speed_demon24

iTrader: (6)

I've been chasing down a vibration at 80+ mph for awhile now. It's more like a buzz/hum and not an imbalanced tire. It's speed related and not RPM related. It does it in 3rd-6th gear gear, neutral, on the gas, off the gas, and at a steady speed. I can feel it through the shifter and clutch pedal, never through the steering wheel. The wierd thing is sometimes there is no vibration, and other times it shakes the change in my cupholder. For example last weekend I took a 300 mile trip. For around 200 miles it was vibration free, then I stopped for a snack and gas and the vibration appeared. It only goes from no vibration to vibration or the other way after I stop and park the car. I've tried pushing in the clutch a bunch of times, tried changing gears a ton of times and nothing I do while driving either brings the vibration on or makes it go away. It also does it on an empty tank and full tank so changing the weight over the axle has no effect on it.

Things I've checked/tried
-Ballanced driveshaft (3.5" LPE aluminum driveshaft)
-tried LS1 driveshaft that's in a vibration free car
-had a bunch of different wheels/tires on the car
-Just put in new pinion/carrier bearings in the rear
-did it at .007" backlash, I have .010" now since it was .002" after the bearings and I had to re-shim it.
-Tailshaft bushing still feels night, no leaks coming from it
-u-joints in driveshaft feel fine.

I had a loose pinion nut so I pulled the rear end apart and replaced the carrier/pinion bearings with timkens. The old pinion bearings had an irregular wear pattern, it looked like the pinion was wobbling. The part I don't understand is how it can go from being completely smooth to vibrating after parking the car and getting back in it.

speed_demon24

iTrader: (6)

Also I just put in stock lca's with new 1le bushings. I checked all the rear suspension bolts and they are tight as well.

SRfastZ

hub bearings maybe ?

Viper

iTrader: (6)

Mine does the same and has for about 8 yrs. No problems yet, just annoying. One day I'll drive to work and be absolutely in love with the car (vibration free) then the next day it will vibrate and be annoying.

98cherrySS

iTrader: (2)

Tailshaft bushing is a common cause for higher speed vibration.

FancyFarmSS

iTrader: (5)

Mine does the buzz/hum thing too at almost exactly 80 mph. Very weird. Sounds like mine is coming from the glovebox area. It stops once I get above 80 or so. Never really worried about it much since it doesn't seem to be caused by anything that is out of balance.

speed_demon24

iTrader: (6)

Tailshaft is still tight and it's not leaking at all so I doubt that's it.

MY99TAWS6

iTrader: (3)

Similar problem. speed related not rpm. Had driveshaft balanced by local shop its strange driveshaft. I will shortly change out tires on the car for test purposes have some on my 96z28 and some et street radials on extra rims.
I will look close at my trans mount and trans shaft bushing. I am thinking its torque arm related on my car.I have dana 60 so read might have to do different things with my torque arm angle.
Mine is very very bad past 80mph or so.Fact won't take car past 70mph until figure this out.

98cherrySS

iTrader: (2)

FWIW - My tailshaft didn't have much play nor did it leak but after i replaced it the humming/vibration went away...

edwardzracing

iTrader: (59)

I'm gonna throw in a guess for something in the transmission. Does it happen when it's cold? I honestly have no idea what it could be... you did all the things I would have done, and to me it seems the only thing left is the transmission. Could you try getting the car on stands and having a friend come by and go through the gears while you're under the car and listen for the noise you're hearing? Might be worth a shot. Maybe verify pinion angle too. Hope you figure it out. Keep us posted on what you find. Good luck!

speed_demon24

iTrader: (6)

It does it hot or cold. I already tried the running it in gear thing and I couldn't figure anything out that way. The tires/axles were straight and nothing seemed out of place.

edwardzracing

iTrader: (59)

Pinion angle looks good? These are the times you wish you had a spare 6 speed hanging around to try, lol. Really though, I don't know what else you can try. Verified all the bolts were tight for trans & torque arm mounts right? Hope you figure it out. Damn cars.

Mark_O

I picked up the very same problem after changing the rear pinion seal, differential fluid and gasket. However not only do I get the vibration at 80mph I frequently also experience it at 45mph. No noises coming from the transmission or rear-end and everything is tight.

I was thinking of spending $ on getting my drive shaft balanced seeing as my mechanic and I are scratching our heads on what the problem is. Sometimes I think it's just my 3" exhaust and polyurethane motor and transmission mounts causing harmonic vibrations at certain RPMs. In reality I'm clueless but would love to solve the issue.

Regards,

MY99TAWS6

iTrader: (3)

I have heard the crap about poly mounts especially poly trans mounts not actually causing vibration but simply relaying any vibrations that are there.
Whatever.I put poly mounts on my 97 ta and on my 99 ta. My 99 was first manual and now auto car.On both cars which were pretty much brand new at the time the poly mounts were horrble.It made my car sound like Russian tractor. I did mods on the energy suspension one..or maybe it was prothane one.Didn't use plate, shaved bumps, put in washers. etc but evertime those mounts came back out same day as fast as I could remove them! Go back to rubber trans mount. You might keep breaking them so then go to relocation mount setup.
I have poly trans mounts .I think they are adding some vibration maybe.I have horrendous vibration now past 70mph or so. I am pretty sure mine is from torque arm set wrong and mechanic racer buddy shimmed up my trans a lot trying to get it to be straight with no down angle. I think that is causing problems and will be taking them out and resetting pinion angle to zero. See what happens.
Bascially for vibrations you look at tires.you could try another set from buddy or move front to back even. Driveshaft ..make sure it balanced and the old steel ones are usually horrible they dont' call them vibeshafts for nothing! LOL
Other things to check would be broken trans mount, poly trans mount,or possibly play and shot bushing in tailshaft. These would be most of the vibration causes.
Other ones for manual cars are unbalanced flywheel. Maybe bad flexplate for auto cars.

But seriously dump the poly trans mount and see how much better it is.iF it don't get a lot better its likely something else. Exhaust rubbing can also cause lots of vibrations as well.