for ohms reading.  Thought it could be the feed limit actuator that is known to bore itself out (still unsure if that is damaged but ordered a whole new valve body with upgraded transgo feed limit).  So in preparation for the new valve body to arrive I decided to take out the old one last night.  When I dropped the valve body along with it came half of the 4th bolt or 4th clutch bolt.  The other half was stuck in the transmission.  I assume it was over torqued at one point causing it to crack and when the fluid gets thin it escapes through the threads instead of providing constant pressure to the 4th piston.  Had to use a tap and screw to get out the half stuck in the transmission.  Now not sure if this is the exact thing causing the issue but I assume it will be.  So a $5 part was causing me to lose 4th gear when the transmission reached over 150 degrees.

 

Just wanted to update the thread in case anybody has issues later on and doesn't know where to start.  If everything checks out with the solenoids i'd take a look at this bolt.  And I'll update this weekend after I put in the updated valve body and new 4th bolt in to verify everything is good to go now

Edited by spiGini

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