1987 F-150 XLT Lariat, 4WD, 166,000 miles. Just started a bad vibration at any speed, 25, 40, 65, doesn't matter. Only when accelerating or travelling. Let up on the gas and it goes away and feels smooth again. Seems to have started all at once and not gradually.

Any ideas would be greatly appreciated! email: bwduerr@yahoo.com

Thank you very much from snow-buried Vermont!

 

check the drive shaft u-joints

 

I have an 87 that had the same problem. You probably have a rear u-joint that has gone dry and has gotten sloppy. If you decide to replace it yourself, go to one of those places that sells cheap imported Chinese tools and you can get a nice bearing press for about $100. Be sure that when you install the new one that it is correctly centered in the yolk or you will likely have the same problem with a vibration. When you buy your new u-joint, take the old one to the parts store and make sure that you get an exact replacement. There are about three listed that fit an 87 f150. I had to make a trip back for an exchange.