speedo hay wire

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Dec 15, 2003 | 11:26 AM

scooter_1968

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speedo hay wire

My speedo goes hay wire. Meaning that it starts out fine then jumps from 35 to 70 back to 20 up to what and down to what ever. would this be the speed sensor back on the differential? If so I guess just unplug it and plug the new one up.? thanks.

scott

Dec 15, 2003 | 11:51 AM

fordman300

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From: clarks mills, PA

if your truck is older than 92 it doesn't have a speed sensor on the rear diff just an abs sensor. check the speedo gears in the transfer casre or back of the transmission

Dec 15, 2003 | 01:52 PM

scooter_1968

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nOpe my truck is a 93 AOD tranny. 5.0 So it should have a speedo sensor on the rear axel...

scott

Dec 15, 2003 | 02:07 PM

MustangGT221

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From: Topsfield, MA

Yup, it could be a dirty sensor. Theres only 1 bolt holding it on, pull it out and clean any metal shavings off it. There isn't really anything to go wrong with it becasue it's just a magnet so, just clean it. The next step if that doesn't work is to remove the rear diff cover (you probably should change the fluid if you already havn't). Inspect the toothed ring behind the ring gear for any missing teeth or wear, if so it must be replaced. If that checks out...then follow the wires from the sensor back as far as you can. It's a pulse signal and any bad connections can screw it up. If you have a dead spot at 2-3 mph where the engine wants to die, that is 100% a bad PSOM (programable speedometer/odometer module). These trucks are known for those failing, do a search under "bad psom" for more information. Thats it.