Do you think that the rear could have anything to do with the vibration/shimmy that I experience in the steering wheel? I never checked the rear or even thought about it, thinking that I am only noticing problems with the front end. This has been a crazy experience, everything else about the car is wonderful, just that occasional shimmy and shaking of the steering wheel are the only things I have to complain about. Every once in a while that steering wheel will shake pretty bad, sometimes it shimmies also, but I never feel anything in the car. Its just all in the steering wheel.........

 

You never know, it could be another place to check. Most likely not but you never know. Did you check the run out on the edge of the rims? Do you still have the factory rims/wheels to try? Something still does not sound right. I forget, you had ball joints, tie rod ends and rack checked? When you press the brakes hard, do you get any pulsing ont he pedal? My gues is not because you checked the run out on those surfaces.

Here is a thought, you said the rotors are a little out right. Could a caliper be sticking and the brake is slightly dragging and the uneven surface, thus giving you the affect? You did say temp related. The brake pads and rotors are the components that go through quite a bit of temp range.

Also, are you using a torque wrench to apply even torque on all lugs?

 

Contrary to opinion, the "Road Force" wheel balancer does not put enough force on the tire and wheel assy to simulate the road. This is a sales job by the manufacturer and a good one. There are many computer wheel balancers on the market that will diagnosis, suggest solutions and balance the tire and wheel assembly accurately, ie; Bosch, CEMB, Coats and in most cases with less effort and operational proceedure. If the operator of the equipment is experienced in the operation of the equipment, diagnosis and balancing of the assembly, it will be performed correctly on all these machines. I am sure there are other manufacturers of the same equipment that will perform the same given the opportunity. Finding a reliable repair facility that has that experience no matter what manufacturer of equipment they have, is the problem.

 

I still have the factory rims on the Pacifica, I hesitated to put aftermarket rims on after the trouble I am experiencing. Slamming on the brakes does not result in any vibration at all, I think we can be sure that they are not warped enough to cause the vibration. I certainly agree that with the vibration being both speed and temp related we have to be looking at an item that does experience quite a bit of temp change. I have considered replacing the rotors, unfortunately they are a little costly and I am tired of replacing parts with no results.

Here is what I have replaced so far:
One rim (but swapping the rims around from front to back and so forth doesn't seem to make a difference)

A new set of tires.

Both half shafts

I have had an alignment done, have had the tires balanced several times with no real difference.

What is crazy is I'll leave the house sometimes, get up on the freeway and the car is as smooth as can be, little vibration felt in the steering wheel. Then the steering wheel will start shaking/vibrating and it will kind of fade in and out, never going completely away but getting to the point it doesn't bother me. Then the vibration will come back and the wheel will shake in my hands again. The whole time the wheel is vibrating I generally don't feel a thing in my seat or in my feet. I take my hands off the steering wheel and if I wasn't looking at the wheel, I'd never know it was shaking. You can actually physically see it shake and sometimes shimmy.

Other than an occasional rumbling noise when the wheel does this, the car is quiet and smooth everywhere else i.e. in my seat, etc.

Other times the steering wheel shakes/vibrates as soon as 60 mph is reached and stays that way til I get off the freeway.

The vibration in the steering wheel generally only happens between 65 and 75 mph. Occasionally I'll feel it slightly at 45 mph and up, but at those speeds it is almost negligeable. Over 75 mph steering wheel hardly has any vibration at all.

I have had the front end checked multiple times, everyone feels that it is just fine. I have learned to just live with it, when I get some money I will try to take it to a dealer. I am afraid that they will simply tell me to replace the components I already have, such as the tires and I will end up dropping money on replacing parts until they find the problem if they ever do.

 

Do the aftermarket rims have tires on them? It would be interesting to see how they ride if you do. What is funny is what you describe is typically a wheel balance problem at those speeds.

You have a spare right? Can you swap that in on the other 3 one at a time to see if that make any difference?

Also.. read here.. interesting about how fast the speed balancer goes
http://pacificaworld.com/smf/index.php?topic=698.0

 

Sounds like you need to take your Pacifica to a shop that knows what they are doing. Your problems can be diagnosed if the technician knows what they are doing. It is hard to find one so ask around.