Hard Shift

Good Morning, the last couple of days my 91 Ford F150 XLT Lariot, 302 V8, Automatic trans w/Electric O/D

button on dash, has started to do a not so smooth up shift from 1st to 2nd to 3rd. It goes into O/D smooth. It is

a solid shift with a slight jerk. I can manualy shift it and the shift is smooth. The down shift is smooth. Can

anyone give me some advise. Thank you in advance.

Before trying to diagnose a transmission shifting problem, always make sure the engine is running properly. Even though most late model computer controlled transmissions dont have a vacuum modulator, vacuum still plays a part in the proper shifting. If an engine isnt running right, the vacuum will be off for a given throttle opening, and this can cause delayed, harsh upshifts. A bad VSS can also cause harsh, erratic shifting, but make sure its running good first.

Thank You

unclebubbles: where would I find this vss sensor on my truck. 302, automatic, F150. Thanks again

Hey Sparky
It sounds like you probably have an E4OD trans. In 91, i think the speed sensor was still on the tailshaft of the transmission. Look at the rear of the trans, where the speedometer cable would normally go(drivers side). If you see a wiring harness attached to a device inserted in that hole, that is it. Somewhere around 92 i think, they quit using the trans mounted sensor, and started putting it in the rear differential. If yours is not on the rear of the trans, its on the top of the rearend. You might want to take it somewhere and have the codes read, or if you have a manual, on the 91 you could read them with the MIL.

unclebubbles: I found these two connections. One is at the end of the trans. and the other is atop the differential. Which one do you think it could be. Do you believe that my local ford dealer wanted a min. of $65 to have a tech crawl under to look an tell me what they were. Needless to say, I told him where to go. Thanks

http://i144.photobucket.com/albums/r194/sparkyrhett/atopdifferential.jpg

http://i144.photobucket.com/albums/r194/sparkyrhett/rearoftrans.jpg

Hey Sparky
It is the one on the transmission. The one on your differential is for the rear antilock brakes. Some models only have the one on the rearend which serves both purposes. I would have the codes read first, if you have an Auto Zone near, most will do that for you no charge. You can test the sensor by: Remove the harness and cable from it, remove it from the trans. Youll need a voltmeter that will read AC down to .5 volts( i like to use an analog meter for this to see the needle sweeps, but digital is fine). attach the meter, and give the sensor gear a spin . It should generate a pulsating reading of around 1/2 volt. Also, be sure you check all your fuses.

Thanks unclebubbles!!

Did you think of checking the tranny fluid?

Worn clutch packs greater than .078 will cause harsh shifting..