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