Chasing vibration...help!!

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plymouth67

It be a lot cooler if you did...
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So I'm chasing a surging type drive line vibration. 75 Duster 360/727/ 8.75 3.23 open 489 case. Let me start by saying...trans is rebuilt, new converter, had driveshaft made and balanced, new tires...yrs they are balanced...I even pulled the extension housing off the trans last week and put a new bushing in just to try and eliminate that. Still there....the only thing I haven't messed with is the rearend...I'm 46 and still have all my hair but if this **** keeps up I'm gonna start pulling it out..lol. This vibration starts about 35 to 40 mph and gets a little stronger as you go up in speed. It surges in and out of vibration....What am I missing?
 
Is the new converter weighted ,mabey not for a 360 ?my 2 ?
 
Double check the balance on the rear tires.
Unless you just recently did. Then ignore me.
 
Did your transmission have one of those huge cast iron weights on the tail shaft?? Is it there now?
 
Have you checked your pinion angle.
I have not but...it didnt do this with the old drivetrain in it...the 3rd member was also changed along with motor and tranny, before I started doing this car. My buddy owned this car years ago and with his drivetrain and 3rd member it didnt do this.
 
Does the drive shaft have the C-clips on the rear U-joint that keep it centered in the pinion?
 
Tires are like a month old and balanced when mounted
There is some pretty lame tire guys out there. Not to mention new tires get out of balance sometimes easily. It’s a long winded explanation. Another time.
Anyways I had a weird pulsing in and out vibration recently and double checked the balance on the rear tires, 1 wasn’t to bad. The other was way out, and I haven’t felt it since.
 
I have no ideas to help.... but keep holding on and you'll find the problem... or end up like me where a suspension rebuild turns into a disc brake swap which turns into a cam swap which turns into a transmission rebuild.... Good Luck and enjoy the ride!!!
 
If the tires are the same size on all for corners try swapping around to see if anything changes
 
It's clearly a drivetrain issue, if I move tires around I wont feel any difference. You would have to ride in it to understand. I have also noticed some times when I let out of the throttle it seems to go away immediately....but only sometimes..??
 
My heart shaped bed sometimes vibrates like that then stops till I put another quarter in it. Then it Starts all over again.

I’m sorry, but I have no answer for you, other than what has been mentioned in prior posts.
 
My heart shaped bed sometimes vibrates like that then stops till I put another quarter in it. Then it Starts all over again.

I’m sorry, but I have no answer for you, other than what has been mentioned in prior posts.
Maybe if I add some quarters I can make it shake all the time...lol
 
It's clearly a drivetrain issue, if I move tires around I wont feel any difference. You would have to ride in it to understand. I have also noticed some times when I let out of the throttle it seems to go away immediately....but only sometimes..??
Rpm affects it...so how could it be tires??
 
It's clearly a drivetrain issue, if I move tires around I wont feel any difference. You would have to ride in it to understand. I have also noticed some times when I let out of the throttle it seems to go away immediately....but only sometimes..??

Could be ball joints. Death wobble in jeeps is from a bad ball joint, death wobble is felt when the jeep hits a certain mph. At that mph the ball joint starts "wobbling" around causing a vibration in the vehicle which is described as "death wobble," slowing down usually allows the ball joint to settle down and the vibration goes away.
 
It's clearly a drivetrain issue, if I move tires around I wont feel any difference. You would have to ride in it to understand. I have also noticed some times when I let out of the throttle it seems to go away immediately....but only sometimes..??
This sound like a diff issue changes from drive to coast time to open up the diff for full inspection and set it up correctly.
 
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