Erratic Speedometer
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Erratic Speedometer
1995 F150, 5.0, 4R70W, 2WD 149k
Picked truck up yesterday and during the test drive I didnt notice it, but on the freeway heading home I noticed the speedo bouncing around 60-70mph
Im unfamiliar with these... Is this an electronic issue? A wonky gear drive somewhere?
Gear @ the speedo? Sensor in the tailshaft?
Thanks
Picked truck up yesterday and during the test drive I didnt notice it, but on the freeway heading home I noticed the speedo bouncing around 60-70mph
Im unfamiliar with these... Is this an electronic issue? A wonky gear drive somewhere?
Gear @ the speedo? Sensor in the tailshaft?
Thanks
Fleet Owner
Joined: Oct 2005
Posts: 20,784
Likes: 1,751
From: Kentucky
There can be several causes of a wavering speedometer. The VSS is the easiest to check. Remove it from the top of the differential then inspect it for signs of debris. If it is caked with shavings/grease you can try to clean it off then reinstall. If there is that kind of build up the rear bearings may be going bad.
FTE Chapter Leader
Joined: May 2006
Posts: 12,321
Likes: 1,298
From: Central Mississippi
If the bearings are going bad the tone ring can outright chew into the vss.
Follow the harness up from the sensor because there can be multiple damage points, particularly melted wires from exhaust pipes.
Follow the harness up from the sensor because there can be multiple damage points, particularly melted wires from exhaust pipes.
Hotshot
Joined: Sep 2001
Posts: 11,958
Likes: 228
The VSS on the rear axle is a likely issue. Check the connector on it also for damage or corrosion. When replacing use the Motorcraft part.
The PSOM and the RABS share the signal from this and I have noticed that sometimes the signal is too weak since disconnecting the RABS often gives the speedometer a strong or clean enough signal to work correctly.
It could also be the PSOM itself, but this is least likely.
The PSOM and the RABS share the signal from this and I have noticed that sometimes the signal is too weak since disconnecting the RABS often gives the speedometer a strong or clean enough signal to work correctly.
It could also be the PSOM itself, but this is least likely.
The Southernmost Mod
Joined: Dec 2004
Posts: 6,902
Likes: 20
From: Caracas, Venezuela
VSS, tone ring (both in the differential), and PSOM (dashboard) can cause this. First you should check the differential, as already stated. The PSOM is the least probable cause. I have this issue where the speedometer needle will jump slightly. In my case, the differential gear imploded and damage a tooth of the tone ring (I was actually pretty lucky it didn't break it too).
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Frdbuy8589
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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Aug 25, 2003 07:24 PM
