Car vibration at freeway speeds; why?

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Portuguesesax

Portuguesesax

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Hello fellow A-body enthusiasts,

I recently purchased a 1971 Dodge Dart Swinger with a 318 swap (original 225 inline six) and original 904 transmission. Every time I drive in excess of 65-70 MPH, the car starts making this humming, vibrating noise. I recently put all new tires and had an alignment done, so I know its not an alignment issue. I had a mechanic look at the driveline (thinking it may be an issue with the u-joint) and he greased the shaft on both ends to help. He said its a little better but it continues to vibrate.

Any thoughts on what may be causing this???

Antonio
 
Where are you hearing the vibrating noise ? Fire wall area , rear of the car ? or the hole car is vibrating ?
I am thinking the high speed noise could be in your air box vibrating noise, Just a thought.
 
The vibrating noise sounds like it emanating from the firewall area and/or drive shaft area. Its just odd that it only occurs going faster than 70 MPH.
 
welcome to my world..My car goes fast, but when you get to speed, it gets pretty dicey...
My next fix is to rebuild the front suspension.
 
Can you touch the floor board and feel the vibration ?
If not you have air vibrating something, set on jack stands and safely
supporting the rear tire of the ground see if you get the vibration.
if you do it could be as simple as a wheel/tire, or drive shaft is out of balance that will take your tail shaft seal out, check your pinion for play, but I would figure the mechanic checked that.
Air is a funny thing sometimes, ever herd a emergency brake cable rattle and vibrate . I have, but I think it was in a truck.
 
i have an all stock car with a 225/ and my car starts to shake a bit around 80mph do you have the stock rear end in the car still also?
 
Everybody's replies are great! I'll be taking a look this weekend and try to nail down the reason. I doubt it has anything to do with wheels and tires, since I just had those replaced or an alignment for that matter...
 
I've experienced a vibration, at speed, three times, in my darts. Each time it was something different.
Once it was indeed the parking break cable, as Memike cautioned against. Adjusting it tighter took a couple of minutes and the problem was solved.

Another time it was after market rims. Even though I had them balanced they still shook your nuts off between 65 and 75 mph, after which you would drive out of it.

The third time it was the front Roll pan (under the front bumper). I had it off for a while and while reassembling the car it some how never got tightened, or came loose. It was still bolted to the car, but not securely. As a result at about 50 mph, it would "plane-out", and start to vibrate. It drove me crazy for about a month.
Finally, I have a couple of friends ride in front of me, and behind me, looking for issues.

Just about the time it started to vibrate, the guy in front of me started wave his hands. We pulled over and he said the roll pan was moving up and down.
Sure enough I grabbed it, and there was about a 1/4" of play in it. I tightened it all down (up), and the problem went away.
 
Just because a U joint feels tight doesn't necessarily mean it's not bad. I had a vibration in my 03 Ram truck and checked the U joints two or three times and finally discovered that it was in fact the rear joint, replaced it and problem solved.

I would take a second look at those.
 
After an engine conversion, I would suspect that the pinion angle of the rear diff isn't correct. The pinion angle of the differential should be very close to matching the angle of the transmission, but in the opposite direction. So if the rear of the trans is pointing down, then the nose of the pinion should be pointing up at the same angle, or down a degree or two less (for hard launches). Otherwise your u-joints will be binding and causing the car to vibrate with speed. That's why they use constant velocity (CV) joints on FWD cars.

Buy a cheap angle gauge from Horror Freight and check this out in no time.
 
antonioi'm thinking it's u joints.i have a set i bought but never used .i will install them for forty bucks and you can have them for free. at least that will eliminate that variable pm me
 
if it was a slant car and was swapped to a v8 then theres no way it still has the original transmission, the bellhousings are way different. Accordingly the driveline may have been swapped. After 30+ years of use (or rusting in a field) sometimes the balance weights that are tack welded to some shafts jump ship. Also people forget to mark the yokes to the shaft when changing u-joints and sometimes that can be very critical, if it is, and its done wrong, u-joints will brinelle, thats when the needle bearings create a groove in the trunnion (the main cross) and the joints become stiff and usually fail fairly quick. Bent yoke ears can make the joint tighter than it should be. Ive had worn transmission mounts do something similar to that as well. Gunk in the inside of the wheel can throw balance off enough to notice at high speeds like dirt or the neighbors cat. A failing tire can distort at higher speeds, cords separating or chunking out, maybe a flat spot? Dont overlook something if it seems too stupid to be the problem, it usually is. haha!!
 
Oh another thing too! I bought a 73 D100 that was supposed to be a 318 4-speed. well come to find out someone pieced the poor thing together and put a 318 flywheel, harmonic balancer, intake, and exhaust manifolds on a 360 short block. it shook really bad above 55-60 ish but ran pretty damn smooth at lower speeds. I ended up finding it by the casting numbers on the block, the front pad that should have been stamped was unreadable. So sometimes its the things that most would assume should be right.
 
I'm having a similar issue on my 65 Vali Vert. front passenger area. Loud hummm after 50 mph. I'm suspecting bearing issues, although my mechanic has also suggested possible the ujoints as well.
 
My dads Charger cant get over 90 without it starting to pulsate and he said the driveshaft is out of balance. Been like that for 20yrs and still aint fixed
 
okay need more info on this is the vibration felt in the steering wheel why you drive. this is a problem that a lot of jeep people deal with. one it could be any part of your suspention even thow it was checked does not mean that the parts are good, new tires on it if they are not properly ballaced they will cause a vibration front wheel bearings. get some one else in the car and have them find the location and then go from there
 
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