Clunk, Vibration
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Freshman User
Joined: Feb 2002
Posts: 33
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Clunk, Vibration
I have a 84 F-150 w/ 351W and C-6 Trans. I have the problem of vibration @ highway speeds when deccelerating and a clunk noise when going from reverse to drive or drive to reverse. I have checked the U-joints, but they all seem tight, rear axle doesn't seem to have much play in it. At the front of the driveshaft, where the yoke goes into the transmission, it has a little play, I can push it up and down a small amount. Could this be causing the problem? If not, what might be, and what would be involved with fixing it?
:-X12 
Senior User
Joined: Nov 2002
Posts: 164
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From: Seattle USA
Clunk, Vibration
More than likely:
Check the U-joints. This will cause a harsh vibration between 50-55 and less at lower and higher. Also, as you let off the gas quickly you will hear a clunk. The clunk could be play in the rear end, but the U-joints are cheaper, and easier to check first. Simply drop the driveline out and rotate them. If they move easy and seem to "glide" together, there is not a problem there. If they are hard to move, and it feels like there is dirt or pits in the glides, replace them. They typically run about $15 per joint.
Check the U-joints. This will cause a harsh vibration between 50-55 and less at lower and higher. Also, as you let off the gas quickly you will hear a clunk. The clunk could be play in the rear end, but the U-joints are cheaper, and easier to check first. Simply drop the driveline out and rotate them. If they move easy and seem to "glide" together, there is not a problem there. If they are hard to move, and it feels like there is dirt or pits in the glides, replace them. They typically run about $15 per joint.
Junior User
Joined: Jul 2002
Posts: 81
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From: The Rock, BC
Clunk, Vibration
[updated:LAST EDITED ON 19-Dec-02 AT 07:44 PM (EST)]You should be able to check the u-joints while the shaft is on the truck ... block the rear wheels and puth the trans in neutral. give each joint a wiggle, also check the CV and slip joint for play, both of these will also cause the vibes you mention. ANY play at these points will require the replacement of the u-joints (there are 3, two 1330 series in the CV along with a centering kit, and a 1204 series at the axle end) you may be able to half *** the slip shaft by filling it with grease but if there is play it's done and needs replacing. The front shaft won't cause vibrations unless it's turning (only when in 4wd) but the same rules apply here (both U-joints in this shaft are 1330s) U-joints are cheap, like the previous post about $15, a centering kit should be around $50. It's pretty simple to redo the CV (the Ford shop manual has plenty of details on it) but the slip will have to be cut off and replaced (probably about $250 with parts and labour/balancing)
