Pulsing vibration at highway speeds

96Firebird said:

But I'm still not happy with the way the car rides on the highway.

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Does this mean that the problems you are describing in this thread existed before the tires and alignment?

Alignments don't typically fix vibration issues.

I would take it in have the front end inspected. I can almost guarantee your problems lies there. Tie rods, control arms, sway bars end links...there are several front end components that can make the front end feel loose when you hit a bump.

Check the sway bar in the back too, if so equipped.

A quick driveway check would be to jack up the front end so the front tires are off the ground and try to move the tires, back and forth, side to side, in and out, etc. If there is ANY play, you have just now discovered that your front end is in need of attention.

I guess I should add that even if there is no play, it doesn't mean there isn't an issue.

http://www.knowyourparts.com/technical-articles/diagnosing-and-replacing-chassis-ride-control-parts/

I own a 2003 Park Avenue...and I think you had it right in your first post...the front struts are likely weak, thus causing that oscillation at certain MPH and the bouncy/uneven symptoms you are mentioning. I have driven a lot of clapped out crap cars earlier in my life and seen this issue a number of times. Also, my own PA only has 60K miles on it now...and I had to replace struts at 37K, when I bought it a year ago due to similar issues.

How many miles on your PA? Also, how many on the struts themselves?

Also, the rear shocks are not actually air-ride, or air shocks. They are a hybrid of a regular shock for driving purposes, and an air-leveling component that only is a factor when very slow speeds or stopped. Usually they should be replaced too. The springs are standard coil springs.

Good news is that Moog offers a good quick-strut assembly replacement that is easy to install on the front, but it will require an alignment. (By easy, I actually mean easy, only 3 bolts on top and the two bolts that hold strut assembly to steering knuckle, along with a few bracket bolts). Monroe offers them too, but I have had mixed results with the Monroe offering on different vehicles...plus the Moog was a few bucks cheaper.

As long as there isnt any other obvious bad part, this should solve your problem. i would definitely replace the rear shocks as well. the monroe part is a bolt in deal and pretty cheap. MA822...also get the shock mounts

While your struts need replacing I think this is it... (Rinse and repeat until I drop below 60mph.)

Meaning you have tire balance issues... With new tires it sure sounds like it to me...

Uh that .02 cent thing...

COPOHawk said:

http://www.knowyourparts.com/technical-articles/diagnosing-and-replacing-chassis-ride-control-parts/

I own a 2003 Park Avenue...and I think you had it right in your first post...the front struts are likely weak, thus causing that oscillation at certain MPH and the bouncy/uneven symptoms you are mentioning. I have driven a lot of clapped out crap cars earlier in my life and seen this issue a number of times. Also, my own PA only has 60K miles on it now...and I had to replace struts at 37K, when I bought it a year ago due to similar issues.

How many miles on your PA? Also, how many on the struts themselves?

Also, the rear shocks are not actually air-ride, or air shocks. They are a hybrid of a regular shock for driving purposes, and an air-leveling component that only is a factor when very slow speeds or stopped. Usually they should be replaced too. The springs are standard coil springs.

Good news is that Moog offers a good quick-strut assembly replacement that is easy to install on the front, but it will require an alignment. (By easy, I actually mean easy, only 3 bolts on top and the two bolts that hold strut assembly to steering knuckle, along with a few bracket bolts). Monroe offers them too, but I have had mixed results with the Monroe offering on different vehicles...plus the Moog was a few bucks cheaper.

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This.

I would rotate the tires (fronts to the back) & see what happens.

Also, inspect your motor mounts & make sure that the service agent didnt get brake or steering fluid on one or more of the motor mounts when trying to change the master cylinder & brake lines. (A bad motor mount can create the vibrations being experienced - happened to me. You dont want to get brake or steering fluid on these flexible parts as that will cause the motor mount material to degrade resulting in weird intermittent vibrations.)

Technically, if something is too loose in the front end (like a tie rod end or swing/control arm), then the alignment service agent should have picked that up as an inability to align the car as there is too much play or slop in the linkage/wheel system to accurately align (or hold alignment).

- Inspect shocks using standard bounce test
- Jack car up (front wheels off ground) & inspect wheels and steering linkage for play
- Run the car with the drive wheel(s) jacked up to test for vibration

Ultimately, you'll need to have the car analyzed by a competent service agent. They will need to test drive it.

96Firebird said:

my last winter tires cupped bad so I figured I'd better not ruin my new set.

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You need struts. Which unfortunately will necessitate another alignment. And as was said, I would replace the rear shocks at the same time. GM struts and shocks typically last 100K on the originals before requiring replacement. You're past that window and the cupping and your complaints point to struts and shocks needing replacement.

If the vibration still exists afterwards, although I don't think it will, I would be talking to the store that sold you the tires. You may have a balance problem or more likely IMO, a tire with a bad or shifted belt. The tire store should be able to figure this out and replace the bad tire or tires.

To get off on a tangent, if the front struts are shot, that makes the back shocks work harder and vice versa. You have to look at the car as a whole not a front end and a back end. Replace all four. Additionally, if the tire store you got the tires from was aware of the cupping problem and did not tell you that you needed struts and/or shocks, I would find another tire store. Cupping is a dead giveaway that those components need attention. Any tire store that also did alignments and suspension work would be more than happy to sell you struts and shocks.

Sinusoidal, or "pulsing", vibration is almost always a ujoint.

Did you ever solve the problem? I’m dealing with an identical issue as to what you’re describing. A building and falling vibration at highway speeds particularly when accelerating.

I had a couple ideas but realized the thread is 8 years old, so i was about to quit. But there's a new "me too, how to fix?" query.

I'd check the antisway links front and rear. In my recent experiences I did not get symptoms OP reports, but I have heard loose rattling in the suspension that could be traced to worn links.

Also this oddity, maybe. I'm very fussy about tire and wheel changes, and do my own on three cars twice a year each. We live in a cold area so fall and spring are times to swap between summer and winter tires - each set on its own wheels. When I do that, I use a rotary wire brush in a drill to scrub clean of all old rust, dirt etc. the flat mating surfaces - inside of the wheel hub and outer face of the brake rotor. Also the bolt holes in the wheel. Then I ensure the threads of the stud bolts and the wheel nuts all are clean and turn smoothly. Then make sure all things are clean before installing. Why? One time I had an experience like the reports above after a shop did some repairs involving wheel removal and replacement. I hypothesized that there could be some dirt or grit bits on one wheel between wheel and brake rotor so the wheel was mounted a a very slight angle and wobbling when running. I just went around one wheel at a time, removed, cleaned surfaces, and re-mounted. Vibration gone! So now I habitually clean every surface, but that's a fiddly job that takes time and no shop would be so fussy.

Another possibility. OFTEN the third-party steel wheels one buys to mount a set of spare winter tires are made for many similar cars, and the hole in the centre of the wheel is just a little too large for YOUR car's hub. So when you slap the wheel into place it is slightly off-centre down, so that the gap is zero at the top where the wheel sits on the hub, and big at the bottom. Right here things depend on HOW the shop put on the stud nuts. IF they go around with an impact wrench and whip each nut on tight, one at a time, the wheel may get locked into that off-centre position, and it will certainly be "bumping" slightly as it runs. I don't have an impact wrench. I put all the nuts on by hand to just gently finger tight and rotate the wheel as I do to ensure it IS centred evenly. I check by eye. Then I use by hand my socket wrench to snug up each nut, alternating every second one around (on a 5-nut set), then again for a hard whack or two to get them all pretty tight. AFTER the wheel is back on the ground I go at the nuts with my torque wrench, again every second one around, in two stages. First stage to about 75 -80 Ft-lb all, then final to required (typically 95 ft-lb on my cars). That way I am sure the wheel is centred on the hub before its position is locked in by the proper torque. IF this is your problem the fix is easy. One wheel at a time, slack off all its nuts a bit, then start with the finger-tight step and check visually whether that wheel is centred on the hub. If yes, proceed with progressive tightening to get to final torque.