highway death shake

[2003BlackSapphireSLE]

i have a 2003 sle that has a death shake at speed around 75 or so that seems to go away to co9me back to get worse. ive checked over the entire car and replaced some parts as well. everything is tight, tires were balanced and balanced again and they balanced out according to the machine but still has this issue and the alignment was done and is right on the money. what the hell could be causing this? i know there is the tsb for control arm bushings but how do i know if it was done already as im not the first owner. please help.

[myfirstbonnie]

We need a little more info here. What parts were replaced? How long ago was the balancing and alignment? Have you rotated the tires, front to rear and rear to front? Does it vibrate at any other speeds? Does it stop if you apply a little pressure on the brakes while maintaining speed? Have you checked the lug nuts for tightness?

[2003BlackSapphireSLE]

it was just aligned, the balancing was done a few months ago, but it had the problem a few months ago. i have replaced the rack, tie rod ends, iss, left cv shaft, and checked everything for tightness. ive rotated tires around to no avail. it almost seems like it doesnt do it all the time or at least not as bad and for no ryme or reason it gets better and worse. i was thinking maybe tires out of round but they are wearing just fine. i was also thinking struts, but then again they're not leaking and the tires are wearing fine and show no excessive bounce. my only other question was about the lower control arm tsb which i dont know if its ever been done. how do i tell?

[carl]

Strangely I have developed a silimilar issue at low speeds taking off from a stop light. I also get a nasty front end vibration just after the downshift, when I hammer it. Everything has been tight since last fall, but then this really wicked shimmy recently started. I too have checked the entire front end. I did replace the cv shafts last fall, I'm wondering if this could be related. The tie rods inner and outers have been replaced, both bearings and ball joints also and tires good, rotated, balanced again and new alignment done.. You might want to take a look at the ball joint play with a dial indicator. The only thing left for me is the rack or maybe the cv's again?? There does seem to be some extra play at the inner tie rod/rack when both tires are up, but I have no reference to compare.

[03SSEISUPERCHARGED]

Flat spots maybe?

[00Beast]

Move the front tires to the rear and see if the vibration moves with the tires. If it does, there's your culprit.

[carl]

Pretty sure we both rotated tires front to back. But one thing I think we both overlooked were motor/transaxle mounts. Maybe more-so for me since this issue seems to happen under initial throttle torque and then downshift.. I'll wait for more warm weather to check.

[dpcookson]

I'm leaning towards a bad CV shaft, you said you replaced the left one but but what condition is the right side in?

[carl]

Yap, that might be my issue too. I don't trust rebuilt crap at all. I've gotten burned too many times and esp. with Delco rebuilts...garbage quality control.

[2003BlackSapphireSLE]

well the left was replaced due to spitting of grease but miraculously no tear in the boot. anyways i never checked for any up and down or in and out play in the right side one. yeah ive rotated and balanced to no avail. ive also replaced the front trans mount and the others are tight. i only have the issue at around 75 or so being the worst. and even then it will get bad and subside and bad and subside. its so weird and its driving me up the wall but i love the car.

[bonnevillain]

The 70MPH shimmy is fairly common on the 00+ models, although it doesn't usually come and go as far as I know. I have a vibration that's worst at 70 and is almost completely gone by 10mph in either direction.. It's not the tires/wheels. People have replaced many parts trying to solve it.. some say they have, some haven't.

[Oldman]

I would definitely replace transmission/motor mounts. and 2003 guy, at high speeds, if it's a transmission mount, it would be worse when going uphill or anywhere where there's more of a load than on a flat surface. Though the vibration occurs at the same speed, think of things other than speed that exist when the problem occurs, like cold weather, hills, just look for what situations cause the vibration.
The worst vibration I ever had was caused from a little "end play" from a worn rack. It only happened a few times but when it did it was scary. It was about a couple of inches of back-and-forth shimmy in the steering wheel, and vibrated the entire car. I couldn't believe it when I found just a very slight bit of "play" in the rack. It was amazing that this little bit of play under the right conditions could cause this. It only happened twice. Both times were at 80 MPH after passing a car and easing back into the right lane. It scared me to death. If you can find an old gas station that has the machine that spin balances the tires while they're still on the car, it will usually help find the problem. I used to use one of those, but I haven't seen one in operation in about 25 years.

[imidazol97]

If you can find an old gas station that has the machine that spin balances the tires while they're still on the car, it will usually help find the problem. I used to use one of those, but I haven't seen one in operation in about 25 years.

http://www.hunter.com/PUB/PRODUCT/balan ... /index.htm

I'll bet there are real alignment shops in small towns that still are in business who have the older ones from the 80s that are serviceable. But I'd check with shops able to doing trucks--note that's what they're showing in the advertisement.

[olblueeyesbonne]

Brake rotors been checked? Are they cracked? Warped? How do the pads look?

[golfyeti]

I have long had the 70 MPH shimmy. I don't think it is drivetrain related at all, and for the following reason (amongst others). I have put her into neutral at 80 MPH several times (and under several conditions) and the shimmy re-exhibits itself as you coast back into the 70 MPH zone and completely dissapates at about 63 MPH.

I do a lot of hwy driving on rather smooth surfaces and the only variance I ever find is that the shimmy exhibits itself at lower speeds (62-64 MPH ) when driving into a headwind and also exhibits itself at a higher speeds (71-74) with good wind at your back.

It's as though a main factor in this mystery is a specific 'wind resistance level' on the front of the car. Perhaps this means an aerodynamic issue with our 'coke bottle' body design? But then again if this were true wouldn't everyone have it?

If not aerodynamics then perhaps loose suspension or loose body mount bolts? I read a post here not too long ago where someone eliminated a rattling in the rear of a 2000+ by fixing a rusted body mount bolt.

Sure wish we could crack this one and put it to bed. All of my hwy driving is at 70 MPH.

[gmman]

AMEN! count me among the cursed. 1988 and 1996 bonnevilles both have or have had the shakes at exactly the speeds described. only time i have ever smoothed them out was by buying michelin tires and having them rebalanced and replaced (even new ones) until i got some kind of magic combination that ran smooth at all speeds. when i reached that set up, i would not even rotate tires for fear of upsetting the magic.

[2003BlackSapphireSLE]

i have had the shakes for awhile now coming and going and subsiding and getting worse. right around the 75 mph zone it shakes the fillings outta my head. i just noticed this tho... it seems to be the worst when im coming home from work when its warm out like 75 80 degrees. tonight im on the same stretch of road that it always does it on and it like 60 degrees out and im in the same speed bracket and its barely doing it at all, like id be happy if it was like this all the time. which makes me think whats the possibility of it being bushing related? ie control arms or something where a cooler temp would make it more solid versus heating it up and being squishier? we're really splitting hairs here.

[Jerry319]

We've had our 03 since its was new Detroit engineers could not fine the problem with the shake we had the tires Road force Balanced so many times the had to replace the wheels they did find 1 out of round we even had them replace the Goodyear tires with Mich, rack, cv's, lower control arms, everything they could throw at it the only thing that worked for a while was new brake rotors? It lasted about 10000 miles each time and Pontiac said they were done looking the last time we were in? and the did make it better but as I told them it would be back and it is I just did brakes and rotors again now have to take to shop for the road force balance? but right now shakes like a dog? if anybody has any more suggestions I open for them. this thing only has 56000 miles and its done it since new.

[olblueeyesbonne]

Wheel bearing.
My Grand Prix has a good vibration, especially on corners. Buddy said his GTP Daytona Pace Car was doing the same thing and couldn't figure it out so he took it into school (going to school for automotive -mechanical). In school his instructors and classmates tried everything down to new Rack, calipers, rotors, tires, swapping wheels and finally changed 1 rear hub and the rumble was half gone. Did the other side and car rides as good as new.
That's my project this week -change the rear hubs. Putting used ones in since I have a couple from the parts car -I hope they are good -I never got to drive the car and the battery was out so any ABS codes were erased before I got the car and could hook up the tech 2.

[golfyeti]

Wheel bearing.
My Grand Prix has a good vibration, especially on corners. .

We're discussing a "whole-car shake and shimmy" which occurs only at a specific hwy speed range. We call it the "65-70 MPH Shimmy". It's not a wheel bearing vibration issue.

Would anyone have a diagram of where all the body-to-frame mounts / bolts are? This is my new focus area on this issue.