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Old 06-27-2009, 05:34 PM   #1
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Automatic Transmission Revs Up/Revs too High on WOT

Hello everybody,

I've got a 1990 IROC-Z with a 305 TPI (not sure if engine makes a diff.)...
It has an automatic transmission which I assume is stock...

It shifts fine while coasting along, however whenever I get on it and go WOT, the shifts seem to rev to high.

An example would be, if I was coasting along at 50 km/h (31 mph) and then opened the throttle (accelerator to the floor) the transmission seems to jump to a lower gear as it revs way up to 5000 (almost instantly), and then moves to about 5800 before changing gears.

It seems that the transmission is shifting to the wrong gear or that the shifts are off. The shifts also drag into the 5000's and 5500's when I have the throttle wide open.

I'm not sure where to start with this one, I have checked the transmission fluid and it's topped up.

If someone could point me in the right direction that would be great, thanks

PS. I have considered installing a shift kit, however I wanted the transmission to work like it does stock, before doing that, or would that fix this problem?
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Old 06-27-2009, 07:27 PM   #2
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Car: '88 Camaro SC/Z28
Engine: 305tbi
Transmission: 700r4
Axle/Gears: 2.73

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Re: Automatic Transmission Revs Up/Revs too High on WOT

Quote:
Originally Posted by SRRF View Post
Hello everybody,

I've got a 1990 IROC-Z with a 305 TPI (not sure if engine makes a diff.)...
It has an automatic transmission which I assume is stock...

It shifts fine while coasting along, however whenever I get on it and go WOT, the shifts seem to rev to high.

An example would be, if I was coasting along at 50 km/h (31 mph) and then opened the throttle (accelerator to the floor) the transmission seems to jump to a lower gear as it revs way up to 5000 (almost instantly), and then moves to about 5800 before changing gears.

It seems that the transmission is shifting to the wrong gear or that the shifts are off. The shifts also drag into the 5000's and 5500's when I have the throttle wide open.

I'm not sure where to start with this one, I have checked the transmission fluid and it's topped up.

If someone could point me in the right direction that would be great, thanks

PS. I have considered installing a shift kit, however I wanted the transmission to work like it does stock, before doing that, or would that fix this problem?




Yes, this is very strange indeed. I believe the tach on your car should be yellow at 5000 rpm, and redline at 5500 rpm. I agree that 5800 rpm is too high. Two common third-gen problems that could cause this are innacurate tachometer readings that read anywhere from a few hundred rpm off to thousands off, as well as the TV cable for the transmission. The TV cable is connected to the throttle linkage onder the hood, and goes down to the side of the transmission and controls the shift points based on throttle opening and load on the engine. Test the accuracy of the tachometer, then check the TV cable. I hope this helps
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Old 06-28-2009, 01:11 AM   #3
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Oops...

Thanks for the quick reply,

It seems I may have made an error/misjudgment...

I just took my car out for a cruise and made sure to fool around with it a bit, (WOT from coasting, WOT from stop, etc.) while watching my tachometer.

It seems that the car ACTUALLY shifts right at redline (which is 5000) and when I give it WOT it either jumps straight to 4000 or 4500 and then runs till 5000 (start of redline) before shifting....

I'm sure this make a huge difference as it isn't really going past and into red line as I originally thought...

This leads me to ask if thatís the normal thing for it to do... jump to 4500 RPM almost instantly and run to about 5000Ö before shifting. It seems inefficient as it loses a bit of power near the end of the shift, once the transmission shifts you can feel a jerk and sometimes the tires squawk and away you go... (Seems to only happen when going above/around 50km/h (30 mph)Ö not sure if itís a specific gear)

I was wondering if this was the natural thing for it to do, or if it provides the optimal speed vs. shift, maybe a shift kit is the way to go?

Sorry again about the error and thanks again for reading
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Old 06-28-2009, 08:00 AM   #4
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Location: Richmond, Virginia
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Car: '88 Camaro SC/Z28
Engine: 305tbi
Transmission: 700r4
Axle/Gears: 2.73

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Re: Oops...

Quote:
Originally Posted by SRRF View Post
Thanks for the quick reply,

It seems I may have made an error/misjudgment...

I just took my car out for a cruise and made sure to fool around with it a bit, (WOT from coasting, WOT from stop, etc.) while watching my tachometer.

It seems that the car ACTUALLY shifts right at redline (which is 5000) and when I give it WOT it either jumps straight to 4000 or 4500 and then runs till 5000 (start of redline) before shifting....

I'm sure this make a huge difference as it isn't really going past and into red line as I originally thought...

This leads me to ask if thatís the normal thing for it to do... jump to 4500 RPM almost instantly and run to about 5000Ö before shifting. It seems inefficient as it loses a bit of power near the end of the shift, once the transmission shifts you can feel a jerk and sometimes the tires squawk and away you go... (Seems to only happen when going above/around 50km/h (30 mph)Ö not sure if itís a specific gear)

I was wondering if this was the natural thing for it to do, or if it provides the optimal speed vs. shift, maybe a shift kit is the way to go?

Sorry again about the error and thanks again for reading


Yes, its 100% normal for these cars to shift at redline. That is how they are set from the factory. Using a shift kit is fine to enhance the firmness of the shifts for performance purposes, but any shift kit settings that would let the engine go past redline are NOT to be used. This will most likely damage the engine and transmission over time if you tend to drive the car hard.
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Old 06-28-2009, 01:04 PM   #5
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Re: Automatic Transmission Revs Up/Revs too High on WOT

Oh, I see...

Well it's good to know there are no issues with my transmission,
thanks again for the fast and knowledgeable reply
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Old 02-13-2010, 09:21 PM   #6
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Location: Campobello, SC
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Car: 1990 Trans Am
Engine: 305 TPI L98 cam
Transmission: 700R4
Axle/Gears: 3.42 eaton

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Re: Automatic Transmission Revs Up/Revs too High on WOT

i have been looking for an answer to this question for a long time!! and now i finally have the answer that i was looking for! thanks guys.
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Old 02-13-2010, 09:21 PM
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