Speedo Sensor in Diff

[winstontj]

What diff comes in an auto car? Car was an auto that was converted to a 5spd. Car now has a 4.10 diff. Question is regarding the speedo sensor in the diff. Is the sensor on the wheel side or the driveshaft side?

If the wheel side than as long as the wheels are stock size (circumfrence) than it shouldn't matter what diff is in there (4.10, 3.45, 3.64, etc.) because the sensor is wheel speed related correct?

Can anyone confirm for me please?

[PeaveyBassist]

Wheel side. You should be correct.

Will

[winstontj]

so that means the speedo is accurate as well as the tach?

thanks! Makes me feel better to know how fast I'm really going.

[PeaveyBassist]

Speedo sensor is. Tach signal is from somewhere else. Should be accurate though.

Will

[winstontj]

didn't mean to be confusing. Tach is off the coil IIRC but I did some simple math (diff x gearbox x tire) to get an approx speed. I didn't mean to imply that the tach was inaccurate, more to imply that the tach AND the speedo are now 100% accurate.

Thanks for the reply!!!

[PeaveyBassist]

Its cool ;)

Will

[kkamakasi]

So my car is reading 80 MPH when I'm doing 70 MPH (according to GPS-enabled device)...

[jlevie]

If the car has OE sized tires, the speedometer can read 73.1mph when traveling at 70mph and be within specification. If you are reading 80mph at 70 something is wrong.

[FLG]

Ratio does not matter, speed is read by a toothed gear in the diff (dependent on tire speed)

Tach is read off the CPS sensor, not the coil.

[ButtJuice]

I have OE sized tires and my speed is about 7-10 mph above the speed I'm actually traveling at. What will cause this inaccuracy?

[FLG]

Speedo that needs calibration most likely.

Do you have a 13 button obc? Good way to check if its speedo or something else is to click the avg speed on the obc while your on the highway and can keep a constant speed, then hit reset, the speed displayed will be your current speed. Compare this to a gps or something, if its correct the fault lies with the speedo.