bad vibration above 65mph

[Foxfan88]

ok i am trying to solve my vibration problem.

ok when i got my t5 swap done, we thought my AOD DS wouldnt fit, so i borrow my friends DS, worked great and dandy, so i get a t5 shaft for myself, replace the ujoints and then it shook VIOLENTLY above around 60-65, i mean it was bad.

so i got my AOD shaft to fit, turned out it would fit. the vibration is still there, but not nearly as bad as before.

It will do it in 5th gear at 65mph, i downshift to 4th and it still does it. So whatelse could it be?? when downshifting, the speed of the ds changes but there is still vibration, so the DS may not be the cause??

and on the highway, going maybe 65 or 70, there will be a humm that will come about every 2-3 secs.

hmmmm...................hmmmmmm.................hmmmmmm just does that repeatedly, always the same amount of space b/w each hum.

any ideas??

 

[HISSIN50]

Once you reach a given driveshaft speed (moving towards its critical speed), the imbalance should become noticable and not really go away till you slow down.

I think I misunderstood. If it vibes in 5th at 65, downshifting to 4th only affects the transmission, not the DS (in terms of speed).

EDIT'd out the mish-mash of trans and DS info that made no sense.

Since the issue changes with different DS's, it seems like that is atleast a good part of the problem. You can get your existing DS dynamically balanced if you desire. Or the always pricey alum DS is a good route to go.

It's tough to rule out other items when the DS's balance is questionable.

Oh, the DS is not rubbing anything, right? With older bushings, the pinion angle changes when you change gears or are at different loads, so I had to ask.

Good luck.

 

[Foxfan88]

i dont think its rubbing anything.

can a shop that balances them check if its bent b4 they balance???
can something like a ds fallling of a table hurt its balance???

i would like to get a good alum shaft, how much can i find them for??
if i get a good alum ds and when i get my new t5, everything tranny back will be rock solid and ready for some power

 

[onefstsnake]

How would downshifting speed up the driveshaft?

The driveshaft will always turn at whatever ratio your rear end gear is.
Maybe im reading you post wrong Hissn...


Anyways, I have the same problem right around 65-75mph.
Shakes so bad the mirrors get blurry... Im pretty sure my tranny mount is worn out and the DS might be out of balance as well as bad U joints.

Would the tranny mount cause bad vibrations if it was worn out?
b/c my shifter vibrates alot as well...

 

[HISSIN50]

One fast, you are right. I was trying to make sense of his comments, which I actually thought pertained to his trans, not the DS. I managed to tangle myself in doing so, it seems. I will simplify that so it kinda makes sense (it doesnt right now).
Thanks.

 

[onefstsnake]

Someone just mentioned to me to check the cross member gromets.
The round gromets near the frame rails.

I plan on checking out my car tomorrow in my suspension class.
Ill let you know if I find a cure.

Good Luck

 

[tony91723]

when you did your trans swap did you support your motor? if not you coulda torn your motor mounts, since you allowed it the motor to lean back. WHen you have torn motor mounts it'll cause vibrations.

 

[86bluecobra]

yah im with the checking all the mounts. i hope you did up the tranny mount.

 

[onefstsnake]

I checked the tranny mount today with a big pry bar...
WOW Holly Slop!
Thing stretches over an inch.


Bought a new mount from Ford for like $30 And its VERY stiff, almost no give at all.

I also took off the giant weight that is bolted to the bottom of the differential.
Will this hurt anything?

 

[86bluecobra]

many peeps remove the done bone off the diff. I believe it is there to dampen vibration.

 

[ninety15.0]

yup the dog bone is meant to dampen vibration. One fast, what are the results of that new tranny mount being in place when u drive the car? i know the mount on my corss member is not looking to great and the bushing on the side are rubbish too. Im interested to see if it makes anything smoother, because i get that humming noise in my car at like 80+. thanks

 

[HISSIN50]

Seems to me that the dogbone is 'tuned' to dampen harmonics with stock gears. Once aftermarket gears go in, it is much less effective.

Being anal, I would leave it but that is just me.

 

[onefstsnake]

No Luck today...

Changed the tranny mount. That helped with the shifter vibrations, but its still vibrating badly over 70mph
Took off the dogbone, nothin either.

How much play should the Driveshaft yolk have?

This is really getting annoying...

 

[Black1987Stang]

ok i am trying to solve my vibration problem.

ok when i got my t5 swap done, we thought my AOD DS wouldnt fit, so i borrow my friends DS, worked great and dandy, so i get a t5 shaft for myself, replace the ujoints and then it shook VIOLENTLY above around 60-65, i mean it was bad.

so i got my AOD shaft to fit, turned out it would fit. the vibration is still there, but not nearly as bad as before.

It will do it in 5th gear at 65mph, i downshift to 4th and it still does it. So whatelse could it be?? when downshifting, the speed of the ds changes but there is still vibration, so the DS may not be the cause??

and on the highway, going maybe 65 or 70, there will be a humm that will come about every 2-3 secs.

hmmmm...................hmmmmmm.................hmmmmmm just does that repeatedly, always the same amount of space b/w each hum.

any ideas??

Sooo you tried your friends driveshaft and it was all fine and dandy...so wouldnt that mean that is ur problem?


I have the same thing too, I know exactly what you mean with the Hmmmms, I was going to try rebalancing my tires at school since I can do it for nothing, and i have pretty new energy suspension motor mounts and pretty decent tranny mount too so im leaning towards driveshaft etc.

 

[timewarped1972]

well the driveshafts definatly can cause a problem......but

not to sound stupid but......as tires wear they sometimes become un balanced, if you've had any panic braking situations that could flat spot them, that will do it too........burn outs have been known to toss wheel weights as well

as for fox fans original post, while i'm sure his drive shaft is outa whack.......if he's running those worn drag radial on the back those probably arent helping any.....at those speeds......probably a combination of things...i just know many times when i've been in a car after having new tires puton it made a world of difference......