Speedometer off
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Mountain Pass
Joined: Apr 2020
Posts: 189
Likes: 25
Speedometer off
Truck (in sig) has a 3.55 rear (according to tag) and I'm running 235/85/16 tires on the rear. For some reason, my speedometer is consistently showing me running faster than GPS. For example, at 55 (indicated), my GPS shows 53/54. At 75 (indicated), GPS shows 67-68.
This doesn't bother me so much, because I am a slow driver, but I cant figure our why it would be showing as faster than I am actually travelling (and so, I guess it does bother me). I would have thought with the 3.55 and taller tires, the error would be a speedo that showed me going slower than I was actually travelling. What could the issue be? I mean, did ford make a speedo cable gear for an even lower diff? Were these Speedometers always off?
This doesn't bother me so much, because I am a slow driver, but I cant figure our why it would be showing as faster than I am actually travelling (and so, I guess it does bother me). I would have thought with the 3.55 and taller tires, the error would be a speedo that showed me going slower than I was actually travelling. What could the issue be? I mean, did ford make a speedo cable gear for an even lower diff? Were these Speedometers always off?
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Joined: Jan 2001
Posts: 56,992
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From: Virginia
I don't trust GPS. Get on the interstate that has the miles marked, and while you hold it at 60mph, get someone riding with you to time how long it takes to go between the markers. It should take 1 minute to go one mile.
Actually at the slower speeds your GPS is very close. I have had speedometers get farther off the faster I went, and it ended up being a lubrication problem in the speedo head or a problem with the cable. Does your needle vibrate back and forth any at all? If the cable is not smooth, it can "flick" the speedometer needle up to a average faster speed.
Actually at the slower speeds your GPS is very close. I have had speedometers get farther off the faster I went, and it ended up being a lubrication problem in the speedo head or a problem with the cable. Does your needle vibrate back and forth any at all? If the cable is not smooth, it can "flick" the speedometer needle up to a average faster speed.
Lead Driver
Joined: Jun 2013
Posts: 5,668
Likes: 1,159
From: Tolland, CT
I got over mine reading off many years ago, along with the gas gauge that drops quickly to a 1/4 tank left and then stays there for a long time. With just below a quarter tank, it only takes about 6 gallons to fill it.
If the truck runs well...find something else to worry about,
LOL
If the truck runs well...find something else to worry about,
LOL
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Mountain Pass
Joined: Apr 2020
Posts: 189
Likes: 25
Thanks guys. I suppose I can/will live with it - Max's truck seems eerily similar to mine -haha.
I have noticed the speedo being a bit jerky on acceleration sometimes - but I have to imagine dealing with that cable is more work that its worth.
I have noticed the speedo being a bit jerky on acceleration sometimes - but I have to imagine dealing with that cable is more work that its worth.
Lead Driver
Joined: Jun 2013
Posts: 5,668
Likes: 1,159
From: Tolland, CT
My Dad bought my truck used in 1990. I've always assumed it had its transmission replaced before he bought it, that's my rational for the speed being off...LOL
It's easy to except things when you learn how to rationalize...
It's easy to except things when you learn how to rationalize...
Senior User
Joined: Nov 2008
Posts: 200
Likes: 13
From: Sheridan, Wyoming
My speedo is off as well. I have a `986 F350 4x4 with 3.55 gears and a 4 speed. I just live with it, it isn't that bad. My gas gauge does bother me. When it's full It reads empty, at 3/4 tank it reads at half and at a half it reads at a 1/4 then goes to empty again very quickly. So when it goes to empty again I just go fill up, lol.
Lead Driver
Joined: Nov 2013
Posts: 7,178
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+1 on that. Instead of relying on a potentially inaccurate GPS reading, try Waze or a similar traffic app. Find an active speedtrap and blast through about 20 over the speed limit. Police radar is calibrated frequently and should be very accurate. Compare the number on the ticket with your speedometer and then you'd know for sure.
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FTE Legend
Joined: Nov 2015
Posts: 30,935
Likes: 4,123
From: Angier, NC
I dont have any issues with my Rand McNally truckers GPS.
I use it all the time in my 18 wheel work truck and it reads the same as the speedo in it.
We also had camras that posted the speed and it was dead on with it also.
It is also on the money with my and the wife's DD so that is what I used when checking the speedo in my truck and it reads pretty close to not worry.
Maybe it's the cheap GPS you guys use
Dave ----
I use it all the time in my 18 wheel work truck and it reads the same as the speedo in it.
We also had camras that posted the speed and it was dead on with it also.
It is also on the money with my and the wife's DD so that is what I used when checking the speedo in my truck and it reads pretty close to not worry.
Maybe it's the cheap GPS you guys use
Dave ----
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Mountain Pass
Joined: Apr 2020
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Likes: 25
Haha, by GPS, I mean my phone-indicated speed through navigation and/or a speedometer app. It's been accurate in my other vehicles.
My pops hauls fuel and has the same impression of his Rand GPS.
My pops hauls fuel and has the same impression of his Rand GPS.
FTE Legend
Joined: Nov 2015
Posts: 30,935
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From: Angier, NC
That's a lot of grille tanks
Like any GPS it's a tool like a road map you still have to think when driving.
Dave ----
Lead Driver
Joined: Apr 2002
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Phone gps works very well for me. I think it varies when you are remote from towers or when the triangulation is acute between towers. Try it on the freeways through well established communities and it's probably more accurate there.
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
GPS uses satelittes not cell towers, but if the phone has problems tracking them the apps performance will be glitchy. Older phones have trouble processing newer apps as well and that can impact an apps performance, when I first got my current phone a few years ago the GPS navigation app I use worked really well, but the app has been updated a couple times to include more features and now the phone really struggles with it.
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