Suspension Vibration 2000 Buick Lesabre

I notice a frequently requiring vibration through the seat mostly when after I Pass over a bump. It doesn't happen on every bump just some, but when your
traveling at highway speeds thus occurs a few times a minute. Its like you are traveling across an washboard road for about 2-3 seconds after you hit certain bumps. I've had a total 4 wheel alignment at that time they replaced the front drivers side wheel bearing and a control arm ball joint on the passenger side. I've had all 4 tires replaced and balanced. When the tires were replaced I had the ASE certified Alignment shop go over the suspension again to see if they could see anything that might be causing this problem. They are the ones that did the first Alignment. They didn't find anything that might be causing it and the new tires did help. They conducted a ten mile road test with me. After about 1500 miles the problem is back and seems to be worse. I did have a break job done on the rear wheels they replaced the disks on the back wheels. This was prior to the alignment being done. Anyone have an Ideal what may be causing the vibration? I'm worried that the vibration will cause more sever damage and also want the us this car for a 2000 mile vacation in June or July.
Thanks Bill
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Bill wrote:

Have the shocks and steering rack checked out.
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The rear shocks or the front struts? The rears are air leveling shocks. Also the steering seems tight its only when you hit a certain type of bump.
Thanks Bill

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Check to see if the bell housing bolts are loose.........
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Where would I look for that on a front wheel drive vehicle? I didn't realize it would have one?

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Bill wrote:

Front shock/struts. I have heard, but never seen personally, that the rack sometimes exhibits an oscillation. I forgot what goes wrong with them.
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I'm having the struts and air shocks replaced tomorrow. Will let you know how it turns out. I bought the car for the long term and trips so want it in good shape to travel in worry free comfort.
Thanks

Also
them.
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If you are feeling this through the seat, I would not replace the struts and shocks. If it was play in the steering, you would feel it through the steering wheel. My guess is that you have a bad rear tie rod end. It connects to the rear spindle and play will show up after hitting bumps. Shocks and struts do nothing more than control spring action. If it is not the tie rod ends in the rear, it would be a rear bearing or some play in the rear suspension. If it seems fine after you spend all that money for shocks and struts, it will be because they are deadenning some of the vibration to the rear suspension. Just as you stated from what happened before, it will not last.A 200 car should not need shocks/struts yet unless you go to a tire store then they tell you they are "weak" I know I have worked for tire stores before as well as dealerships(GM) for the last 22 years.

shocks.
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    Document ID# 1455223 2000 Buick LeSabre      Shake/Vibration in Steering Wheel, Floor, Seat at Highway Speeds on Smooth Roads (Diagnose/Balance Tires/Wheels) #00-03-10-007F - (02/05/2004) Shake/Vibration in Steering Wheel, Floor, Seat at Highway Speeds on Smooth Roads (Diagnose/Balance Tires/Wheels)
1998-2004 Buick Park Avenue, Park Avenue Ultra
2000-2004 Buick LeSabre
1998-2004 Cadillac Seville (SLS, STS)
2000-2004 Cadillac DeVille (DTS only)
2001-2003 Oldsmobile Aurora
2000-2004 Pontiac Bonneville (17" Tires only)
This bulletin is being revised to add the 2004 model year and delete the screened tire program information for all tire manufacturers except for Continental General. Please discard Corporate Bulletin Number 00-03-10-007E (Section 03 - Suspension). Condition
Some customers may comment on shaking/vibration in the steering wheel, floor or seat while driving at highway speeds (typically between 60-72 mph (96-115 km/h)) on smooth roads. Cause
These specific vehicles may be sensitive to various rotating mass assemblies, especially if they are considered to be out-of-balance. Correction
1. Visually inspect the tires and the wheels. Inspect for evidence of the following conditions and correct as necessary. * Missing balance weights * Bent rim flange * Irregular tire wear * Incomplete bead seating * Tire irregularities * Mud/ice build-up in wheel * Stones in the tire tread 2. Set the tire pressure to 30 psi (205 kPa) COLD. 3. Road test the vehicle with the Electronic Vibration Analyzer (EVA) essential tool for a sufficient distance on a known, smooth road surface to duplicate the condition. Record the Hertz (Hz) reading as displayed by the EVA onto the tire data worksheet found at the end of this bulletin. This should be done after a tire break-in period of at least 10 miles (16 km) at 45 mph (72 km/h) or greater, in order to eliminate any possible tire flat-spotting. 4. If the road test indicates a shake/vibration still exists, check the imbalance of each tire/wheel assembly on a known, calibrated, off-car dynamic balancer. If any assembly calls for more than ounce on either rim flange, remove all balance weights and rebalance to as close to zero as possible.
Important
Some GM dealers may have a Hunter GSP9700 Road Force Balancer. This will simplify Step 5 by not requiring dial indicators. If a Hunter GSP9700 machine is available, it may also be used to measure the radial force of the tire/wheel assembly. A guideline here is 18 lbs or less. 5. While on the balancer, measure wheel runout. If radial or lateral runout exceeds .020 in (0.50 mm) for aluminum wheels (.030 in (0.76 mm) for steel wheels), replace the wheel. 6. After confirming wheel balance and wheel runout, if any changes were made, road test the vehicle again. 7. If the smooth road shake/vibration still exists: *
Important
The completed worksheet must be attached to the hard copy of the repair order. Record Radial Force Variation readings if you have access to Hunter GSP9700 Wheel Balance equipment. Use the worksheet found at the end of this bulletin to record the readings. * If one or more of the tires have RFV readings in excess of 18 lbs, match mount the tires to get below 18 lbs. Readings of 12 lbs. or less are preferable for critical customer concerns. * If the RFV can not be reduced to an acceptable level, replace the affected tire with one obtained locally. * The screened tire program is no longer in effect for Bridgestone/Firestone, Goodyear and Michelin. Low speed screened tires are available from Continental General only, and only for the Buick LeSabre. * Road test the vehicle to ensure the shake/vibration has been resolved. 8. Replace both lower control arms on vehicles built prior to the following VIN breakpoints. On Aurora, Bonneville, DeVille, Park Avenue, Park Avenue Ultra and Seville models, a newly developed hydro-bushing lower control arm with improved damping characteristics has been released. This control arm is not used on the LeSabre. The new lower control arms may provide an incremental improvement to the vehicle ride. Customers who have become "tuned in" to the shake condition may still feel some shake in the vehicle after the new lower control arms are installed. Refer to Lower Control Arm Replacement in SI (refer to the Parts Information table below for SI document ID numbers).
Important
THE CONTROL ARMS SHOULD ONLY BE INSTALLED ON VEHICLES IF, AFTER THE TIRE AND WHEEL DIAGNOSIS AND REPAIRS HAVE BEEN PERFORMED, THE VIBRATION CONDITION STILL EXISTS.
Model     
VIN
Park Avenue     
34175493
Seville (SLS, STS)     
3U247643
DeVille (DTS only)     
3U247644
Aurora     
34175503
Bonneville     
34175497 Parts Information
P/N     
Description     
SI Document
25746324     
Lower Control Arm, Left (Aurora, Bonneville, DeVille, Park Avenue, Park Avenue Ultra, Seville)     
Aurora -- 639351
Bonneville -- 657809
DeVille w/FE1, FE3 -- 724856
DeVille w/FE7 -- 724858
Park Avenue, Park Avenue Ultra -- 657760
Seville -- 539332
25746325     
Lower Control Arm, Right (Aurora, Bonneville, DeVille, Park Avenue, Park Avenue Ultra, Seville)
Bill wrote:

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I got the tires replaced on my Bonneville last Wednesday. So far, so good, but its VIN preceeds the stated break point.
After over 30000mls it's nice to get brand new tires and the car going smooth again on the highway.
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