94blackz

Iv had the same problem with. 2 f bodies one was a loose pinoin bearing and other was a tweeked axle put it on jackstands in high gear and look at all the moving parts.you will find it

ThoR294

iTrader: (6)

pinion is set to spec. whatever that was, I set it when I put the T/A in. didn't change a thing.

I am really really hoping its something in the rear... when I swap it on friday ill post here

BoostedDSM

iTrader: (6)

My m6 car had it really bad at anything over 80, my a4 car not so much, it starts at about 85 now. But goes away too, this car has been to over 120 and no shake there, my m6 to 140 and no shake past 100.

ThoR294

iTrader: (6)

my car death wobbles over 70mph. in neutral also, no matter what gear in its, its the same, so I dont think its the 5/6 vibration like in the other thread. If I replace the rear and it doesn't fix it im driving my car off a cliff i cant handle it anymore. lol

93M6Formula

Did you have your clutch balanced with the flywheel? I just did this to fix a virbration on my car,

TrickrTreat

iTrader: (3)

Pinion angle , and drive shaft length are two things that jump out .

My best friend and i chased a horrible vibration in his car for a long time like two years. tried balancing drive shaft swapping trans's and wheels yada yada yada, finally determined (by accident) that his drive shaft was a little too short causing his yoke too wobble slightly , but at 65-70 it was awful!

Also i had a real bad vibration in my car when i first put it together that i couldn't track down and i started playing with my pinion angle and got it to all but disappear. i also believe my driveshaft is a tad too short. ill post in here if it smooths it completely.

although both cars were a4's , both did have aftermarket rears, so not sure if it still applies to you but hey ya never know.

mikey67

I'd experiment with the pinion angle. I know you said it was set to "spec" but every car has it's quirks. One thing I think has been overlooked is the impact that centering the rear axle with an adjustable PHB may have on vibration. The stock PHB on f-bodies sets the rear axle slightly off center. Along with proper pinion angle, I suspect the offset was done to ward off drivetrain vibration. This may or may not be the case, I don't have any hard evidence, but I've never heard an explanation as to why GM offset the rear axle.

Just my thoughts, ymmv.

SS RRR

iTrader: (2)

There was a TSB about this in the early 90's. It stated the steel DS may cause excessive vibration at "highway speeds" and to replace it with a 1LE/aluminum DS. I had it done while I was still under warranty, had to fight for an hour with four service "techs" and a manager to have it done and it solved all problems.
If the DS is still stock and has not been replaced with a quality aftermarket piece then that could be the issue with most vibration problems.

unioncarpenter84

iTrader: (22)

ya but mines perfectly balance they welded another weight on it.

could my pinion angle be off being stock torque arm??


my buddy has a 98 camaro z28 with aluminum ds and umi suspension and his vibration is worse than mine

unioncarpenter84

iTrader: (22)

seems like it really doesnt matter if its a a4 car or a m6 car

ThoR294

iTrader: (6)

I had an aluminum d/s that was balanced, and my steel d/s that was balanced. both had same vibration.

Why would the clutch/flywheel have anything to do with the car going over 70mph? Its something on the drivetrain end. but, stock clutch, new spec clutch/new flywheel, same. exact. vibration.

I changed the pinion angle and the vibration didn't change.

unioncarpenter84

iTrader: (22)

i just dont understand that its only 70 mph plus why not do it at all speeds

ThoR294

iTrader: (6)

because something is out of round. just like tires dont vibrate till highway speeds.

NAMYZZO

1994 firebird, m6, bmr 1le suspension goodies, edelbrock torque arm, hal shocks, 3.5"X.125" alm driveshaft with weighted oem slip yoke, spicer uj's, poly trans/torque arm mounts..bfgoodrich tires, new tread but dry rotted..
(first week I had it I was showing off with a girl in the car and I shifted wrong and hit 1ST gear...!! .. the whole center console jumped up!!..lost a couple of teeth in the diff..Haha.. Warranty covered the 900.00 dealer repair...)

In my car I can see the passenger side Seat and Floorboard shake!..
I can't remember if it did this before I started putting all this stuff on..
(kinda moved on to my next projects)..I know it needs tires

does anyones PASSENGER side seat shake - or is it in the center console?

>> You mentioned only happening at 70..
I work at a driveshaft shop.. I think most of the M6 shafts had a Harmonic Dampner on the slip yokes..

Just curious if everyone having this issue - do they have a shaft with this on it????

As far as pinion angle.. I am not too sure what mine truly is. I have never checked angles.. Arvin Meritor used to have a video that showed them adjusting the transmission and pinion angles of this mobile test machine in real "REAL TIME".. it was showing how the best angles counteracted each other.. +1 on trans... -1 on diff = ok... (but how often is this really able to happen! and drag race guys usually want a -2 or so at the pinion? i think?)

Do the v6 guys have this problem? = they have a 2PC driveshaft with a carrier bearing/cv type assembly...


The stock 1PC driveshafts varied.. They made one that is approx. 40 1/2"C-C and another that is 41 1/2"C-C .... Sometimes people interchange parts...make a new driveshaft with the wrong slip yoke = and as such the overall length of the shafts is wrong (not enough slip yoke in the trans OR too much)... some forget the inside snaprings on the rear uj LOL ...

just some thoughts .etc..FYI

ThoR294

iTrader: (6)

I am contemplating a PST driveshaft. I know I have to measure it... so I know that would be a perfect fit and a great driveshaft. I just wish I had a solid answer lol I've thrown everything at this damn thing

F0x Slaughter

Running stock bell housing?

speed_demon24

iTrader: (6)

I put in an ls1 rubber trans mount to cure my vibration.

Motorvation

I've never noticed any problems with the old 2.73 rear end in mine, but when I swapped a 3.73 rear in it I get all kinds of vibrations. I was going to get the D/S rebalanced, but that sounds like a no win. Good luck!

spike30th

iTrader: (6)

I know when I swapped out my stock 10 bolt for a moser 9 inch I replaced the driveshaft with a spohn stock length ds.I had the nastiest vibration above 70mph when I let off the gas It felt like the ds was wobbling at the ujoint.I replaced it with a PST ds which was a inch or so longer and that solved my vibration problem.
I know you have a stock rear but it sounds maybe your driveshaft length might be the culprit,I would look into that.

ThoR294

iTrader: (6)

Ty for the input. It's the stock driveshaft, but the car is on strano springs... and I adjusted the pinon angle via the adj torque arm... I knew I shoulda tried a PST before I sank $400 into another rear. fml. we will see friday