96 Deville Shimmy

[rockfangd]

Hi all I am going to try to be very specific on this, my 96 deville has had a shimmy for the last 5-6 months and I am getting concerned and irritated because I cannot seem to find the problem. here is a description

felt mainly on deceleration and at 30-45mph

noted on curves/ slight turns

cannot be felt in the brake pedal

cannot be felt in the wheel

Here is what I changed to try to remedy the problem

new pads and rotors all around, new front calipers, then new front pads and rotors again, just in case of a bad set of rotors.

new rear insulator bushings

new rear knuckle bushings

new dogbone mounts(bit worried because they seem cheap. but not half as bad as the originals ) about 6 months ago

new balljoints, right inner and outer tie rods

4 new tires, then swapped in my 2 spare rims, then rotated them again

all 3 lower engine and trans mounts.

have shaken down the front and back end many times and have no play

have had the alignment done 4 times(they can never get my wheel perfect)

very slight humming coming from one or both of tthe front bearings but no play, abs light, or anything to make me really worry.

I am at a loss on this one but Other than this problem the car rides wonderful, other than one thing but I dont think it is related, even after changing the hangers, engine mounts, and dogbones, my exhaust pipe just after the resonator(or before I dont quite remember) has always rattled on the brace that is under the car between the front and rear doors. Does this when it is cold and on hard acceleration.

If anyone has any tips on this I would very highly appreciate it. I planned on new hubs in spring but may get them sooner if I cannot solve this problem.

Thanks again

[BodybyFisher]

hint is deceleration

explain shimmy better

Have you checked both front axles?, inner and outer joints?

Have you checked your AC hub bearing?

Check for play where the axles insert into the transaxle, we have seen bushing problems on both sides

Check the torque converter bolts for proper tightness

[rockfangd]

sorry, best way to explain is almost feels like a wheel wobble, sometimes worse sometimes not

[BodybyFisher]

Besides considering the issues I raised above, consider that you have an exhaust leak or an EGR pipe leak. When you decelerate you can pull air into the exhaust system, if it comes into the EGR pipe it can create a lean condition. We have seen members complain of a 'fish bite' due to a bad air leak into the EGR pipe. If you pull air into the exhaust it may affect O2 sensor readings, but I think that 'might' set a code.

Also consider that increased VACUUM pulls air into the intake system, look at intake gaskets, injector o-rings, etc. Maybe at normal vacuum say 18 to 22 there is no problem but at high vacuum at 30 to 40 on deceleration the seals leak air into the intake.

This may not be enough to set a code but enough to cause a stumble, or hesitate that you feel through the powertrain, that is why you are looking to suspension. Just a thought

Do a search under "fish bite" and "fishbite" and see what you find, you will find a KEN who had problems. Link that thread back here if it seems related to your problem.

Why I say AC hub bearing is because when the hub bearing begins to go, it will actually stall the car when it binds, so a fishbite feeling due to a bind caused by deceleration as the engine rpm slows could be possible..

By the way, I chased down 'oddities' on my 96 also and your replacements have mirrored my repairs, I am sure that your car is riding better, you will get there, the ride on that car is outstanding

[rockfangd]

well I would be very surprised if it was an engine issue as the engine runs flawless and the trans shifts flawless. I have heard of the torque convertor bolts coming loose and also about the trans bearing issuee, but if it was would it leak or not necessarily?

I would say it feels like a wheel wobble especially around 30 mph. Not bad but enough for me to notice.

Anyone that has driven or rode in my car says it rides wonderful and have never said anything but not many people I know are so meticulous to detail.

Maybe I am losing it I dont know.

[BodybyFisher]

For the hell of it review this thread

http://caddyinfo.ipbhost.com/index.php?showtopic=20770&hl=fishbite&st=0

[CarlaValentine]

You said you have some humming in the front wheel bearings, but no play, and this vibration is noted in curves. If the bearings are just starting to go bad, then you may not have play when shaking the wheel by hand, but that doesn't mean there isn't a little play when taking a curve. A car taking a curve is capable of putting a lot more stress on the bearing than anyone could do by hand, and it could cause a slight vibration.

Since you know they are humming, then you WILL have to replace them in the not-so-distant future anyhow...I would suggest replacing them now and see if it resolves your issue. Do you notice if the bearing hum gets louder when you turn?

[rockfangd]

no it is consistent. They are on my list next for replacement, then I would like to figure out the broken parking brake cable

[winterset]

while you are decelerating, put the car in neutral. that will rule out engine/transmission causes. Come to a complete stop before puting it in drive again, as not to put excessive pressure on your torque converter.

[BodybyFisher]

GOOD idea winter

[joeb]

if you really want to get crazy, shut off motor and coast thru the speed you feel the vibration. no power steering so that will be hard to do in corner. that would take out an engine miss or egr issue. you have not changed wheels though. you did tires. try another set of wheels. borrow some from a friend? i had 3 gm cars with same wheels/tires at one time.

[rockfangd]

I did change wheells,

That is a wonderful Idea, I use that same concept to diagnose bad driveshaft support beearings and transmission output bearings on tear wheel drive

[rockfangd]

ok This does occur in neutral and without the engine running, I am guessing front hub assemblys also