1965 Dodge Dart high RPM issue

Who knows, maybe somebody slipped a low gear into the rear axle?

This is EASY to chase down. Just google and find an online speed calculator, like this:

http://www.kabamus.com/garage/gears.html

http://vexer.com/automotive-tools/speed-rpm-calculator

etc etc. You can Google

You need your tire size, and Google around until you find a tire chart that shows the diameter of your rear tire size

Then figure your rear axle ratio.

First, block the front tires, and jack up ONE rear tire, be sure the parking brake is released, and that the trans is in neutral.

See if you can turn the jacked up wheel. If you can, you don't have Sure-Grip (limited slip) rear axle.

Now, watching the driveshaft, turn the tire EXACTLY 2, that's right 2 full turns, and count the driveshaft turns. A 3.55 will turn the shaft just a tiny bit past 3 1/2 turns, a 2.76 about 2 3/4, etc

Now, if you can NOT turn the one wheel, (AND CHECK that the parking brake is off, and in neutral) this means that you have a Sure Grip/ limited slip rear axle.

So now you will have to jack up BOTH rear tires, and turn one of them (the other will follow) just ONE turn, while watching the driveshaft. As before, the driveshaft turns will give you the axle ratio

WITHOUT doing this, and WITHOUT an engine tach, you are just guessing.

Another good cross check nowadays is if you have or can borrow a GPS which will give you just about the most accurate speed reading you can get.