on throttle vibration, would like to find an answer
 

so ive had my 05 ss/sc for just about 4 years now. when i purchased the car it had some mods (stage 2, 2.85", exhaust and shorty header, airbox mod, lowered and urethane mounts). now the car always has had an on throttle vibration that i used to chock up to being the urethane mounts. a couple years ago when the powell mounts came out i bought a set of those hoping to get rid of the urethane mount vibration, and as it did make it a little better it was still very noticeable. fast forward to just this past week, i had the passenger side inner cv fail (the needles in 2 of the 3 rollers were turned to filings), and while waiting for a new axle i started hoping that maybe this was the cause of the vibration. well, no luck there, vibration still the same as always.

i have tried some things to get rid of it. years ago there was a post about the strut top hats being out of place causing vibrations, and as mine were out of place, no luck. since installing the powell mounts i have re-adjusted the mounts as per gm shop manual (loosen all mounts, rock the car back and forth with it in gear, tighten everything down), and made sure the motor is square in the car. the top mounts are in good shape.

i have thought about the lowering springs. they are H&R race springs, and i know they are an aggressive drop. they are on stock struts and hadnt been in the car long when i bought it, and over the past 4 years i havent noticed any real degrade in ride quality, although the car has always been a little rough feeling. now im not thinking its the struts/springs themselves, however the driveline angle is terrible, its even bad with the rotated mounts. now i know driveline angles are critical, however cv joints dont typically vibrate unless they are binding.

so everyone knows exactly what its doing, its an on throttle vibration, usually medium to heavy throttle. if i take off with my foot through the firewall its very mild, its often the same if im cruising and drop 1 or 2 gears and step on it. its the worst when i step on it at low to mid rpm range when cruising, say in 4th at 65km/h to go up a hill and maintain speed. once the vibration starts itll be there till i go for the next gear or lift. another time it does it is take off in first at normal throttle, get into 2nd gear and step on it.

basicly im after some input here. anyone every experience something like this? what did you do to fix it? what about people who are lowered with an aggressive drop or coilovers, did you get vibrations after the drop? a question for john powell (i hope you read this topic , im interested to hear your take on this), how much lower are the koni cup cars and aside from the solid rotated mounts, is there anything else done to correct the driveline angle.

my take on it (all i can come up with) is the cv shafts are binding when under heavy load as the back of the tranny will drop a little. when i get on it hard and its able to quickly get into the power band it lifts the front end a little, flattening the driveline angle, hence why it isnt so bad.

I have this problem I'm an auto sedan
Tho so powells rotated mounts
Won't work for me

Subd

what springs are you on. the automatics shouldnt get a driveline vibration as the axle centerline of the auto trans is higher than the manual trans. the cobalts were designed for automatics. so what you have, and possibly what i have might not be because of driveline angle

sharkey check your IM shaft. the splines are maybe rusty the bearing may be bad, and both contribute to what you are describing.

if the plunge joint failed, that surprises me. You say it was the passenger side, so I am suggesting the bearing in the IM. I have successfully replaced the bearing alone, btw, the whole IM shaft assembly is a 300+ dollar part.

Chris all the times you are by here you never said that you had vibes, or I wasnt listening :spam:

so let me check it out next time u come by....
and sharkey said it right, thats a 10 4 the auto is already well positioned.

BTW the Grand Am cup cars had about a 1 inch drop axle in the rear beam and the front is about 25. 25 or so to the fender lip though axle center line to the ground on 17 inch wheels and hoosiers.

ill have to look into the im shaft bearing. is there a gm part number for it, or did you have to remove the bearing to find a bearing number on it and cross refference?

i had the IM shaft out a few months back changing an axle seal and i felt nothing wrong with it, no play at all. i also have had no noises at all. even when i changed the axle it seemed alright. the autopsy on the axle showed needles in 2 of the 3 rollers turned to complete dust, i found 2 of them floating around in the boot, along with the retainer clips. i cant say ive seen an axle fail that way before.

so a little update

i had a slow day at work tuesday and decided to put my gmpp clutch in. pulling it apart i discovered the drivers side inner cv joint felt a little loose. i cut it apart to discover all the needles in one of the 3 rollers were missing/ ground to dust. so ive changed that axle and the vibration is now completely different. im not sure if its because all the mounts are re-positioned or if it was the axle, but the car is much smoother. there is still some on throttle vibration that i can pick up on. i did have a close look and feel of the intermediate shaft bearing and i have a hard time faulting it.

im thinking i might try a couple of spring spacers to try and get the front end to sit up a little higher and see if anything changes. if it does ill chalk it up to the car being too low.

Having a hard time finding a part number for the IM shaft bearing

OP: Its definitely the lowering springs you installed. You've changed the working angles of the CV axles and it does have an affect on ride quality and, appearently, part longevity.

The same thing would happen with lowered trucks unless the working angles of the U-joints were maintained.