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2004 GM W-body ride issue

Man I am tired of this bouncing while riding. I have never put this much effort into fixing something that seems to be so simple. I know we have slightly discussed this in a different thread about road force balance. I decided it was time to just discuss the entire problem…

2004 Monte Carlo SS with FE4 suspension. 86Kmiles with factory struts. ATE rotors with ATE ceramic pads. Factory wheels and new Uniroyal Tiger Paw GTZ tires in the correct size per the door sticker (replaced previous tires due to wear and were a slightly smaller size previously). Road Force numbers from 14 to 25 lbs calculated by the GSP9700 Hunter balancer. New axles about 1K miles ago. New wheel bearings at 60K. No play in any suspension components noticed when at the tire shop… I cannot remember how long this has been doing this but I think it was very near when the tires went on in November last year. I cannot remember for certain. Driving impression, car is planted on the road other than this bounce. Handles well when pitched around corners.

Here is what I have noticed so far. Some days on the same stretch of asphalt it rides like glass and others it is like riding a buck board. Much worse when the fuel tank is almost empty as compared to a full tank. Tire rotation does nothing to improve. Tire pressure has been varied from 35 LBS down to 28 LBS cold tire pressure with almost no change. Door sticker says to run 30 PSI… Can be very severe at speeds as slow as 20 MPH and when it is doing it the problem is just there up to 70 but there is an improvement as it speeds up.

All rotors look the same no bluing from a dragging pad. All pads look like the same amount of material still left on the pads. The brake system has not been taken apart in 25Kmiles but inspected when the tire store threw on the tires almost 5K miles ago.

The output trans axle extension was taken out and checked. No discernible warp seen and the differential looked good with no funny wear patterns. This is when the axles were replaced and lower motor mounts were replaced. I rotated the upper radiator support mounts like the GP guys claim helps. No codes from the trans or the engine to boot.

The kicker in all this, a romp on the gas once it starts to bounce usually pulls it out while the car is under acceleration. It returns as soon as you release the throttle though.

I would really like to fix this. It is making the short drive to work very hard to handle.

Forgot to mention the alignment was checked/changed 2 weeks before the new tires were installed.

Sorry if I missed some information in your other post. Could you be more specific about the bouncing/bucking? Is it mostly vertical, or horizontal like an engine surge, or a combination? If the motion is vertical, does it seem to come from the front or the rear, or does the car rock fore and aft on the suspension. Roughly, what is the frequency? Is it a vibration or does it feel like someone is jumping the bumper. Is the frequency always the same or does it change with speed? Once it starts, what does it take to get it to stop, accelerate, slow down, brake or something else? The only clue is the amount of fuel in the tank. That could change three things I can think of, a change in the resonant frequency of the suspension (or the drive train), a change in the suspension geometry or something that effects how the engine runs. Any additional clues would be helpful.

I say bounce because the motion is very slow. It is felt in the seat mostly making me go up and down in motion. The frequency is very slow and yes like a kid is bouncing up and down in the back seat. Changing gears from OD to D to second does not make a difference in this feeling.

Once it starts, I haven’t figured out how to get it to stop. I know acceleration makes it much less but comes right back upon returning to standard driving. Also applying more fuel to the tank makes it much less. It is there while braking and there while coasting without braking. I cannot remember it being this bad with the previous tires but I knew they were worn and not rotated properly on the first interval so I have assumed the cupping in the old tires was a lot of the old issue and hoped the new tires would smooth the ride.

I know this is almost immaterial but I can hear a change in the pitch/sound of the tires that follows this bounce. Not sure if it is the cause or the effect. 3 day weekend coming up and the car is almost out of gas. I will get my wife to drive it while I pace her in another car. Maybe then I can see what is going on from the outside of the car. Such as the tires are pretty much planted but I can see body movement, that might be a clue. Or conversely a tire is hopping off the pavement, well I have a new place to look suspension tire related right.

It sounds like you have a mismatch between the springs and dampers. Are you sure you both the shocks and springs are for the FE4 suspension? This is a bit esoteric but it might point to something useful. The suspension spring has a resonant frequency determined by the spring rate and ratio of the sprung to unsprung weights.One of the jobs of the shock is to dampen that oscillation.The tire sidewalls also act like a spring and have their own resonant frequency. The two “springs” are coupled through the suspension. If the two rates have a common multiple they can reinforce each other. The damper might not be able to compensate. Still, this shouldn’t be a problem if if you have the right springs and shocks. Watching while someone else drives is a good idea. You might see something that gives you a better idea of what’s happening. You might also try throwing some sand bags in the trunk just to see what happens. Best of luck.

Am I sure all components are the FE4 suspension pieces? I bought the car with 42K miles on it. The previous owner never rotated the tires and therefore believe that owner would not have changed the struts so I would think the struts are factory installed. I have not changed them either. Now, GM has been known to make some errors but I am assuming right now that all components are correct. Worn as they may be, but correct.

I will keep an eye on this thread for other thoughts but report back this weekend after seeing someone else drive the car.

I didn’t find the time to get a pace car this weekend so I could look at mine going down the road. Maybe later this week since it is still low on fuel.

I missed the fact that you have 86K on the original struts. My bad. You need new struts.

Well, what part should be used to replace this worn strut? Rockauto has many different types to replace teh strut on there. I am assuming the FE4 suspension has to be maintained because of dampening the stiffer spring rate but does it matter if is Delco or KYB? Neither claim FE4 suspension but do claim with special performance handling… Whatever that means…

A friendly call to your Chevy parts department would be a good place to start.

I usually steer away from stealership prices when I can. I will see what the cost is and see how to proceed.

This weekend I decided it was time to really narrow down what is causing this bounce. The Monte was low on fuel which is when it bounces the worst. I checked on line and the Magnum has the same 115 bolt circle so I took the wheels off the Magnum and threw on the Monte for a short time. I know how they ride on the Magnum so I had a baseline there. I could not put the Monte wheels on the Magnum as a true cross check because the offset was wrong and hit the suspension in the rear.

I have to say the bounce was gone…

So I thought, well maybe something else is different. Checked the tire weight on a bathroom scale, both types weighted 48.0 so that was no different. The only difference is the tire height is slightly taller on the Magnum wheels and the offset is different. I checked air pressure, 30 PSI in the Magnum, 34PSI in the Monte… This was after the Monte tires had sit in the garage floor all day with the garage door closed. I thought I had them set to 30… I released some air back out to 30 cold tire pressure.

I put the Monte wheels back on and went to work this morning. Bounce is back. Time to make a decision about the next tire I guess. The Uniroyal sucks on this FE4 suspension.

I have to admire the work you have put in to resolve the problem. I would still recommend trying the dealer’s parts department. You don’t have to buy from them. At least you can get the parts # you can use to cross reference to an after market strut. With luck you might get some specific information about the FE4 suspension package.

I’m assuming we’re talking about a Dodge Magnum - and if true, then the Monte has different tire size.

So now I’m wondering what else is different. Offset? tires?

Some Magnum’s would have P225/60R18’s, while the Monte would have P225/60R16’s - 2" difference in diameter. So what does that mean?

With that kind of difference, we could be talking about some worn out part that is allowing the bouncing, and when the larger diameter tires are appled, pushes the part to it’s extreme limit, taking out all the slop and - Viola! Problem gone.

Yes Dodge Magnum and the tire size you state is correct for that one at 28 inches by TireRack specs. The Monte has 235/55/17 for the SS/SC package at 27.2 inches.

You’re still a firm believer that the issue is a strut aren’t you?

I’m confused. Unless I’m mistaken, the FE4 suspension is a performance suspension system. These do ride like buckboards, and of the springs was upgraded but the OEM shocks retained, there will be a mismatch between the springs and dampers. The ride should be expected to be terrible.

As to upgrading the dampers, it’s always a crap shoot when mixing one company’s upgrade springs with another’s upgrade dampers, unless the damper manufacturer lists the parts as compatable. Keep mixing parts and you may never sort out the ride.

Same mountainbike, as of today the car is still stock. I have not changed the struts. I was asking what struts to change to if I decided to.

Yes I know the FE4 suspension is tight and I would expect some bounce over varying road surfaces. What I am trying to figure out is why the car bounces much worse one day over another on the exact same stretch of road for no apparent reason.

I called and filed a claim with Uniroyal last week. They said to take it to a tire dealer with Michelin and have the tires inspected. The gentleman that inspected them said they are very out of round and helped finish the claim on the tires. Uniroyal and I settled on a discounted price for my usage and offered the Michelin Pilot Sport as the tire that I should try on this car. The tires came in today but will not get put on for a couple days because of logistics on my side. I really hope this tire change finishes my issue with this bounce.

The new Pilot Sport AS tires are on. The car rides much better on the first 15 miles. I will report back to this thread if anything changes.

Only responding to this so anyone watching it will have an answer on what fixed my issue.