Chevrolet C60s - Front Wheel "shimmy"

[Hanno Spoelstra]

Originally Posted by Richard Farrant

Much better to reset the springs than go for all these compromises, the settings for springs are listed in the manual.

Sorry to hear about your problems John.

I agree with Richard, replacing or re-arcing the springs, combined with non-worn bushings would be the best basis for the rest of the improvements.

[Phil Waterman]

Hi

Like everyone else this is a puzzler, would be interesting to measure the caster of a CMP that dose not shimmy so what are you using to measure caster and camber?

My C60S is the best driver of my three with no hint of shimmy. Just had it out this morning running along on fresh asphalt roads at 50-60 MPH it is just as smooth as you could want. I don't have a front end gauge unit to measure what the various angles. Suggestions on what type equipment you are using and I'll check around.

My C60L and HUP will shimmy but it is well above their comfortable driving speed neither of these trucks is really happy above 45 MPH.

As other people have said the geometry of steering is complicated, may not even be the front springs at fault but flattened out rear springs changing the angle at the front end.

Cheers Phil

[cordenj]

Originally Posted by Phil Waterman

Hi

Like everyone else this is a puzzler, would be interesting to measure the caster of a CMP that dose not shimmy so what are you using to measure caster and camber?

My C60S is the best driver of my three with no hint of shimmy. Just had it out this morning running along on fresh asphalt roads at 50-60 MPH it is just as smooth as you could want. I don't have a front end gauge unit to measure what the various angles. Suggestions on what type equipment you are using and I'll check around.

My C60L and HUP will shimmy but it is well above their comfortable driving speed neither of these trucks is really happy above 45 MPH.

As other people have said the geometry of steering is complicated, may not even be the front springs at fault but flattened out rear springs changing the angle at the front end.

Cheers Phil

Hi Phil,
I've measured camber with a spirit level and steel rule.
I have no way to measure castor, so have been experimenting. The previous owner had fitted what I am guessing are 1-degree wedges, so I've tried 3 and 6 degree. A previous reply on this thread referred to 9-degree set, but my 6-degree seemed to make matters worse.

I must say, I've been concentrating on the front springs, that look flat with weight on them, no real visible curve. The rear springs look to still have a good amount of curve.

[Lynn Eades]

John, do you have a smart phone?
I have a Samsung S5. I have downloaded a clinometer app.
Make sure your veh. is on level ground and then lay the edge of the phone against your spirit level.
Does that help?

[cordenj]

Originally Posted by Lynn Eades

John, do you have a smart phone?
I have a Samsung S5. I have downloaded a clinometer app.
Make sure your veh. is on level ground and then lay the edge of the phone against your spirit level.
Does that help?

Thanks Lynn,

Good idea. I dont have a smartphone but my children do

[cordenj]

Some more progress tonight

Picked up two wheels and "round shouldered" 11x20s from James's LAAT. Identical tyres to my troublesome set, thought it was worth a try to see how they went but was expecting bad shimmy.
Fitted these to the Chev.
Replaced 6-degree wedges with 3-degree versions


Test drive on James's tyres and they performed the same as Neil's . i.e. ran well at reasonable speeds, some minor shimmy when hit a pothole but controllable.
Removed these wheels tonight (as not fit for a long run) and Chev on blocks ready for new tyres in a couple of weeks.

So it means that my first replacement ex-Bedford RL tyres were probably a major part of the issue.....don't know why as look to be a better set than the ones I've trialled tonight.
But truck is also now running 3-degree wedges, new Pivot bearings on one side and numerous other tweaks and adjustments.

As a previous poster suggested....shimmy is probably due to a range of minor issues that cumulatively cause the violent reaction.

Am also going to tweak up the steering box as per the manual. Seems to me I need a 2x2/3" spanner....any recommended work arounds? I see previous owners have used a hammer and chisel, but don't want to follow suit.

Plan to investigate new springs later in Summer/Autumn

Thanks everyone for all the ideas, support and comments

[hrpearce]

In my experience big spanners are too expensive for one off jobs. The easiest way to manage the nut and screw on the Chev steering box is to weld two bits of flat to a bar to make a spanner and drill a hole between the flats for screw driver access to hold the bolt steady.