As some of you might remeber from
an earlier post that my 1970 barracuda had a vibration problem when traveling at 60+mph to the point that the car would shake violently enough to make the hood move around and touch each side of the fenders, and the car has good pins.

here is what has been done on the car:
slant 6 car converted to v-8 kmember and big block torsion bars.
440 engine anto trans. Good set of kyb shocks for street driving and converted to late model b-body discs.
Steering box was leaking so I converted early to a FF2 box and pitman arm. Took car out for it's first run and noticed it steered better, still had the vibration. Had old tires rebalaned to see it it help, no diffrence. Bought new Cooper cobra for the front, still no change.
So members said since the tierods were a little loose that thouse could be the culprit. Used the PST larger tierode and solid sleves. Still no change.
Reinspect frontend and decide that is worn enough that a full rebuild will need to be done eventually, so the decision was made to do it now. Tore frontend apart and inspected the k-member, no cracks. Reassembled frontend with new brake rotors, beating, pads, pst polygraphite kit, Magnum Force adjustable control arms and same kyb shocks as they were still in very firm condition. Took car down to a shop for a fun fronend alignment and adjusments. The guy had 30+ years experience with frontend and was using the latest Hunter allignment equipment. Even had one of the guys over from Magnum Force to check all the specs on the frontend while it was being alligned, everything was fine. Take the car out for a test run and it gets to about 5mph higher and the same dang problem is there! also put in new motorounts and tranny mounts.

ok, so now we are sure the problem was in the frontend, even check column and floors for vibration, which were being transfered through to them. Decided to check the rearend out. We jacked up the rearend and blocked the front tires. Ran the motor up to 60-65mph and there was no vibration coming from the front. The rear tires seem to be going out of round in about 1/2 inch and look suspect. Apon further inspection, the driveshaft seems to back out of the tranmission tailshaft at can see about 1/3 of shinny metal at high rpm's.

Since the rear tires are old and suspect those could be part of the problem, going to install new tires today. Now if that does not help, will have to address the rearend itself and driveshaft and possibly a cracked wheel Mind you, I've had 4 mechanics and 2 friends in the car, and nobody seems to guess what the problem is. Any thoughts on the problem?

did you have the car on the rear suspension when it was lifted? or was the rear hanging free in the air?

I had a similar issue, vibrations at 60-65 in my big block Dakota. with the weight off the driveline, and no load on the engine, there was very little vibration, but it would rattle your teeth out when you were going down the road.



my problem turned out to be an out of balance driveshaft, but my point is that don't be surprised if the vibration goes away when you are free-spinning the wheels with no load and no weight on them.

got a chassis dyno nearby? that will let you run it up to speed, under load, and be able to see everything, without having to jack it all up in the air.

I agree, if the rear was just dangling and the body supported, you probably aint gonna feel it. I'd be pulling the driveshaft, checking u-joints and tail shaft slop on the trans. My 68 Dart drove me nuts like that. Turned out to be a crack in the rear yoke obviously. New u-joints balanced shaft and everything. Still did it then it finally split and my driveshaft flew out and into the Flint river.

A 1/2" of run out is a lot for a tire

Welllllll, my first car - a '70 Cuda 340 had this same problem! I bought the car in 1976 with 44,000 miles on the clock. When I'd get it on the highway & hit about 65 MPH, the whole front end would feel "light" & start vibrating like crazy. The hood would shake & hit the fenders just like you describe. However, if I stayed in it, the vibration would subside at about 85 MPH. No vibration after 85. I did have the car up to 125 a couple of times - that's all it would do with the 3:55 gears. I always thought this was very wierd. I know it was not tires or U-joints because I replaced them & it did not change this symptom at all.

Sorry to inform you, but I never did find the cause.

Just got back and good news, vibration is all gone!

looks like the tires and the driveshaft were both the culprits in this. Tires were off balance from age and sitting, so new Cooper cobra 295's took their place. Took the car out and slowly went to 65, no vibes. Then 70,75 and still no vibes. Got up to about 95 and was feeling good and could feel a little movment and figured the drivshaft could use some work. I was tempted to go up higher, but I rolled on on a chp officer and she looked a bit suprised when I had blurped the flowmasters next to her.
lucky there was a exit right there, so I waved hi/bye to her and exited pretty quick there.
thanks for the help everyone.

You went past her at 95 (plus got her attention ) & not pulled over