Can't diagnose problem for sure

Hello,
I've been trying to find out what the source of the instability when driving down bumpy roads. I thought it might be a suspension component (watt's linkage). It was suggested that tires may be the
problem. A rear tire was 10 psi low. I hadn't checked it for over a month and probably damaged the sidewall from some aggressive cornering. Tire center checked in water and no leak. That means air is escaping during driving. I noticed that more air escapes the more aggressive the driving (for some reason I've never experienced this type of problem before). These are Michelin energy LX4 on an 04 Town Car. The car was bought used at 36.5K miles in Feb 07 and I didn't put the tires on. They're dated 43rd week of 06. The TC now at Oct 07 has 44Kmiles. The tread are ~1/4". Michelin said I should have a tire removed and inspected for damage. I tell the guy at Sears to do it and he looks at the tires and says it's something else - didn't see the need to look inside.
Struts and shocks were replaced with KYB (551600 strut, 551601 shock in 07 cat.) and front end aligned. No loose suspension components were detected, even after several inspections at various places. Problem still exists. There's that irregular lateral movement over bumps. Shocks have nothing to do with lateral motion. It was never there until a few months ago.
So maybe I should get rid of these tires and consider what they put on a CV interceptor. Hell, I already ruined that "Town Car ride" with KYB urethane strut and shock mounts, which only made the bumps more noticable, but didn't help cure the problem. Why not just change to some less comfortable tires that have more durable sidewalls.
It doesn't make sense. I called one limo/livery service at random and the mechanic says they just go to sears and have michelins put on - didn't say which model though. So, I have 44k miles and those livery cars go 200k-300k.
The new dampers and mounts apparently increased city mpg from 16.2 to 17.4. Big-O tires decided to set the fronts to 35psi. The sticker says 32 front 35 rear, but Big-O says it's for the "dealer ride". That's comical. I suppose Ford has the sticker just for the test drive and the shops know better. The service advisor at the dealer didn't seem to care, however. I guess it's safe to set the fronts anywhere between 32-35.
Thanks for any suggestions
Ben
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wrote:

What kind of rims are on the car? If it has any sort of Aluminum rim (cast or forged), you can easily get rim edge leaks at the beads, all it takes is a scratch in the seal coatings on the tire seating area of the rim.
You can also have cracks/porosity in the wheel rim casting itself that will leak up through the wheel and come out on the inside of the rim - the inside of the rim is normally coated with a layer of epoxy as a sealer, but that can get damaged and allow a leak.
The tire place is normally only looking for bubbles from the tire, and the tire bead area. Unless they submerge it all the way and deliberately look for a bad and leaking RIM, they won't see it.
Steel rims can also develop cracks or leaks, but it's a lot less common. And the car is too new for fatigue cracks in the rims, the only thing that could cause that would be physical damage. Has anyone slid your car sideways in the rain or snow lately, and found a curb the hard way?
Or a huge pothole with the back bumper of a Beetle sticking out?

Police cars use regular tires - just ones with a higher speed rating and a more aggressive tread pattern.

Limos are much heavier because of the extra 4' of body they spliced in, and are often using "Extra Load" P-series (passenger) car tires - which are constructed just like Light Truck tires with heavier sidewalls and more sidewall and tread ply reinforcement.
The difference being they don't have the big letters on the sidewall and you can get whitewalls - big whoop. Anything with a higher load rating and more plies is going to ride stiffer.
Extra Load P tires are usually Special Order only - but you can get a good selection of Light Truck tires with 'highway' tread patterns right off the rack at any decent tire shop. Have them mounted 'white letters in', and nobody will know.

Huh? Shocks and struts aren't going to affect fuel mileage *that* much, unless they cured a big alignment problem at the same time.
If you change tire size or load rating you need to modify your pressures from the doorpost sticker values - get a copy of the Load/Pressure chart from the tire store for your new tires. Then get the vehicle weighed for Axle Weights at a truck scale when it's loaded the way you normally drive it, and adjust pressures to match the load chart. (Tire Load = axle weight/2 )
But before you start condemning the tires, get them rotated front to back, and see if the problem moves with the tires. Might just be one tire with internal belt problems, and you can isolate and replace it.
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wrote:

They are lincoln 14 spoke aluminum. Don't know if cast or forged.

That' s what I'll have done. I don't know why the tire center didn't look into repairing the rim or just reseating the tire.

Not by me but I don't know the whole history of the car. It's not too fast a leak. If I check every two weeks it'll be OK for now.

I should have clarified. I meant the livery service (that limo services also offer) which uses the "L" Town Car that is 6" longer (159 lbs heavier in 04) than the standard sedan for more legroom in back. Other than that there's no difference; their gross weights are the same.

That's what the dash is showing. I didn't have bad alignment. Perhaps I'm being lighter on the gas lately with the problems. And another dealer (Ford, not Lincoln Mercury) said not to set the fronts to 35.

I just had the tires rotated and balanced. There was little difference.
Today I brought it in to a Ford dealer. (the Lincoln dealer service advisor was probably sick of seeing me) The service advisor took it for a test drive (the 3rd test by various mechanics) and on the highway he said the car is dangerous. There is definitely a problem with the rear suspension with all the lateral movement. He didn't see problems with the tires. He said they have a guy that specializes in suspensions. It will be very interesting to see what they find 'cause I had it inspected twice and nothing shows visually.
Ben
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H Ben-
I hope this stuff helps a bit...
At that mileage, there shouldn't really be any problems in the suspension. Usually a low tire of bad alignment will cause what you describe. I am a little surprised that the tires are newer than the car since factory tires on those things usually go 60-70k. You might want to have a good tire shop actually dismount the tires and check them if you think you really hurt them. Did this behavior come with the car or start later?
Tire pressure settings front and rear are subjective to a point. My experence in the last 10-20 years is that cars ride and handle best at the inflation on the door sticker. All bets are off it the tire size is changed from spec, tho.
Does the car pull at speed or when you brake? How about vibration or excessive road noise? A good independant tire and suspension shop can sometimes work wonders...
PoD

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Paul,
Good point. Why the original owner had to replace the tires so early on. I didn't ask them at the time since I wasn't aware they were so new.

The problem started in about 6 months (purchased 02/01/07 w/36.5K). It's at another dealer now. The advisor took it for a test drive and on the highway and said it handles like crap and is dangerous. There's lots of lateral movement coming from the rear that also affects directional stability. Now he didn't see a problem with the tires. The front end and tires were OK as he rocked the steering back and forth on the highway. It corners mostly flat on the entrance ramp so the sway bars are working. He even noticed that when first getting into the parked car, it rolls or sways more than it should which indicates a problem. I had two prior visual inspections that found nothing broken or bent.

No pulling during braking. No vibration. The tires make a little noise.
I ordered KYB gas-a-just and strut and shock bushings which are urethane. Big-O installed them two weeks ago. It made no difference to the lateral motion problem in the rear. Of course they had to align the front end and didn't find any worn parts. The KYB parts are listed for the 03 thru 06 Town Car in their 07 catalog. They are correct parts for the car and are not causing any issues.
It may have 44K on it but I probably broke something. I never do donuts or brake torques, or squeal the tires on turns. However I once got my foot caught between the brake and accel pedals. First and last time this ever happened. This caused one wheel to spin while desperately applying the brake trying to avoid going into the car in front of me at a stop light in traffic. The traction control light was blinking. After about 15-20 seconds of this I thru it into park and naturally took my foot away from the pedals. I had previously read in a customer report where the writer thought the car had a defect and would accelerate unexpectedly, but the dealer said this occurs to some people (w/big feet?:)) with E-frame cars. Once aware of what really happened it doesn't occur again.
Ben
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If a leak can't be found with a trip to the dunk tank, smart money is on looking inside the tire (look - don't run the hand around inside). Often, one can find a nail or similar that wont leak if the tire stops in the "right" place.... and no obvious signs of a puncture on the outer surface. Take it apart and there it is...
At the same time, the bead surface of the wheel can be inspected for damage/flaws as well as the bead of the tire... But most times, it will be a puncture not visible from the outside.
Your tire guys sound a tad lazy....
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Jim,
I should have insisted on a through inspection. Right now it's at a dealer. The advisor test drove it and says the rear suspension has got problems and is dangerous on the highway. I've had it test driven two time before and only one said there's a little hopping on some bumps. (see my other post) So now it's about suspension and will probably learn tomorrow about it.
Ben
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On Thu, 18 Oct 2007 01:19:40 GMT, "Jim Warman"

Another possibility is the steel belts starting to come apart inside the tire casing - running your bare hands along the inside of the tire is NOT advised until after a thorough visual inspection with proper lighting, and then feel for sharp bits with sturdy gloves on.
You could hit some steel wires that will flay your hand but good.
But I'll bet if you get a mechanic that agrees there's something seriously wrong (and isn't NOT looking for a non-problem to make the corporate folks happy*) is going to find something. A broken weld on that locating rod bracket, or another suspension anchor point that is floating when it should be solid...
(* - If you are looking for a problem you can find it. If you are looking to NOT find a problem, you can overlook all the clues pointing to the problem as anomalies.)
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Rotate the tires and see if the problem is better. Sometimes you get a tire that just doesen't seal well. Your choice is to keep putting air in it and just wear it out, or get new tires.
Ted
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