ted tcb Posted August 4, 2005 Report Share Posted August 4, 2005 The 3 week saga of buying a 99 STS finally came to a head tonight. The dealer put new rotors and pads on the car, hoping to silence a shudder that I feel over bumps and at high cruising speed. My mechanic went over the car, and all the obvious things look ok. I test drove the car after the work was done, and when you go over broken pavement, you feel a shudder, kind of like an oscillation or small wave of vibration ... one bump in the road = a small series of vibration. Long story short ... I said fix the shudder and I'll hand over my cash .... the dealer is taking it for a wheel balance, but I'm starting to think about motor mounts or possible frame damage ( it looked unrepaired up on the hoist). When I rev the engine while applying the breaks in drive or reverse, the engine barely moves ... wouldn't a bad mount cause the engine to jerk under load? Any thoughts .... I assume a tire or rim imbalance would be a constant vibration, as opposed to a series of quick shudders over each bump. (of course, when I had the dealer join me, he only felt the slightest of bumps). The ball is back in the dealer's court, but any advice on the shake would be appreciated. 1989 FWD Fleetwood, Silver 1995 STS Crimson Pearl on Black leather 1997 STS Diamond White 1999 STS Crimson Pearl 2001 STS Silver 2003 STS, Crimson Pearl Link to comment Share on other sites More sharing options...
JimD Posted August 4, 2005 Report Share Posted August 4, 2005 This won't fix the problem but it might help the service people "see" what you could be feeling. Place an open container of liquid (a coffee cup works for me) in a cup holder and observe the surface of the liquid while you are driving.... Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
jhall Posted August 4, 2005 Report Share Posted August 4, 2005 ted tcb, This sounds strangely like a possible bad strut. Has anyone tried to replicate the vibration by pushing / lifting on the car body? Another source might be a bad drive axle joint that is causing the vibration when it is moved slightly off the normal operating plane - the kind of angular displacement of the shaft that you get when the car runs over bumps and the suspension is lifting / returning. This type of vibration is a higher frequency than the typical engine speed vibration. Just some thoughts. Link to comment Share on other sites More sharing options...
KevinW Posted August 4, 2005 Report Share Posted August 4, 2005 It's possible one or both rear wheels are hopping off the ground following a road impact; a wheel imbalance could magnify a loss of damping control within a certain speed range. Try adjusting the rear tire pressures downwards (to 24 psi) or have someone follow the car and observe the wheel movement over disturbances. ___________________________________________________ Link to comment Share on other sites More sharing options...
bigjayzway Posted August 4, 2005 Report Share Posted August 4, 2005 This sounds strangely like a possible bad strut. Has anyone tried to replicate the vibration by pushing / lifting on the car body? This is where I would definately start. Big Jay Life is too short to grow up! Link to comment Share on other sites More sharing options...
JohnnyG Posted August 5, 2005 Report Share Posted August 5, 2005 What kind of car did you drive before? The Seville has a few odd (mild) suspension tendencies that I likened to a shudder when moving from a rear wheel drive car. My '99 was my first front wheel drive and it took some getting used to. On the other hand, I have some experience with tire vibrations and have cured that issue on my '99. I don't know what makes these cars so sensitive to tire imbalances, (more like tire roundness issues) but they are. A tire problem (rarely a wheel) usually manifests itself as a speed connected vibration. It has nothing to do with bumps in the road. Since your car is doing this after a bump, it is definitely suspension related. It could be a bad shock, it could be a bad set of bushings in a sway bar, it could be the upper control arm bushings in the rear suspension, or it could be a motor mount if you feel it more up front. There is a test for a bad motor mount (a common failure for some '99s) and it's NOT rocking the engine from forward to reverse, like in the old days. Get a good GM mechanic....to check it out. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
ted tcb Posted August 5, 2005 Author Report Share Posted August 5, 2005 Thanks ... its going into a balancing shop tomorrow, at the dealers' expense ... I'm holding off on the $$$ until its perfect. My existing car is my 5th Cadillac ... only my 90 Fleetwood had similar oscillations, and it was caused by a disintegrated motor mount, eaten away by brake dust. Its really the dealers' problem ... fix it or I keep my 97 which drives and brakes perfectly smooth. 1989 FWD Fleetwood, Silver 1995 STS Crimson Pearl on Black leather 1997 STS Diamond White 1999 STS Crimson Pearl 2001 STS Silver 2003 STS, Crimson Pearl Link to comment Share on other sites More sharing options...
keith_99_sts Posted August 5, 2005 Report Share Posted August 5, 2005 Make sure you check for codes. Can't recall the exact sequence, but you need to hold down two buttons on the dash and read out the codes on the information display below the gauges. My '99 STS drives fairly normal but is throwing a P0741 transmission code. That's why you need to check the codes. A common problem is oil leaking from the engine half seal. Usually not fatal, just messy. Horrendous oil consumption (1 quart / 1000 miles) is 'normal' according to GM. Fortunately the car has an oil level sensor. Check the head gaskets, because replacing those and timecerting the engine will cost a small fortune. Water leaking into the trunk is another speciality. Look into the trunk area where the spare wheel is stored and check for dampness or rust. As you may be finding out, shocks are an area where the replacement cost will bleed you dry. Does the AC blow cold? For some reason, fixing car AC systems costs more than buying a 25 cubic foot refridgerator. As with most cars, if the engine and transmission and drive shafts are good, the rest can usually be fixed without a huge expense. If you buy the car, have fun with it. It really comes alive when the gas pedal hits the floor. All in the interest of preventing carbon build up of course Link to comment Share on other sites More sharing options...
caddypete Posted August 5, 2005 Report Share Posted August 5, 2005 Check the rear knuckles, my eldo did the same thing, going over bumps the rear end made clunks and felt like it didn't track proper and the rear end felt like it would drift when cruising freeway speeds I took it in for an alighnment they told me the rear knuckles were shot (and they were) and could be replaced for 640.00 a side. I did them myself and it still cost me $340 per knuckle, once the bushings wear out you have to replace the whole knuckle Link to comment Share on other sites More sharing options...
JohnnyG Posted August 5, 2005 Report Share Posted August 5, 2005 Thanks ... its going into a balancing shop tomorrow, at the dealers' expense ... I'm holding off on the $$$ until its perfect. My existing car is my 5th Cadillac ... only my 90 Fleetwood had similar oscillations, and it was caused by a disintegrated motor mount, eaten away by brake dust. Please keep in mind that just any old tire balancer won't work. You need a "road force balance" and the numbers need to be UNDER 15 pounds road force. A Hunter GSP9700 is prob. best for this. Get all the tires matched to the rim and make sure they are warm when you do it. Otherwise, they will be flat spotted from sitting overnight and won't give true readings. I'm still suspicious of that front motor mount, under the front of the engine. Particularly if you feel movement in the steering wheel. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
stscaddylac Posted August 5, 2005 Report Share Posted August 5, 2005 I recently bought my caddy, an 02 seville sts with 19,000 miles on it. When I would go over bumps, I would here a clunking coming through the stearing wheel, also would vibrate at higher speeds. It felt and sounded like the front end was loose. Brought it to the caddy dealer, and it was a stearing bushing, somewhere in the stearing column. This is a common problem with the sevilles. One of the techs told me that they recently upgraded this bushing. Maybe that is your problem Link to comment Share on other sites More sharing options...
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