Hey guys,

Working on my '73 Barracuda. It has been through a re-power (LA to stroker Magnum), front end resto-mod, subframe connector/torque boxes welded in and a custom drive shaft. Brakes have been completely rebuilt with modern friction materials and new rotors/drums/front bearings, wheel cylinders and rebuilt slider calipers and they perform flawlessly. 3.55 8.75" with old school XHD MP leaf springs (Made in USA) with good bushings. 3.55SG with cones machined and all new axle bearings (standard outers) done 5 yrs/12K miles ago, endplay corrected in other vibration chasing.

I have got this thing as dialed in as I can, no binding in the suspension, solid alignment, nothing moving in any way that it shouldn't. Handles very well on the street. I had the chassis shop that did the SFC's and torque boxes check the body it for square and make sure everything was in spec dimensionally (with the improved K-frame installed) and was told it is good to go.

I'm down to a vibration that the car has always had (I've owned it since 1988, bone stock when purchased) that comes in at around 65MPH, gets worse until around 75 and remains minimal but constant as fast as I go, and goes away completely when I decel below 65. These speeds are on smooth highway. If I'm on bumpier roads the onset speed is lower, but everything else is the same. The vibration I believe to be drive-train independent as it is present regardless of gear. I've had 3.23, 3.55 and 3.91's over the years with the same vibration pattern at the same speed.

One other observation that is hard to explain, but I'll try is that the vibration escalates in intensity and settles down, then de-escalates and mirrors the behavior on decel through the speed range. Always. It doesn't just start and stop.

Any ideas on the brain trust on this one? Monday car

Thanks
Chris