Steering Shimmy

[car04]

So I'm at wits end - thinking I may have to deal with this shimmy in the steering wheel. Posting here to confirm my thinking or get ideas to troubleshoot

At about 65 mph I get a shimmy in the steering - nothing on the pedal or in my butt - doesn't change under acceleration or on coast - it comes and goes slightly so I think it's the tire and the road irregularities - but it's annoying as hell and I want to eliminate if possible

Tires - road force balanced & wheel run out verified under .050
255/35/18 YOKOHAMA ADVAN A052
315/30/18 YOKOHAMA ADVAN A052
Wheels - Forgestar F14
FFR steering rack
Toe 1/16 in
Caster 7.5
Camber .5
Bump steer kit - almost zero bump
No poly bushings - solid front lowers and trailing arms / 3rd link
Borgesom universal steering joint with damper and one normal u-joint

Any thoughts are appreciated ....

[michael everson]

power or non power steering? If non power check the rack for play at the ends. I have come across 2 now that the bushing holding the inner rack have disintegrated. I was able to move the tie rod quite a bit.
Mike

[car04]

Thanks Mike -- power steering and it was new when installed -- during troubleshooting I did check and couldn't find find any play in the rack, lower/upper ball joint, wheel bearings, heims, etc.

[Norm B]

It is speed related and you have checked all the pertinent mechanical stuff. That leaves the tires. Check the sidewalls for a bulge.
I do this by jacking the car until the tire just clears the ground, placing a small carpenters square on the floor so one side just clears the tire side wall, and then spinning the wheel.

HTH

Norm

[car04]

Norm B - good call on the tire -- when I did the RF balance they found a bad tire -- it's been replaced -- that made things better but still have a slight shimmy / pulse

[Norm B]

Find a shop that does road force balancing and see if they can find an issue.

Norm

[turbodon]

Heims at end of rack?

Heims with slightest play will cause shimmy.

[AC Bill]

Hopefully the tires were balanced on a high speed balancer.
When I sold Repco wheel balancers way back when, I sold a lot of them after I would demonstrate how the high speed balancer was so much more accurate than a regular wheel balancer.

[car04]

Yes - road force balanced twice -- not sure if that qualifies as high speed

[Garry Bopp]

car04, where are you located? If you are in the Atlanta area, Gran Turismo East does spin balancing, then fine tunes the balance by spinning the wheels when they are mounted on the car, with one of the techs sitting in the car, holding the steering wheel to check for vibration.

Garry

[AC Bill]

Yes - road force balanced twice -- not sure if that qualifies as high speed

Not quite the same, although the road force type seem to be growing more popular. They do simulate weight being on the tire, as when driving but may not be as sensitive for high speeds
Regular wheel balancers run to about a 35 mph spin test on a tire/rim combo. That normally will cover speeds up to 60 mph, unless a tire or wheel is damaged in some way.
High speed balancers have sensors designed to detect imbalances for a tire going 60+ mph. Just a 1/2 ounce out of balance can multiply into several pounds of imbalance at a 100mph.