Best way to adjust speedo?

[Skunksmash]

After working on my gauges quite extensively, I noticed that my speedometer is about 8 MPH fast. So if I'm doing 20 it will say I'm doing about 28. I pulled the needle and painted it bright orange again. It was faded and ugly. That is probably where my trouble started. I was just wondering if there is a simple trick to adjust the speedo, without having to pull the needle off again.

[78 Chevyrado]

Adjusting the needle is the worst way to account for wrong speed.  it would work except for the amount its off changes with speed.

My speedo is off by about 5mph (AT 70MPH.)  at 35MPH it's correct.  I have checked this through local police and their radar guns. (some are friends and will let me use them to test this)   

At 70MPH  I'm off by about 5mph.  at 35MPH its correct.  I assume between 35MPH and 70MPH Im off by halfway.  locigally. 

To fix this.  you must find out what your tire diameter is, and try to find the approriate speedo gears for it.  there's a gear goes on the output shaft of the trans, and with tire size in mind you can pickj the right gear for this tire size.  some tire sizes may require a new gear on the output shaft which is expensive.

If you know how much its off by, drive it knowing this.  i do and its not worth the expense to me to fix this... yet.  yet means until i have my trans rebuilt

[Irish_Alley]

My speedo is off by about 5mph (AT 70MPH.)  at 35MPH it's correct.  I have checked this through local police and their radar guns. (some are friends and will let me use them to test this)   

reminds me of a cop around here had a guy ask him if he could see how fast he was going. the cop said yes, so the guy pretty much does a quarter mile run by the cop. the cop pulls him over and gives him a ticket for speeding. the cop never said he could speed just he would tell him how fast he was going lol

[ehjorten]

What year is your ride?  The answer depends on that.  There are two different systems: 1) Mechanical, 2) Electronic.

Either way the speedometer isn't off so many miles per hour; it is a percentage of your speed.  So if it says 25 when you are actually doing 20, that is 25% over.  At 80 MPH it would then read 100 MPH!

If it is consistently off by only a certain MPH then your needle is just off from you removing it, and the gearing for the speedo is correct.

Correcting a mechanical speedo involves either changing the driven gear or sometimes you need to change the drive gear.  An alternative is to get a speedometer correction box.  It goes between the output on the transmission or transfer case (in the case of a 4x4) and the speedo cable.

Correcting an electronic speedo involves pulling the DRAC from under the dash and replacing the jumpers on the circuit board with a 7-pin DIP switch.  This involves de-soldering and soldering.

[Skunksmash]

Well mine is an 87 model. It has a cable, but it also has this weird little sensor eye thing that sort of plugs into the speedometer. Where exactly is this DRAC thing? I don't have a problem with soldering. I've recently had to get good at it.

[ehjorten]

Your speedometer is not electronic.  It is cable driven, so you will not have the Digital Ratio Adapter Controller (DRAC).

You need to determine if your speedometer is off due to gearing or if it is off due to you removing the needle and replacing it.  If it is indeed off because of gearing then you can get a mechanical ratio adapter like this one:


This website has lots of information: http://www.transmissioncenter.net/speedometer_calibration_______va.htm?gclid=CM7338qElLACFUKDpAod9xSxyA

Also...I have seen somewhere on the 'net information telling you how to get your needle off and put it back on properly so that it is in the correct spot.  I don't remember where, but if you do some searching for speedometer repair you may find it.

[TimberwolfFXDL]

if he took the needle off to paint it, then put it back on in the wrong place it could be off a set mph and not necessarily a percentage.  Alternatively, if it was off a percentage before, and THEN he put it back on in the wrong place, he could have a compound problem to solve...

[Skunksmash]

Doesn't seem like it would be a ratio problem, cause the problem wasn't as bad before I took the needle off. Before it was only about 4-6 MPH off instead of somewhere in the area of 8-12 MPH off. There is a little white mark on the speedo, way below the 5 MPH mark. Its just out there all on its own. I'm thinking that mark is where you are supposed to set your needle when you're putting it back on.

[bake74]

reminds me of a cop around here had a guy ask him if he could see how fast he was going. the cop said yes, so the guy pretty much does a quarter mile run by the cop. the cop pulls him over and gives him a ticket for speeding. the cop never said he could speed just he would tell him how fast he was going lol

     That right there is funny. 

[78 Chevyrado]

What you run into is that the needle itself itsnt constant.  if you reposition the needle, it will def be off somewhere.  only reliable way is to change the speedo gears in the trans.  Reason I havent corrected mine is, the speedo gear I need to use means changing the gear on the output shaft.  your's may not require this.

[DnStClr]

Sometimes even changing the gear at the end of the speedo cable still doesn't correct the reading, and when that happens it's possible that the speedometer magnets have simply lost their mag power and need to be replaced by a speedo shop.
 Another option, of course, (might be a lot cheaper)  to go to the local pick & pull. Or see if you can get one on eBay.

[Skunksmash]

Yeah that is why I think they should take that writeup down that they have around here somewhere.... about pulling off your needle. Completely unnecessary. All you need to do is cut a slit in two separate sheets of paper and you've fully masked off the needle for painting.