Speedometer error after removing needle

[kaku]

Can anyone help? I had to remove the speedo and tachometer needles to fit Glow Gauges. After refitting, the tacho reads fine but the speedo reading is in error, when driving at 30 it reads 25, at 40 it reads 30 and is 10 mph slow uptp 80 mph, haven't checked above that speed but it seems to be a constant 10 mph slow above 30.

Any ideas?

 

[MiaTurbo]

so take it back off, and put it back on in the proper spot..

 

[traitorhound]

i'm with him ^^^^^^^^^^^^^^^^

 

[kaku]

Thanks for the advice, but it's not quite as simple as that I think.

What I didn't say was that I have tried that, and have reduced the error by fitting the needle with it pointing at 5 mph when at rest. When it was fitted pointing at 0 mph at rest the difference was 15 mph at speeds above 30. ie , when indicating 30 we are actually doing 45!!

Something msut have caused this to happen while the gauge was apart, or do you think I'm missing something obvious?

Thanks.

By the way, how do you add a photo below the text in these posts?

 

[FunkyBuddha]

Are the needles slipping?

 

[MiaTurbo]

here's my guess: the gauge itself is off. if it's cheap, then the whole scale for MPHs could be off.. How did you check it?

 

[-pixy-]

line up the old gauge & new gauge... all the numbers should line up.

 

[blue_potato]

I have done a zillion gauge installs for Miatas and most likely you have done one of 3 things for your speedo to read incorrectly:

1) Make sure that you have actually set the speedo needle at the bump stop of the new gauge which should be at 0 (obviously) with car not moving.

2) You may have pushed the speedo needle in too hard so that it binds on the new gauge face. Check to make sure it clears the new face through full swing.

3) Your new faces may be bad copies and off in general. Match them to your OEM just to make sure.

Rule of thumb for gauge installs - be very gentle on the needle installs. Make sure you set the tach, oil and water temp needle with engine running (at idle 650-750 rpm) and at proper operating temp.

Good instructions here: http://www.miata.net/garage/gaugefaces.html

Let us know what you find out.

 

[kaku]

Thanks for the continuing advice.

Before installing the new gauge face they were checked by overlaying one on top of the other and the markings are identically spaced. Also,when originally refitting the needle it was fitted at the "0" stop and the discreppancy was even greater than it is now, I fitted it again pointing at 5mph to reduce the difference. Perhaps if I fit it pointing at 10-15 it may be closer to the true speed at 30-60!!

Don't think I pressed it on too tight, I know it's not fouling, but next time I have the dash apart will check.

As for checking the accuracy, didn't suspect anything till we noticed that in 30, 40 or 50 speed limits we were flying by everybody. So followed our other car at set speeds and compared, the Grand Cherokee has a GPS with a very accurate speed readout. (To confirm the accuracy of the car{removeable} gps checked it against the two GPS in the helicopter I fly for a living.

I'm running out of ideas, please keep yours coming.

 

[MiaTurbo]

well, if you are 100% it's not an install error, then my guess would be a bad/cheap gauge face..

 

[z00mer]

Just restore it to the original face plates, and see if the problem still occurs. If not....you're problem is the aftermarket ones.