Hi

My automatic transmission has been shifting funny meaning it goes through gears it drops down gears for no reason one time I was driving at highway speeds and it dropped down a year and all the sudden it was going at 3,000 RPMs !

Anyways I'm driving a 1990 Ford F-250 4x4 truck with diesel engine and I did notice that my speedometer was jumping up and down ....

That made me think that I needed the speed sensor that was mounted on the transfer case ... My theory being maybe that piece was messed up or maybe the cable was messed up so I figured I'd get both the speedometer cable and the sensor on the transfer case (actually what is that called because when I went to try to buy another one I kept on calling it a vehicle speed sensor and they kept on giving me the one for the rear end which does not the one I needed as far as I know) .

Anyways I wanted to replace that one since I was there figuring maybe the speedometer cable is bad because the speedometer was making some noise...

Anyways long story short I put a new cable in made sure it was all lubed up with graphite Grease or basically graphite I should say not necessarily Grease

Anyways the cable is running smooth because I took the end off and I twisted it with my fingers and it ran really smoothly it turns out I think my speedometer was bad because now it made some horrible screeching noises and it just finally stopped working.

So with that I'm still getting funny shifting to the point where I don't really want to drive the truck because it just shifts randomly and frequently I don't want to mess something up in the transmission

Does mine not having a working mechanical speedometer have anything to do with that? Or is it solely the sensor on the transfer case? Or maybe it could be the sensor on the rear end?

How which one to replace or fix? ...

Thanks in advance for annual help

Edit oh it's a 4-speed automatic e4od transmission. Thanks

 

what trans, E4OD , or C6?
E4OD needs proper tach signal to shift properly along with speed signal to the computer.
C6 is a mechanical trans and just needs vacuum to shift properly.

 

Not sure how the c6 gets a vacuum signal with the IDI as inherently diesels dont produce any. So are they strictly throttle controlled?

 

Hi

I updated my original post but it's the e4od transmission ... My tachometer seems to be reading correctly it's just the speedometer is not working correctly ... It used to jump up and down a bit so I used to blame that on the cable having friction so I replaced the cable and verify that it is very smooth in operation as far as the cable...

Eventually over time the speedometer made some horrible screeching noises and eventually stopped working ... Or maybe working so poorly I know it's not even really working... I was going to get the speedometer worked on ... There's a shop in Richmond that apparently fixes these things but they charge $300 to fix speedometers I really would like to speedometer to work but $300 right now pretty steep so I'm holding off on that a bit.

I don't know exactly how the speedometer is driven I would imagine electrically since there's no cable for it but the speedometer does seem to be working correctly

I don't know if I change the right sensor or not but the one I changed was the one on the transfer case I know there's another one that's sitting on top of the rear differential but I don't think I messed with that one yet or maybe I did I just can't remember it but I know it's got to be a speed sensor somewhere that's messing with my transmission shifting although I will say this the other day when I was driving I used the left turn signal and that caused the transmission to act up ... It was really weird you could be driving along and then you would left turn signal and the transmission would act up I think I do have an LED bulb in there I might have to change that because I read somewhere where LEDs can somehow mess with the mind of the transmission? ... If so it's just a more recent occurrence I was seemingly doing fine running One LED and one incandescent bulb when I tried to run two LEDs one on each side for the brake lights the truck was too crazy but when I got rid of one of the LEDs it seemed to get better although now for some reason it seems like maybe the one might be messing with it because when I use the turn signal on the left hand side with the LED it does cause the transmission to shift or come out of overdrive Etc

 

No, the C6 is vacuum controlled, even with a diesel.

There is an electrical vacuum pump and a control lever attached to the injection pump. This control lever controls how much vacuum reaches the transmission.

 

by the same vacuum pump that controls heater/ac circuit and power brakes.

 

the speedometer on your 90 is strictly cable controlled.... BUT there is a separate vehicle speed sensor connected to the speedometer cable where it plugs into the output shaft of the transmission on a 2 wheel drive, or the output shaft of the transfer case on a 4 wheel drive that gives speed signal to the trans computer.
the $300 PSOM repair those people are talking about is for 1992 and newer trucks.