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Automatic Tranny: Highway rpm Off & On Throttle?

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Old 10-17-2011, 10:33 PM   #1
SD 197
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Default Automatic Tranny: Highway rpm Off & On Throttle?

My automatic is doing something interesting I didn't really notice before, hoping to see if anyone else has experienced it?

Cruising at steady throttle in 5th gear at 70 mph, my rpms stay at around 2,100 (3.31 gearing ).

When I lift off the throttle, the rpms drop slightly to about 1,900, but when I apply the throttle again, the rpms go a couple of hundred higher than the original cruising rpms to about 2,300 rpms, and the after a second or two, drop down back to the normal 2,100 rpms.

It's almost like the car went down a gear and then back to fifth, even though I know it stayed in 5th gear the whole time. I tried the same thing in 4th gear, keeping the OD off, and it does the same thing.

It could be normal, just not sure. Anyone else notice this?

Last edited by SD 197; 10-17-2011 at 10:35 PM.
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Old 10-17-2011, 11:00 PM   #2
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Yupp mine does it too with a tune, 4.10s and all. I believe its the converter locking up from what I have heard or something like that. Its completely normal.
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Old 10-17-2011, 11:32 PM   #3
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Originally Posted by grabber blue gt View Post
Yupp mine does it too with a tune, 4.10s and all. I believe its the converter locking up from what I have heard or something like that. Its completely normal.
Thank you Grabber, I can sleep tonight
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Old 10-18-2011, 07:17 AM   #4
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Yup. Probably converter thingie.
Mine does it at 40mph, but it depends on the tuning.
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Old 10-24-2011, 07:42 PM   #5
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It is the converter unlocking (rpm rises) then locking (rpm drops). The more torque the engine makes, the more it will happen. The more it happens, the more heat is generated in the tranny. The rpm rise is sorta like slipping the clutch in a manual car.
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Old 10-24-2011, 08:11 PM   #6
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Quote:
Originally Posted by SD 197 View Post
My automatic is doing something interesting I didn't really notice before, hoping to see if anyone else has experienced it?

Cruising at steady throttle in 5th gear at 70 mph, my rpms stay at around 2,100 (3.31 gearing ).

When I lift off the throttle, the rpms drop slightly to about 1,900, but when I apply the throttle again, the rpms go a couple of hundred higher than the original cruising rpms to about 2,300 rpms, and the after a second or two, drop down back to the normal 2,100 rpms.

It's almost like the car went down a gear and then back to fifth, even though I know it stayed in 5th gear the whole time. I tried the same thing in 4th gear, keeping the OD off, and it does the same thing.

It could be normal, just not sure. Anyone else notice this?
The converter would not be my guess...tell ya why I think this.
First off, if you are cruizing at 70mph @2.1rpm...you are currently in o/d my friend. When you let off the throttle the decrease in rpm is the converter at work, but depending on your throttle input upon the next press, you are dropping her back in 5th (producing the higher rpm) quickly followed by o/d engaging once again (lower rpm). Right or wrong it's no biggie, mine does the same thing and I have the same gear.
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Old 10-24-2011, 08:11 PM
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