Effect of tires on front end shimmy

[JohnFornaro]

I have a 93 Explorer, w/ Goodyear 235-75-15 tires. All Terrain somethings. (I should have this info better at hand, but I don't think that the brand and type of tires is the problem.) These tires should have at least a full season (Summer 2003 and the following winter) left on them. Over the last 18,000 miles, there has been a front end vibration, slightly noticeable at 35 mph +/-, and rather more pronounced at 65 mph. At 55, the ride is pretty smooth, at 75, the ride is smoother than at 65.

I just had (5-16-03) the tires dynamically rebalanced on a Hunter machine which also measures out of round. My mechanic tells me that the tires are so out of round that they're causing this front end vibration. However, I he's balanced them before, and the vibration came back. The Right front tire has very obvious signs of cupping. It seems more to me that there is some other problem here with the front end. Any ideas?

I replaced the front and rear sway bar bushings last year, the front bearings last year, and the shox two years ago. Mechanic poo-poohed the brand of shox: Advance Auto Top of the line gas ones - $35 each, with a lifetime warranty. He proposes the Federated equivalent, a $35 shock that he'll give me for $75. Mechanic reports that ball joints are ok.

The manual shows an unusual frame to engine shock mounted at the front left wheel, but this option (or fix) is not on my Explorer. Actually, I've looked at several older Explorers in parking lots to see if I could see this vibration control device, but haven't seen it yet. (Hey Ma, why is that man crawling around on the pavement around our car?)

I know that this all sounds like a lot of front end issues, but I put it here because mechanic is adamant about the problem residing in the tires.

Any ideas or comments would be welcome. Thanks

 

[Crankcase]

Were the radius arm bushings checked?

 

[JDraper]

When was the last time you had it aligned?? If your alignment is out of whack it can cause the cupping of the tires and the vibration. Also, have you tried rotating the tires to see if the vibration changes?? That can help isolate the problem. And, as Crankcase said, check the radius arm bushings.

 

[JohnFornaro]

RA bushings already replaced

Gosh, I write this wordy thread, check it for spelling errors, and forget to include one piece of info.

Yes, the same mechanic replaced the RA bushings last year. In fact, I mentioned this on a thread in the front end section, but forgot to include it here. It was the first time, so he had to cut the rivets, etc. I looked at them yesterday before it started raining, and they seem to be in good shape, and they are bolted on to the correct force (as per my Sears Torque wrench)

Also, in this last go around, the tires were re balanced (dynamically) and also rotated, with the bad one from the RF being sent to the rear. I no longer get the "rowr, rowr, rowr" sound when driving slowly in a parking lot, but the vibration is still there, and I think that it is this vibration which causes the tires to go bad.

Incidentally, my mech gave me an incomplete printout from his Hunter GSP 9700 Vibration Control machine, along with an incomplete explanation of how to read the print out, which contributes to my developing lack of respect for his methodology. This report shows that the worst tire had a lateral rim runout of 0.002" and a radial rim runout of 0.007", along with a remark: "Assembly limits exceeded which cannot be fixed by ForceMatching." I cannot believe that tires and wheels need to be accurate to within a thousandth of an inch. Is this true?

I'll be contacting Hunter to find out more about this printout. In the meantime, I'm looking for a long term relationship with another mechanic in the Charlottesville-Waynesboro area of Virginia.

Thanks much for the response, guys. Any more ideas?

 

[Fish Man]

i dunno about the vibrations but if it helps any, my good years cupped like that after about 35 or 40k miles