Engine Vibration at highway rpm/speed

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Tooljunkie said:
I wouldnt run it with a yoke in trans. That 5 lb yoke would be a dangerous thing if it comes out at 3000 rpms. Even running it on axle stands is a little sketchy.
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Good point.
 
d1970 said:
High speed vibrations at 60 MPH and higher are usually caused by a bad tire, rim or a bad brake drum or rear disc rotor. Lower speed vibrations at 35 to 45 mph are usually driveline related and could be an out-of-balance drive shaft or improper u-joint alignment. If the vibration can be felt in the shifter, it is likely a front of the driveshaft balance problem or a bad u-joint. If you feel it in the back seat or in the floor at the rear, it could be a rear of the driveshaft balance problem or u-joint. However, a bad rear tire, drum or rotor (if you have them on the back) can cause the same vibration in the rear. Before pulling the suspected driveshaft, swap the front wheels for the back and back to front or borrow a known balanced set of wheels to test drive the car. If you haven’t balanced your wheels for a while, it wouldn’t hurt to do so to ensure they are indeed balanced.
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New rims and tires are going on today... so I will remove the old ones as a culprit today. New rims are wheel vintique black steelies with new lug nuts and cooper cobras.
 
It doesn’t do it in nuetral its no the engine. Pinion angle or driveshaft phasing. You can mark the shaft and pinion yoke then take ot apart and spin it 180 degs. Then see if it changes the vibration. I had the same thrummm. Pinion angle and new/bal shaft took care of most of it. New tailshaft bushing?
 
Search for a video from Dana for pinion phasing. Its very educational.
 
Tooljunkie said:
I wouldnt run it with a yoke in trans. That 5 lb yoke would be a dangerous thing if it comes out at 3000 rpms. Even running it on axle stands is a little sketchy.
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I know it was my suggestion..... it just sounded like he was getting desperate. It will be interesting to see how he gets her figured. He could use one of those transport plastic plugs, but risks it getting chewed up. Usually they are held in by the seal? There isn't a lot of centrifugal force on the rear with wheels removed so jack stands, although they have their risks as well.... seems minimal.
 
I wouldn’t run it without the shaft in it. Get an angle finder and find out what the angles are.
 
furrystump said:
It doesn’t do it in nuetral its no the engine. Pinion angle or driveshaft phasing. You can mark the shaft and pinion yoke then take ot apart and spin it 180 degs. Then see if it changes the vibration. I had the same thrummm. Pinion angle and new/bal shaft took care of most of it. New tailshaft bushing?
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yes new tailshaft bushing....completely rebuilt trans.

its a brand new driveshaft, new ujoints, and new trans yoke....all computer balanced. trans has all new seals, bearings, bushing, etc. third member was completely rebuilt and converted from 3.23 to 3.73. pinion yoke is the only thing original on the third member now. Driveshaft should be in phase as it is new and I never took the trans yoke off it. I can disconnect it from the pinion yoke and spin the pinion 180 and reattach, but man you think Dodge would have made it to where the driveshaft would only connect one way and not both if that was really an issue.

i'm really hoping this is related to the rims/tires. if not...i'll take the car over to my cousins automotive repair business and have him check the angles in driveline and pinion. sticking it up on jack stands and running it doesn't bother me any either. I've already done that a few times....but this time I can stick a camera down there to watch the driveshaft spin, etc.

everything is brand new except engine internals, rims and tires, rear axles and rear outer axle bearings.

rear axles look okay and bearings good and greased.

drums/shoes/rotors/calipers/pads/front bearings/driveshaft/flexplate/balancer/converter/trans/trans mount/engine mounts/etc......all new. yes it is a cast crank....and yes the flexplate has the notch taken out....and the balancer has a weight on it. it is setup for external balance, based on the fact that I have cast crank. converter is neutral balanced. the only thing old on the motor is crank, bearings, rods, pistons, rings, block, heads, valves, valve springs, rockers, push rods, cam, and power steering pump. the rest of the outside of the motor is all brand new.

tires and rims being replaced today.....so that leaves pinion angle and engine internals. I can't think of anything else that would make a pulsating droning vibration between 4k-5.5k rpm that changes oscillation with rpm change. letting off the gas changes the oscillation as well. give it gas and it changes again. vrump...........vrump........vrump vs. vrump..vrump..vrump

its not so much that i'm desperate...I'm just tired of it, its been there ever since I was a little kiddo, and I want my dad to finally beable to drive this car for once in his life, and since he bought it in 1989, without feeling that vibration....its a mission. its personal now....I got a big middle finger pointed at that vibration and i'm coming for it.
 
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furrystump said:
Search for a video from Dana for pinion phasing. Its very educational.
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I just watched video on phasing and angle...it was very informative...thanks!

this is the video I watched and I can tell you that the sound the card makes is very similar to pulsating vibration I get... since the driveshaft is new and in phase to itself...its gotta be the angles are off. man I never even thought about angles...I sure am glad for the help!

not sure how to get this video to link right...here is the link with a space before and after the be. delete the spaces.

https://youtu. be /Idk3BVDVHq4
 
That’s the video. The phase being off is just a shot in the dark. I wouldn’t change the trans side at this time for phasing. The idea of pinion angle isn’t difficult to understand. Put angle finder on end of output shaft. Write down the angle, put angle finder on rearend yoke ears. The difference between the two is the number you want to change. Search pinion angle. This will provide the amount of down angle you want to shoot for, taking in consideration your rear suspension type. Down angle because under load the nose of the pinion rises.
 
Transmission mount more than likely. I would replace it and make sure the motor mounts are good...it solved this exact same issue on my car when I was experiencing vibrations from 60-120+mph.
 
As mentioned, the mounts, all 3 are new.
The driveline angle app should give you a close approximation.
 
You kindof have to run it with the D-shaft off and the yoke in;else the tailshaft is unsupported and it will whip around, screwing with your head. I have done this several times, with the rear of the trans centerline, a tiny bit higher than the front. This has always worked for me.

Another thing that has worked, is to drive it up into the vibration zone, and then change transmission gears to increase the engine rpm. If the vibration remains unchanged then you have eliminated everything from the trans input and forward.

Tires also have to be round,not just in balance. Else they hop the axle up and down relative to the road. The shocks pick it up and transfer it to the chassis. This can excite the A-body's natural tendency to oscillate at about 55 mph.
I run reduced tire pressures, in part, to help reduce this.
This body vibration is not actually felt but is heard everywhere inside the car with some ares louder than others. It's kindof a ; whooo-whooo-whooo sound, starting quiet,getting louder, then decaying; and repeating.If you put a stopwatch on it, you'll find it oscillating at about 60 or so cycles per minute at 55mph, and it doesn't seem to change progressively much with speed. It just changes volume/intensity, mostly.
 
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No not desperate......on a mission.....that is better wording. I cant wait to find out what is the problem. Keep on it!
 
I just went through the same struggle and tried all the same stuff as you.

I solved it going to a different driveshaft shop #2 and the guy mentioned I had some cheap U joints from Shop #1. He said even tho they were new they could be a problem. He put in some spicer joints, rebalanced it and boom no more vibration. Might be worth a shot as its not too expensive.
 
I have had dealings with bad u-joints also.
But i think this is something that was already ruled out with a new driveshaft.
 
I wish all my new parts performed as advertised. Just saying we all know that just cause it comes "new" ....means that you have a better chance it will work. Thats why I like the eliminate as many factors as possible like running it without wheels and driveline then introduce parts. I dunno it might only produce the symptoms while on the road for all i know. I liked that driveline vid. very informative.
 
snailpower said:
Mine was new too haha. Didn’t matter, u joints were bad out of the box.
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If i read correctly ^^^ the op had a new driveshaft made,and balanced and problem still exists. Not saying it cant be u-joints, but highly unlikely. My thoughts are all the things done and driveline angle has never been checked. Its almost free and takes little effort. Easy enough to rule it out.
 
cli55er said:
.....It only does it when driving and only at highway speeds. 60-75mph.

Oscillation is def coming from the floor and trans tunnel. Trans and engine both have brand new mounts. It is def mounted tight, but I need to retorque since remounting the crossmember and driving 100 miles or so now.

Brake drums and shoes are brand new. Back right does rub a bit on the backing plate, but is wearing down now and the vibration was there when the old original bell shaped drums were on anyways.
The pinion angle looks okay to me... but 4 degrees would be hard for me to see with my eyes.....
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Brother, I have the same issue and I too have new drums fitted to my car. I think I've found my problem.....see video below:


 
Mr. Gorsky, your video really helped. those appear to be the same exact drums that I bought. so I decided to give them another look. One of them has grinded on the backing plate since the beginning, but I took that one off and put the original back on months ago. Then recently when I did all this work to the third member I put it back on and thought it'll just grind down eventually and it did. also one of them had a HUGE amount of balancing weights on them, while the other did not. so yeah....crap drums i'm sure.

anyways.....I got the new tires mounted and balanced and before I put them on the rear I took off these new "china" drums and put back on the original Chrysler bell shaped drums. I had to adjust the shoes out too.

so now I have the original drums back on.....and new tires/rims. BAM 80% of the vibration is completely gone!!!! I can't believe it! drums/tires mimicking a driveshaft out of balance. crazy!

so for the other 20% vibration I can still feel, and mind you it is VERY tolerable, I'm going to have the pinion angle checked over soon.

Man, the car is like a whole different beast, especially with these new rims. and wouldn't you know.....I had some old dog dish caps that my Uncle gave me for my old 69 dart (long gone...both uncle and car) and I like them better then the red circle ones I have.....the red clashes with the orange....these ones my uncle gave me are just black, although faded a bit....the stainless is perfect and no dents at all....might be the cop version. idk. but I like them.

also as a side effect of the larger rims and slightly taller tire...the car is higher and the deep pan on the trans sits higher now.

Thanks SOOOO much to everyone for the suggestions and the information. the pinion angle will be checked next! FABO 4EVER

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Nice car!
Cooper cobras, the same ones i decided to use. Once my car is rolling, that is.
 
thanks! paint is from early 90s. top is original, interior is original.
 
car looks great by the way, these old cars take some figuring out when you have a problem.
 
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