Speedometer drops below zero, always 10mph slow
10-25-2013, 05:42 PM
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Speedometer drops below zero, always 10mph slow
Did some searching and all I could find was fixing speedo readings for different size tires/gears. Also found a ton of broken speedos, but nothing like my problem.
When stopped, my speedometer sits below zero, pegged down to around -10mph if such a mark existed. When I'm doing 15mph according to the dash, GPS lateral speed and radar read 25 mph. Reading 35 at an actual 45mph. Speedometer at 60mph means truck is moving 70mph. You get the point. It's off by 10mph at EVERY speed, it's not a ratio thing. I assumed it was because of tire size, but if that were the case it would be off by twice as much at 70mph compared to 35mph. Also, I'm running 265/70/R16s which are comparable to the stock 31" tires listed inside the door sill.
Is there any way to take apart the dash and manually re-zero the needle? My friend said to leave it in case I get pulled over for speeding but not only do I not really speed, but that feels sleazy. I accept responsibility for what I do and I want my speedometer to be accurate in case some one else is driving.
When stopped, my speedometer sits below zero, pegged down to around -10mph if such a mark existed. When I'm doing 15mph according to the dash, GPS lateral speed and radar read 25 mph. Reading 35 at an actual 45mph. Speedometer at 60mph means truck is moving 70mph. You get the point. It's off by 10mph at EVERY speed, it's not a ratio thing. I assumed it was because of tire size, but if that were the case it would be off by twice as much at 70mph compared to 35mph. Also, I'm running 265/70/R16s which are comparable to the stock 31" tires listed inside the door sill.
Is there any way to take apart the dash and manually re-zero the needle? My friend said to leave it in case I get pulled over for speeding but not only do I not really speed, but that feels sleazy. I accept responsibility for what I do and I want my speedometer to be accurate in case some one else is driving.
Last edited by AshenCrow; 10-25-2013 at 05:44 PM.
10-25-2013, 06:58 PM
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Don't know yet, but it is stock. As I said before, this would not have anything to do with the gear ratio. If it were the gear ratio and I were off by 10mph at 70, I would be off by 5mph at 35. It even works exactly as it should when the needle is below zero, when I'm at 1-10mph... it's just below the scale. As far as I can tell the needle is just turned to the left by a few degrees, equal to around 10 mph. Can that needle be adjusted manually if I open my cluster?
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10-27-2013, 10:25 AM
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I'm really not trying to be an ass, I promise, but I've dealt with tire size differences on several cars before with cable and electronic speedometers and it never did this. Please don't take offense to my wording, I'm not being mean and I appreciate you trying to help.
Actually, they're about 31", nearly equal to the stock 31x10.5s that came on my 4R from the factory. Two sources confirm this. Circumference is the important stat here.
Let's look at this empirically. First is stock vs my tire, speedo vs calculated actual vs GPS-verified actual. I am ALWAYS 10mph over. Not a percentage of speed difference, but a constant difference at every speed. I actually tested this at 15, 25, 35, 55, 60, and 70mph with two GPS devices to account for error because it seemed so strange.
Here is what it would look like if I had put bigger tires on a truck that had smaller tires from the factory. The difference in circumference would lead to a percentage difference in speed. I.E. the example tires are 9.2% bigger in circumference, so 9.2% extra of 35mph is 38.22mph and 9.2% extra of 70mph is 76.44mph. That's a 3.22mph bigger difference at 70mph vs 30mph. Mine is 10 over at 30 and 10 over at 70.
Do you guys understand why I have ruled out gear and tire sizes now? I feel like I really beat a dead horse but I wanted to be clear from every angle. I really believe my cluster just needs to be manually adjusted but I didn't want to tear into it unless some one knew it could be done... that's really all I was asking. =\
Actually, they're about 31", nearly equal to the stock 31x10.5s that came on my 4R from the factory. Two sources confirm this. Circumference is the important stat here.
Let's look at this empirically. First is stock vs my tire, speedo vs calculated actual vs GPS-verified actual. I am ALWAYS 10mph over. Not a percentage of speed difference, but a constant difference at every speed. I actually tested this at 15, 25, 35, 55, 60, and 70mph with two GPS devices to account for error because it seemed so strange.
Here is what it would look like if I had put bigger tires on a truck that had smaller tires from the factory. The difference in circumference would lead to a percentage difference in speed. I.E. the example tires are 9.2% bigger in circumference, so 9.2% extra of 35mph is 38.22mph and 9.2% extra of 70mph is 76.44mph. That's a 3.22mph bigger difference at 70mph vs 30mph. Mine is 10 over at 30 and 10 over at 70.
Do you guys understand why I have ruled out gear and tire sizes now? I feel like I really beat a dead horse but I wanted to be clear from every angle. I really believe my cluster just needs to be manually adjusted but I didn't want to tear into it unless some one knew it could be done... that's really all I was asking. =\
Last edited by AshenCrow; 10-27-2013 at 10:30 AM.
10-27-2013, 10:48 AM
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Thought about it, but from what I've seen on the board it seems like my SR5 cluster is highly sought after and it would be wise to attempt to fix it first. What do they usually go for, anyway?
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Jimkola (02-16-2021)
10-27-2013, 11:27 AM
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Bend a plastic needle 15-20 degrees in an arc? Sounds like a good way to break it, lol. I will try to pop it off, thank you nothingbetter. =)
10-27-2013, 02:27 PM
#13
Don't count on it popping right off. It's going to be on there pretty tight. You've got a fairly high chance of breaking something doing that too, if you're not super careful. But you can always replace just the speedo/odo unit. They're only about 150 bucks or so new. And yes, a used combo meter(with a good used speedo/odo in it) is going to run you way less(usually). I see them going for as low as $50. Sometimes a little less, sometimes 3x as much. Check ebay and/or car-part.com.
I bet that's pretty common. I did the same thing to the speedo in the Camaro I used to have(except I did that on a highway, not a strip). But, from what I can remember, the speedo in mine only went to 90. And once I pushed it about 40 mph past that, it read around 15 mph low. 90 mph speedo in a Z28...ummm o.k., sure. Like that's even close to high enough. WTF?
Last edited by MudHippy; 10-27-2013 at 02:51 PM.
09-08-2014, 09:18 AM
#15
I'm having the same issue in my 91 PU after replacing the speedometer cable. It's not a gearing issue because it read correctly before the cable broke. Now it sits at -10 when stopped.
09-09-2014, 03:41 AM
#18
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