For a while now I have been trying to track down a strong viabration in my '73 Dart 4-door that comes and goes every 2 seconds or so anywhere above 50mph, never below. So far I've had the wheels balanced (twice). The shocks are good, the u-joints are tight (no movement of any kind) and the driveshaft looks straight (not sure of this, but a straight edge finds no gaps). Front wheel bearings are good (not sure of the rear but think so). The viabration shakes the whole car, so I can't determine where it's coming from.

I'm stumped! Anyone have any ideas? Thanks!

Swap your tires front for rear and see if the vibration changes. That kind of trouble can be alignment issues also.

This TSB on vibration may help you, there are 20 pages total;

http://www.hamtramck-historical.com/images/TSBs/1974/25-02-74D%20page1.jpg

Go to that link, then just keep changing the end from page1, page2 and so on in your browser up to 20 to see them all.

Excellent stuff!! I've got some reading to do. Thanks!

yah, but who has the same tire size front to rear?

if you have yet to get the drive-shaft balanced you are shooting in the dark. What size tires do you have? Also, what rear gear is in the diff?


My '76 Valiant 4dr had a vibration kind of like what you describe and upon inspection at the driveline shop it was twisted in an s-shape, but didn't really appear to be upon visual inspection. I think they charge 50-65 dollars to balance it and straighten it at most shops. It might be worth a look.

tires

That really sounds like a problem I had on two of my cars, it turned out to be the transmission mount.
If you can duplicate the harmonic with the car in neutral sitting parked in the driveway or at the curb, that would be my bet. Took me a long time to figure it out the first time it happened.

u-joints have "no movement of any kind"?

...."is bad" that means they have rusted and need replacement.

maybe....

Have you replaced the u joints recently? If so, did you install the clips on the rear u joint to center it in the rear yoke? That can cause a bad vibration if you don`t install the clips. Mike

Had that happen on my 'Cuda and it was the torque converter. There was a weird balance issue on early 70 models where they had 3 different sets of weights used. Might be something to check, or maybe you lost a weight.

By no movement in the u-joints I meant no sloppiness. They look clean and newish, but where there when I got the car maybe half a year ago. Looking at the rear u-joint, I don't see any 'clips' as mentioned. I suppose it's possible the joint is not centered. I should also have mentioned that the rear of the car seems to bounce a bit (up and down) in the rear as I come to stops. This only happens at very slow speeds such as coming to a stop sign. The rear shocks are good. It's a bit confusing.

Reving the engine up in park causes no viabration, so I don't think this is engine/converter related.

The u joint caps that bolts to the yoke should have the clips installed. It centers the u joint in the yoke. I bought a 74 dart and it had a vibration. I installed the clips that the previous owner left off and the vibration was gone. Mike

I had this same type of problem before, I got rid of most of it by changing the U-joints and correcting the pinion angle. I fear that the rest of the vibration is coming from a sloppy tranny slip yoke/internal bushing. I got a new trans and driveshaft coming soon, but it is 95% better by swapping the U-joints and adding some shims to the rear end.

Just because the U-joins seem ok doesn't mean they are. Drop the shaft and at least check to see if any rollers got out of place when the original install took place, mine seemed fine and there were at least 2 pieces of roller in the original caps.

Tom

I had a similar problem, try removing the fan belts from the engine. A lot of stuff is spinning up front. Mine turned out to be the fan. You don't even want to know all the BS I did to my car trying to fix the problem...