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Highway shimmy/ vibration finally solved!


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First of all, yes I'm still driving my 01 STS!  After years of tire rebalancing and several small fixes including new front hub assemblies, all of which seemed to make a difference on the severity of that dreaded 65mph + shimmy or vibration through the car, each never eliminated the problem. But first, let me bore you how I got to it.  A couple months ago I had the unlucky task of replacing the water crossover gaskets.  That was a crap job of all crap jobs. Mind you, I'm not a professional mechanic, nor would I claim to be, however this stuff doesn't scare me from trying it.  That being said, I decided I was not paying someone half the cars value to repair that crossover pipe that was spewing antifreeze out as fast as I could pour it in. After a week with the hood open, and every possible thing to replace was replaced, water pump, thermostat and housing, all hoses, gaskets and clamps. I even cleaned the fuel injectors and replaced the O-rings since I had to pull the fuel rail. All I can say is... Never Again! I was nervous to start the old girl when I was done out of fear something wasn't going to be right with all the work I just committed my life to.  My fears were calmed by the fact it even started first try!  Yay me!  Having my pride crushed after a good road test wasn't a good feeling as the smell of hot antifreeze could be found within a 10 foot radius around the car.  I couldn't find leaks so that was a good sign.  Topping off the expansion tank and repeated road tests revealed that I must've been smelling the last of the antifreeze burning off the engine and tranny.  I replace the expansion tank cap which may or may not have helped, don't know, don't care... I stopped losing coolant which I'm sure was just air working out and the smell was eventually gone! Again, Yay me!! What has that to do with the vibration?  Absolutely Nothing!   What a crap job that was!!  However that lead me to really paying attention to the engine, as I searched for coolant leaks, I noticed my belt tensioner (serpentine belt on the passenger side) was jumping a lot... as I scoured around looking for an out of round culprit, there it was, holy mother of grails... the harmonic balancer looked like it was a spinning egg!  Though I hadn't quite related that to the highway vibration at this point, I just knew I had to change it.  So the deed was done just before I had to make a 400 mile trip and with the coolant issue behind me I felt safe to make the journey in my Seville.  I have now logged over a thousand miles and that car is smoother than it ever was in the previous 8 yrs I've owned it.  Sorry I put you through "the story" to get to my Title but every time I work on this car, its a story!  I'll save the sunroof drains for another day! lol

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@Kodiak I love your story, thanks for sharing it. 

3 hours ago, Kodiak said:

and every possible thing to replace was replaced, water pump, thermostat and housing, all hoses, gaskets and clamps. I even cleaned the fuel injectors and replaced the O-rings since I had to pull the fuel rail

We think alike!, your statement above is me!

And let me tell you, you are CORRECT, the first time you do the crossover job it is a Fn bear of a job!  But guess what, it is SO much easier a second time, with all that you learned the FIRST time :hatsoff: I have done it 5 times now, and its a breeze :blink::D But now you know why the dealers were getting 700 for the job!   It makes a big difference when those 4 seals leak, you smell coolant and leak pressure...  My 96 thrived on that crossover job...

Thank you for relaying the information on the harmonic balancer, that is terrific.  Please post a video if you took one.  This is how it begins.......  haha..good for you

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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2 hours ago, BodybyFisher said:

 I have done it 5 times now, and its a breeze :blink::D 

You are a hero!  I can't think of a much worse job that wouldn't require pulling the engine. So many little things I've done to that car with little to no room to work on it. I didn't get a video, However I did take several photos, and those were to help me remember where all the parts go.  I did get pics of the crossover pipe and failed gaskets.

I remember the day my buddy and I were reinstalling his rebuilt 400 small block it into his 1970 Monte Carlo.  Each of us were standing with feet on the ground, inside the engine compartment on either side of the engine. Those were some good days!

Speaking of which, I grew up near the Fisher Body plant in Wyoming, Mi.  Still remember the "Body by Fisher" carriage emblem.

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You are a good mechanic sir I like that you're taking photos I do the same thing to jog my memory please post post the photos when you get a chance definitely interested in seeing the harmonic balancer and crossover seals.

Don't kid yourself many of the Chryslers and Cadillac had plugs and we're very difficult to get at under the generator under the air conditioning compressor way in the back and while the North Star is tight I believe that you will buy the tools necessary to accomplish the task. Since I have owned Northstar my tool box has expanded greatly.

I remember the body by Fisher on all the cars when I was growing up and wanted to have a name that tied back to my childhood, I appreciate.

I will link you to my first crossover job I believe my impression about the job was about the same as yours it was back-breaking lol.

Come on back when you need help we're here to help.

I'm in the car using voice recognition so excuse the punctuation.  You just gave me my 100th like thank you :-)

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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hmm. My 97 Seville has a slight vibration at higher speeds. starts around 45+ seems to be a little worse around 80+. Livable though.

Have checked everything including new tires with roadforce. 

My 97 Deville is the same way but vibrates worse. More like a shake in the front end. Replaced many things but still has the same problem.

Thanks for sharing

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I will say that my 96 had a vibration when my front and right motor mounts were bad.  All vibration stopped when I replaced them.  Just an additional thought 

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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