Vibration / Shimmy at Cruising Speed

I experimented with tire pressures hot and cold.
Recorded the pressures and temp. Started at recommended pressure of 30 psi cold and took a run up the highway and recorded the seat of the pants vibration. Then recorded the tire growth when I returned with "hot" tires.
The pressure increased by about 2 psi all around.
The following day same A.M. temp increased tire pressure by 2 psi increments and recorded seat of the pants vibration.
Did this over the course of a week by increasing pressure up to a max of 36 psi and all the way down to 26 psi in 2 psi increments.
Found the best to be at 30 psi. Any pressures above that magnified the vibration exponentially. Anything below 30 wasn't as bad an increase in vibration but still had an increase.
Have settled with 30 psi cold and the vibration associated with it.
Which just so happens to be where i started from. I had been running at the manufacturers recommended pressure of 30 psi.
Rather than spending $100.00 for the Radial Force Balance I'm going to change wheels and get new tires as I have noticed some dry rot (cracking) on 2 of the 4 tires even though they have more than 50% life remaining on the tread. The mfg date on the two that are cracking is about 6 years old. The other two are 3 years since mfg, even though I bought them maybe 2.5 years ago. Didn't pay enough attention to the mfg dates when i bought them. But you wouldn't think you would have to when you buy them from a Goodyear Dealer and pay premium money.
Oh well, a lesson learned that won't be repeated. I'll buy tires with a softer, stickier compound that are only expected to last 20 -25K miles and that will translate into 4 years based on the amount of miles the Riv gets per year. If I'm going to spend a lot on tires i may as well enjoy them and use them up.
I personally think the problem is all in the tires. But I will find out one way or another just out of curiosity mainly. I hate leaving a technical issue unresolved.

Rickw wrote:

I experimented with tire pressures hot and cold.
Recorded the pressures and temp. Started at recommended pressure of 30 psi cold and took a run up the highway and recorded the seat of the pants vibration. Then recorded the tire growth when I returned with "hot" tires.
The pressure increased by about 2 psi all around.
The following day same A.M. temp increased tire pressure by 2 psi increments and recorded seat of the pants vibration.
Did this over the course of a week by increasing pressure up to a max of 36 psi and all the way down to 26 psi in 2 psi increments.
Found the best to be at 30 psi. Any pressures above that magnified the vibration exponentially. Anything below 30 wasn't as bad an increase in vibration but still had an increase.
Have settled with 30 psi cold and the vibration associated with it.
Which just so happens to be where i started from. I had been running at the manufacturers recommended pressure of 30 psi.
Rather than spending $100.00 for the Radial Force Balance I'm going to change wheels and get new tires as I have noticed some dry rot (cracking) on 2 of the 4 tires even though they have more than 50% life remaining on the tread. The mfg date on the two that are cracking is about 6 years old. The other two are 3 years since mfg, even though I bought them maybe 2.5 years ago. Didn't pay enough attention to the mfg dates when i bought them. But you wouldn't think you would have to when you buy them from a Goodyear Dealer and pay premium money.
Oh well, a lesson learned that won't be repeated. I'll buy tires with a softer, stickier compound that are only expected to last 20 -25K miles and that will translate into 4 years based on the amount of miles the Riv gets per year. If I'm going to spend a lot on tires i may as well enjoy them and use them up.
I personally think the problem is all in the tires. But I will find out one way or another just out of curiosity mainly. I hate leaving a technical issue unresolved.

From my experience I think you're right. I'm not doing GoodYear tires again that's for sure. I'm unfortunately using the Riv as my daily driver, and I drive over 800 miles each week easily. I'd love to save the Riv and keep it as a weekend driver, but it's just not happening. It's a good thing I found one with lower miles on it. I'm looking at Michelin tires right now. Again unfortunately I drive in an area with a tough winter, so I'm thinking of getting snow tires considering it's winter 8 months out of the year. We seem to be the only ones experiencing this issue, and we both have the same type of tires. When you get the tires changed let me know how things go.

Well, maybe on this board we are the only one's complaining of this issue right now. But GM had started issuing Technical Service Bulletins to the dealer network starting in about 1998 regarding this very issue.
The first bulletin was about 10 pages long and required a lot data be gathered by the Technician and fed back to engineering in Michigan at first.
Subsequent revisions were a little more informative to the tech as to what to do to try and fix the problem, but none the less it was still very involved and didn't guarantee you'd find the problem. These were new cars then under factory warranty and new wheels and tires were replaced by the dealers after approvals from the home office. Then in about the year 2000 Hunter came out with the balance machine we've talked about and helped solve the problem. The latest revision to the TSB instructs the mechanic to use it for solving the problem.

Rickw wrote:

Well, maybe on this board we are the only one's complaining of this issue right now. But GM had started issuing Technical Service Bulletins to the dealer network starting in about 1998 regarding this very issue.
The first bulletin was about 10 pages long and required a lot data be gathered by the Technician and fed back to engineering in Michigan at first.
Subsequent revisions were a little more informative to the tech as to what to do to try and fix the problem, but none the less it was still very involved and didn't guarantee you'd find the problem. These were new cars then under factory warranty and new wheels and tires were replaced by the dealers after approvals from the home office. Then in about the year 2000 Hunter came out with the balance machine we've talked about and helped solve the problem. The latest revision to the TSB instructs the mechanic to use it for solving the problem.

Interesting. So it's still essentially the tires, just the riviera seems to be more sensitive to tire abnormalities?

The title to the Bulletin is:
Shake / Vibration in Steering Wheel, Floor. Seat at Highway Speeds on Smooth Roads. Latest revision dated Dec, 2000 added more models affected by this problem.
And was directed at the Riviera - all years 95-99
97-01 Park Ave, PAU
2000-01 LeSabre
98-01 Cadilac Seville
2000-01 Cadilac DeVille
1995-01 Olds Aurora
2000-01 Pontiac Bonneville
Although this problem was also felt in other GM cars at the time and the technicians were using the same TSB to try and solve other customer complaints.
I had the pleasure of working for a GM dealer during the year 2001-02.
So i was aware of the problems.

Rickw wrote:

The title to the Bulletin is:
Shake / Vibration in Steering Wheel, Floor. Seat at Highway Speeds on Smooth Roads. Latest revision dated Dec, 2000 added more models affected by this problem.
And was directed at the Riviera - all years 95-99
97-01 Park Ave, PAU
2000-01 LeSabre
98-01 Cadilac Seville
2000-01 Cadilac DeVille
1995-01 Olds Aurora
200-01 Pontiac Bonneville

Funny, my grandfathers Seville has the vibration too. Mechanic said it had something to do with a bent rim, and basically he left it at that. I don't know if it's related or not, but who knows.

Have him look at TSB 00-03-10-007 dated Dec, 2000
and Also TSB 00-03-10-006 dated Nov, 2000 which introduces the use of the Hunter GSP9700 Radial Force Balancer
The Bent Rim Theory was what everyone thought in the beginning until engineering got more involved due to the flood of customer complaints. The TSB doesn't specifically address the 30 mph wobble although almost every car that had the high speed vibration also felt the wobble which we were all taught is a bent rim. But in this case it is not necesarily a bent rim, but you have to check the run-out of the rim to rule it out. It proved to be a combination of tire and rim tolerances that when assembled just the right/wrong way would cause the problem. That's why not every car off the assembly line exhibited the problem. GM finally solved it on their end (at the factory - assembly line) after several years of the Dealers chasing ghosts and spending a lot of money to make customers happy.
You can imagine buyers of expensive luxury cars did not like vibrations right at normal cruising speed on smooth highways.

GMFreak8 wrote:

Rickw wrote:

Well, maybe on this board we are the only one's complaining of this issue right now. But GM had started issuing Technical Service Bulletins to the dealer network starting in about 1998 regarding this very issue.
The first bulletin was about 10 pages long and required a lot data be gathered by the Technician and fed back to engineering in Michigan at first.
Subsequent revisions were a little more informative to the tech as to what to do to try and fix the problem, but none the less it was still very involved and didn't guarantee you'd find the problem. These were new cars then under factory warranty and new wheels and tires were replaced by the dealers after approvals from the home office. Then in about the year 2000 Hunter came out with the balance machine we've talked about and helped solve the problem. The latest revision to the TSB instructs the mechanic to use it for solving the problem.

Interesting. So it's still essentially the tires, just the riviera seems to be more sensitive to tire abnormalities?

Yes, the Riv is *Very* sensitive to tire abnormalities. And the thing that angers me is that many if not most tire places, if they don't have a machine that checks for radial force variation they will pretend that you don't have a problem. It is an attitude I would not want to emulate. I think it is analogous to putting clear plastic bags over their heads, cinching 'em shut at their neck, and when they gasp for air say "What problem? there's plenty of air in this room, can't you feel it?!?!"

Albertj

Albertj

Thanks guys for all the help and support. At least I don't feel crazy here haha. I don't even know if any shop around this area has one of those Hunter machines.... Anyway to find out, besides calling three dozen places?

The only way i found out was to look up different web sites of what i know to be the larger tire installers in this area and I found one within 30 miles.
There is probably a way to go to the Hunter site and query the local users of their equipment by zip code also.

My car started vibrating at 55-60 and got worse as I went faster. I took it to the local custom/speed shop and had my tires balanced. The son of my mechanic, a guy in his 20's told me they have the best machine. Probably a Hunter.
Long story short.... no more vibration/shaking.
Go somewhere that has good equipment ans if it is wheel balance, they'll fix it.

Rickw wrote:

The only way i found out was to look up different web sites of what i know to be the larger tire installers in this area and I found one within 30 miles.
There is probably a way to go to the Hunter site and query the local users of their equipment by zip code also.

Hunter has a web site for the GSP 9700 and it shows where to find one. There is not one in the county I live in, I have to go to the next county east to find one. That said - within the first 6 months or so after I get new set of tires, I have them checked on the Hunter - it is near the regional airport so I drop the car off when leaving town and pick it up when I return.

Albertj

How much did they charge you the last time you them checked using the hunter machine??
Does $25.00 per wheel/tire sound about right????

Interesting that you guys bring up Goodyear tires to go along with the vibrations. I had Goodyears on it when I first bought my car, and thought the vibrations were terrible. I think they were the OEM or OEM-type Eagle LSs maybe? Anyway, they sucked. I didn't put a lot of effort into them though, just replaced with Michelin Pilot XGH-4 (I think) and never had any vibrations until 45000 miles later... Rims and Tires are most definitely the major players in the vibrations.

I also fought through the same issues on my mom's old '98 PA. It had continuous vibrations, and after having the tires balanced many many times and replacing wheel bearings, we finally replaced the cheap-ass tires she had bought and the better tires... well the car rode like glass.

You can definitely have a tire that 'balances' correctly but has shifted belts or some other issue, and the vibrations only show up under load. So this Hunter Radial Force Balancer you guys speak of makes a ton of sense to me as what you need to track these issues down.

typically the issue is that the tire is so much stiffer where the belts overlap that it makes it feel as if it's out of balance or kind of like you're driving over pavement dividers that are not really there. Called radial force variatin because the force needed to press the inflated tire down at the belt seam, depending on how the tire is made, can be much, much greater than the force needed to press it down at almost every point away from teh seam.

Some tire manufacturers (Michelin comes to mind) have ways of reliably minimizing this variation by applying know-how of various sorts in tire construction that minimize radial force variation.

Albertj

An update on my on-going battle with vibration at highway speeds.
Yesterday I removed the tires from the wheels, cleaned all the bead seating area on all 4 wheels and used a tire balance machine as a fixture to hold the wheels and rotate them while I measured them for Radial and Lateral run-out.
The maximums that I recorded were .008" Laterally and .030 Radially.
With those numbers I am confident I don't have any bad wheels.
So we mounted 4 New BFG Advantage T/A's and balanced.
Today I had to do a 200 mile all Highway trip and still have a vibration between approximately 60 -80 mph.
It isn't as bad as it was with the old tires but I attribute that to the fact the new tires just have more rubber and are a softer compound to possibly absorb a small portion of the vibrations. IDK
All I can think of doing next is to re-check with dial indicators all my Hub/Bearing assemblies and if they check good again (checked several times over the past 2 years, then I have to figure out a way to check the run-out of the front drive shafts or just replace one at a time with re-man units and see what happens.
I don't know of any inexpensive way out of this.
Any body have any further ideas.?
I probably haven't written everything I've done to check for vibration over the last couple of years but I think I have been able to accurately measure all components for wear and run-out except for the half shafts.

Have you looked at tranny mounts and engine mounts? are they in good shape? i'm sure you have looked

Have you tried shutting off the engine and putting the car in neutral while going down a steep enough hill to keep your speed in the range where the vibration is occurring to see if you can hear/feel any other clues. You might could also try letting someone else drive and opening the pass. door to see if you hear anything that gives a hint to what is causing the problem.
I wonder if a chasiss dyno would be of any benefit while looking for that gremlin...

There is a section in the FSM about diagnosing vibrations just as you describe.
Please keep us posted

Bert

I have tried putting it in neutral and coasting through the vibration speeds and the vibration remains.
Don't remember turning off the engine though.
Thanks for the reminder I'll do that the next opportunity I have.

Rickw wrote:

How much did they charge you the last time you them checked using the hunter machine??
Does $25.00 per wheel/tire sound about right????

I missed answering this before.

Last time I had it done $15/wheel but it's been a while.

Albertj

Well, after doing run-out checks on the rims and installing new tires i don't think the Radial Force Balance will help me now?????
One more thing i do want to do though is jack up the car and check the radial run-out of the tires by setting up the dial indicator on the center of the tire thread while they are new and see what i measure.

Rickw wrote:

An update on my on-going battle with vibration at highway speeds.
Yesterday I removed the tires from the wheels, cleaned all the bead seating area on all 4 wheels and used a tire balance machine as a fixture to hold the wheels and rotate them while I measured them for Radial and Lateral run-out.
The maximums that I recorded were .008" Laterally and .030 Radially.
With those numbers I am confident I don't have any bad wheels.
So we mounted 4 New BFG Advantage T/A's and balanced.
Today I had to do a 200 mile all Highway trip and still have a vibration between approximately 60 -80 mph.
It isn't as bad as it was with the old tires but I attribute that to the fact the new tires just have more rubber and are a softer compound to possibly absorb a small portion of the vibrations. IDK
All I can think of doing next is to re-check with dial indicators all my Hub/Bearing assemblies and if they check good again (checked several times over the past 2 years, then I have to figure out a way to check the run-out of the front drive shafts or just replace one at a time with re-man units and see what happens.
I don't know of any inexpensive way out of this.
Any body have any further ideas.?
I probably haven't written everything I've done to check for vibration over the last couple of years but I think I have been able to accurately measure all components for wear and run-out except for the half shafts.

IMHO on a RIv you will feel that .030 radial runout unless you can mount the soft/low spot on the tire at the high spot on the rim. A proper mount on the Hunter would deal with that.

You may be onto something with the half-shafts unless you have not replaced them before and the car has not been in a wreck. Reman shafts are IMHO better than new (at least the Cardone ones are) BUT you still have to watch for bent shafts... My guess would be that if you already have 1 or 2 reman halfshafts and you have vibration above 55-65 miles per hour, you may well have a wacked halfshaft.

I know it sounds repetititve and you probly don't wanna do it but if I was you I'd have those wheels spun on a road force balancer like the Hunter GSP 9700. THe reason it is priced so much per tire is to give the shop a margin in case the machine tells the tech to dismount/remount the tire. Unlike plain spin balance, if wheel/tires are not already match mounted the tech will have to dismount/remount those tires to get the balance right on the Hunter. If it's any consolation, though, in my experience unless you throw a weight, you probably won't have to spin 'em again because tire wear probably won't change things like with a conventional balance.

A shop with a Coats 1050 will get you close to the Hunter - Coats 1050 has a match mount mode, but does not have a force wheel to measure/correct for radial force variation. The Hunter does. The Point Is that even if you check for runout (basically this is what the Coats does) if the tire carcass is not uniform (hint - basically no tire carcass has uniform radial force, they all have a "high" radial force spot where the belts overlap. Michelin puts in extra wrap plies to deal with this somewhat but even their tires have some RFV.

Bottom line is that even with the measurements you can do, you can still have enough radial force variation in the tire carcass - and by the way it *won't* show up as a runout spot on the tire - to cause vibrations above ~40 MPH. Have to use a Hunter or an ITW match mounter to get it right (auto factories use the ITW machine)

Albertj

I know exactly what your talking about.
I do not know the history of the drive shaft's, so that is why I was thinking they should be next.
I hate shot gun maintenance but i am so frustrated and annoyed with this problem after 2 years.
It certainly makes more sense to pay the other shop with the Hunter RFB first though.
I guess I should have just bought the tires from them and had it done at the same time for a discounted price.
They offered the RFB for 15 per wheel if I bought tires from them, but I didn't because i wanted to clean and measure my own wheels.
Now I'll have to pay the $25.00 per wheel for proper indexing of tires and wheels.
And if that doesn't do it then I'll move on to the drive shafts.
This sucks out loud.

Rick,

We should swap your wheels/tires for my snow tires/winter wheels, they ride smooth like glass. (my summer tires have a _little_ vibration to them). See if the problem goes away then.

deekster_caddy wrote:

Rick,

We should swap your wheels/tires for my snow tires/winter wheels, they ride smooth like glass. (my summer tires have a _little_ vibration to them). See if the problem goes away then.

Derek,
Thanks for the offer. I'd like to take you up on it.
Also, need my idle adjusted up a little with the tuner.
I'll PM you about this.