I recently purchased a 66 dart wagon that starts howling while at freeway speeds. Around town it is not apparent, but once the car gets above 45mph a low hum starts and by the time the car is at 55-60mph it is at a much higher pitch. Im new to the slant six, but it also feels like the car is struggling to keep the high speed. The car is in 3rd gear by 45mph, and even without a tachometer, I can tell the motor is working overtime when its traveling at 55-60mph. Also it tops out at about 70mph.

I was able to put about 2 cups of fluid into the rear diff, which makes me wonder what else has been overlooked in the rear end.

The previous owner also stated that the E-brake "sticks". But by this time, if it was a brake problem I figure I would seen a red hot brake drum, or heard that horrible brake grind. Ive heard high pitched brakes, but only with disc, not drum.

Any ideas?

My guess is the wheel bearings, and I will be replacing them soon.

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1966 Dart Wagon /6 225 AT

You need to figure-out the rear end's gear ratio. The ratio was stamped onto the housing and on the gears inside.

What size tire is on the rear of the vehicle? Is it an automatic trans?
DD