I cannot figure out why my speedometer is still off. It is right until around 35mph according to GPS, and then it gets 5mph ahead. Today I used an 05 Tahoe and made some distances to compare to the odometer in my Camaro. On a 1.3 mile trip my odometer was about .1 miles ahead, and on a 2.8 mile trip my odometer was .2 miles ahead. So I know it isn't from putting the needle back on wrong when I swapped the odometers in my original cluster and my 145mph cluster. Today I took apart the 145mph speedo and put the odometer back in my 110mph speedo and everything is still off the same.

I do have different size tires than stock and different rear end gears than stock, but I should have fixed that. I have 275/40/17 tires on it now, which are .3" smaller than stock. The Miata.net Tire Size Calculator says the tires should actually be slowing my speedo down by .8mph at 60mph. My car came with 3.23 rear end gears, and it has 3.73 in it now. So, following the guide on http://www.transmissioncenter.net/sp...n_______va.htm, I put in a 15 tooth drive gear and a 43 tooth driven gear to correct the speedo.

Are these gauges that bad, or is there something I missed?

 

I was looking through Transmission Center's web site again, and I noticed there are two different speed sensors. One for 35-39 tooth driven gears and one for 40-45 tooth driven gears. I called them, and the guy I talked to said he didn't know if that was causing my problem. He did say that the 40-45 tooth sensor has a different offset for the driven gear because of teh bigger gear. He said that if I stayed with my stock sensor, the bigger gear would eventually wear out the bushing in the sensor.

Does anything think that is actually causing my speedo problem?

 

Compuwiz,
My speedometer is not working correctly either. It works intermittently at highway speed. Do you think the sensor would cause this? Can you tell me where it is located?

 

If the sensor is going out, I don't see why it couldn't cause that. If you have access to another gauge cluster, you may want to swap them and see if the problem is still there first. The speed sensor is located on the tail housing of the transmission.

 

Would a faulty speed sensor kick off a trouble code to the ECM?

 

I have no idea on that one. Probably not since these cars don't have everything wired up to a central computer like new cars do.

 

No one else has speedo issues?