Electrical Problem

Help! I have a 1996 F-250 7.3 Powerstroke, with 370000 miles. I'm on my 3rd E4OD tranny.  On occasion my electronic speedo gauge just goes blank and at the same time my tranny warning indicator light on the shifter will come on.  When this happens it seems to change the line pressure in my tranny causing harsh and erratic shifts.  The dealer can't seem to pin point the problem as well as a tranny shop.  Only mods to engine is a K&N air filter.  The truck is lifted, 4", stock gearing 4:10 ratio, I did install a Dana 60 front end but can't see where that would affect anything.  I did change out the rear wheel speed sensor on the rear diff thinking that may be the problem, but wasn't.  Are there any other sensors or items anybody thinks where I might start looking?

Thanks in advance - Tom  

I think I would start by looking for a bad ground in dash area or with related tranny controls. BTW, the reason you have gone through so many trannies is because with lift and tires you are working tranny pretty hard. You should be running 4.56 or maybe even 4.88's  

My Excursion did the same thing but the speedo never came back. The dealer replaced a VSS which may be the same as you had replaced. There is another sensor on the trans. I didn't do the work  myself because of the warranty, So I don't want to steer you in the wrong direction with bad info.While this is a great site for aftermarket applications, here are two sites that really know their Fords. They would be a great resource for a problem like this.

http://forums.thedieselstop.com/forums/ubbthreads.php?ubb=cfrm

http://www.ford-trucks.com/forums/index.php

Jerry  

Good tip, that year Ford should have a speed sensor in rear axle housing.