Wicked vibration, cant seem to kill it

[B4C]

Pendulum thing?

[WildBillyT]

Originally Posted by B4C

Pendulum thing?

Probably a plumb bob off of the quarter panel to the axle flange. That's what I've done in the past.

[LTb1ow]

Assuming you are correct at pinion angle here, I fail to see what changing the drive line angle will change for the better. Unless you have a very ****** front U joint pinion angle, what does the trans care what angle its at? (within reason)

Are you sure you are setting pinion angle correct and have good U joints?

[WildBillyT]

Originally Posted by ThoR294

I did the whole pendulum thing to center the rear when I first installed that bar.

On LS1TECH, I was told to try and measure the transmission angle from the shifter plate. i may be getting a bad reading from the transmission under the output shaft. Also, was told to have -2 total angle... so if the trans is -3 the rear should be -1 and that should work for me. so I am going to try to pull the console out on my uncles alignment rack and do it AGAIN... and pray to the vibration gods

If you have -3 off of the trans and -1 off of the rear you have -4.

[LTb1ow]

Originally Posted by WildBillyT

If you have -3 off of the trans and -1 off of the rear you have -4.

Pinion angle does not care about trans angle (to an extent)
http://ls1tech.com/forums/gears-axle...ion-angle.html

I am confused why you changed or messed with driveline angle at all.

[ThoR294]

so eff my trans angle and just measure at the rear?

Im messing with everything because I can't kill this vibration no matter what I set my rear at...

http://ls1tech.com/forums/suspension...vibration.html

http://ls1tech.com/forums/lt1-lt4-mo...vibration.html

http://ls1tech.com/forums/suspension...o-parts-2.html

[Featherburner]

Originally Posted by LTb1ow

Pinion angle does not care about trans angle (to an extent)
http://ls1tech.com/forums/gears-axle...ion-angle.html

I am confused why you changed or messed with driveline angle at all.

Why?

[WildBillyT]

Originally Posted by ThoR294

so eff my trans angle and just measure at the rear?

Im messing with everything because I can't kill this vibration no matter what I set my rear at

There's conflicting info on the "best way" to do it.

Mike @ Chris Alston's told me something like this:

any engineering principle or drive line theory or power transmission theorist will tell you 2 u-joints must be in phase for minimal loss or vibration. both u-joints must be acounted for .

what I find many people get confused about is the difference between pinion angle & u-joint angle.

pinion angle is the difference between the angle of the engine (power output) & the angle of the pinion ( power input), in degrees.

u-joint angle is the angle from the transmitting shaft across the joint to the input or output.

example:
jacked up 4x4 truck.. engine level to ground 3 feet higher than pinion which is also level to ground.
pinion angle = 0 degrees
u-joint angle = 35 degrees

same 4 x 4, but engine is down in back 5 degrees to ground, pinion is up 3 degrees from ground.
pinion angle= 2 deg. down
u-joint angles =20 front 24 rear

hope this helps.. my fingers are tired from typing...

[LTb1ow]

Originally Posted by Featherburner

Why?

Perhaps I am mixing up terms, but I am referring the only point of adjustment on a 4th gen torque arm suspension setup, which is at the rear end via torque arm. I have rarely read of F-bod three link guys adjusting transmission angles at mount, but, to be fair, I am a close minded LT1 person who goes straight with racing.

I do not see why a trans angle would have changed or need to be changed enough to affect what the torque arm adjustment couldn't bring into spec. Its a low power car, so no need for crazy angles, just make it factory stock and be content. Since he has done that (assuming correctly) already with a stock torque arm etc, I just don't see what adding in another variable is gonna help.

But, this is a lot of assuming.

[WildBillyT]

Originally Posted by LTb1ow

Perhaps I am mixing up terms, but I am referring the only point of adjustment on a 4th gen torque arm suspension setup, which is at the rear end via torque arm. I have rarely read of F-bod three link guys adjusting transmission angles at mount, but, to be fair, I am a close minded LT1 person who goes straight with racing.

I do not see why a trans angle would have changed or need to be changed enough to affect what the torque arm adjustment couldn't bring into spec. Its a low power car, so no need for crazy angles, just make it factory stock and be content. Since he has done that (assuming correctly) already with a stock torque arm etc, I just don't see what adding in another variable is gonna help.

But, this is a lot of assuming.

He's been kicking this around for a while now so any discussion is good IMO.

If the motor mounts are aged (or aftermarket) and the trans mount is aged (or aftermarket) the angle of the crank/trans output shaft could be different than stock and would require a different setting out back if it's far enough out. I'm not saying that the torque arm couldn't be adjusted to correct the issue, just that you might not be able to say "set the rear at -2" or whatever and assume you are good.

[ThoR294]

New trans mount... Motor mounts LOOK OK and seem OK lol.

[ThoR294]

bumping this up.

Currently, the vibration is still present. It is no where near as bad as it used to be, but it is still there. I can move the angle and the vibration gets worse in any direction, but I can't get it to go away. I am beginning to think it is just because I have the torque arm relocation Xmember, or I just can't find the right angle.

Does ANYONE have the same T/A setup as I do, and not have this problem?

[greenformula92]

Well I had a adjustable tq arm on a 3rd gen. Xmember relocation and a t56. I had no vibration what so ever.

[ThoR294]

Originally Posted by greenformula92

Well I had a adjustable tq arm on a 3rd gen. Xmember relocation and a t56. I had no vibration what so ever.

I wonder if I'm just setting my angle like an idiot

[LTb1ow]

We also do not know your definition of driveline vibration.

[ThoR294]

Originally Posted by LTb1ow

We also do not know your definition of driveline vibration.

Cruising at 75 maintain speed you feel nothing.

Take foot off gas you feel a little rumble in the car

Push clutch pedal in and it feels like driveshaft is out of balance and going to fly out of the car

[LTb1ow]

Just reread thread, so you have OEM rubber motor mounts and a poly trans mount...?

[ThoR294]

Yup. I've put rubber trans mount in and that changed nothing. Only thing that changes this is adjusting the torque arm.

In the process of putting prothsne motor mounts. Just need a day at my uncles garage to do it lol