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 Vibration / Shimmy at Cruising Speed

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Buapo
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Sun Jun 29, 2008 5:07 pm

TonySmooth:

I'm re-evaluating my problem, and I think it might be the trans or motor mount.

Here's the skinny.

The vibration starts at about 70 MPH. It shakes the steering wheel a little, AND the seats. I had a bottle of water on the seat next to me, and it was moving around.

At 80 MPH it seems to disappear. Newer rotors and pads on the front, the rear rotors are a little worn, but they don't seem to be the culprit if I'm getting steering wheel shake.

The rear air shocks have been replaced, less than two months ago. I've never messed with the rear struts, and the front struts are the original stockers for sure. I just turned over 60k miles.

So, what should I do? Repeated balancing and alignment and rotation do nothing, same results every time. Firestone does it for me and I have unlimited service on these things, so it's done 5 or more times a year.

I don't know if I could do the trans or motor mounts in my garage. Obviously I don't have a lift, so a 2-ton and jackstands/ramps are all I've got to work with here.

Anyway, let me know what everyone thinks. I've read through all these posts and there doesn't seem to be one definitive answer, but TonySmooth, it looked like you were onto something.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Sun Jun 29, 2008 6:30 pm

I'd do the front struts. It can only help things. How many miles are on the car? I'd also check the tie rods for wear.

There's no definite answer because it's likely a combination of things making your car vibrate,

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Sun Jun 29, 2008 8:57 pm

I still say it's a tire. If your tire shop is worth their weight, they'll be willing to take a couple of new tires of the same type and swap them around until they've ruled out all 4 tires. It'll be labor intensive and take a good tech who knows what he's doing, but the vibe you describe is exactly what I've experienced when 1 tire had a shifted belt.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Sun Jun 29, 2008 10:34 pm

deekster_caddy wrote:
I still say it's a tire. If your tire shop is worth their weight, they'll be willing to take a couple of new tires of the same type and swap them around until they've ruled out all 4 tires. It'll be labor intensive and take a good tech who knows what he's doing, but the vibe you describe is exactly what I've experienced when 1 tire had a shifted belt.

I was not going to bring it up because of all the balancing but...

I was thinking the tire(s) were very possibly the culprit.

Bert:tavis:
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Sun Jun 29, 2008 11:15 pm

I'm still not ruling out the tires, but I know at least it's not an alignment issue.

My car has 60,500 miles on it. Logic says that the trans mount wouldn't be worn yet, but hey - it's a 10-year-old car, you never know.

The front struts need to be replaced with the KYB's, I know that. Struts last for about 50,000 miles (or so I'm told) and I've surpassed that.

I'm going to do the struts myself using the excellent write-up (Aaron's, I think) before the summer is out. But maybe I can at least avoid this stinkin' vibration if I find out that the tire is the problem.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Mon Jun 30, 2008 12:07 am

It also makes me a little ashamed to admit this, but I'm not very familiar with the Riviera's suspension. I know we have struts and springs in the front, but do we have struts, springs, AND airshocks in the back?
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Mon Jun 30, 2008 8:38 am

Our cars have struts and coil springs up front, shocks and coil springs in back. The rear shocks happen to be the air filled type. To my knowledge, no car has both struts and shocks on any one axle. A strut is just a schock that also functions as the upper control arm, and as a steering pivot, as well as absorbing bumps; shocks only absorb the bumps. You only need one or the other.

I'm also betting it's wheel balance. Seems it always is...

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Mon Jun 30, 2008 1:44 pm

I just realize that I have a set of tires in the shed - my old stock alloys! And they have tires on them that are good enough for the street, probably 50% treadwear left.

I could swap them all out... or swap them out one at a time to see if the vibration disappears when one of the chrome rims is swapped for an alloy.

I still want to do the front struts this summer, regardless.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Jul 16, 2008 3:50 pm

I am having very similar vibration issues with my '98 with 87K on it. I had the rear shocks replaced because they were shot and I've had the tires balanced and an alignment done twice. I also had the driver-side front hub assembly replaced because I was told it was necessary. If anything the vibration is worse now. Before it vibrated some, mainly in the steering wheel, at 70, but now starting at 65 the entire car vibrates. I'm pretty bummed out about it.

I also suspect tires because it seems that if it was transmission-related or motor mounts, it wouldn't have been altered by the tire balancing and alignment. Anyway, I think I'm going to take it to a different shop to get another tire balancing because I don't trust the one I went to earlier.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Jul 16, 2008 5:36 pm

You can *look* at the engine and trandmission mounts to find problems. If the rubber is cracked or torn, you have a problem. You can even go so far as to have a buddy rock the engine by hand while you look at the mounts.

I have heard that another way to tell: open the hood, set the parking brake and step on the service brake firmly - then shift car into gear while watching the engine. Supposedly if it moves a good bit when the tranny engages *without* reving the engine it's likely one or more of your mounts is wack. However I don't recommend this approach for those who can't take/manage the risk themselves. One bonehead move and you have a Riv On THe LoosE and that's really, really bad.

Albertj
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Jul 16, 2008 7:55 pm

Try rotating the tires and see if the vibration moves to a new place. I've seen tires that are 'balanced' but have thrown a belt that vibrate like crap. Most often with store brand tires...
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Thu Jul 17, 2008 3:32 pm

I have the same vibration in my 98 that starts in the mid 70's till 80 then goes away. I had a 97 new 11 years ago that had the same vibration. Dealer could not recreate it since they could not do 70+ in the car. They suggested it might be harmonics created at that speed. I am having all 4 mounts replaced as they are worn & will see if it still vibrates.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Thu Jul 17, 2008 6:08 pm

Oh, Buapo - logic does *not* say the engine/tranny mounts are not worn out yet. They deteriorate with age, oil, and other factors. If you do spirited starts from a standstill they will fail sooner.

To understand why this is, take a look at 'em. You are going to be shocked how little rubber is in the mount. It's mostly air gap. Kind of like suspending the engine with heavy rubber bands. There is not much there to begin with.

Albertj
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Thu Aug 07, 2008 9:19 pm

Just wondering if anyone figured out what the cure is for the 70mph vibration. I just had new tires put on the car and it vibrated before and now it still does after the install and rebalance. It only does it between 65-70mph. My brakes and rotors are fairly new all the way around as well.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Thu Aug 07, 2008 9:40 pm

On the other hand has anyone tried this route?http://www.flickr.com/photos/2088/ I am going with this mod if my mounts are shot.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Thu Aug 07, 2008 11:05 pm

96RIVMANN wrote:
Just wondering if anyone figured out what the cure is for the 70mph vibration. I just had new tires put on the car and it vibrated before and now it still does after the install and rebalance. It only does it between 65-70mph. My brakes and rotors are fairly new all the way around as well.

I wonder if it has anything to do with the harmonics of the car. My 97 when new in 97 had the vibration at around 70 & my 98 that I just got has the same vibration at around 70. I wonder if it has anything to do with body tuning as I remember something in the brochure in 97 about something about how the body was tuned or something like that. It seems almost all of us have that vibration.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Fri Aug 08, 2008 12:41 am

Get tires balanced, check tie-rods and balljoints and then most important get the car aligned on a Hunter Road Force Balancer machine!
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 3:33 am

Well, I finally got my stupid vibration to go away.

I was thinking about this problem for some time, and it's really irritating to have your car shake and rattle when it's supposed to be a smooth cruiser. I was almost starting to forget how the car is supposed to ride.

So I figured it was this: when I brought my car into Firestone, where I have LIFETIME alignment and balance, I think they didn't even bother to balance the tires. They did the alignment, but they didn't balance. Even though I have the lifetime service, I figured I was getting the shaft because they didn't have to "charge" me for the work that was getting done.

So I went back to this fuckin' place. I made a big stink about the vibration. I even had them look up when they did it last - which was in JUNE. And the problem did not change between those times.

One of the guys behind the desk said that if they already balanced the tires, then it might be different problem. I'm like... just do the balance anyway. And make sure you drive it to see what's going on.

So I left the car with them for like four hours, and they call me and tell me that each tire was unbalanced by 1-2 ounces (which apparently is a lot). They rebalanced it, and one of my tires was leaking because of a corroded rim, and they took care of that too.

So I get the car back, get it on the freeway, take it up to 70. No vibration. Simply amazing.

It's too bad that I had to make such a big deal out of this to get a service that I ALREADY PAID FOR.

Anyway, I'll let everyone know if this problem STAYS gone.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 7:22 am

Thats great.clap

Bert:tavis:
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 8:10 am

...my entire car shakes for about a minute getting past 65mph, then stops for 5, then comes again for another minute, and so on...the steering wheel vibrates a lot but if I pull it down tight I can keep it straight...now, I know this is bad but does it sound bad as far as fixing it goes? It's so embarassing with people in the car...
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 8:57 am

Wheels out of balance, imo.

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 9:35 am

Sounds right, because the guy we bought the car from had the tires changed, and as a farewell present we found out the mechanic filled the tires to an average of 47 PSI.


I'll check to make sure they're balanced properly, definitely. There are weights on the wheels, but who knows if they're right or not.
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 10:58 am

Over time, tire wear can cause the balance to go out. Also, weights can fall off. It's happened to me a couple times. My shop (Firestone) just got a new machine that they say is more accurate than the old one. Fixed my problem in under an hour.

Remember everyone, take those center caps off before letting them touch the car!

_________________
'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


'05 GTO 49k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 11:29 am

There have been a few causes of NVH (noise vibrationand harshness) on my RIv.

One was tire balancing. Some people might want to go back to balance school. Even in one shop, technicians can vary a good bit.

One was tire mounting - that is, putting the wheels on the car wiht an air wrench give the mechanic the opportunity to get the wheel on eccentric. Get it? the tires are balanced but screwed onto the car wrong. That has happened more than once to me.

One was tires. I had a set of Firestone Affinity LH and Bridgestones 9same shop) that were flawed - the radial force variation was too high. In my experience Michelin tires usually don't have this problem. I am told that some tire makers will send better tires to certain markets depending on competition and the clout of the retailer. This one was hard for me to deal with, I suspect because it is difficult to figure out how to politely motivate the retailer to fix this sort of issue - retailer did not manufacture the tires, just sells them.

One is the original struts. If you put on stiffer ones it will change the suspension harmonics somewhat. Monroes, Gabriels, and KYBs all cause some degree of (beneficial) change. Originals are fine if you can mount the tires like they do at the factory - pretty much nobody can do that , factories use a very sophisticated machine from Illinois Tool Works that checks/rejecs tires and rims and matches them to a degree of roundness that is nigh impossible to match in the field.

Further on the mounting point, the tires can be within a good spec for radial force variation but if the hard radial spot is not matched to the low spot on the rims (all rims are a little eccentric on purpose) then the tire will thump at some speed.

Also some higher-spec/higher spped radials use cap plies of Rayon, which will flat spot until they get warm. That is, if you run the car till the tires warm then park it a while (1/2 hour ought to do it), the rayon belt will take on a temporary set... and when you hop in and drive up to highway speed the flat spot will thump until the tire warms back up.

Sometimes a vibration is due to brake rotor runout. If you use the low-cost rotors, they tend to warp in use after they wear some, or afer a very hard stop. Better rotors (Bendix, Raybestos higher-spec units) are alloys that tend ont to do that (and tend to cost twice as much or more at retail). Since the clearances are so thin (when not applied you could barely get a trash bag between brake rotor and brake pads) if there is any warpage the turning rotor will whack the brake pads. Causing a vibration at speed dependingon the degree of warpage.

Hope this helps

Albertj
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PostSubject: Re: Vibration / Shimmy at Cruising Speed   Wed Sep 10, 2008 12:03 pm

Quote :
Remember everyone, take those center caps off before letting them touch the car!

Is that so they dont damage them when removing?

I was thinking about getting new tires for the wifes Riv but am concerned that it will start this same vibration problem when the tires are changed...
Right now it has Michelin tires.

Bert tavis
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