hazard2k

iTrader: (10)

Trying to hunt down a vibration in my 99 Z – mods below
It starts getting pretty bad around 100 and keeps getting worse.
If I get up to 120-130 it feels like I am in a paint shaker. If I press the clutch in, the vibration is still there.

This is what I have done so far, with no luck:
Swapped rims/tires with a known good set.
Bought a brand new fabbed 9” rear end.
Switched to a tunnel mount torque arm set up.
Tried different pinion angles, none seemed to make a difference.
Bought a new 3” chromoly driveshaft.
Swapped out my tranny mount from a poly mount to a new stock one. no change.

I don’t know where to look next. It is definitely a rotational vibration at higher speeds. My only other idea was to pull the drive shaft out and put it in gear and get it to 100+ mph while stationary, just to see if it is something tranny related. Is it possible to have a bent output shaft or something similar?

Please help me figure this out!! Thanks guys…

ROCNDAV

iTrader: (100)

Could it be your drive shaft that needs to be balanced? Most are balanced for 70mph (or so I've heard). I told the guy that balanced mine that I frequently drive triple digits and would like to make sure it is balanced for higher speeds.

Jimmard

iTrader: (12)

Could be that you either need a longer driveshaft, or the tailshaft bushing in the transmission needs to be replaced.

edit: I've also read in a few cases that warped rear rotors have caused that

leadfoot4

iTrader: (1)

Your signature says Rochester, NY....Take your driveshaft to "Fleet Pride", or Fleet Maintenance, or whatever they're calling it these days. They're on Scottsville Road, right near where Behan Road intersects, on the south side of the airport.

Have your driveshaft balance/u-joints checked out. If the problem is somewhere there, they'll find it.

Manic Mechanic

iTrader: (3)

I went through a similar experience. Mine finnally went away when I installed new lower control arms and shimmed up the trans. I'm thinking the bushings were mush and allowed varied angles that looked good at rest but twisted out at high speeds. Shimming up the rear of the tans brought the two u-joint angles equal and opposite.

Vernon

SS1875

iTrader: (34)

I went through some of the same stuff. Check your crank pulley as well...I found that mine was wobbling on the crank from someone not installing it correctly. I had the clutch rebalanced, drive shaft rotated and rebalanced, tires dismounted rims checked for trueness and tires remounted/balanced. Found a crack in thr tranny mount so I replaced it along with the crank pulley( ATI instead of an ASP). Did all the rearend checks such as pinion angle, bolts being tight etc.etc.
Definitely time consuming/ money consuming and a major pain in the *** trying to track the Vibration issue. I wish you the best of luck in finding it!

jmilz28

iTrader: (13)

Make sure your lugnuts are torqued evenly.
Tires may balance but still have roadforce that is out of spec.
Driveshaft balanced?

hazard2k

iTrader: (10)

I switched from my stock aluminum one to my new strange 3" chromoly and the vibration is exactly the same, so I dont think thats what is causing it this time.



Well i am sure the driveshaft is not too short, there is only a tad bit sticking out of the tailshaft housing when installed.
Tailshaft bushing? First i have heard of this. How hard is it to get to? Do i just need to take the tailshaft housing off and get to it that way?

As for the rotors, I just put new fronts on a short while ago. I think i have an extra set of rears laying around i will have to throw on and try. Thanks!



I know right where you are talking about, but I dont think its a drive shaft problem because the old driveshaft and the new one both do it.



My lower control arms are UMI rod/bushing combo units that are about a year old. I never thought control arms would be the culprit, but i could swap some stockers in there to find out.
I have tried shimming the trans up and down with my poly mount and the plate it comes with. I tried it with it, without it, and with the stock mount (resetting the pinion angle after each swap). With no luck.



I have the ASP pulley on right now, I know a few people have had problems with them, but when i get into the high speeds and i push the clutch in, the vibration is still there. So i dont know how it could be the pulley. Thanks for all the other tips too, unfortunitly i have done all of them and still no solution



I did torque them down in 3 steps the other week to see if that helped, but it didnt. I even swapped a stock set of rims/tires on which i know dont vibrate, and i still had the same vibration at high speeds.



Guys, thanks for the replys and ideas. As of right now i think i am going to look into the tailshaft bushing, and the rear rotors. I am not sure how old the rotors are, but they are worn quite a bit. They might even be stock.
-Jeff

ElChiefWS602

iTrader: (1)

I would say check that strange driveshaft. I had strange make one for my S60 it was an ounce out of balance.

Also in dealing with my vibration issues it seems that the larger rears are more prone to vibration. From discussion with UMI they recommended a pinion angle 0 by their method for s60 and 9" applications. I can't stress enough that the angle needs to be dead nuts. Until I had mine set exactly I would get high speed vibration.

This took me months to work out. I figured with everything new in the car it would be just fine. However the driveshaft was out of balance and my pinion angle was just a hair off. Those 2 things made the car ride like a tank.

Good luck.

Justin00SS

iTrader: (5)

Has the car ever been wrecked? Check the carfax on it.

Mean Green z28

iTrader: (17)

Do you feel it in the back or in the drivetrain? Maybe you have a slightly bent axle shaft? Check the run-out on the hub mounting surface with a dial gauge. If there a chassis dyno nearby where you can put your car on the rollers and look for vibration?

Manic Mechanic

iTrader: (3)

You reminded me of a Lexus with a similar vibration that kinda ate my lunch once. It would be fine for about 5-10 miles then start with the high speed vibrations that diagnosed just like a driveshaft. After a $900 driveshaft from Japan was installed customer returned with same complaint. We went to push it asside and couldn't budge it. Turned out that a rear caliper was hanging up and had warped the heck out of it's rotor. It didn't get bad until it was hot then shook the whole rear driveline.

Vernon

Mean Green z28

iTrader: (17)

Hmmm, interesting story, very possible in his case too.

Jimmard

iTrader: (12)

I was told you have to replace the entire tailhousing as you cannot buy just a tailhousing bushing, might want to check into that some more. Also, you cant pull the tailhousing without pulling the transmission out of the car first.

CW00BlackTA

iTrader: (31)

That was my experience as well. I had to be within a half degree window to get rid of it.

02Z28LS1

iTrader: (2)

it could also be a wheel bearing going bad, too

lift the wheels up and try shaking them while holding the wheel at the top & bottom, and see if there's any play in them

leadfoot4

iTrader: (1)

As someone has mentioned, the pinion angle is very important. I made a mistake a whle back, in that I changed several parts all at once, and wound up chasing a vibration problem for quite a while. I put on my car:
A) A Fluidampr crankshaft pulley/damper;
B) A Random Technology adjustable torque arm;
C) An Energy Suspension poly tranny mount;
D) A LPE aluminum driveshaft.

I did this over the winter, several years ago, while the car was off the road. After everything was installed, and adjusted properly, SO I THOUGHT, the car always had a slight but noticeable vibration. Since all of those parts, even individually, could induce a vibration, it took me a while to get to the bottom of the problem.

Initially, I had a problem with the larger diameter driveshaft hitting the "e-brake cable clamp" in the tranny tunnel if the suspesion fully compressed when hitting a dip in the road. I was finally able to fix this situation when I read the various discussions of the poly tranny mount on this forum. I removed the "pre-load plate" from the tranny mount, and ground down the "humps" of the poly material, as several people here have recommended to do. This lowered the tranny in the tunnel, and gave me some more clearence.

I watched the BMR pinion angle video several times, and finally got the pinion angle correct, and this, in combination with the tranny mount fix, is what finally got rid of the vibration, as well as allowed me to leave the aluminum driveshaft in the car. I had the pinion angle at 1 degree "positive" instead of "negative", and that angled the shaft upward, and further up in the tunnel. The larger OD of the aluminum shaft caused this interference. (as a side note, when trying to troubleshoot the vibration, I also had both d'shafts in and out of the car a few times).

I also had the Fluidampr on and off a couple of times during this fiasco, thinking that it was the problem, but it turned out to be just fine. In the end, it was simply getting the pinion angle set correctly. (To that end, I used a digital carpenter's level, purchased from Sears.)