Speedometer Hijinx
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Mountain Pass
Joined: Nov 2021
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Speedometer Hijinx
1991 F150, 4.9 liter, automatic transmission 3 speed with overdrive, standard cab.
When I first drive the truck after it's been idle for maybe several hours to a few days the speedometer is off from 5-10 mph. depending on the speed limit.
An example would be 25 mph. on the speedometer, but 19 mph. on the phone app. 50mph. on the speedometer, but 41 mph. on phone app. By the way the phone app. always matches the speed signs around town.
After driving around town for sometime however the speedometer comes very close to matching the phone app. within 1-2 mph.
Any ideas on this anomaly?
When I first drive the truck after it's been idle for maybe several hours to a few days the speedometer is off from 5-10 mph. depending on the speed limit.
An example would be 25 mph. on the speedometer, but 19 mph. on the phone app. 50mph. on the speedometer, but 41 mph. on phone app. By the way the phone app. always matches the speed signs around town.
After driving around town for sometime however the speedometer comes very close to matching the phone app. within 1-2 mph.
Any ideas on this anomaly?
Hotshot
Joined: Jun 2015
Posts: 12,871
Likes: 2,443
Ford never made a 3 speed with overdrive. You have a 4 speed. The transmission is either an E4OD or an AOD. Is there a button to turn off the overdrive?
Back to the topic: The speedometer in 1991 is cable driven. Does the speedometer needle jump or is the movement smooth?
Back to the topic: The speedometer in 1991 is cable driven. Does the speedometer needle jump or is the movement smooth?
Thread Starter
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Mountain Pass
Joined: Nov 2021
Posts: 227
Likes: 75
P,R,N,D,2,1. I'm assuming the overdrive kicks in unless I've turned it off. Maybe D(rive) is the overdrive. I'm pretty sure it's not a two speed, and it's also not a manual since there isn't a stick shift or clutch. Did I cover all the bases?
Now, back to the speedometer it holds steady. Everytime the truck sits for any length of time longer than an hour or two the speedometer reverts back to being off roughly 5-10 mph. depending on the speed I'm traveling. The slower I go the less it's off, but it is off every single time. After a few miles the speedometer comes closer to actual speed, within 1-2 mph., sometimes right on. Why this speedometer , being cable driven, is consistantly returning to the same under speed circumstances makes no sense to me.
Now, back to the speedometer it holds steady. Everytime the truck sits for any length of time longer than an hour or two the speedometer reverts back to being off roughly 5-10 mph. depending on the speed I'm traveling. The slower I go the less it's off, but it is off every single time. After a few miles the speedometer comes closer to actual speed, within 1-2 mph., sometimes right on. Why this speedometer , being cable driven, is consistantly returning to the same under speed circumstances makes no sense to me.
Hotshot
Joined: Jun 2015
Posts: 12,871
Likes: 2,443
P,R,N,D,2,1. I'm assuming the overdrive kicks in unless I've turned it off. Maybe D(rive) is the overdrive. I'm pretty sure it's not a two speed, and it's also not a manual since there isn't a stick shift or clutch. Did I cover all the bases?
Now, back to the speedometer...
Now, back to the speedometer...
There is a drive gear on the end of the transmission (2wd) or transfer case (4wd). Then there is the driven gear, a cable and the speedometer head. It could be that the cable is dry causing it to bind up. Once it warms up it starts working? Disconnect the end at the trans/transfer case and try turning the cable.
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Mountain Pass
Joined: Nov 2021
Posts: 227
Likes: 75
I wlll try this when the weather warms and dries up because lying on my back in the gravel isn't my thing.
I wasn't sure if there was a modulator, or sensor that might be the issue, but if it's just the cable I'll check.
I wasn't sure if there was a modulator, or sensor that might be the issue, but if it's just the cable I'll check.
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