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Loss of Overdrive on interstate


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#21 Galaxie500XL

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Posted 26 September 2017 - 07:41 PM

It's a problem if the sensor is faulty and giving incorrect readings.  I have a tough time believing that the trans can have fluid-temperature related problems while the sensor is showing "175 degrees".

 

It might be a problem if the sensor isn't reading the temp of the fluid in the pan.  The Old Wisdom about fluid temperature assumes that the temperature reading is from the pan, not the torque converter, or somewhere buried in the line-pressure circuit.

Actually, Shurkey, it doesn't do that at all...the temp reads 175, but what causes the lack of overdrive is the ECM detects excess slip from the TCC ( because the TCC apply piston is sticking, meaning insufficient pressure to lock the TCC), and sets a DTC (but doesn't light the check engine light), and then disables overdrive.

 

With a proper scantool, you can see the DTC that's set,  P0740.


Edited by Galaxie500XL, 26 September 2017 - 07:43 PM.

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galaxie500xl

1988 Camaro IROC-Z 5.7 TPI 5-speed

2011 Chevrolet Equinox LT

1994 LeBaron GTC Convertible

GONE to a new home... 1995 Cutlass DOHC Convertible, 3rd Quarter 2012 W-Body.com COTQ

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#22 cutty collector

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Posted 28 September 2017 - 01:55 PM

100% right on Galaxie mine packs it in at about 160 on the scan tool like clock work .Sorry haven't got the sonax part numbers on hand haven't repaired mine yet either .She needs lots of tlc over the winter



#23 Mstg007

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Posted 28 September 2017 - 05:31 PM

Got some more to the story. I was driving home on the interstate yesterday. Top down and windy day. Anyways, I think I felt the transmission thump (change gears) alittle while going around 70 MPH. When it did do it, the engine would rev up just a little. I then had to push harder on the accelerator and let off to get it back to over drive. It did it a couple of times.

 

Is this still linked about to the TCC Piston possibly getting stuck?



#24 55trucker

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Posted 28 September 2017 - 07:29 PM

Are you absolutely sure that what you felt was the trans shifting from 4th to 3rd or was it the TCC unlocking and what you saw on the tach was the engine rpm rising. The trans shifting from 4th to 3rd at that speed WITH the converter locked up is hard on the clutches without the 4th clutches first releasing before the downshift takes place, at that speed the 4th clutches are applied by a signal from the TPS & the VSS that intern the ECM allows shift solenoid *A* to energize, the clutches won't release unless there is a command by the ECM to do so by downshift via accelerating. The TCC will stay locked up unless the driver relaxes their foot on the throttle pedal or depresses it to accelerate. 


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Steve


#25 cutty collector

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Posted 08 October 2017 - 03:04 PM

sure sounds like a tcc going in and out the shift from 4-3 would be fairly violent compared to the tcc going in and out .If youre sure it was a gear shift pull it into third from overdrive and nothing should happen unless it is still in fourth



#26 Mstg007

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Posted 09 October 2017 - 04:21 PM

Just got an update on this this weekend. We were looking MAF sense and was unclamping the throttle body from the intake. We noticed that the was a kink in where the throttle body lip connects to the intake. Guessing it was open as I was driving it. Anyways, so far I have not had any of the problems I was experiencing so far... something so simple. can cause all sorts of weirdness.


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