Weird shift issue
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TECH Enthusiast
Joined: Jan 2010
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From: Corpus Christi, TX
Weird shift issue I don't know if it's just me being paranoid but the tranny shifts fine no problem. The issue is, is once I reach 55 mph my Rpms will drop to around 1500. Like I'm getting up to speed shift Rpms rise shift Rpms still climb normally n then hit 55 n then boom it drops suddenly. Am I being paranoid or is there a tuning issue or what. I have a 3600 stall in it.
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Joined: Aug 2010
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From: Ann Arbor, MI
It is normal for the lockup clutch (TCC) to engage at that speed and drop your rpms by 150-200 rpm. If its dropping by e.g. 500, then your converter is too loose or your fluid is too low.
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Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
Any transmission gear ratio under 1.00 is consider "overdrive"; therefore 4th gear (ratio of 0.70) in a 4L60E is overdrive. Lockup is completely independent; it locks up up the converter so there is a direct connection between the engine and trans with no fluid coupling. In theory, lockup could be engaged in any gear, but it is commonly only engaged in 4th gear when a certain speed is reached. It could be as low as 40 mph, but with a performance cam, you might need between 50 and 55mph to prevent surging at low rpms. And yes, the Tune determine when lockup is engaged.
Any transmission gear ratio under 1.00 is consider "overdrive"; therefore 4th gear (ratio of 0.70) in a 4L60E is overdrive. Lockup is completely independent; it locks up up the converter so there is a direct connection between the engine and trans with no fluid coupling. In theory, lockup could be engaged in any gear, but it is commonly only engaged in 4th gear when a certain speed is reached. It could be as low as 40 mph, but with a performance cam, you might need between 50 and 55mph to prevent surging at low rpms. And yes, the Tune determine when lockup is engaged.