vibration after suspension install

[Tarheel'Z']

well just as the title says i have a vibration that feels like a typical u-joint type vibration.only problem is it wasnt there until i installed my strano springs which lowered approx 1.2 inches give or take.has anyone else had this happen after spring install?fyi vibration starts around 80mph

[Sinister95Z]

Was anything else installed when the springs were changed?

[96LT1355Z28]

Do you have an adjustable TA? Check your pinoin angle and make sure it's near -2 degrees (down).

[95LT1Z28]

I would investigate the pinion angle as said.

[Tarheel'Z']

Was anything else installed when the springs were changed?

nothing but shocks,,all other suspension is stock..
im not super mechanically inclined so dont laugh at me when i ask this but is it possible that when the car went lower that its pushing the shaft into the tranny more or something?
im gonna have to check on the pinion angle thing,,not sure how though??i didnt realize lowering such a small amount would change the angle enough to hurt???

any tips on pinion angle check and adjustment?

[96LT1355Z28]

If you want to PM me I'll give you my cell number and explain how to check it as well as some other things. You can do a google search or check LS1Tech but your gonna get several different and some complicated ways to do it. It's really much simpler than many make it out to be.

Your basiclly measuring the angle of the pinion in relation to the driveshaft. Your suspension bushings in the TA and LCA are rubber and will flex upon acceleration. This allows the front of the rearend to rotate upwards toward the bottom of the car. You want the pinion to be as straight inline with the driveshaft as possible creating the least amount of movement from the u-joints when the car is in motion. 2 degrees down would mean when your car is sitting on the ground your pinion is actually 2 degrees less than whatever your driveshaft angle is (every car can be different). Your DS angle and suspension alignment is affected by ride height, tire size, and stance of the car. -2 degrees is the generally agreed upon as the optimal setting for stock suspension setups.

Ex. DS angle 0 degrees pinion should be -2

I can expalin better in person as this would be a long and probably confusing post otherwise. Your gonna need an angle finder to do this. 1.5 inches is not alot when you think of ride height on the street, but in the world of adjusting suspension for optimal geometry and moving the instant center 1.5 inches is a ton. I don't know what you plans are with the car but odds are you LCA's are now parallel to the ground or facing down (as in if you put a ball bearing in the center of a LCA it would roll towards the front of the car). This creates axle hop at the drag strip and sometimes on the street which kills 10 bolts! I'm sure you didn't plan on all this when you got springs to lower your car but I sugest checking and correcting you pinion angle and if needed and investing in a set of LCA relocation brackets. They lower the mounting point of the LCA on the rear end correcting the improper alignment when a car is lowered. You should also make sure the rear is still centered in the car. When the rear end of our cars is lowered the PHB has a tendency to push the rear to one side off setting it from left to right under the car. You can do this by simply taping a string with a washer on the end of it to the center of the outside of your wheel well creating a make shift plum bob. Then measure from the string to a specific spot on the wheel. Make sure you use the same reference point on the fender and the wheel on both sides. If the measuremants are off you'll probably need to get an adjustable panhard bar to recenter the housing.

With all that being said the pinion angle is the only thing likley to cause your vibration other than u-joints or an off balance DS. Yes, when the car is lowered your DS will go into the trans more (very little) it should not be anything that would create a vibration. The other things are just some things you should at least check to ensure your car was lowered properly! How this helps! ;)

P.S. Welcome to the site!

[BLOWNDFIZ]

With all that being said the pinion angle is the only thing likley to cause your vibration other than u-joints or an off balance DS.

^^^What he said^^^

It's most likely your driveshaft out of balance. If I remember correctly there was a service bulletin that came out (not a recall) on the LT1 Steel Driveshafts because of higher speed imbalance vibrations. The DS imbalance will also speed up the deterioration of the u-joints. The vibration was probably already there but now that your ride is stiffer and the pinion angle changed it's now just more pronounced.

[Tarheel'Z']

If you want to PM me I'll give you my cell number and explain how to check it as well as some other things. You can do a google search or check LS1Tech but your gonna get several different and some complicated ways to do it. It's really much simpler than many make it out to be.

Your basiclly measuring the angle of the pinion in relation to the driveshaft. Your suspension bushings in the TA and LCA are rubber and will flex upon acceleration. This allows the front of the rearend to rotate upwards toward the bottom of the car. You want the pinion to be as straight inline with the driveshaft as possible creating the least amount of movement from the u-joints when the car is in motion. 2 degrees down would mean when your car is sitting on the ground your pinion is actually 2 degrees less than whatever your driveshaft angle is (every car can be different). Your DS angle and suspension alignment is affected by ride height, tire size, and stance of the car. -2 degrees is the generally agreed upon as the optimal setting for stock suspension setups.

Ex. DS angle 0 degrees pinion should be -2

I can expalin better in person as this would be a long and probably confusing post otherwise. Your gonna need an angle finder to do this. 1.5 inches is not alot when you think of ride height on the street, but in the world of adjusting suspension for optimal geometry and moving the instant center 1.5 inches is a ton. I don't know what you plans are with the car but odds are you LCA's are now parallel to the ground or facing down (as in if you put a ball bearing in the center of a LCA it would roll towards the front of the car). This creates axle hop at the drag strip and sometimes on the street which kills 10 bolts! I'm sure you didn't plan on all this when you got springs to lower your car but I sugest checking and correcting you pinion angle and if needed and investing in a set of LCA relocation brackets. They lower the mounting point of the LCA on the rear end correcting the improper alignment when a car is lowered. You should also make sure the rear is still centered in the car. When the rear end of our cars is lowered the PHB has a tendency to push the rear to one side off setting it from left to right under the car. You can do this by simply taping a string with a washer on the end of it to the center of the outside of your wheel well creating a make shift plum bob. Then measure from the string to a specific spot on the wheel. Make sure you use the same reference point on the fender and the wheel on both sides. If the measuremants are off you'll probably need to get an adjustable panhard bar to recenter the housing.

With all that being said the pinion angle is the only thing likley to cause your vibration other than u-joints or an off balance DS. Yes, when the car is lowered your DS will go into the trans more (very little) it should not be anything that would create a vibration. The other things are just some things you should at least check to ensure your car was lowered properly! How this helps! ;)

P.S. Welcome to the site!

holy cow you said a mouth full,,,thanks so much for the help,,so if i get it right i need lca relocation brackets and adjustable panhard bar and i should be straight??oh yeah and i already plan on a ls1 shaft...thank god for tax time

[96LT1355Z28]

holy cow you said a mouth full,,,thanks so much for the help,,so if i get it right i need lca relocation brackets and adjustable panhard bar and i should be straight??oh yeah and i already plan on a ls1 shaft...thank god for tax time

Definate yes on the LCA brackets, adj. PHB wouldn't hurt but may not be a necessity.

[Tarheel'Z']

great advice guys,,i just installed a set of UMI lca relocation brackets..vibration is completely gone..yipppeeeee now i can break the speed limit again..thanks again