Driveline vibration out of now where! Help!

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Moog I am finding is "Old Stock" here are some of the other suppliers to choose from like TRW:

Universal Joint Items
Item Chrysler Precision Dana TRW
(Detroit ref.) (OEM or MP) (Moog) (Spicer) (Federal Mogul)
-------------- ------------ --------- -------- --------------
7260 joint 4364400 315G 5-1306X 20030, 20030P
7290 joint 4057025 316 5-1309X 20059, 20059P
Combination * --- 347 --- 20226
1330 joint 2533202 354 5-213X 20064, 20064P
7260 strap kit P4120468 318-10 2-70-38X 20704
7290 strap kit P4120469 492-10 2-70-28X 20705
 
mopower440 said:
1972 dart swinger, 440/727, 3.23 geared clutch type 8 3/4 rear. I just got finished rebuilding the front end and doing the K-H disk swap. Finally got that all done and now noticed i have this pulsating vibration in the driveline somewhere.. Almost like swerving over onto the rumble strips back and forth..not quite that bad but... It had been fine and sits most of the time in the garage so i dont know where this came from all the sudden. I jacked it up and ran it through the gears on the jackstands and it still did it. I crawled under the car and grabbed the drive shaft and shook it and there doesnt seem to be any play in the u-joints..Im stumped. Like i said, its been fine and seemed to just develop out of now where.. any ideas?
Click to expand...

Does it come and go at a particular speed
or just get worse and worse the faster you go?
Is it tied to a particular rpm
or throttle opening?
What happens if you cruise the car into the vibration zone, and then put it into neutral?
Did you change the ride height?

If it does it on jackstands with the wheels removed, and has a sweetspot speed where it is worse than at other speeds, then you have eliminated several usual suspects; namely all of wheels and the entire front end.
I assume the jackstands were placed under the axle tubes,out near the bearings. And I assume the rear springs and more specifically the bushings in them,were not touched. Those springs are pretty good amplifiers, which is why they have rubber isolation bushings.
With 3.23s, the rear axles turn at 1/3.23=31% of driveshaft speed, and so, at a cruising speed of 60mph, or about 2400rpm, the axles are only turning at 740 rpm. And so it's hard for me to think your large amount of "rumble-strip" vibration could originate in the axles; they would have to be bent fairly badly to cause that degree of vibration.
And I know of no single source of vibration that can come and go.
But I do know that the A-body has a natural frequency of about 1 cycle per second that can be excited by another vibration, and the two together can combine to make a come-and-go, whoooooo-whoooooo-whoooooo, which can be both felt and heard. But it's not a sudden onset, and is far more subtle than "rumble-stripping". I also know that the tires, at 740 rpm, are far more likely to aggravate this ~60 cycles per minute body vibration, because they are related like 740/60= ~12 to 1 ; so the whoooooo-whoooooo-wh increases and decreases both in volume and intensity, at various speeds often being worst at 55/60 mph.
But, by taking the wheels off, you have eliminated this.
But the driveshaft can also excite this body frequency, when the U-joints cycle thru their angles of operation. I don't know if you are aware of how a U-joint works so A quick review is this; Any time the driveshaft and the thing it is driving or being driven by, are not in a direct line from eachother, the crosspins speed up and slow down with every revolution. When the angle difference is small the vibration is small and vice versa.
The front angle is usually 1 to 3 degrees depending on the ride height and rear tire size. The rear angle changes with the rise and fall of the rear ride height AND the amount of power input as the springs wind up. For a streeter the rear angle can vary from zero to maybe 7 degrees.
The ideal would be if the rear angle is equal AND opposite to the front angle, as then the vibrations cancel out and you get a smooth ride. But this situation,in a non-stock vehicle, if it happens at all, only happens at one ride height and power input. And worse is if the rear end winds up on the springs with the nose going up and the angle going negative; then the angles add up and instead of cancelling the vibration, now they amplify it. That's bad news.
But again, on the jackstands, with the wheels off, and with no load applied,This is not likely to be a factor.

So IMO that kindof leaves just two options; driveshaft run-out and crosspin wear. And as mentioned, a worn out trans mount can allow the vibration into the body at the front, and worn-out eyebushings can allow it to enter the body at the rear.
Crosspin wear is usually caused by little to no pinion angle at all in the rear, which causes the needle rollers to hammer grooves into the pins. So the recommended minimum angle is one to two degrees to keep the bearings rolling and working the grease around. Crosspin endplay does not change much over the life of the joint, cuz that's where all the grease piles up. So depending on how you push/pull the driveshaft,a worn-out joint may not be felt. But as said, as soon as it's out of the saddles, you'll know.
Driveshaft run-out is easily measured, but the joints have to be known to be good first.

None of this,however, addresses how it could have been fine before the work began, and now, it's not.; except perhaps a rideheight change, or a spring swap....... I'm guessing.
 
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Update: Today i pulled the driveshaft only to find the u-joints are absolutely fine! Still just as smooth as the day i had them put in, no binding at all. I was hoping thats all it would be but no such luck. So i spun the pinion on the rear end and in turn, it spun the wheels, both forward (suregrip) and no noise. I had my grandson spin the wheels while i laid under the car where the rear end is and no unusual noise. So, i put the driveshaft back in, installed it 180 degrees off from where it was just to see if that would help. After i got the shaft bolted back in, i had my grandson spin the rear wheels again while i laid under the driveshaft and i could here a boom...boom..boom...boom coming from the tailshaft of the trans. So i scooted myself up under the tailshaft and had him keep spinning the wheels and sure enough, its coming from the tailshaft and i could slightly feel it in the tailshaft..So, im assuming this is where the problem is. Obviously he couldnt spin the wheels very fast but enough to make the pulsating boom and i guess when its spinning fast, it causes the bad vibration. I fired it up on the jackstands again and it seems to have kind of a slight vibration going all the time, but the pulsating bad vibration comes in about 40-45 MPH and way worse in 3rd gear than second..I can run it up to 45 in 2nd and its not near as bad as when it shifts into 3rd and at that same speed. I dont know much about transmissions so this really has me upset! when i bought this transmission, it was freshly rebuilt and when i got it, my friend tore into it to verify and it had been for sure. I bet i have not put 1000 miles on it since then, which has been around 2002 or so. It shifts fine and all, no slippage or anything. The ONLY thing i saw questionable when i pulled the driveshaft out was the shiny area on the front of the driveshaft that slides into the the transmission had some pitting going on and IF the tailshaft bearings used that shiny part of the driveshaft that slides into the trans as the inner race, then it would make sense as to this vibration being from the pitting..but i dont think its made like that..?
 
mopower440 said:
it seems to have kind of a slight vibration going all the time, but the pulsating bad vibration comes in about 40-45 MPH and way worse in 3rd gear than second..I can run it up to 45 in 2nd and its not near as bad as when it shifts into 3rd and at that same speed.
Click to expand...
This is your clue right here.
After the trans shifted, nothing changed from the trans back.
At 42mph in second gear, the engine was at about 2500 rpm.
After the shift into third, the rpm dropped to about 1750, and the vibration was waay worse..

So now, run it at 1750 in the other gears and see if the vibration is the same or similar. if it is, then look to the engine or TC....If it is not, then I would suspect the vibration originates inside the trans, and oldkimmer may have nailed it
 
AJ/FormS said:
This is your clue right here.
After the trans shifted, nothing changed from the trans back.
At 42mph in second gear, the engine was at about 2500 rpm.
After the shift into third, the rpm dropped to about 1750, and the vibration was waay worse..

So now, run it at 1750 in the other gears and see if the vibration is the same or similar. if it is, then look to the engine or TC....If it is not, then I would suspect the vibration originates inside the trans, and oldkimmer may have nailed it
Click to expand...
I did that and its worse in 3rd at the same speed than it is in 2nd at that same speed..I can hold it at 45 in second and its just a steady small vibration, but when it shifts to 3rd, that pulsating vibration kicks in bad! Is this what a bad tail shaft bushing acts like? Never have heard exactly what one does when this goes bad..?
 
I have never had a vibration traceable to the bushing period. And yes I have had bushings wear out.
But I have had an engine-originating vibration traceable to too much ignition advance, that felt like a driveline vibration.

Think about what is happening engine wise;
running up to 42 mph and then cruising, brings the Vcan on line, which combines at 2400 with the mechanical plus initial to total a large number which while cruising at very light throttle; the engine may or may not be happy about. So maybe you get a bit of complaints which manifests as a slight vibration.
Then at the shift, the rpm drops to 1750, but to maintain the 42 mph, you have to increase the throttle opening. So, maybe now the engine is steadily detonating, or misfiring, and the vibration gets worse...
My Vcan kicks in 22/24 degrees, and not all engines will accept that with 20* of mechanical, totalling 42* at 1750 rpm.... but might be Ok with 48 total at 2400.
So the first thing I would do is disable the Vcan and back the timing down to something like 12* at idle, with no more than 24 at 1750; and if you are running a full-time source of vacuum to the Vcan, I would later return that to the spark-port which brings it in at a later throttle opening.
So now, the engine will be starved for timing. If the vibration goes away, on the roadtest, hallelujah you found it. But if it doesn't, well then you can put it all back together and sleep better at night. This test is not valid on jackstands because; A) if the vcan is full time and not disabled, then the advance will be very high, and B) if the v-can is on the spark-port and still connected then at 1750 rpm, and no load, the throttle opening may not be sufficient to deliver full advance and maybe none at all.
Good luck!
Of course, now, the problem almost has to be inside the trans, altho I can't see it, cuz everything is locked up and all rotating together in "drive"....... which pretty much points to oldkimmer's response;the rear bushing,lol. And since he said it twice, I think he knows more than I do.
 
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AJ/FormS said:
I have never had a vibration traceable to the bushing period. And yes I have had bushings wear out.
But I have had an engine-originating vibration traceable to too much ignition advance, that felt like a driveline vibration.

Think about what is happening engine wise;
running up to 42 mph and then cruising, brings the Vcan on line, which combines at 2400 with the mechanical plus initial to total a large number which while cruising at very light throttle; the engine may or may not be happy about. So maybe you get a bit of complaints which manifests as a slight vibration.
Then at the shift, the rpm drops to 1750, but to maintain the 42 mph, you have to increase the throttle opening. So, maybe now the engine is steadily detonating, or misfiring, and the vibration gets worse...
My Vcan kicks in 22/24 degrees, and not all engines will accept that with 20* of mechanical, totalling 42* at 1750 rpm.... but might be Ok with 48 total at 2400.
So the first thing I would do is disable the Vcan and back the timing down to something like 12* at idle, with no more than 24 at 1750; and if you are running a full-time source of vacuum to the Vcan, I would later return that to the spark-port which brings it in at a later throttle opening.
So now, the engine will be starved for timing. If the vibration goes away, hallelujah you found it. But if it doesn't, well then you can put it all back together and sleep better at night.
Good luck!
Click to expand...

I dont run the vacuum advance.. Its definately a pulsating vibration..Is there anything in the trans that could cause this? Like i said, with my grandson turning the rear wheels and the trans in nuetral and the driveshaft spinning, i am hearing a pulsating boom....boom....boom.....boom... coming from the tail shaft of the trans..That has to be whats causing this..
 
I have never heard a pulsating boom-boom-boom from a tailshaft so cannot say.
But if it is the rear bushing, you should be able to reproduce it by manipulating the trans yoke in multiple directions, to find the loose spot. Now keep in mind that rear-end noises will travel up the driveshaft, so if you cannot find the looseness in the bushing, then.......... perhaps it doesn't originate there.
When you checked the rear U-joint, did you also check the front one?
 
AJ/FormS said:
I have never heard a pulsating boom-boom-boom from a tailshaft so cannot say.
But if it is the rear bushing, you should be able to reproduce it by manipulating the trans yoke in multiple directions, to find the loose spot. Now keep in mind that rear-end noises will travel up the driveshaft, so if you cannot find the looseness in the bushing, then.......... perhaps it doesn't originate there.
When you checked the rear U-joint, did you also check the front one?
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Yes, checked them both, no binding, no slack, nothing..I wish i could crawl under it while someone ran it through the gears so i could check it out, but no way im doing that! There has got to be a way to track this down better..like i said, with the driveshaft disconnected from the rear, and then spinning the rear wheels or pinion, there isnt any noise, but we cant spin them that fast either, but after installing the driveshaft and doing the same spinning the rear wheels, i can get under the tailshaft and hear/feel this..
 
OK mopower440 good diagnostics so far, getting to the bottom of it.

Here is a picture of a 727 tail shaft, there is a large ball bearing that installs by the key in the picture.

727 tail shaft.jpg


You could take the speedo gear out and have your grandson turn the rear wheels again, then you can see if you can feel (or see) that bad bearing by carefully touching the shaft at the speedo gear grooves as he turns the wheels. That large ball bearing is real close to the speedo opening in the tail case. May be able to feel on the shaft that it is further up the line into the transmission more like at the Planetary Gears on the trans end of this same shaft.

This is one thing to check before we go further, that bearing can be changed just by taking the tail shaft housing off if it is noticeably bad.

Was talking with my guy Brian that builds all my mopar trannys. He was saying that he doubts it is that large tail shaft bearing and more than likely the Planetary Gear Assembly. He was saying that the Panetary Gears can get lots of slop in them.

The guy that built the trans probably put new clutches, and new bands in it but probably reused the used planetary gear setup and that is a good chance why it is failing now . . just wore out. Unfortunately the transmission has to come out to get to it.

On to the next tests . . .

Can also drop the trans pan and see if there is lots of metal shavings in it, if so take the trans out and replace the faulty parts. They are one of the easier automatic transmissions to rebuild.
 
George Jets said:
OK mopower440 good diagnostics so far, getting to the bottom of it.

Here is a picture of a 727 tail shaft, there is a large ball bearing that installs by the key in the picture.

View attachment 1715331034

You could take the speedo gear out and have your grandson turn the rear wheels again, then you can see if you can feel (or see) that bad bearing by carefully touching the shaft at the speedo gear grooves as he turns the wheels. That large ball bearing is real close to the speedo opening in the tail case. May be able to feel on the shaft that it is further up the line into the transmission more like at the Planetary Gears on the trans end of this same shaft.

This is one thing to check before we go further, that bearing can be changed just by taking the tail shaft housing off if it is noticeably bad.

Was talking with my guy Brian that builds all my mopar trannys. He was saying that he doubts it is that large tail shaft bearing and more than likely the Planetary Gear Assembly. He was saying that the Panetary Gears can get lots of slop in them.

The guy that built the trans probably put new clutches, and new bands in it but probably reused the used planetary gear setup and that is a good chance why it is failing now . . just wore out. Unfortunately the transmission has to come out to get to it.

On to the next tests . . .

Can also drop the trans pan and see if there is lots of metal shavings in it, if so take the trans out and replace the faulty parts. They are one of the easier automatic transmissions to rebuild.
Click to expand...


I dont know what ill do if it is the trans..i refuse to tear into it fearing i will never get it back right..Transmissions just scare me! Ive watched videos of people rebuilding the 727 and just dont think i could do it. Bad thing is, i dont know wnyone who knows about them.. first thing though, i got to make sure 100% it is in the transmission.. not really sure how to be sure though..Can i remove the drive shaft and run it on the jackstands and see if it still does it or will it spit the trans fluid out of the tailshaft..? Like i said though, just mysterious how it just suddenly started doing it..
 
Someone on here should be able to help you find a reasonable tranny man in your area that can help you out. So yeah just drop the trans pan and trans fluid, and see what is showing up for steel in the bottom of the pan, if there is lots of steel in there then it needs to come out.

See if you can find another Mopar Guy in your area that can assit you and help find that right guy to get the trans fixed. Can walk into the local tranny shops in your area and ask if anyone is familiar with rebuilding the mopar 727 trans then go from there. You can feel them out at the same time to see if this is someone you want to do business with, or maybe they are just a good sales man.

From everything we have gone over so far with the info you have supplied I would say that it is the Bad Panetary Gears.

Keep looking into it a little farther, there are more things to discover . . .

Check to make sure the Torque Converter to the crankshaft Flex Plate Bolts are tight too. That could make some odd noises too if they came loose. Probably have to pull the starter and the front trans dust shield/inspection to get in there properly. Just in case . . .
 
When I was young and didn’t know anything about trannys, I went into a trans shop and asked if they worked on mopars. The guy asked “what’s a Mopar”. Needless to say they didn’t get my tranny to work on. That’s when I decided to do them myself. Kim
 
Actually what u can hear feel may be normal. How is the pinion angle? Is it a factory drive shaft on ur car, or 1 u had built/shortened? Kim
 
He was saying it was a used driveshaft off like a Cordoba Big Block that he had shortened.
 
Can i run it with the driveshaft removed to see if it still does it or will it spit out all the fluid through the tail shaft hole?
 
Good Thought Kim,
Things were working proper before he did his last front end work here lately, then something odd happened. Just thinking something in the Planetary Gear setup in the trans was just on the verge of letting go, and it finally did let go on his startup after his last front end upgrades.
 
You can put in a used driveshaft front yoke to keep the fluid from running out while you quick test it. Not too long or the yoke can slide off the tailshaft.
 
George Jets said:
You can put in a used driveshaft front yoke to keep the fluid from running out while you quick test it. Not too long or the yoke can slide off the tailshaft.
Click to expand...

Do you think it would stay put long enough to run it up through the gears to test?
 
Yes, I would raise the back of the car up higher than the front, so that gravity wants to keep the used yoke in the back of the transmission,
 
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