front end shimmy blues

What have you done to cure straight axle shimmy? My set up is: superbell axle, F1 drum brakes, F1 steering box, Posies transeverse spring with reverse eye, steering damper, chrome wheels(balanced). I have about 8-10 deg. pos caster, toe in set approx. 1/4", tops of the tires tilt in,not sure if this affects anything. Everything is tight,including the box, king pins etc., but i get a strong shimmy which shakes the car at 52-60 MPH and thereafter a slight shimmy. The car is no fun to drive like this. I feel it's tire RPM related so I'll probably get the wheels rebalanced. Ironically the first several months after I built it the car didn't have any problems. Any suggestions?
Thanks,
Don

 

Toe in or not enough can be a cause of front end shimmy .Are you running cross plies because these can go out of round too.To check this jack the car up one side at a time and place a piece of wood close to the tyre,spin the wheel slowly and check to see if there is a lump.If there is a lump there are a number of ways it can be dealt with .First you can up your pressure a few pounds ,if it is still noticable you can grind the lump away with an angle grinder but go carefull and most times you don't need to grind all the way back as once youi have started it a little it will sometimes right itself.I'm told in the States there are machines to do this but over here it's either grind or burn out.Cross plies are known for out of round 1 in 8 in -fact.check king pins for play but make sure that it is not your wheel bearings first.It does sound like tyre out of round as these only go out after a litle while of use.......Marq

 

1/4" of toe-in seems a bit much. Since everything was fine until now, you may have worn the tires to the point that it started affecting the ride. Sometimes it's hard to see tread wear. I would borrow or try another pair of wheels and tires before anything else. I just went through this on my modified and the culprit turned out to be too much toe-in. I don't know what kind of vehicle you have but toe-in is very critical on light cars. I actually have 0° to a slight toe-out now and it drives fine. This contradicts everything I've ever heard or read but it worked for me. Sam

 

have the tires & wheels balanced ON THE VEHICLE.

 

Thanks for the replies,
Car is a 30 model A roadster. King pins and wheel bearings are virtually new,with no play. Tires are radials with no wear. I'll rebalance and recheck toe in.

 

I had front end shimmy that came from nowhere and I had never had it before.

The cause?

Loose wheel nuts!

 

Ha! The only loose nut on your car Clark, is the one behind the wheel!