My coronet drives nice but when i go over 60mph it shakes, is it the driveshaft or the harmonic balancer? The tires, and rims are new and balanced.






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1966 Coronet 440 318 long block

 

It's probably a universal joint in the driveshaft. Crawl under the car, grab hold of the driveshaft and see if it will wiggle.

If it's a harmonic balancer, you should be able to pull it down a gear and recreate the vibration at a different speed.

 

I wouldnt think ether its most likely tie rod ends or drag link

 

It also shakes around 30mph but not excessively, but when i get up to 100mph its like something is holding the car back from accelerating.. Like its a heavy vibration that feels like its coming from underneath the front seat

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1966 Coronet 440 318 long block

 

Transmission mount?

 

i changed both motor mounts and transmission mount

 

Is there a weight on the torque converter for an engine with a cast crank?

Or vice versa?

 

I would think it would be on the torque converter, but im not sure....


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1966 Coronet 440 318 long block

 

I would have to agree with Neonz1, my Plymouth shook and vibrated at high speeds, I polyed it and it rides like new

 

Poly what? the drag link or the tie rods?

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1966 Coronet 440 318 long block

 

The u joints, I had a similar situation and that was the problem. best wishes CD

 

the Poly bushings go in the suspension in place of the rubber original ones.
I hope that it is not a tire starting to come apart, especially at 100mph.
I dont think I'd go that fast again 'til you figure it out.

 

all 318's were internally balanced. no weights on the convertor.

 

It sounds like it is proably the U joints. Inspect your driveshaft and trans mount.

Not as likely but if you had a torque converter ment for a 360 then you would be out of balance on an internally balanced 318. If you are stopped and rev the motor up and it doesnt shake then I would not worry about engine balance. Worn suspension components generally do not cause vibrations. They cause alignment issues that are hard to track sometimes and they cause sloppy feel in the steering. Vibrations are caused by something that spins. I bet you lost a clip out of one of your U joints and the drive shaft is not spinning on center now.
I also once had a car that I got from a junk yard. It ran great but if you got above 40 mph it would shake so hard that you could barely control it to get it off the side of the road. It was easy to find as the junk yard had used a forklift to move the car and that had bent the driveshaft.

 

The car is all original never modified or tampered. im the second owner on this mopar(still have the bill of sale too, with matching owners manual certificate), and he's said that nothings been done, other than regular maintenance. and the both motor mounts and the tranny mounts are brand new. All Shocks are new also. Had an alignment done also.

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1966 Coronet 440 318 poly

 

Take a close look at that drive shaft and u joints. If you loose a clip out of the u joints they will slide off center in the yoke. If that happens they vibrate badly.

 

Ok Thanks for your help!

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1966 Coronet 440 318 poly

 

Look at the drive shaft. i think you can get them balanced. stuff wears out . you could go with a new alummiun one also lighter in weight.

 

Geez, 44 years on a set of U-joints? I'd say they served well and replace them anyway! Then we go from there. I have had brand new tires with a bad belt in them. But start with the joints first cause they are simply due, and they are cheap! Also, be sure to use proper torque on them. It is easy to apply too much and I read from a shaft-shops website that it can cause some warpage that can shorten the life of them.

 

I had a similar problem in my '02 jeep wrangler. Only when I got up to about 50 it would start shaking.... NO ROCKING, almost like it was going to flip itself over or literally throw itself off the road. I was thinking I had some KILLER major problems with it. After a long run around with a few different mechanics and fixing a bunch of crap that didn't need to be fixed lol.... it turned out to be one of the U joints on the drive shaft! I fixed that and it drove straight as an arrow almost like it was brand new again lol. So I would definately look into those. Get under it and see if you can wiggle your drive shaft at all. Your really gonna need to twist and jerk around on it. Also make sure you are parked in a level place and put your E brake on if it works and don't let it roll forward. Try to get all stress off of the drive shaft. It will make it much easier to tell. Hope this helps. If this don't work try an alinement (don't think I spelled that right) Could also be an alinement shim fell out.. I had that happen on a little s10 one time. I would be willing to bet its a U joint though. On my jeep it didnt feel like it hardly had any play in it. So I blew that off for a while. And when it got to the point that that was the only thing it could be... lol yeah I felt stupid.

 

02 Wrangler, did you have the LUBED FOR LIFE, non-serviceable u-joints?

 

I don't think so that has been a while ago. But I believe they had grease serts on them. I didn't have the jeep too long before it started doing that. I did it about 3 months after I got it. I did learn from that experience though, that a U joint can make it seem like you have some crazy bad problems lol. It literally started rocking that thing. lol. I don't have the jeep anymore though I sold it a while back to have money to buy more toys lol.