what are the possible causes?
Out of balance front wheel(s)?

TIA for all inputs.

 

Wheels/tires out of balance? Tie rods? Control arm bushings?

 

Balance shimmys hit right at 60mph 90% of the time.

Steering wheel = front wheels
Seat = rear wheels

Test it when the tires are warm.

 

Is that because most spin balance machines rarely exceed 60 mph (or the rotational equivalent thereof)?


Andreas

 

If not very severe, it could be the rotor vents and/or holes are clogged with dust.

 

Mine does too. Everything has been checked already.

 

Me between exactly 55-60, but smooth as silk everywhere else ...ah hem, even markedly north of 60mph. Everything checks out, and it has been like this for some time without any change or degredation whatsoever. I choose to live with it until I feel something merits attention, personally.

Edward

 

Control arm bushings?


Andreas

 

Wheel bearing/s? Internal fault/s in tire/s? To check for internal faults, raise tire pressure to 50 psi in all four tires. If that eliminates the shimmy, drop tire pressure in one tire at a time until shimmy comes back. That will indentify the bad tire.

 

Bingo!

Had the same problem. Wheels were balances but still had the vibration. Changed the control arm bushings and no more vibration.

 

Now I don't feel so bad since there are a few others with this issue.
I have had a slight shimmy right at 52mph since I got her 3 yrs ago. And like Edward, smooth as silk everywhere else (especially over 100). I've gone through three different tires, been balanced twice. It does seem a little more pronounced when SLOWING to 50-55 (not braking) than speeding up past 50-55.
I've just chosen to live with it but I sure would like it to go away.
Guess I'll check the control arm bushings next.

 

Yessir!

My money is on the bushings. I changed them and it is smooth as silk.

 

As noted above, if smooth just below that speed very unlikely to be wheel imbalance, would bet dimes to donuts it's the control arm bushings. My current 993 and the last one both had the symptoms you describe. Installed Chris' bushings and bingo, all is right with the world.

 

Agreed! The most common cause at 50-55mph is the control arm bushings.

Heavier wheels or poorly worn tires can mask it a bit so if you change wheels/tires and it appears, you can be tricked into thinking it is tire balance.

My $$ is on control arm bushings.

 

Before you do anything, & all the advice is good, but CHECK YOUR TIRE PRESSURE! Mine started to shimmy, & one tire was down a few PSI.