Vibration at 80mph+ since gear install.

TheDamned · Nov 24, 2006

Since my gear install, I have some vibration coming from the crankshaft I think
when i'm cruising on highway speed. Is it dangerous ? Since i'm running with new gears since August I didn't bother because I don't go alot of highway but i wouldn't make a 4 hrs trip with that vibration. Also, I can feel the vibrations just by putting my foot and not pushing on the clutch.

Any ideas ?

smitty_64 · Nov 24, 2006

Sounds like they didn't shim your gears right or you used used gears that already had a wear pattern for the car they came out of.

TheDamned · Nov 24, 2006

No, it's not gear grind.
The vibration doesn't occur under 80mph everything was installed right
after a guy specialized in transmission fixed it. It really comes from like the upfront not the rear.

1TallMF · Nov 24, 2006

Your driveshaft is spinning a good deal faster now with the new gears at that speed. This is actually a pretty common problem if you do a search, your driveshaft may be ever so slightly out of balance or you may have a u-joint thats getting slightly worn out. I have this exact same problem above 70mph, the whole shifter shakes and becomes a blurr. I'm trying to decide whether its worth it to get an aluminum DS or just try replacing the u-joints. Mine gets alot worse as I let off the throttle though.

If there was an engine vibration, it would be strictly rpm-related and not speed dependant. Is this a super-high frequency vibration or more consistent with tire rpm? The driveshaft vibration mentionned above sounds kind of like a loud humming.

TheDamned · Nov 24, 2006

1TallMF said:
Your driveshaft is spinning a good deal faster now with the new gears at that speed. This is actually a pretty common problem if you do a search, your driveshaft may be ever so slightly out of balance or you may have a u-joint thats getting slightly worn out. I have this exact same problem above 70mph, the whole shifter shakes and becomes a blurr. I'm trying to decide whether its worth it to get an aluminum DS or just try replacing the u-joints. Mine gets alot worse as I let off the throttle though.

If there was an engine vibration, it would be strictly rpm-related and not speed dependant. Is this a super-high frequency vibration or more consistent with tire rpm? The driveshaft vibration mentionned above sounds kind of like a loud humming.

It's exactly like you described.
Gets worse when I let off the throttle easwell.
It's not the engine it's really from the driveshaft.
And more like consitent with tire rpm since it's speed dependable.

TheDamned · Nov 24, 2006

Oh and it's starting to do it at like 70mph not 80mph.

So it's not by anykind dangerous ?

94GTMOOSE · Nov 24, 2006

is it a better idea to get a new driveshaft, or have the old one balanced. or what about buying a driveshaft from a custom builder. i think i have the same problem so i want to get it right the first time so i do not have to spend money a second time to get it right. measure twice cut once.

TheDamned · Nov 24, 2006

damn, gear install cost alot more then we all think in the end eh... damn with the price of the gear install I could've got a new cat-back, headers and intake!

TheDamned · Nov 25, 2006

So the only solution is to get an alu driveshaft ?

OrangeMustangGt · Nov 25, 2006

my car has done that since i bought it. Ive been putting it off though till i destroy my tranny. I usually dident drive that fast anyway since i had 3:73 gears.

smitty_64 · Nov 25, 2006

I would definitely change the u-joints. They're cheap considering... If the car has a lot of miles and you never have changed them, they are probably getting close to finished.

TheDamned · Nov 25, 2006

Ok.. i'll look into this.

94 Black GT · Nov 26, 2006

Honestly..money not an issue i would just get the new aluminum d/s and new u joints...your problem should be resolved after that..Also u may just want to check the bolts that hold your driveshaft in..when they start to lossen up it is a wicked vibration that is very speed dependent..

urban96 · Nov 26, 2006

if you have the $200 to spend, get an alum one.. if not just get your stocker balenced and replace the u-jounts

MadPony · Nov 27, 2006

one quick thing to try us unbolt the rear u-joint (connected to the ponion side). flip it 180 and bolt it back up. Don't know why but I have sen this before.

Anytime I replace ujoints, I always mark each piece, so it goes back in the same way. I have seen too many driveshafts vibrate after changing the u-joints. I know this IS NOT supposed to be the case.

Pokageek · Nov 27, 2006

I know why. I had the same problem turned out to be LOOSE DRIVESHAFT BOLTS!!

Took the car to the same shop for the 3.55's as for the 3.90's and first time like a dummy, I went out and bought an alumn ds. Another mechanic put it on (who knew how to tighten bolts!!) Second time it happened I said NO WAY! Then I took it to the guy who knows how to tighten and he showed me.

TheDamned · Nov 27, 2006

Pokageek said:
I know why. I had the same problem turned out to be LOOSE DRIVESHAFT BOLTS!!

Took the car to the same shop for the 3.55's as for the 3.90's and first time like a dummy, I went out and bought an alumn ds. Another mechanic put it on (who knew how to tighten bolts!!) Second time it happened I said NO WAY! Then I took it to the guy who knows how to tighten and he showed me.

Wow, i'll check that out, thanks for the headsup.

Engel · Nov 28, 2006

I had the same problem as you only mine was at 90+ and I replaced the driveshaft with an aluminum one problem solved..

vladasap · Feb 1, 2007

I have the same EXACT prob but i have 4.10s
how much is an aluminum D/S and just how big of a job is to relace it???

RyClef331 · Feb 2, 2007

Pokageek said:
I know why. I had the same problem turned out to be LOOSE DRIVESHAFT BOLTS!!

Took the car to the same shop for the 3.55's as for the 3.90's and first time like a dummy, I went out and bought an alumn ds. Another mechanic put it on (who knew how to tighten bolts!!) Second time it happened I said NO WAY! Then I took it to the guy who knows how to tighten and he showed me.

WERD. I found the same thing on my car. MAKE SURE your flange is SEAT FLAT. My aluminum wouldn't seat all the way and the bolts would get tight and you could visually see it was crooked. I've also found my bolts loose.

Did you mess with the pinion angle at all? Like put new control arms on or anything?

Vibration at 80mph+ since gear install.

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