First of all, this is a great site. I have searched it and the fluctuating speedomer seems to be a somewhat common problem. However I am hoping for some different info than has already been posted.

I have a 1992 F150 4x4 with the 302 engine and 5 speed manual Mazda Transmission. The truck has 184,600 miles on it. About a 1.5 weeks ago, I noticed that my speedo was jumping. At the same time the speedo started to jump, I had a clicking noise (sounds like it is coming from the ABS valve assembly) when I hit the brakes. When on long trips the ABS light will come on after about 30-40 miles and will go out after turning off the ignition. When the ABS light is on, there was no clicking.

I have replaced the VSS twice (just incase the first sensor i got was bad), replaced the VSS connector, replced the instrument cluster, replaced the RABS (still had the clicking), and can not find any pinched wires.

Right now I have the RABS un plugged and that got rid of the clicking noise but my speedo is still jumping. I have absolutely no clue what to try next.

Any suggestions, thanks in advance.

 

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Hi !

I still have the original speedometer cable in my old Ford. But I have pulled the inner cable out twice, lubed it, and fed it back in. From what I understand the cable get's dry closest to the transmission where all the heat is.

Hope this helps.

LeRoy Wolff, original owner of
1984 Ford F150
300 six 3 speed with overdrive
optional dual rusted out fenders
truck's nick name "Old Red"

 

Howdy-

Thanks for the above. I forgot tomention that my speedo is electronic. Well atleast as far as I know. I have looked a couple times for a speed sensor on the transmission, but cannot find one anywhere.

Thanks again-

L.Wood

 

I WOULD IMAGINE THAT THERE IS A DRIVE GEAR IN THE TRANS EVEN THOUGH ITS ELECTRONIC,,, MIGHT CHECK THAT ,,,

 

I also had this problem on my 92 F150 4x4. The problem ended up being some gunk built up on the magnetic ring inside the rear end. after it was cleaned off and the rear diff lube changed it stoped the fluctuation on the speedo.

The reason you can't find the speed sensor on the transmission is because it's not there. the sensor is actually in the rear end.

Hope this helps.

 

RABS not working
and the speedometer not working

Replace the sensor on the rear diff housing it is your culprit
have had to do it twice

 

Hey All-

Thanks for your replies, they led my to finding the problem. I thought I would give her a gear lube change. So I poped off the back plate, and was able to see the exciter (tone) ring and noticed a couple teeth were damaged. When I was cleaning the back cover I noticed that on the inside of the cover there was some damage also.

So I jacked up the rear end and spun the tires and noted more teeth on the eciter ring were damaged and some were bent. Not a good sign.

Then I found the root of all my trouble. One of the teeth off my spider gears was broken off and a couple others were chipped. So I took the magnet out of the tool box and fished the rest of the shrapnel out of the bottom of the pan.

Looks like my $50 repair job may cost $500. But altleast I know what the problem is. I just hope she makes until I can get her to the shop.

Again, thanks for your posts. If I didn't find out what it was things could have been worse.

Now here is some info for those others who have a problem with their speedo. I found these on the NHTSA web site. You can search their data base for technical service bulletins. Here is what I found for 1992 F150s:

Service Bulletin Number: BC1401960813
Bulletin Sequence Number: 44
Date of Bulletin: 9608
NHTSA Item Number: SB049276
Make: FORD TRUCK
Model: F SERIES (LIGHT)
Year: 1992
Component: ELECTRICAL SYSTEM:INSTRUMENT PANEL:CLUSTER MODULE
Summary: SPEEDOMETER NEEDLE FLUCTUATION &/OR A LIGHT SURGE WHEN SPEED CONTROL IS USED AT HIGHWAY SPEEDS BETWEEN 50-70 MPH.


Service Bulletin Number: BC2810930403
Bulletin Sequence Number: 010
Date of Bulletin: 9304
NHTSA Item Number: SB033002
Make: FORD TRUCK
Model: F SERIES (MEDIUM)
Year: 1992
Component: ELECTRICAL SYSTEM:INSTRUMENT PANEL:CLUSTER MODULE
Summary: SPEEDOMETER FLUCUATIONS/LIGHT SURGE TT

 

I had...have...the same problem with my '95 Bronco. Same speedo jumping, same ABS light on. Replaced sensor too, also didn't help. Opened the rear end, had the same teeth missing from spider gears and teeth missing from speedo exciter gear. Had spider gears and speedo gear replaced ($650). It worked fine for about a week. Now it jumps and winks at me again. I took it back to the mechanic and he can't find anything wrong with it(big suprise) I'm just gonna drive mine until something breaks(again). If I wanted to remove the rear diff cover do i need to buy a new gasket or use silicone?(I'm more of a suspension person...still learning about drivetrains)


Jon
1995 Bronco- Eddie Bauer, 351W, E40D, too much to list....
1989 F-150- XL, 4x4, 302, M50D, much more to come...

 

 

I use an RTV gasket maker stuff to seal up the rear end. This time I used the copper colored stuff but I have used the blue stuff. You can get it at any Autozone or NAPA. Just apply it liberally so that is squeezez out the sides when you put the cover back on.

Hope this helps.