Rebuilt 4L65E: Now shifts hard from 2nd to 3rd

[m1949]

Well, the build is almost complete. The punch list is down to the last few items. One item yet to be fixed is the transmission shifts hard from 2md to 3rd gear when above 50% acceleration. It shifts smoothly from 2nd to 3rd at normal acceleration. But when acceration gets above around 50% throttle the transmission holds to higher rpms then slams from 2nd to 3rd when it finally shifts. I'm wondering if this might be a shift table issue? The GM Performance engine we installed after rebuilding the transmission increased power by almost 100hp. We rebuilt the transmission while the much lower HP LQ9 was still installed. It seemed to work fine with the LQ9, but we didn't think to run thru the gears at WOT. I've read that rapid acceration after increasing HP can cause mph and rpm shifts table conflicts that can produce shift hesitation until higher rpms are reached, which then causes a hard shift. I'm keeping my fingers crossed its a program issue and not something internal. Has anyone run into this issue?

 

[iamdub]

Really sounds like it needs more tuning. Or, is the throttle position scaling the same between your original LQ9 TB and the one you currently have? I thought you got the Gen 4 TB along with the Gen 4 intake manifold.

 

[Mudsport96]

Yeah you will need to do some driving for the shift adapts to learn some and you may want to have your tuner go over the shift tables again too.

 

[m1949]

Really sounds like it needs more tuning. Or, is the throttle position scaling the same between your original LQ9 TB and the one you currently have? I thought you got the Gen 4 TB along with the Gen 4 intake manifold.

Yes, they did replace the intake and Throttle body with Gen V when they installed the new engine. The transmission rebuild was done while the old LQ9 was still installed, before we replaced it with the higher HP engine and new intake and TB. So, its likely no changes were made to the original tune. I hope you are right and its a tuning issue. What is causing me to lean toward a tune issue is the hard shifting doesn't occur unless the throttle is at 50% or more acceleration. Less than that and it shifts smooth. I'd hate if its something internal and the trans must be torn down. Hopefully, I'll know something by the end of the week.

 

[Rocket Man]

If you recently pulled the pan and changed trans oil and filter and used RTV on the pan gasket it’s possible the servos aren’t releasing since their drain holes are at the pan rail. Never use RTV on the pan gasket, just a fyi. Otherwise it’s probably a tune issue like mentioned.

 

[m1949]

If you recently pulled the pan and changed trans oil and filter and used RTV on the pan gasket it’s possible the servos aren’t releasing since their drain holes are at the pan rail. Never use RTV on the pan gasket, just a fyi. Otherwise it’s probably a tune issue like mentioned.

My builder is concerned it may be a sticky servo. The trans was rebuilt by a shop who does all the builders transmission work. So I'd think anything like what you suggest would be unlikely, since it would have come back to the builder on transmission work done before now. Could be wrong though. Could be someone mistakenly used the wrong sealant.

 

[Rocket Man]

My builder is concerned it may be a sticky servo. The trans was rebuilt by a shop who does all the builders transmission work. So I'd think anything like what you suggest would be unlikely, since it would have come back to the builder on transmission work done before now. Could be wrong though. Could be someone mistakenly used the wrong sealant.

If it was only worked on by a trans shop it’s highly unlikely. The pan gasket is supposed to go on dry with no seal and I would think every trans shop would know that. I only found out because I was the one to do the fluid and filter on my expensive Performabuilt 4l65 level 3. Their warranty stated to change the filter at 2000 miles after break-in which I did and I used the RTV as added insurance against seepage or so I thought. Their builds normally shift pretty hard so I didn’t notice that it was shifting even harder. I’m supercharged with AWD and on one WOT pull from a stop, it twisted the output shaft in two on the 1-2 shift. They found the RTV on disassembly and informed me about the issue. They also covered the damage under warranty even though it was my fault, and added this info in their install instructions.

 

[rockola1971]

Were all valve body updates performed?

 

[m1949]

Were all valve body updates performed?

The builder still has the paperwork so I can't give you a definite answer. I'd think it did have any updates done to deal with known issues since it went in for a complete rebuild and be beefed for added HP.

 

[Mudsport96]

I’m supercharged with AWD and on one WOT pull from a stop, it twisted the output shaft in two on the 1-2 shift.

Like this? Lol