Vibration at highway speeds

[jp_gramps]

Vibrations aren't news for our cars, or the DTS cousins; but I'm going to try a tire swap-out.

I've had 3 mechanics hunt down what the heck is causing vibration around 55-65 mph. There's already a thread by another member who tried to track this down: Lucerne Ride Vibration. But I've had 2 mechanics do frontend multipoint inspections with both coming back to say that nothing is wrong with the suspension.

This latest mechanic, whose done great with tires on my truck, noticed that one tire is not true. I'm running new Conty TrueContacts. He moved this bad tire from the front to the back, and admitted that the ride and type of vibration changed, but that the vibration is still there.

He also double-checked the previous road force balancing and alignment. He got everything aligned to spec, and found some weights that didn't make sense for the balancing. So the previous work has been double-checked.

Because the vibration is only at highway speed, and he can visually see the tire isn't true, he suggested new tires. This is the 2nd mechanic to suggest I replace these new Contys. That mechanic also found a bad tired, and was able to talk to Continental and replace it under warranty at no cost to me. That was right after I had them installed last year. These tires have got <10k miles on them 🙁 Maybe a bad batch of tires?!

So I'm going to put Michelin Defenders on ... the Caddy DTS forum members rate them highly. I didn't want to throw away these new Contys and but I've been riding almost a year with this vibration and trying to hunt it down but am sick of it.

 

[2007LucerneCXL]

Forums are best guessing especially on vibration and not being on site. Thanks for posting the details on what was found and finding a good mechanic to troubleshoot is maybe the best route on this type of problem.

 

[jp_gramps]

Forums are best guessing especially on vibration and not being on site. Thanks for posting the details on what was found and finding a good mechanic to troubleshoot is maybe the best route on this type of problem.

Yea, online diagnosis of cars is like Internet doctors -- it could be totally wrong.

The hard part here is people's different meaning of "vibration" versus shaking versus wobbling versus "not a smooth ride". At least 2 mechanics admitted they felt what I call a mild but annoying vibration.

I'll report back after tires are swapped.

 

[JLF_1977]

Something that I notice in general is that not all the roads are smooth. Sometimes you can see it, sometimes you can just feel it. I'd go over that same stretch of road with a different vehicle and see if you feel anything.

 

[jp_gramps]

Sadly, new Micheline Defenders and SAME problem.

55 MPH on highways starts the vibration / shaking of the whole car. 58 MPH is a sweet spot of reducing the vibration. So it was not the Continentals.

@JLF_1977 it doesn't matter which road. Newer roads that have been paved in the last 1-2 years are worse. New roads are so butter smooth that its clearer the car has a problem. Older roads are so rough with patches that the ride just masks the vibration, but its still there.

One good thing: a wheel bearing failed just before I pulled into the mechanic's shop. A growling sound had started in the front just a few days before my appointment. So the mechanic replaced the hub assembly of the passenger front on the same day as the new tires. I was hopeful that a failing wheel bearing had been the problem all along.

Nope! Same vibration. No change.

Do I need to say that burning $$$ on this car is upsetting me? 2 sets of tires in 1 year, 3 road force balancings (from 3 shops), alignment, and now a new hub.

In my 35 years of driving so-called "crappy" Fords, Chevys, Jeeps, etc., I've never had a vibration at highway speeds that won't go away.

 

[2007LucerneCXL]

Vibration forum guessing can only be done with details. Is the vibration steering wheel or floor board, front or rear etc as the word vibration isn't much detail. List of potential problems engine or transmission mounts, axles shafts, hubs, brakes, transmission, suspension components etc

A shop or the tech needs to take the vehicle out and actually feel the problem, then make the decision on troubleshooting. If the vehicle is sitting in the shop and they are just desk guessing it will be as good as asking on a forum.

Hopefully a good shop will find the issue.

 

[jp_gramps]

Vibration forum guessing can only be done with details. Is the vibration steering wheel or floor board, front or rear etc as the word vibration isn't much detail. List of potential problems engine or transmission mounts, axles shafts, hubs, brakes, transmission, suspension components etc

A shop or the tech needs to take the vehicle out and actually feel the problem, then make the decision on troubleshooting. If the vehicle is sitting in the shop and they are just desk guessing it will be as good as asking on a forum.

Hopefully a good shop will find the issue.

Online troubleshooting is tough, but I'm sharing encase folks have found fixes.

2 mechanics have taken it out on drives. Both confirm that whole body starts a vibration/shimmy starting at 55 MPH. It's not just the steering wheel vibrating, and its not vibrating only on acceleration, or only on braking. After getting to 55 MPH, setting cruise on a flat new road, the vibration will come and go. It ranges from shaking enough to rattle coins in the car, to butter smooth; and cycles through the 2 extremes on&off randomly.

1 tech road with me after denying there was an issue other than bad roads, and backed down after feeling it on a newly paved road. (I got a bit susicious of this shop after that ride.) The other tech at another shop simply said he felt the vibration when he test drove it.

Every mechanic had blamed the new Continentals I had put on last year, but now new Michelins are on the car. No change.

There is a probability that I got 2 sets of bad tires. There's also a probability that I'll be struck by a lightening. I'm not holding my breath that I will die from lightening, nor that the cause is TWO sets of bad tires.

Road force balancing was done 2x on the Contis by 2 different shops. It's not yet done on the Michelins. I'll schedule a road force balancing for the new Michelins -- my local shop doesn't have that machine so I need to take it into the city for that job -- but I'm not holding my breath that balancing makes the vibration goes away. If vibration didn't go away with balanced Conti's, I don't see a reason that balanced Michelins will make it go away.

I found a very long thread on the Caddy forum about vibration testing. The test eventually needs a device, a Smart EVA. I've never heard of that device. Even without the device, the testing is a thorough process that no shop would probably bother with. So it sounds like I take a clipboard and go through the tests this summer.

I've thought about mounting a cheap spycam on the undercarriage near each wheel. Like this. I already have a cheap cam gifted from a friend and just need to mount it securely to see the suspension in action while driving on highways ...

 

[BuickGirlFromMars]

Online troubleshooting is tough, but I'm sharing encase folks have found fixes.

2 mechanics have taken it out on drives. Both confirm that whole body starts a vibration/shimmy starting at 55 MPH. It's not just the steering wheel vibrating, and its not vibrating only on acceleration, or only on braking. After getting to 55 MPH, setting cruise on a flat new road, the vibration will come and go. It ranges from shaking enough to rattle coins in the car, to butter smooth; and cycles through the 2 extremes on&off randomly.

1 tech road with me after denying there was an issue other than bad roads, and backed down after feeling it on a newly paved road. (I got a bit susicious of this shop after that ride.) The other tech at another shop simply said he felt the vibration when he test drove it.

Every mechanic had blamed the new Continentals I had put on last year, but now new Michelins are on the car. No change.

There is a probability that I got 2 sets of bad tires. There's also a probability that I'll be struck by a lightening. I'm not holding my breath that I will die from lightening, nor that the cause is TWO sets of bad tires.

Road force balancing was done 2x on the Contis by 2 different shops. It's not yet done on the Michelins. I'll schedule a road force balancing for the new Michelins -- my local shop doesn't have that machine so I need to take it into the city for that job -- but I'm not holding my breath that balancing makes the vibration goes away. If vibration didn't go away with balanced Conti's, I don't see a reason that balanced Michelins will make it go away.

I found a very long thread on the Caddy forum about vibration testing. The test eventually needs a device, a Smart EVA. I've never heard of that device. Even without the device, the testing is a thorough process that no shop would probably bother with. So it sounds like I take a clipboard and go through the tests this summer.

I've thought about mounting a cheap spycam on the undercarriage near each wheel. Like this. I already have a cheap cam gifted from a friend and just need to mount it securely to see the suspension in action while driving on highways ...

I dont think you need a EVA to examine the road forces.
Have you tried putting it in neutral at a speed higher than 55 , letting it coast without being in gear through the speed that you have issues, then coast below it

If you want to do a second run, throw it in neutral above the speed and then slightly throttle the engine while it coasts down again, report behavior.
There is a TSB for your car that involves using shims on the engine/trans mounts to eliminate vibrations, and doing what i suggested above will help determine if that is the fix.

 

[BuickGirlFromMars]

Tighten
Tighten the bolt and nut to 70 N·m (52 lb ft).

======================================================================
This is for a 3.8. if you have a 4.6 i can get the procedure specific to that one. this specific procedure is about removing preload on the engine mounts which could contribute

 

[2007LucerneCXL]

The year and unknown mileage would suggest that the mounts, engine and transmission, should be considered if as described entire vehicle vibration. What happens over 55 mph does the vibration increase?

Again it's best guessing not knowing the service history and not being on site so it's tossing out possible suggestion.

 

[jp_gramps]

I dont think you need a EVA to examine the road forces.
Have you tried putting it in neutral at a speed higher than 55 , letting it coast without being in gear through the speed that you have issues, then coast below it

If you want to do a second run, throw it in neutral above the speed and then slightly throttle the engine while it coasts down again, report behavior.
There is a TSB for your car that involves using shims on the engine/trans mounts to eliminate vibrations, and doing what i suggested above will help determine if that is the fix.

Hey, yea I did the neutral test, and the downshift test.

I read about that test in the long forum post I put up earlier in the thread. That link calls it the "neutral coast-down test" and the "downshift test". There's several flat and straight stretches of road where I live way out in the country where it's safe to try those at 60+ MPH. I wouldn't do the neutral test on an interstate!

The vibration remained in both tests. I'll retest them both again with some revving up in RPMs just to be sure.

If the vibration remains, then I think that rules out the transmission and mounts. But thanks for the info about the shims for the mounts. 1st I've heard of that TSB.

 

[jp_gramps]

View attachment 48734View attachment 48735
Tighten
Tighten the bolt and nut to 70 N·m (52 lb ft).

======================================================================
This is for a 3.8. if you have a 4.6 i can get the procedure specific to that one. this specific procedure is about removing preload on the engine mounts which could contribute

My 08 Lucerne is the 3.8. It's at 90k miles.

 

[jp_gramps]

The year and unknown mileage would suggest that the mounts, engine and transmission, should be considered if as described entire vehicle vibration. What happens over 55 mph does the vibration increase?

Again it's best guessing not knowing the service history and not being on site so it's tossing out possible suggestion.

It's a 2008 that just turned over 90k miles.

The vibration frequency -- if "frequency" is the best phrase -- increases at higher speeds. The vibration still comes and goes. 55 MPH feels more obvious because the "frequency" is low enough that it's more of a shaking that rattles things like coins in the cup holders. At 65 MPH it's less annoying because the vibration "frequency" is higher/faster and more like an unsolicited and uncomfortable massage. (I never liked massage chairs that vibrate.)

The only thing replaced on the frontend is the passenger hub assembly, and all new rotors last year. A wheel bearing failed last week in the passenger front wheel. The brakes were causing a big body shake when braking, but new rotors fixed that. And 2 sets of tires, of course.

 

[BuickGirlFromMars]

It's a 2008 that just turned over 90k miles.

The vibration frequency -- if "frequency" is the best phrase -- increases at higher speeds. The vibration still comes and goes. 55 MPH feels more obvious because the "frequency" is low enough that it's more of a shaking that rattles things like coins in the cup holders. At 65 MPH it's less annoying because the vibration "frequency" is higher/faster and more like an unsolicited and uncomfortable massage. (I never liked massage chairs that vibrate.)

The only thing replaced on the frontend is the passenger hub assembly, and all new rotors last year. A wheel bearing failed last week in the passenger front wheel. The brakes were causing a big body shake when braking, but new rotors fixed that. And 2 sets of tires, of course.

get a road force balance

 

[2007LucerneCXL]

If struts / shocks are original then they are another good suspect. Vehicle components have a end of life cycle that age, driving environment, mileage all come in and can affect the ride. Focusing on one element and not looking at all other possible causes is just part of the troubleshooting process. If the struts are original then assuming on this side of the screen that a alignment hasn't been done or has been done with worn parts is another best guessing.