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Rumbling Dart

My 1966 Dodge Dart rumbles when under power. As soon as I let off the gas it stops the rumble. My guess is the torque converter or the transmission. Any ideas?

One thing you might check is the universal joints on the car. If new universal joints are needed, these are easy to replace.

Without more specific details I would start with a points gap/dwell and timing check. Also vacuum advance and distributor advance mechanism.

It could a number of things. Such as a bad bearing or a tire. The way to start checking is to place the car on a lift and try to get it to rumble. Have a mechanic under it to see if he can locate the noise area. Remember this is only a starting point, but may help you pinpoint the area you where your problem could be.

I second the universal joints as a possibility. Fairly easy to check, remove the drive shaft and check the joints. It might also be your differential going out - my '72 Duster’s went out, lots of rumbling.

The only effect ive ever had with bad vacuum advance is poor low end power. The universals in my experience you can check without any disassembly. Just check for slop with driveline free to turn or in neutral. block the wheels

Also. torque converter would be a possibility

From the sound of your description I lean towards the rear diff., U-joints will usually grumble or bind under load, not so much when you let off. It is possible the pinion bearing is worn or the spider set is binding. There are many ways to examine this, you could look for a shop with a dyno in the floor, (becoming rare) or jack up the rear end and examine the back lash and check for any movement at the pinion shaft. Another good indicator would be the GL 5 leaking from the pinion seal where the yoke connects at the rear of the drive shaft.

Will try replacing the u-joints first. I have heard them clank once or twice and have been meaning to replace them. These are the easiest. With luck I don’t have to get into the pinion bearing. Or the spider set. Especially that, since I have no clue what a spider set is. Thanks for the help.

Good luck! If it turns out to be a problem inside the differential, you might check into just putting in a replacement from the junkyard. I did that in a parking lot, it’s not that hard if you have 2 jack stands.

One other possibility would be the wheel bearings, they’re also not too hard to replace.
Here’s a picture of the spider bearing, they are the gears (#5) that allow the wheels to turn at different speeds:

Changed the u-joints and the old girl purrs like a kitten. Did have one problem changing them out, though. One set of new u-joints had slightly longer arms than the other and would not fit. Identical part number on the box but it was 1/8 in. larger. Not sure if this was simply the wrong part in the box or if the chinese parts are that bad. Thanks for the advise. She is my only car and I would love to keep her running until I am an old, old man.