Highway vibrations... (checked the usual)

Hi! New to the forums... I just bought a 2005 Grand Prix GT... but I am having some issues, and I can't resolve them... (mind you I am a mechanic... so this is getting frustrating...) I havea vibration, which can show up any time between 45 and 75... it is there more harshly upon acceleration, and eases up some when I let of the gas. (all these repairs within the last week)... I replaced all four tires. Replaced the rear brakes and wheel bearing... (had some runout in the hub surface)... replace the front brakes, replaced both front cv axles with new ones (not remanufactured)... replace the main engine mount on the passenger side by the balancer. I can take the wheels off the car, take the front brakes completely down to the hubs.... The vehicle will shake the entire two post rack, you can see the engine bobbing up and down a little... so I have completely illiminated the brakes and tires as a problem. And with axles replaced... I am at a loss here... is there a trans issue which could be causing a vibration...? The CV shafts seem kind of loose to me where they go into the transmission... I'm sure there should be a little bit of play... but I think it might be a little much. The engine runs great, and the trans shifts smoothly. I have good plans for this car, but I'm not gonna do anything til I can get this resolved... any help would be REALLY appreciated...

How's the trans mount? No cracks in the arms connecting to the dogbones/upper motor mounts? Not seeing any misfires?

I didn't notice any defects really in the trans mount, but I may try replaceing that anyhow. The dogbone mounts seemed a little squishy, but not any more really then other cars I see come into the shop regularly. I did take my Matco Determinator home with me tonight and watched the misfire datastream all the way home for 30 minutes, along with some trans data, and I didn't notice any misfires at all, or any trans data that seemed out of the normal... I am worried about the amount of play that was present in the output shaft. I could just grab it with my fingers and move it all around freely. I am wondering can a output shaft seal warp... cv shaft bearing be worn badly...? I looked at the needle bearings and didn't notice any signs of wear on them... I am over all happy with everything else about the car. I am just getting really frustrated with the vibration issue at this point.

flip the dogbone mounts anyways.

Although putting in the engine mount seemed overly hard compared to others I have replaced now that I think about it, I just couldn't get it to line up for the life of me :P no matter how big the prybar... seemed like the engine wanted to be forward in the lower right corner. Never really noticed that much trouble before, and I have done quite a few of these to do oil pan gaskets.

Flip them? Just unbolt them, turn them over, and rebolt....?

and I meant to say can an output shaft warp? (not output shaft seal)

Originally Posted by Raviaan

Flip them? Just unbolt them, turn them over, and rebolt....?

take this



and turn it into this



unbolt the mount. then put the bolt back through the bushing. now grab some wd-40 or any lubricant that sprays on and spray the crap outta it. i used a screwdirver to pry around the bushing to spray the lube in there.

now hold both sides of the of the bolt with socket/wrench and jerk it till it spins. and looks like the second picture. then reattach.

as far as your vibration goes...maybe cradle bushings? can't say i've ever heard of anyone changing em but a thought. but if you just replaced that motor mount and it didn't seem to want to line up it could easily be that.

i'm no mechanic just brainstorming.

Anyone ever got a bent NEW axle. (Not reman....)

i have a good feeling replacing that tranny mount (even if it doesnt look bad) might take care of your problem. engine/trans mounts gave me the same issue on the starting off and vibrating relatively between those same speeds.

i could be wrong. but. it can never hurt to have new parts that are already worn out to some extent.

New engine mount.... new tranny mount. Flipped the torque arm bushings. 2 new rear bearings. 4 new rotors and all pads. 4 new tires. Ten times balancing. Rotated. NEW axles. New intermediate shaft. Vehicle vibrates on a two post lift... with tires and brakes removed. And i did have stands under the control arms so they werent hanging freely. Harshest at 65-68. And it isn't a slight vibration. Worse on acceleration. Vehicle runs great. No codes. No pending codes. No misfire counts. All of this in the last week. Ive only owned it a week. I am so beyond frustrated... :-(

how's the alignment??

Lol... not a great answer. Drive straight... wheels straight. Lol... I've never seen an alignment cause a vibration... but I haven't checked. Im just starting ti think the problem is unsolvable.

the problem is right under your nose. thats how it was when i had this similar situation.

unless the alignment is so far out of whack they are mis-tracking each other and bouncing...i don't see it causing vibrations.

did you check the subframe to see if its cracked or broken or something?

No... subframe is real nice and clean... who car is amazing except for this issue. I am thinking maybe I got a bad cv axle. Ill check runout on the center of the shaft tomorrow if I have time... Idk what else... I would do an alignment... im just afraid im gonna have to keep redoing everything.

alritey. good luck. and may i ask how you're checking for run out?

Mounting run-out guage to a solid non moving surface around the shaft. Setting the pintle of the guage on the center of the axle shaft. And spinning the shaft by hand.

Originally Posted by Raviaan

Mounting run-out guage to a solid non moving surface around the shaft. Setting the pintle of the guage on the center of the axle shaft. And spinning the shaft by hand.

yup, what he said, did that shiz in school.