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post #1 of 4 (permalink) Old 07-03-09, 06:52 PM Thread Starter
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mad jerky shifting 98 taurus

I recently had the transmission replace (used one) on my 98 taurus by a backyard mechanic. This one shifts rough (jerks), especially from first to second. The service engine light came on right away - code P0715 Turbine/ input shaft speed sensor circuit. Could the speed sensor be causing the rough shifting or what else should I look at, and where exactly is the sensor? The speedo works fine and doesn't jump around. Thanks for any help!

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post #2 of 4 (permalink) Old 07-05-09, 07:53 AM
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Re: jerky shifting 98 taurus

My sister has a '99 Sable with similar symptoms. On the 1-2 shift it feels to me like it slips, then it catches and jerks, sometimes hard enough to squeak the tires just a bit. But not all the time - sometimes in driving it 8-10 miles it will do it maybe once pulling away from a light, or do it 3 or 4 times from light to light - then it won't do it again for a while.

Someone I talked to suggested it might have the wrong trans fluid in it, and she had it flushed and refilled, but it didn't change much - it didn't do it for a while that I knew of, then started in again.

I don't know if it's even worth fixing given how cheap I see these go for at the state surplus auctions, usually with a bad motor or a bad trans, and this car has a lot of coolant leaking issues too (it's had three heater cores put in it in the five years she's had it; in all the years I've had cars I've only had to put a core in one car and it came to me that way).

But it would be nice to have an idea what causes this problem and if it's a simple fix or a sign of major trouble.
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post #3 of 4 (permalink) Old 07-15-09, 04:43 PM
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Re: jerky shifting 98 taurus

Well I recently had a 96 Sbale that did the same issue. It would kick/Jerk into 1st-2nd gear. Come to find out the tranny was leaking fluid due to a metal bar on the inner most part of the car when you open the hood. If your car has that metal pipe on the bottom check it to see if it is leaking tranny fluid by starting the car and watching it. Otherwise if that is not it then take it to a garage and have them check the sensor and tranny.

The Input Speed Sensor, AKA Transmission Input SPeed Sensor, sends a varying frequency signal to the TCU to determine the current rotational speed of the input shaft or torque converter. The TCU uses the input shaft speed to determine slippage across the torque converter and potentially to determine the rate of slippage across the bands and clutches. This information is vital to regulate the application of the torque converter lock-up clutch smoothly and effectively.

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post #4 of 4 (permalink) Old 07-15-09, 05:39 PM
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Re: jerky shifting 98 taurus

It is possible for that sensor to cause the concern you have. I would swap it with the one on the old tranny if that was not a concern on that one and go from there. Also- this may seem obvious- but make sure it is plugged in and the connector is seated all the way.

It is possible that the accumulator spring is broken for the low reverse piston. This will cause a hard shift because the piston is being slammed instead of being softened by the spring.
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