wpriller

I ran over a concrete block that was laying in the middle of the highway that I didn't see. I blew a tire and damage the rim and strut. I've replaced the strut and had the front end check. Technician stated they did not see any problems
with front end and no bends in the A arm. The suspension has been checked by several Techs and they state the front end looks fine.

I have no premature wear in tires but as car gets up to 70mph I start to get a shimmy. Is it possible that the A arm has a slight bend that can not be notice by the naked eye, that will cause the shimmy. I've had my rims refinish and balance and the shop stated my rims are okay. All technical advice welcome

User 4221

Did they do your wheel bearings, too? Is the wheel new?
Did they do a road force balance?

These are all contributors to shimmy

wpriller

They did an high speed balance and stated the rims were okay. I did not check the wheel bearing and the front end did take a wheel alignment.

whalebird

I have seen an aluminum hub bent. This will cause brake shimmy-like a warped rotor, but can go unnoticed. FWIW.

wpriller

Whalebird, should I be looking at the hub and the bearing before considering the A arm?

Steve Weiner-Rennsport Systems

I would be checking the axial and radial runout of the hub and spindle with a dial indicator to see if you sustained any hidden damage.

whalebird

My story begins with an SC that had a brake shimmy. A couple of shops had thrown brake rotors at the car with no appearent result. What I did was mount a dial gauge on the strut housing and check the runout on the rotor(both sides). One side had a clear problem, but had a new rotors. I relocated my dial gauge and was able to get a reading on the flange surface of the hub - bingo there was a problem. Just for clairification, I was thinking that there could be some kind of problem with the mounting surface of the rotor(rear of the hub) that would hold the rotor off the hub and create runout. I went back and forth from side to side and it was clear the hub was out of round for whatever reason. Bearings were inspected and confirmed to be installed correctly. New(used) hub was installed and problem solved.
This may or may not have relevance in your situation, but I really like to eliminate the obvious things before digging deeper. My first step would be to lift the front of the car and spin both wheels. If you are on the ground, I would place a block of wood next to the wheel and use a pencil as a referance pointer placed on top of the woodblock and hold the point of the pencil as close to the WHEEL lip( close to the tire bead) and see if there is the smallest bit of deviation. Do this for both the inner and outer wheel lips on both sides. If you see a millimeter of lateral (back and forth) or axial (up and down) don't sweat it, but 4,5,6 mm or so will indicate problems. If you find a problem, check the runout on the rotor using a dial gauge, or a suitable referance mounted on the caliper.
Thats my story. You may want to look at the top strut mount and bushings. An impact can damage these and it won't be clearly evident - look close for splitting or seperation in the bushing/mount material.
Good luck and let us know your findings.

dshepp806

Good stuff, Bird and Steve.


Doyle

whalebird

thanks Shepp.
One glaring omission here is the tires. You mention the tire being replaced, were both fronts replaced, and the damaged wheel - what was done there? You may have more than one problem.

rusnak

I felt that I couldn't get really positive runout measurements on my front wheels with my dial indicator mounted on the car. I would probably see if you could borrow a wheel balancing rig, and use a clamp on dial indicator to measure both the hub and wheel without the tire. Radial and lateral runout of both rims and the hub.

wpriller

Thanks Guys, I really appreciate the technical input and will let you know how I make out. Thanks Again