Speedometer Question

[mdmayo]

Good god! You would think with all the knowledge of using the equation to figure speed that there would be someone out there that would be more entertained on how to fix the speedometer...like me......

What is the year make and model. If its a GM and around 1998 or newer then theres a 90% chance that the Stepper motor that drives the needle is bad because the originals have been superceded by a more dependable version.

Here's a question for you! DOES THE ODOMETER STILL ADVANCE WHILE DRIVING? If so then your speed sensor is working and your problem is in your instrument cluster. If not then most likely your speed sensor (VSS) is bad.(most bolt onto tailshaft of tranny, some fords put them on the rear axle).
If your vehicle is so old that its speedo is cable driven then thats a totally different game.

Well, nobody asked that question!

I learned how to fix the older stuff by building street rods with the old man back in the day, and then for the later model cars in the Guarantee Auto/Nationwise Auto days. I didn't become a total dork until much later in life... and we haven't touched on the tire size equations yet!

 

[Moparracer89]

Well, this certainly blew up while I was away! Reason I asked is not because my speedo is broken or that I got in trouble with the law, as people seem to think. I'm building a street rod with a custom dash and gauge cluster. I dont feel I need a speedo if its not required.

 

[1775usmarine]

Known distance divided by time equals speed. Just south of Franklin on US 31 is a speedometer check area. Five miles of accurately spaced mile markers. 60 miles per hour equals 60 seconds. If you complete a mile in less than 60 seconds, you are going faster than indicated. If it takes you longer than 60 seconds, you are going slower than indicated. Stopwatches are your friend. Know the distance between any two points and how long it takes to go between them and your basic grade school math will solve the issue for you.

That is..........assuming you passed grade school math.

Or 6 secs for every tenth of a mile equals 60 MPH. You can then use 5 secs for every tenth to be approx 70mph, 7 secs for 50 mph, and so on. I have an 05 Impala and the gauges work when they feel like it. I heard they have a tech bulletin out for thousands with this problem but no recalls. Cheapo GM can't do anything right. Though I still get good gas mileage for almost 160k miles.

 

[IndyDave1776]

Part of the discrepancy between GPS and speedometer is that the speedometer necessarily is going by the actual distance driven. If you are driving on a grade, the GPS measures horizontal distance divided by time, meaning that it is figuring according to driving on the long leg of a right triangle when you are actually driving on the hypotenuse. In most places in Indiana this won't be a big issue, but I have had some strange things happen in Tennessee.

Another way to check your instruments is while driving the interstate, check your odometer while passing a mile marker. If it still lines up after 10 or 20 miles, you can rest assured that it is close enough for those not engaged in rocket science. Significantly, since the odometer and speedometer work in tandem with each other, this method is absolutely not speed sensitive, either in average travelling speed or variations while driving between points.

Tip of the hat to the OP for asking a question pertaining to a constructive endeavor rather than the popular assumption that he got ticketed!

 

[Redtbird]

Is it Indiana/Federal law to have a functional speedo in your vehicle?

Only if you are going swimming!