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Pete
Pete, Automotive Mechanic
Category: Transmissions
Satisfied Customers: 25417
Experience:  GM and Mercedes vehicle technician.17 years experience.
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1992 ford f350 7.3l diesel automatic overdrive switch on shift

Customer Question

1992 ford f350 7.3l diesel automatic overdrive switch on shift lever when driving without overdrive it seems fine but when over drive is engaged and drive about 30 to 40 miles an hour the engine will decelerate and then accelertate it will keep doing this up and down with tach fluctuating up and down as long as you keep it in overdrive. Push the button to shut off overdrive with button on end of shift lever and it will run constant without the tach and engine reving up then down reving up then down. It seems to be something in the overdrive that keep doing this. Have you got any answers?
Submitted: 1 year ago.
Category: Transmissions
Expert:  Pete replied 1 year ago.
My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
The over drive is designed to lock up around 40 mph or higher in some cases.If you have over drive on and the vehicle speed is fluctuating between 30 and 40 this will cause the over drive lock up to engage and disengage like this here.Usually it isn't recommended to drive with the over drive on when driving under 40 mph.From what you have described here this sounds like the normal operation of the over drive circuit itself.If this is something new occurring that wasn't an issue in the past before let me know.
Thanks Pete