Is there an easy way to correct the speedometer on my 1967 Camaro? It has a 4:11 rear end, 396 engine, and an unknown aftermarket transmission. The speedometer is really off right now. When I am going 35, the speedometer reads 40. Its even worse at higher speeds.

 

What rear gears did you have before? If your speedo was accurate before, I can tell you what driven speedo gear you need if you tell how many teeth your current one has. Your speedo is off by a percentage, not a given number, which is why it's off by more at faster speeds. Depending on what speedo gears you have in the trans, you might get away with only having to change the driven gear; the one in the housing the cable is attached to.
If changing just the driven gear isn't going to get you back in whack, you'd also need to change the drive gear inside the tail housing of the trans. Then, the easiest way would be to install a ratio adapter like this: Speedo Ratio Adapter.
Have someone with an accurate car pace you at highway speed to see how much you are off, and figure the ratio you'd need. Based on the difference you gave at low speeds, you would need a .875 ratio (12.5 % reduction). But check it at higher speeds to be sure, it'll be a more accurate test.

 

Thanks for the response. I'll have to check those options out. Unfortunately, I don't know what gears were in the car previously or originally. I purchased the car with its current setup and the previous driver(s) drove the car with the speedometer off.