Finally think I solved my vibration issue

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skep419

skep419

5.9 Magnum 4 speed afficionado
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I've been dealing with a bad vibration for as long as I can remember. Tonight I was reading a thread about balancers and came across a picture of a 727 flexplate and a 904. I remember a post on here about how the dot was suppose to line up with the weight on the converter. I went out and looked at mine Friday and it didn't have the dot. Well I went through my parts bin and found one with the dot. I went back inside and noticed the difference in flexplates wasn't just the dot but the 904 has triangles and the 727 has circles. Needles to say 12 years ago (I was 18) I paid a shop to swap my 904 for a 727 and they somehow reused the 904 flex plate.

Any ideas on what kind of damage this may have caused? (Things to look for)
 
Explain in GREAT detail your vibration issue, i mean every little detail... what mph, what rpm, when it starts, when it gets worse.... on power off power....everything
 
vibration starts at 55mph and gets worse the faster you go. Light throttle or full throttle doesn't matter. Under deceleration its a different vibration but still just as bad. If I put it in neutral it almost goes away and comes back while reving (above 3000 rpm in neutral while traveling at 55+) Doesn't do it while reving in park.

1969 dodge dart 360 727 8 3/4 742 suregrip 3.91. stock cast crank, pioneer externally balanced harmonic balancer (pre 1992) 904 flexplate midwest converter weighted for external balance. dr diff drive shaft 1350 u joints. tried rear and angle from 4 deg down to 4 deg up no change. Tested with front wheels sitting on old wheels and rear on jack stands. wheels off, drums off, axles out, differenet 3rd members. new transmission mount, new tailshaft bushing. took belts off, factory balancer, swapped motor mounts. The only way i've gotten the vibration to go away is running it with a piece of wood on top of the jack lifting the trans up off the mount.
 
Can you get it to vibrate sitting still? In other words does it vibrate at 3000 rpm in park?neutral? If so, I would rule out everything from the trans back. If it is at a roll, it could be the driveshaft ( bent,twisted, out of balance) or in thr rear diff. Bent axles, bad bearings etc. I had a similar situation in a stick shift car, turned out to be a pressure plate that was out of balance and a driveshaft that needed balancing. I had a vibration sitting still, and at a roll. Check everything, also, don't count out the internals of the transmission either. There are bearings and output shaft bushings that can cause issues. Through the process of elimination, I removed the worst of it ( the pressure plate) then smoothed it out with the driveshaft rebuild.
 
Sounds like it is inside trans. There are a few bushings and roller bearings. Any of the other parts could be broken just not come apart YET.
 
skep419 said:
vibration starts at 55mph and gets worse the faster you go. Light throttle or full throttle doesn't matter. Under deceleration its a different vibration but still just as bad. If I put it in neutral it almost goes away and comes back while reving (above 3000 rpm in neutral while traveling at 55+) Doesn't do it while reving in park.

1969 dodge dart 360 727 8 3/4 742 suregrip 3.91. stock cast crank, pioneer externally balanced harmonic balancer (pre 1992) 904 flexplate midwest converter weighted for external balance. dr diff drive shaft 1350 u joints. tried rear and angle from 4 deg down to 4 deg up no change. Tested with front wheels sitting on old wheels and rear on jack stands. wheels off, drums off, axles out, differenet 3rd members. new transmission mount, new tailshaft bushing. took belts off, factory balancer, swapped motor mounts. The only way i've gotten the vibration to go away is running it with a piece of wood on top of the jack lifting the trans up off the mount.
Click to expand...

How are your u-joints? Drive line balanced?
 
Ryan Ward said:
Can you get it to vibrate sitting still? In other words does it vibrate at 3000 rpm in park?neutral? If so, I would rule out everything from the trans back. If it is at a roll, it could be the driveshaft ( bent,twisted, out of balance) or in thr rear diff. Bent axles, bad bearings etc. I had a similar situation in a stick shift car, turned out to be a pressure plate that was out of balance and a driveshaft that needed balancing. I had a vibration sitting still, and at a roll. Check everything, also, don't count out the internals of the transmission either. There are bearings and output shaft bushings that can cause issues. Through the process of elimination, I removed the worst of it ( the pressure plate) then smoothed it out with the driveshaft rebuild.
Click to expand...

doesn't do it sitting still

cudascott said:
may be a tailshaft bushing
Click to expand...

bushing has been replaced

younggun2.0 said:
How are your u-joints? Drive line balanced?
Click to expand...

old driveshaft was balanced with new joints
new dr diff drive shaft has brand new joints and came balanced.
 
Where do you feel the vibration in the car? steering wheel, floor/feet, seat/butt

Does your rearview mirror blur when its vibrating
 
FredS said:
Where do you feel the vibration in the car? steering wheel, floor/feet, seat/butt

Does your rearview mirror blur when its vibrating
Click to expand...

in the seat and floor. ran it on the hoist at work. the vibration is coming from the rear pinion. But whats causing it to vibrate there is to be determent.
 
ordered a 10239 b&m flexplate. going to swap my 904 with stock converter, use the stock driveshaft from my other slant 69 dart, swap out the 1350 yoke and see what happens.
 
im in the same exact boat as you,tried it all,axles,axle bearings,3rd member,ujoints,drive shafts,trans mounts,new trans,pinion angles,brake drums,different wheels and tires,speed related faster you go the worse it gets,it will knock the rear view mirror down at 70mph.i give up.new front end.really pisses me off
 
Check the rear pinion closely for a flat surface where the snap rings ride. Should be totally flat with no groove worn in. U joint should not move side to side. A pair of different thickness snap rings can be used if needed.
 
skep419 said:
ordered a 10239 b&m flexplate. going to swap my 904 with stock converter, use the stock driveshaft from my other slant 69 dart, swap out the 1350 yoke and see what happens.
Click to expand...

Process of elimination at work here, I just hope it doesn't get too expensive for you. I remember pulling the trans out of my car a couple of nights trying different things.. I got to where I could have it out pretty quick. I had access to a lift though. Good luck.
 
mderoy340 said:
Check the rear pinion closely for a flat surface where the snap rings ride. Should be totally flat with no groove worn in. U joint should not move side to side. A pair of different thickness snap rings can be used if needed.
Click to expand...

tried 3 different yokes. that last one was a brand new one from dr diff for the 1350 u joints. fit perfect no slop
 
Go to a friendly GM service department and speak to the service manager.

Tell him that you would like to take a test drive with their Smart EVA (Electronic Vibration Analyzer).

Whatever is vibrating will be reported in a certain Hz. That will tell you what type of component that
is causing the problem (Ex. a wheel will register at a different Hz than the driveshaft, etc).

It shouldn't cost much (if anything).
 
you checked and validated the pinion angle? You said you ran it on a hoist, was the rear end drooped?
 
FredS said:
you checked and validated the pinion angle? You said you ran it on a hoist, was the rear end drooped?
Click to expand...

I remember my pinion looking like it was "wobbling" when ran on a hoist. I did eventually

get the driveshaft rebalanced and the rebuilder said it was bent a little. The rebuilder was able to straighten it and balance it. He offered to build me a new one though. I don't remember why I didn't get the new one, probably cost at the time.
 
FredS said:
you checked and validated the pinion angle? You said you ran it on a hoist, was the rear end drooped?
Click to expand...

yes.

no. the rear end was supported and the front was supported under the lower control arms.
 
Tested with front wheels sitting on old wheels and rear on jack stands. wheels off, drums off, axles out, differenet 3rd members. new transmission mount, new tailshaft bushing. took belts off, factory balancer, swapped motor mounts. The only way i've gotten the vibration to go away is running it with a piece of wood on top of the jack lifting the trans up off the mount. [Qoute]

So reading this here, you have the vibration sitting in the garage I assume because the axles were out. That is what I meant by sitting still, in other words not rolling down the road. If you had the axles out, I would pull the driveshaft next and run it up, maybe with a yoke in the end of the trans to keep the fluid in. If the vibration is still there, it is in the Engine/trans. If not, Driveshaft/ U joints or combination of both. Or something very loose in differential (third member).
 
Could be the position of the engine. Does the trans mount fall into place without having to use any side force to line it up?
 
If you say that the vibration stopped when you raised the rear of the transmission, you should focus on that. Put some washers between the mount and the trans. Test drive.
Do that before you drop the trans.
 
Ryan Ward said:
Tested with front wheels sitting on old wheels and rear on jack stands. wheels off, drums off, axles out, differenet 3rd members. new transmission mount, new tailshaft bushing. took belts off, factory balancer, swapped motor mounts. The only way i've gotten the vibration to go away is running it with a piece of wood on top of the jack lifting the trans up off the mount. [Qoute]

So reading this here, you have the vibration sitting in the garage I assume because the axles were out. That is what I meant by sitting still, in other words not rolling down the road. If you had the axles out, I would pull the driveshaft next and run it up, maybe with a yoke in the end of the trans to keep the fluid in. If the vibration is still there, it is in the Engine/trans. If not, Driveshaft/ U joints or combination of both. Or something very loose in differential (third member).
Click to expand...

nope just in neutral. still did it with the axles out.

cudascott said:
Could be the position of the engine. Does the trans mount fall into place without having to use any side force to line it up?
Click to expand...

falls right into place.

furyus2 said:
If you say that the vibration stopped when you raised the rear of the transmission, you should focus on that. Put some washers between the mount and the trans. Test drive.
Do that before you drop the trans.
Click to expand...

i will try this before i drop the trans. Think i will start back hacking the old mount to be used as a spacer.
 
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