I'm still experiencing major vibs at speeds of 60mph & up. I've replace all u-joints and have tried 2 driveshafts...1 steel & stock 1LE aluminum. It's still there. Pinion bearing feels tight too. The vib feels like a bad u-joint but obviously isn't. An obvious question would be tire balancing but I had them rebalanced and it's still there. I've also jacked up the car and put it in gear looking for obvious wobbling of the tires from a bent axle and checked the rear alignment and everything looks good. I've called around about putting it on a dyno to check it out under load but no one wants to touch it b/c of safety issues! I'm at my wits end here! Any ideas, suggestions, or similar experiences?

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'91 Z28 1LE; 355, Sportsman II heads, Edelbrock TPI w/ 58mm TB, Tremec TKO 5-speed, 3.73's & much, much more

 

theres a berring in the tail of the transmission
that holds the driveshaft you may have excessive
clearances cousing the vibration
you should be able to replace it your self
and the berring only coust about $4.
but if your not sure take it to a tranny shop
it would only take me an hour to fix if i took my time.
this is the only fix i can thank of sence you
checked every thang else

 

Are you refering to the pinion bearing? If so, I've checked it for play but haven't checked clearance. Good idea, now I know what I'm doing tomorrow!

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'91 Z28 1LE; 355, Sportsman II heads, Edelbrock TPI w/ 58mm TB, Tremec TKO 5-speed, 3.73's & much, much more

 

hey, i went nuts for 3 months with a vibration. Garages insisted it was Universal joints. Replaced them twice. I have had the car for 8 years. Make a long story short, dropped drive shaft, too it to driveshaft shop and had it spun. Found it out of balance, checked further. Found factory weights intact with no sign of any missing,no bends, not twisted according to their tests. Rebalanced and it drives like a new car. Was told universal joints are known to be unbalanced. They suggested rebalance every replacement. Best $50.00 i ever spent.

 

Does it seem to come from one corner or another of the car?

I had some 'flat spots' on some tires I used to have on my '86. Turns out, it was so out-of balance that it messed up the wheel (that's bad...). The wheel needed force-balancing. You cannot detect or correct this with a normal balancing procedure, but take the tire/wheel off (where the vib is) and roll it...look at the wheel to see inside and out and see if it's lopsided at all. The balancing machine come in handy here, you can see the wheel while it's spinning (makes it more obvious). These kinds of wheels need force balancing. Unfortunatly, only some shops can do this because this procedure requires a special (AKA high dollar)machine.

Just my $.02.

 

hello, no there is a bering inside the tail
housing of the trans mission. its like a
small rod bering but all one peace the yoak
of the drive shaft slips into it whin you
install it into the transmission.

 

Here is a commonly overlooked problem according to a guy I know at a trans shop:
Sometimes the rear yoke gets worn out due to impoperly torqued bolts. This allows some play

Unbolt the u-joint and check to see if if there is a small ridge on the yoke. If so, you need a new one.
It's hard to detect - I had the same symptoms as you; the vibrations would only start at around 70 MPH. By 110 MPH, it vibrated so bad I couldn't maintain speed.
I was so frustrated because I couldn't find anything wrong, I brought it to the trans shop to have it fixed.


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89 Firebird Formula
WS6 package,ZZ4 Crate engine
SLP 58MM TB, Edelbrock TES Headers
Random Tech 3" cat, SLP 3" stainless exhaust
9 bolt rear, Hotchiss swing arms, Lakewood panhard rod
Corvette 2/4 servo, kevlar band, full poly rear.
Centerline 16x8 rims, B.F Goodrich drag radials

 

I had a bad vibration last year when I installed the Energy Suspension tranny mount above 60 mph. After a week of that noise I put the stocker back in.
I've installed a PROTHANE tranny mount now... it's the exact same height as the stocker. The ES piece (when installed properly with the metal plate like the directions say) elevates the back of the tranny and throws the shaft out of alignment. At least that's my theory. Yes, I got an aluminum shaft.

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'89 Formula - Thunderchicken - 355 Vette L98/T-5/3.45 9-bolt/black/t-tops - the fun car!
'90 GTA - The GTA - 5.0 LB9/TH700/3.27 9-bolt/black/t-tops/tan leather - the cruiser.

 

Hey Brian! Sounds like a possibility, when I put the Tremec in I installed an ES trans mount too. Guess I'll throw the stocker back in and see if there's an improvement.