Bump Induced Extended Vibration

[BodybyFisher]

Ok, everything on my front and rear suspension is NEW except, the front lower control arm bushings, the rear lower control arm bushings and the rear knuckles.

I have had my car up and tried pushing and pulling at 3 and 9 and 12 and 6 o'clock and I don't have any movement at all NONE.

But, I am NOT happy with my cars ability to dampen bumps such as the expansion joints, and pot holes. I feel than instead of dampening the bump, the bump radiates and continues and my car jumps direction....LIKE the strut is bad or like I have play in my suspension. Keep in mind that everything has been replaced, see the list below.

My question is, what kind of problems can bad lower control arm bushings cause if they are bad, I had ALL control arms off and the bushings DID NOT appear to be bad, but, sometimes the wear is not evident and deep inside the bushing. No looseness or play in any of the bushings.

Secondly, could my carriage be loose or could the carriage bushings be shot?

Third, can engine mounts cause any of this? I tend to think NO, as I would not have directional changes from that....

I don't feel that my steering rack is the problem as I don't feel radiated shock through my wheel, and the rack would not cause continued/extended bump shock only directional weirdness, and I don't feel looseness in the front end as I noted above.

Replaced parts include, new struts (Boston passive), springs, front and rear, spring insulators, new strut mounts, new ball joints, new hub bearings, new stabilizer bar bushings, new strut rod bar bushings.

Don't get me wrong the ride is 1000% better than it was, its just not perfect and something is amiss. It seems to me that the problem is coming from my front, in particular the RF. Any ideas?

[zonie77]

Possibly a tire starting to seperate? Especailly if it's only one corner. Try rotating them and see if the problem follows the tire.

[BodybyFisher]

Possibly a tire starting to seperate? Especailly if it's only one corner. Try rotating them and see if the problem follows the tire.

Thanks for the fast response. Let me add that on asphalt roads with no expansion joints, she is smooth as hell up to 100... you could set a glass of water on the dashboard.. If I had a bad tire would that be possible?

By the way I am using Michelin Symetry (not my favorite Michelin), they have about 15000 miles and have been rotated and balanced constantly. I have had two alignments in the last year while I did all of the work. All bolts are torqued to FSM spec and the control arms are torqued at the ride height.

[Cadillac Jim]

First the free, simple stuff. Check the tire model numbers and make sure that the tires are exactly the same. Even a different production run between the two front tires could make a difference to the knowelgeable and sensitive. Of course, the air pressure must be exactly the same in the two front tires. I would recommend 32 psi cold for testing with the Michelin Symmetry tires.

I'm sure that you have checked your tie rod ends and steering knuckle and that they are tight.

You may be noticing the difference between active and passive struts.

Alignment is critical to response to bumps. What we used to call kingpin inclination, the steering axis, must pass through the center of the tire contact patch, or you will have things like steering transients in bumps and other things like torque steer in FWD acceleration and braking. This is something that tends to drive FWD cars to strut front suspension, because the steering axis is the strut axis so that the suspension is easily designed so that this axis passes through the center of the tire contact patch. You already said that you have a four-wheel alignment, and you did it yourself. Check to make sure that the aftermarket struts mount so that they have exactly the same axis, relative to the tire patch, as the originals. If you have a way to check and correct the steering axis on an alignment machine, make sure that everything is right on the money.

[Bill K]

Did you replace the rear shocks?

[BodybyFisher]

Did you replace the rear shocks?

Yes Bill all the front and rear struts and springs are new

[ted tcb]

Mike, on my 71 Cutlass, going over certain bumps induced a wave of vibrations, not unlike a golfball pinging around in my center console.

I took it to two alignment shops, plus a muffler place.

Everyone agreed their was a problem, but no one could diagnose it.

I put on two new wheel bearings, and the problem was solved.

Are your hubs good?

[BodybyFisher]

Mike, on my 71 Cutlass, going over certain bumps induced a wave of vibrations, not unlike a golfball pinging around in my center console.

I took it to two alignment shops, plus a muffler place.

Everyone agreed their was a problem, but no one could diagnose it.

I put on two new wheel bearings, and the problem was solved.

Are your hubs good?

Both front hubs are OEM new. I still had this immediately after the struts were installed, I am going to put it up in the air fully (not just one side) and see if I get play.

I am going to look into the lower control arm bushings and see if they are available. That is only part of the problem, then I need to find someone that can press them in, it requires special equipment to press them in. Its possible that my lower control arm bushings are worn allowing the wheel / strut assembly to move in and out on impact, transferring the impact and changing the wheel geometry.

[BodybyFisher]

First the free, simple stuff. Check the tire model numbers and make sure that the tires are exactly the same. Even a different production run between the two front tires could make a difference to the knowelgeable and sensitive. Of course, the air pressure must be exactly the same in the two front tires. I would recommend 32 psi cold for testing with the Michelin Symmetry tires.

I'm sure that you have checked your tie rod ends and steering knuckle and that they are tight.

You may be noticing the difference between active and passive struts.

Alignment is critical to response to bumps. What we used to call kingpin inclination, the steering axis, must pass through the center of the tire contact patch, or you will have things like steering transients in bumps and other things like torque steer in FWD acceleration and braking. This is something that tends to drive FWD cars to strut front suspension, because the steering axis is the strut axis so that the suspension is easily designed so that this axis passes through the center of the tire contact patch. You already said that you have a four-wheel alignment, and you did it yourself. Check to make sure that the aftermarket struts mount so that they have exactly the same axis, relative to the tire patch, as the originals. If you have a way to check and correct the steering axis on an alignment machine, make sure that everything is right on the money.

Sorry Jim, my statement was not clear. I did all of the mechanical work. The alignments were performed by a Goodyear shop that has a smart fanatical tech that I trust. I will post my alignment readouts when I get a chance. I for some reason don't think that my problem will be easy to fix....

There is ONE thing that I am going to check. I told my alignment guy to tighten the lower control arm bolts to SPEC (I forget what the SPEC is right now, I think 90 ft. lbs). It is POSSIBLE that he did not do that, even though he said he did, maybe he misunderstood me and tightened something else I have been thinking .... As you may or may not know, its NOT easy to torque your lower control arm bolts to say 90 ft. lbs at the ride height while the car is on the ground due to a lack of room and due to bad angles to use a long handle torque wrench. It is much easier on a lift or a pit with the suspension supported. So its possible that my lower control arm bolts are not to tightened to spec. I will check that.. Maybe if I put the car on ramps, it will be close enough to ride height and i can tighten it then or at least check the torque. I hope I am being clear

[Cadillac Jim]

I certainly wouldn't torqe suspension bolts on a car on the ground. It should be on a lift, perferably with the weight off the wheels, and, if practical, the spring loading taken off the bolt being torqued.

It's a long shot, but do take a look at the steering axis of the aftermarket struts. The strut mounts should be to spec of the application and thus line up perfectly like the OEM struts, but a very small misalgnment of the steering axis will cause pothooles and exapansion joints to propagate through the steering. Your alignment man may or may not have focused on this particular setting; most wheel alignments don't even look at it, but you should always check the steering axis when you replace the struts.

[BodybyFisher]

I certainly wouldn't torqe suspension bolts on a car on the ground. It should be on a lift, perferably with the weight off the wheels, and, if practical, the spring loading taken off the bolt being torqued.

It's a long shot, but do take a look at the steering axis of the aftermarket struts. The strut mounts should be to spec of the application and thus line up perfectly like the OEM struts, but a very small misalgnment of the steering axis will cause pothooles and exapansion joints to propagate through the steering. Your alignment man may or may not have focused on this particular setting; most wheel alignments don't even look at it, but you should always check the steering axis when you replace the struts.

Sorry Jim, I didnt see this. According to the manual, the lower control bolts are to be torqued to spec "AT THE RIDE HEIGHT". This allows for proper bushing preload, if they are torqued with the wheel/suspension HANGING, when the wheel moves upward into its RIDE HEIGHT position, it will TEAR the bushing from the torsion..the internal part of the bushing is steel and its been vulcanized to be part of the rubber portion, the steel part of the bushing becomes immovable when torqued to spec, loading the bushing improperly will damage it.

That is the reason I have been having trouble torquing the lower control arm bolts, I should have thought to use my ramps to gain more clearance for movement of my torque wrench. Mike

[alwing17]

Check the lugnut mounting holes in the wheels.I had a car that would only shake when hitting a large bump,Found the lug holes were egg-shaped...High mile car. I could saw the wheel hard left then right and could get rid of it,until I would hit another bump. GM dealers have a tool called an EVA (electronic vibration analizer) that may be of some help also.

[BodybyFisher]

Check the lugnut mounting holes in the wheels.I had a car that would only shake when hitting a large bump,Found the lug holes were egg-shaped...High mile car. I could saw the wheel hard left then right and could get rid of it,until I would hit another bump. GM dealers have a tool called an EVA (electronic vibration analizer) that may be of some help also.

Thanks, Welcome Aboard

[Logan]

Someone mentioned 'batches' of tires....

Really...tires are one of the most complex things to make...

No 2 tires are exactly the same.

Best road force ones go directly to GM....."let the rest have whats left...". Basically a factory 'GM' tire or a 'screened tire' will be the best.

So Tire Rack, Goodyear, Firestone....who gets the best tires? GM or them?

By far the best tires will be a GM part # tire sold at the dealer. That is, a dealer selling GM part # tires and not just a Cadillac dealer selling Michelins tires.

Something to think about..

Also, IMO, any tire much over about 25-30K will have issues. Balance, belt, roundness, nails, plugs, and of course some wear issues.

Anyway just FYI.