Humming sound from rear end under acceleration?

[1966DartConvertible]

Hi

As the title says...

I've noticed lately that there is humming sound coming from the rear of the car during acceleration and also during normal cruise. It "almost" goes away when i release the gas and coast (still there but very faint can barely hear).

What could cause this? If the axle is low on oil why would the sound go away when I release the gas?

Thanks

Syed

 

[daliant]

If the rear is real low on oil (like empty) and is starting to make noise then the damage has already been done, the ring and pinion is probably smoked. You didn't say what rear you have but a 66 Dart should either be a 7 1/4 or 8 3/4, if it's a 7 1/4 then I would say it's a wheel bearing but without hearing the noise it's just a guess, the 7 1/4 has small wheel bearings that don't seem to last very long.
A good way to find out where the noise is coming from to jack up the back of the car and put a pair of jack stands under the rear end, next start the car and put it in gear so the wheels start turning, then take an old broom handle and use it like a stethoscope: put one end up to your ear and the other end onto the rear end by each wheel bearing and in the center by the pumpkin. This will help you find out where the noise is coming from.

 

[67Dart273]

This can be either axle bearings or ring/ pinion or it's bearings. You are going to have to either live with it or tear it down. Axle bearings are usually more of a low pitched hum, and change when you keep the engine load constant as you can, and move the steering to load first one then the other axle.

Since the axles come out first, take a good look at them, and if the bearings are suspect, I'd start there and try replacements before pulling the axle apart.

Of course if you have anything other than an 8 3/4 you can pop the rear cover off and inspect somewhat.

My 3.89 Ford 9" was bought used, noisy when I got it, but has not gotten worse. I just drive it!!

Also don't discount something weird like an exhaust / tail pipe or other metal--to metal contact with the rear axle which might be transmitting vibration.

 

[pishta]

noises under acceleration or deceleration are sometimes pinion bearings, as they take opposite loads from the ring gear. If they are shot, you can usually literally move the pinion in and out once you take the driveshaft out.

 

[Supershafts]

You may have a bearing issue, if so it could be the carrier bearing otherwise depending how long this has been going on it could be initial set up