Chevrolet C60s - Front Wheel "shimmy"

[motto]

Mention has been made of wheel balancing but what type of balance was done, static or dynamic?
Static balancing has definite limitations in that the location of the 'heavy spot' is not defined axially i.e. it may be toward the inside or outside of the wheel. When weights are added to 'balance ' the wheel they can be just as easily be put on the opposite side of the wheel to the heavy spot and make the dynamic imbalance worse.
Dynamic, on vehicle balancing is a far better option if you can find someone with the equipment to do it as this removes the unknown and also takes the hub and drum into account.

David

[Lynn Eades]

Wheel balance would generally be less of a problem with big old M.Vs. than the likes of modern vehicles with smaller dia. wheels traveling at higher speeds.

In saying that, I do not disagree with any of the above.

John If you have measured correctly then something is definately wrong (1" difference in camber??) were you on level ground to start with?

Jack it up and see if you have any play in the vertical plane (grab the tyre top and bottom and try to wobble the wheel)
If there is any movement get someone else to apply the brakes and try it again
If the movement has gone, it is wheel bearing adjustment. If it is still there, it is in the king pins.
You also need to deal with the toe in as well. 3/8" will be scrubbing the hell out of your tyres with each wheel trying to go in different directions.

If you disconnect the drag link (steering arm end)and then swing the wheel asemblies through their steering arc (left and right) you may be able to pick up any roughness in the king pins.

If you do have to do king pins, keep in mind that king pin bearing preload is normally set without the knuckle seals fitted.

[rob love]

Originally Posted by Lynn Eades

If you disconnect the drag link (steering arm end)and then swing the wheel assemblies through their steering arc (left and right) you may be able to pick up any roughness in the king pins.

Not sure one can swing a pair of 20" tires with the wheels still on the ground unless you have a pair of alignment plates underneath. If the axle is jacked up and the wheels are in the air, then the problem may not be evident as you have transferred the weight away from the kingpin normally under load to the kingpin that normally does not carry a load.

[cordenj]

Originally Posted by Lynn Eades

Wheel balance would generally be less of a problem with big old M.Vs. than the likes of modern vehicles with smaller dia. wheels traveling at higher speeds.

In saying that, I do not disagree with any of the above.

John If you have measured correctly then something is definately wrong (1" difference in camber??) were you on level ground to start with?

Jack it up and see if you have any play in the vertical plane (grab the tyre top and bottom and try to wobble the wheel)
If there is any movement get someone else to apply the brakes and try it again
If the movement has gone, it is wheel bearing adjustment. If it is still there, it is in the king pins.
You also need to deal with the toe in as well. 3/8" will be scrubbing the hell out of your tyres with each wheel trying to go in different directions.

If you disconnect the drag link (steering arm end)and then swing the wheel asemblies through their steering arc (left and right) you may be able to pick up any roughness in the king pins.

If you do have to do king pins, keep in mind that king pin bearing preload is normally set without the knuckle seals fitted.

Hi Lynn,
I rechecked the camber with wheels on level ground, the figures decreased slightly on both side with the weight of the truck on them, but still a difference between left and right hand side.
With the wheels jacked up, I tried shaking wheels to see if any play. There was no perceptible movement, even with a lever under the wheel, so that implies to me that the bearings are not too loose. The wheels rotate freely too, so no reason for possible "grabbing" being the cause.

[Dave Mills]

I am certainly no expert on the CMP and have watched with interest the conversation. I am delving into the unknown here but may I suggest that you check your shock absorbers. If you have checked everything else it seems like you may need to check these, if they are faulty they can cause a shimmy once you increase speed and hit any form of undulation in the road surface.

Dave.

[jake neville]

our marmon herrington gun tractor had this same problem when we first put it on the road. the entire front axle had been overhauled and the wheels balanced. when it got around 20mph it started shaking so violently it was dangerous and uncontrolable. we fitted castor wedges to the front which made a big difference. it now only comes in mildly when you hit a bump around 50mph.

robin mawson had similar problems with his white scout car. he played around with his for quite some time. tried a number of things and still had problems. eventually he tried ajusting the toe in more than what it said to in the book. no shimmy at all from zero to flat out.

we are planning to try the same on the marmon when we get time. this obviously increases tyre ware but for the amount we drive these old trucks waring out tyres is highly unlikely.

give it a try?

[Mike K]

Originally Posted by jake neville

we fitted castor wedges to the front which made a big difference. it now only comes in mildly when you hit a bump around 50mph.

50 mph in a M-H - YOUR KIDDING So what brand of turbo have you fitted on that flathead

[cordenj]

Thanks for advice everyone.
Now off to celebrate 70th Anniversary of the liberation of the Channel Islands (well Guernsey) for a week.

Sadly not in the Chev as planned until this wheel issue is resolved, so having to take the Jeep and one of my trailers.

I'll investigate the shimmy more on my return.

[cordenj]

Originally Posted by motto

Mention has been made of wheel balancing but what type of balance was done, static or dynamic?
Static balancing has definite limitations in that the location of the 'heavy spot' is not defined axially i.e. it may be toward the inside or outside of the wheel. When weights are added to 'balance ' the wheel they can be just as easily be put on the opposite side of the wheel to the heavy spot and make the dynamic imbalance worse.
Dynamic, on vehicle balancing is a far better option if you can find someone with the equipment to do it as this removes the unknown and also takes the hub and drum into account.

David

Hi David,

They were static balanced (on a large machine but off the vehicle) at a specialist truck tyre company. The wheels ended up with weights on both inner and outer faces. Before I changed the tyres, the wheels had large amounts of weight added so clearly been balanced before; so thought that might be the shimmy cause.