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Going With Michelin Primacy

2404 Views 11 Replies 6 Participants Last post by  Glock3540
Hello All,

I have a vibration problem at highway speeds (60mph+). When trying to diagnose what was causing the problem I checked to see at what mph the vibration started and ended. I changed lanes quickly, sped up and slowed down, up hills and down hills, put the car in neutral and coasted, etc with no discernable change in the vibration.

I have done the following trying to correct the problem:
Replaced both outer tie rod ends (pass. side was in poor shape). Moog
Replaced all 4 hubs (drivers side front had a little play). Timken
Replaced front lower ball joints (just to eliminate them being the problem). Moog
Replaced ALL sway bar bushings, front and rear. Moog and OEM
Replaced all 4 rotors. AC Delco
Replaced all brake pads. Top of the line Monroe Ceramic pads..
Replaced both suspension adj links.
Replaced front motor mount. OEM
Fabricated some torque mounts to limit engine movement.

Vibration still there.

Had my tires Hunter "Road Force Balanced". They found 2 slightly out of round rims. They had no lateral runout but were actually bent. Not too bad of a "bend" but I had them order 2 factory rims. They did another Road Force Balance to make sure the replacement rims were not bent also. They said my tires were OK.

Little Better but vibration still there.

Took off wheels and FANATICALLY cleaned all mating surfaces.
There is No rust, No Paint, No foreign objects of any kind (at least to be
seen with the naked eye) on any of the mating surfaces.

Reinstalled wheels and torqued in a star pattern in a three step torque
First 80lbs, then 90 lbs and finally 100 lbs of torque and then triple

Vibration still there.

The other "possibilities" for the vibration that I can think of are;
Possible bad CV joints (although no clicking or any other signs of a failing joints and all boots are in good shape with no leaks). I did notice when installing the new hubs, I noticed some "play" in the spline teeth on the cv axle where it enters the transmission/transaxle. The teeth did not look damaged or even worn but there was what I considered excessive play. I would expect there to be almost no discernable play or at least Very Little.
I have not replaced the CV axle assembly yet. I do not want chinese rebuilt CV joints, nor do I want OEM. After much research, I have contacted for info about complete assembly replacemet. No response from them yet, but I read their owner?, was involved in a small plane accident so it may be awhile before he gets back to work to answer my question (I pray he is going to be OK). MAYBE I have a slightly bent axle shaft and that is my vibration problem?
I have read that some believe the transmission/transaxle/differential has a defect in its design that may cause this vibration. Not sure about that one...
What do you guys think? Could it really be a differential pinion gear issue?

I have read that the front lower control arms might be part of the problem.
I have replaced my ball joints so I do not want to replace the entire lower arm that comes with the ball joint already installed. The Moog ball joints I installed are at least as good as OEM and I suspect better. I do know they have grease fittings;)
I wanted to replace the front and rear control arm bushings but for some reason GM designed them so you cannot replace them. Thanks GM.
I have only found one person that sells replacement bushings but they are poly. I do not want any Squeeky bushings! I have contacted Walton Manufacturing which I think makes very high quality bushings. He thought he had some bushings that would fit my car. I told him I think he was thinking of an earlier model Caddy, and after checking, he said I was correct. He said he was going to check into making some for me but has not got back with me yet. (I think if He would design and manufacture some front and rear bushings for the 2000-2005 Devilles, and made them reasonably priced, he would sell a bunch of them! None of us wants GM forcing us into purchasing an entire arm if we may need just bushings!)

I have read where at least one person thinks it is "air" caught in the power steering pump/lines. Doesn't sound like it could be a factor but who am I?
I cannot find the problem so maybe it is the windshield wipers for all I know!

One question that I do have is; I have measured my ride height on all 4 corners and the front 2 are within 1/8" of each other.
On the rear however, pass side is almost 1/2" lower than the drivers side.
Upon investigating this I realized I have never noticed the rear shocks air compressor running. Is this something that you can hear from inside the car?
I have spent many,many hours in the garage working on this car and I have never heard it. On my late fathers 97'? Deville, we could be sitting outside relaxing and you could hear the air compressor cutting on and off every once in awhile (he had a leaking shock).
I was planning on replacing the front struts and rear shocks with Gabriels but with only 44,000 miles I have not done this yet. Maybe I have some dryrot on the inside of the things but they look great on the outside. No visible damage of any kind. Maybe this is the reason the rear end hops a little sideways when hitting a pothole or road anomaly? It is disconcerting to be cruising down a straight, flat road at 40mph and hit a little pot hole and the rear end steps out like I would expect it to do if I hit a big patch of ice or something...

I have Continential Conti Touring tires on it right now and they have less than
1000 miles on them. I purchased them from an individual so I do not have any warranty as far as exchanging them but they did still have factory stickers on them and were absolutely brand new. I realize this is a relatively cheap tire and I am a Michelin Man (My father worked building tires and in the testing laboratory at Pirelli Amstrong tires for 30+ years. He was fanatical about vehicle tire ride (smooth ride, etc). He said they purchased and tested competitors tires and they were always impressed with Michelin tires. They were baffled how Michelin could make a tire with so tight of tolerances. He said Michelins were the best tire on the road.

So after this Extremely Long Post, I am breaking down and spending almost $1000.00 this Saturday on Michelin Primacy tires for my Caddy. I did extensive research when replacing tires on my wife's Accord (after 2 sets of "upper end" Bridgestone's that wore pretty well but rode like a bucket of bolts). I put Primacy's on her car and it transformed the vehicle. It rides Much Better now and she is very happy (so that makes me happy ;)).
I called Discount Tires and asked the rep if someone could ride with me out on the interstate so I could show him the vibration before purchasing and installing the new tires. They are great people and I am hoping for good results. I really give it a 50-50 chance the tires fix my vibration problem but at least I will eliminate the tires as the possible culprit.

I have replaced the water pump and thermostat and the new "redesigned" cover to fix a leak I had with the factory cover.
I replaced the plenum (just because I know this is a known possible problem with our cars). While I was replacing the plenum, I put on all new OEM intake gaskets/rings and cleaned the plenum as described in the tech tips here on this forum. Big Difference. I had a sticky accelerator pedal and this fixed that as well as made the car idle even smoother. I put Amsoil Synthetic oil and trans fluid in and this also made a difference. The trans shifts so smooth now it is almost inperceptible, LS Lexus smooth.

So now I have this pearl white beauty that purrs like a kitten and runs great.
It stops well and handles as well as expected for a car of it's type (except for the rear end step out that I think fixing the shock/compressor problem will fix).

I hope after these tires she will ride as smooth as she should. If not, I will do a few more things to the car to see if I can fix the vibration issue. If I cannot eliminate or at least make the vibration much less noticible, I will make this car a secondary road car only. I would be embarassed for someone to ride in my CADILLAC that shakes like a worn out Jeep at speed (this is an exaggertion but continued frustration with this issue is starting to aggravate me).

Thanks for letting me rant. I can be a very stubborn person when I think something can be worked out, so I hardly ever give up on anything.
I want So Badly to get rid of this vibration but to be perfectly honest, it is about to get the better of me. Very few times in my 35+ years of amateur wrench turning, have I seen something so elusive....
Blessings Everyone,
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Wow, I would be ready to give up by now. You have done everything I can think of. You might be on the right track with the tires. Have you searched through the old threads here? When I first found this place about 5 years ago I did a lot of reading about vibrations in the new 2000 Devilles. To make a long story short I think they got the best result by switching to Michelin tires. I'm not sure which model though.

Something must be worn in the rear end to make it step out like that; probably a bad strut there.
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