I have an 89 F-150, 4.9, T-18, 4x4 and driving home yesterday the speedometer was reading 30 one second, the next second it was reading 0 and it has not worked since then.

Can anyone give me some troubleshooting tips, or what you think may be the problem. I have not had a chance to look at it yet. Searching the forums I did not see this problem with others, just the speedo's that vary in speed, this one has always been constant.

Thanks for any help.

Joey

 

Assuming you have an electrical speedo, ie not a gear driven speedo. It is very possible that either the wire to the speed sensor has come loose or the sensor has died.

The sensor is a walnut sized thingie on the top front of the differential, at least on my 94 F250 4x4. It is very easy to replace, don't let the dealer do it, it will cost $60, the part is only about $15. The wire plugs into the sensor. the wire is also the tip off that it is the sensor, since on my 94, the sensor is the only thing on the diff that has wires on it.

Check the wiring and the sensor to see if they are OK. I don't know where the other end of the wire is since it probably goes to the computer or maybe directly to the speedo.

Could be other problems too, in my opinion possibly another loose wire, maybe to the back of the instrument panel.

BTW Does your cruise control work? On a 94 the cruise takes it's signal off the speed sensor too. So if there is a bad sensor or connection, the cruise and the guage won't work.

Good Luck,

Jim Henderson

 

Does your 89 not have a speedometer cable? My 88 does. I don't know what year they went to electronic. If it has a cable, sounds like it is either loose or broken.

If electronic, then disregard.

Winford Friday!

 

Its gear / cable driven . Start with the speedometer gear , its mounted in the tailshaft section of the transfer case .