The brake drums are out of spec on the front, and I did feel a pulse in them, but then it stopped. The thing is, those drums have been on there for a while, and this just started not two months ago.

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'74 Duster 225 Super Six w/904
14" Cragar SS wheels

i have the same thing only mine starts at 50mph and lasts to 55. it gets better if i speed up or slow down. also the shudder shakes the whole cab of my truck sometimes. other times its not as bad.... the tires were just installed and balanced though i could get it done again, i kinda question the quality of work from that place now. or is this something completely different?

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for profiles and pictures of my mopars--> http://www.fquick.com/dietz_diggler

If your pinion angle is off your driveshaft will vibrate and cause this problem.

My car starts to vibrate over 65mph and just keeps getting worse, which is why I need to fix the pinion angle.

hi it sounds like the idler arm is worn the bushes may be worn out or it could be the universals joints in the drive train my bet would be the front uni just a thought good luck..

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slants6 forever

The idler arm as well as ball joints, etc... are new. I just had another thought, could it be the pitman arm? Thats the only thing I didn't replace.

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'74 Duster 225 Super Six w/904
14" Cragar SS wheels

yes the pitman arm would make it shake .i replaced the pitman arm on my val but it used to shake when i applied the brakes it didn't shake driving on the highway sitting on 60-70mph so i would check it out it might also be lose.

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slants6 forever

Just figured out my pitman arm is bad. Too expensive to replace though. I guess I will just have to keep it at a lower speed. I drove an 90mi round trip yeaterday at 45mph, 10 below the limit, and made a lot of people mad. It was better than going through a 6.5 earthquake for an hour!

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'74 Duster 225 Super Six w/904
14" Cragar SS wheels

I had this exact same problem but I have front discs and it turned out to be that the caliper was sticking. I tried to drive to work one day and the front end shook so bad I had to pull over and when I got out the rotor was smoking. But the vibration didn't really ever show up until about 50 MPH. I don't know if dragging drum brakes would cause the same problems, but it's another thing to consider.