Speedometer

LeVeL

LeVeL

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I checked my speedometer against our GPS once and found that the former was always exhaggerating by about 5mph. Then my engine went bust and I just got the car back yesterday with the new motor. Half an hour ago I got pulled over for 44mph in a 30 zone (showed me the radar reading), which means that (assuming the 5mph thing still holds) I was travelling at an indicated 49mph. The thing is though, I was definately NOT going an indicated 49, especially since there were cops all over the street due to construction nearby (before anyone tells me off for speeding in a work zone, I was already way past the work zone on a clear two-lane). What I'm wondering is could the new engine affect speedometer accuracy? I don't think the speedometer was changed, so I assumed that that was uneffected and kept driving a tick over what I'd normally drive with a correct speedo, but perhaps that's not the case, since I don't think I was even doing 44 indicated. Any thoughts? Or am I just crazy and grasping at straws?
 
If I remember correctly speedos are connected to the tranny. Maybe the cable wasn't put in correctly when they swapped engines?
 
If its a cable it could be in bad shape, if its electronic then the sending unit could be faulty.

Also the combined size of wheel/tyre will affect the speedometer reading if it is not stock, http://www.miata.net/garage/tirecalc.html

Of course it could just be the gauge, I'd think it more likely to be the cable or sender (sensor? whatever it's called) though.
 
To be honest, having given it some thought I'm not sure how the cable could go bad and rotate faster, I'm not really qualified to say so but since it's (if it is a cable driven speedo and not electronic) just a cable attached to a gear that connects to the output shaft of the transmission it doesn't really have the potential to do anything other than work or break completely.

edit: The car is an Accord right? what age? from a quick google it says the speedo is electronic so you can probably disregard any possibility of a cable being an issue, it's likely the actual sending unit/speed sensor or speedometer that's not working properly.

http://answers.yahoo.com/question/index?qid=20090330000036AAT0Oq1

another edit: Issue could be with the VSS, vehicle speed sensor that sends the signal to the speedo.
https://pic.armedcats.net/w/wa/waydee/2009/08/27/83244559.gif
 
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There are speedo shops that troubleshoot and fix this very issue, look for one local to you.
 
Here's a question, did they replace the transmission and engine as a unit, or did they just replace the engine?
 
Yes, if they replaced the VSS while they were at it, or at least cleaned up the sensor connection. Or the generator wheel that the VSS reads could have been replaced.
 
Bingo! Thanks spectre. Now, is there any sort of official document (Haynes manual would probably work, or something similar) that says exactly what you just said? I can't exactly come to court and say "well this guy I know from the internet said this... he's from texas and loves jaaaaaags, so he must be right!"
 
LeVeL said:
Bingo! Thanks spectre. Now, is there any sort of official document (Haynes manual would probably work, or something similar) that says exactly what you just said? I can't exactly come to court and say "well this guy I know from the internet said this... he's from texas and loves jaaaaaags, so he must be right!"
Click to expand...

Unfortunately, there won't be any cite that I can give you for that - plus it wouldn't matter as you didn't have speedometer certification prior to the ticket. I would suggest that you throw yourself upon the mercy of the court (with a lawyer to hand) and perhaps you can get it bargained down to a fix it ticket if you don't have a pattern of speeding tickets in that jurisdiction. I would suggest that you should see if you can set up and video tape an experiment to prove that the car speedo is reading off (videotape the inside of the car while you drive past a "Your Speed Is" sign, or something like that).


I don't advise that you use the "well this guy I know from the internet said this... he's from texas and loves jaaaaaags, so he must be right!" defense, but it has apparently worked in one case. :lol:

And no, I don't know how the guy got away with it. :p
 
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I'm not sure about MA, but over here if you demand that the local radar technician show up as a witness you are pretty much scott free. Radar techs are not government employees and have no reason to waste their time coming to court so you can get off with a mistrial.
 
Spectre said:
Unfortunately, there won't be any cite that I can give you for that - plus it wouldn't matter as you didn't have speedometer certification prior to the ticket. I would suggest that you throw yourself upon the mercy of the court (with a lawyer to hand) and perhaps you can get it bargained down to a fix it ticket if you don't have a pattern of speeding tickets in that jurisdiction. I would suggest that you should see if you can set up and video tape an experiment to prove that the car speedo is reading off (videotape the inside of the car while you drive past a "Your Speed Is" sign, or something like that).


I don't advise that you use the "well this guy I know from the internet said this... he's from texas and loves jaaaaaags, so he must be right!" defense, but it has apparently worked in one case. :lol:

And no, I don't know how the guy got away with it. :p
Click to expand...

Who did that defense work for?
 
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