speedometer calibration

i have a 95 Camaro z-28, just bought it, and the mph is off by like 20. I'll be driving at 60 on the gauge and im really only going 40-45. My friends say that its got a new rear, so im tryin to figure out how to recalibrate the speedometer. Also the governor kick's in at 115 on the gauge and it's only like 90 can someone help!!!

If the rear was changed and the gears are different, your computer needs to be altered to show the different gears, I think in 95 you need a custom burned chip but i'm not too sure about that part.

I think in 95 you need a custom burned chip but i'm not too sure about that part.

That's a great question. I'd think that if it's OBD I you would need a custom prom, but if it's OBD II, I believe you could have it reflashed.

is it auto or manual? i've heard that the the 4-speed autos in early 4th gen models is almost exactly the same as the 700r4, and for my 3.73's i had to get a different set of speedometer gears that are inside the tranny tailshaft. I don't know if this helps or not because i don't know if it applies to your application as well.

and for my 3.73's i had to get a different set of speedometer gears that are inside the tranny tailshaft.

Interesting, I didn't know that.

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

yea, i read about it in a Chevy Hi Performance mag article, they did the exact same ratio as I did, and they also put a address for thirdgen.org's tech article on it saying that it's where they got their info from.

95's can be programmed for your gears. Find out what gears you have and I may have a program already done up for your car with that rear.

yea its a automatic, but i don't know what gears are in it i'll try and find out

I have a stupid question. What happens when you replace a 0-120mph speedo with a 0-150mph one?

reprogram?

If you have a VSS its fine, if your gear driven. I think it needs to be replaced.