Gears & Axles - Vibration is driving me nuts!

I've got a vibration that starts around 70mph and just keeps getting worse from there up. It's enough of a vibration that it will make change jingle if I put it in the cupholder. It feels very similar to having a bent wheel, but I know that's not it. I'm 99.999% Sure it's coming from the rear of the car.


Here's what I have done to try and fix this problem:
-Rotated Driveshaft 180*- No change
-New Spohn Chromoly Driveshaft - No change
-3 Different sets of wheels/tires - No change
-Checked motor mounts (poly) and they are fine
-Checked transmission mount (poly) and it's fine
-All suspension components are tight
-Pinion angle is -2*, so it's fine


The car has a Moser 12-bolt with a True Trac and 4.11's in it, LS7 Clutch, Stage 2 T56. Adjustable LCA's and Panhard Bar, but the rear is centered in the car, the rear is square to the chassis, and the rear is aligned pretty much dead on. It has an adjustable torque arm with a relocation bracket, so it's a tunnel mount, but still uses a stock style poly bushing.

I do not know what to do next. I'm thinking it's going to be beyond my capabilities and it's going to have to go to a shop, which means $$$. The car will be going in soon anyways, as the rear gears are really yelling at me, but the vibration was there before the gears started being loud.

I posted this in this section because I wanted to see if anybody has had a similar vibration with a 12-bolt, because that thing has been nothing but problems, and I think it's where my issue is coming from...

you may need some fresh universal joints

you may need some fresh universal joints

He tried a new driveshaft so the u joints are covered.

Have you tried readjusting the pinion angle, up and down several more degrees? Bob

I'm not an expert. I remember a few threads where poly engine mounts combined with a poly trans mount was too harsh with noise and vibration. I think the recommendation was to go back to the regular trans mount.

He tried a new driveshaft so the u joints are covered.

Have you tried readjusting the pinion angle, up and down several more degrees? Bob

Yea, it's at -2*, but I moved it up to about -0.5* and down to about -3* and nothing changes.

I'm not an expert. I remember a few threads where poly engine mounts combined with a poly trans mount was too harsh with noise and vibration. I think the recommendation was to go back to the regular trans mount.

I've always heard mixing rubber and poly mounts was a bad thing. Maybe it was just a poly trans with rubber motor mounts that was a problem? The noise is definately something wrong with the gear setup though...

tires...have them rebalanced. maybe a cheap fix..was for me..not for a buddy..he REBUILT his whole rear, new drive shaft..still have the prob. Went and got a used tranny..still.. I told him to try different wheels or have them rebalanced..nope dont listen..but finally he got them balanced..wow it went away..

tires...have them rebalanced. maybe a cheap fix..was for me..not for a buddy..he REBUILT his whole rear, new drive shaft..still have the prob. Went and got a used tranny..still.. I told him to try different wheels or have them rebalanced..nope dont listen..but finally he got them balanced..wow it went away..

Well seeing as I've had 3 different sets of wheels and tires on the car, and they were all balanced by me, doubt that's the case.

Is there any excessive clearance where the driveshaft yoke slips into the tailshaft housing? I know there is a replaceable bushing in there.

Well seeing as I've had 3 different sets of wheels and tires on the car, and they were all balanced by me, doubt that's the case.


Damn dude..lol Well that was my cheap way to fix it. Could the housing be bent possibly so odd non possibly way lol. I had an issue in my third gen with a Moser 9in and I never did find out what it was. Did a new yoke, drive shaft, and did it from day one, stock suspension..Maybe the angle finder is messed up and giving you a wrong pinion angle? idk Im just going on and on about nothing..

I'm having the same problem in my 00 Z28 with the Moser 9". She was fine after the first two months of driving and track use but immediately after I threw her on the dyno the vibration is there in exactly the same way you are describing.

I have comparative suspension mods as you and I'm thinking that by strapping it down in a crossed strapping pattern on the dyno must have f-ed up my pinion angle of something. Or I could have just destroyed my stock motor mounts...... IDK.

Yep my 98 trans am does the same thing at about 70 and beyond, just like u say idk what it is??

yap me too i have it 70 and on.

pm sent, please get back to me.
i have a few ideas as to your problem.

you should share those ideas with the rest of us...

i have one too, and seemed to be real bad after i installed my M12,,, but i think my car had it before, but with the 373's i had, it wasnt as noticable as the 411's i have now.
My vibs are RPM related,,, any gear (even neutral) between 1800 and 2500 rpms the whole damn car shakes real bad. Im about to call it quits and sell it... im sick of workin in it to not get any resolution.
i need to drop my tranny and check out the stuff in there (either clutch, Flywheel, or something must be out of whack to make it do it this bad)
i never noticed any vibs with my 10 bolt,, although it did vib in neutral (it shakes my steering wheel)

Good luck man, i feel for ya.

Wayne

I had a rear end with some turd (used) gears that would vibrate real bad. I knew it would be bad but didnt care and put them in anyway just for the butt-o-meter fun of 4.10s. Anyway, I started out with a stock trans mount and it wasn't too bad, but when I switched to a poly trans mount it got HORRIBLE. The poly engine mounts have always been fine, but the poly trans mount was the catalyst.

I have read where some people don't have any issues with poly trans mounts, but you don't hear too many of those people talking about how rough their suspension/drive train was before they put in the mount. Poly trans mounts definitely magnify any little vibration that might have been there before.

What is the trans angle? Have you tried shimming it up or down a little?

Just shooting out ideas

when did you start to notice the vibration? Did you change anything?

when did you start to notice the vibration? Did you change anything?

It's hard to say, but I really think it all goes back to when I put the 12-bolt in the car.

If I can swing the money, I'm going to put a 9" in the car because of all of the issues with the 12-bolt not liking a torque arm setup and killing gears because of it...

I've got a vibration that starts around 70mph and just keeps getting worse from there up. It's enough of a vibration that it will make change jingle if I put it in the cupholder. It feels very similar to having a bent wheel, but I know that's not it. I'm 99.999% Sure it's coming from the rear of the car.


Here's what I have done to try and fix this problem:
-Rotated Driveshaft 180*- No change
-New Spohn Chromoly Driveshaft - No change
-3 Different sets of wheels/tires - No change
-Checked motor mounts (poly) and they are fine
-Checked transmission mount (poly) and it's fine
-All suspension components are tight
-Pinion angle is -2*, so it's fine


The car has a Moser 12-bolt with a True Trac and 4.11's in it, LS7 Clutch, Stage 2 T56. Adjustable LCA's and Panhard Bar, but the rear is centered in the car, the rear is square to the chassis, and the rear is aligned pretty much dead on. It has an adjustable torque arm with a relocation bracket, so it's a tunnel mount, but still uses a stock style poly bushing.

I do not know what to do next. I'm thinking it's going to be beyond my capabilities and it's going to have to go to a shop, which means $$$. The car will be going in soon anyways, as the rear gears are really yelling at me, but the vibration was there before the gears started being loud.

I posted this in this section because I wanted to see if anybody has had a similar vibration with a 12-bolt, because that thing has been nothing but problems, and I think it's where my issue is coming from...

I had the same issue after installing an adjustable tunnel mount TQ attached to the frame mounted crossmember(Yank) with stock style clam shell bushing.

Out of frustration I removed it and reinstalled my Spohn adjustable tunnel mount TQ that moves backward and forward as the rearend rotates up and down and vibration went away. Model 405 in pic below.

http://www.spohn.net/shop/1998-2002-GM-F-Body/Suspension/Torque-Arms/Standard-Duty-Crossmember-Mounted-Torque-Arms/

IMO the tunnel mount design using a clamshell bushing doesn't work because as the rearend rotates up under accelleration it will pull the forward end of the TQ up as well - mine actually bent the end of the TQ. Once it goes up under accelleration then it doesn't want to unload because it binds (think about it - it's pointing upward in the bushing because it was forced up at least two degrees under accelleration). Two degrees three foot from centerpoint is quite a bit of movement.

On the stock setup the TQ is nearly level with enough flex in the TQ to bend or break the transmission tailshaft but with this design the TQ points downward from the rearend and it is built not to flex or bend so all of the vibration is channeled from the rearend through the torque arm and the poly bushing.

But I am sure the vendors that make these will argue differently.

BTW - the Spohn isn't that noisey if it is set up right. A shop installed mine and had torqued the nuts way tight in the front. I followed Spohn's instructions and now hardly any noise at all. Had I known that I would never had wasted money on the tunnel mount design that was supposed to be quieter.