Chevrolet C60s - Front Wheel "shimmy"

[cordenj]

Hi Dave,

I suspect that this problem is combination of reduced caster angle (overcorrected by the 6-degree wedges so have put the 3-degree wedges in) and the tyre design.

Yesterday's test with wider tyre design gave some real progress.

I've been out to borrow another pair of wheels this morning ....what it is to have friends with CMPs (thanks James).
These wheels have the same pattern "round shouldered" design that originally caused the shimmy, so the test will be to see if they do the same.

All I can say is that I'm getting of of practice in changing 20" wheels

[Richard Farrant]

John,
In MB-C1 manual under the heading FRONT WHEEL SHIMMY it says the following;
Broken or inoperative shock absorbers increase front wheel shimmy and tramp which is annoying and dangerous.

You might need to disconnect them to operate by hand to check their operation, assuming they are topped up of course.

regards, Richard

[Bob Carriere]

........would happen if the 3 degree wedge was installed backwards to decrease camber????? and maybe compensate for the sagging springs..........

Carry on Sherlock ......

Bob C

[Richard Farrant]

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

Might be worth talking to these people at Aldershot;
http://www.frmspares.co.uk/springs.html

(no connection and never used them, but being reasonably near they could be worth contacting)

[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.

[cordenj]

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.

Might be worth talking to these people at Aldershot;
http://www.frmspares.co.uk/springs.html

(no connection and never used them, but being reasonably near they could be worth contacting)

Agreed Richard,
Aldershot isn't too far away. We thought there may also be somewhere near Edenbridge.
I do think new/re-set springs and pins is the ultimate answer....was trying to get a temporary solution for W&P this year though.

[cordenj]

Originally Posted by Bob Carriere

........would happen if the 3 degree wedge was installed backwards to decrease camber????? and maybe compensate for the sagging springs..........

Carry on Sherlock ......

Bob C

Bob,

I dont know.
The wedges were made and fitted on entirely logical advice from Rick Cove and other replies to this thread. Sagging springs would reduce or remove the Castor angle, so fitting wedges from rear of springs re-instantes it.
My experiences over this weekend suggest that 6-degrees is too much, the reason being described by Dave Mills in an earlier post today. Hence I've left the 3-degree wedges in.

[cordenj]

Originally Posted by Richard Farrant

John,
In MB-C1 manual under the heading FRONT WHEEL SHIMMY it says the following;
Broken or inoperative shock absorbers increase front wheel shimmy and tramp which is annoying and dangerous.

You might need to disconnect them to operate by hand to check their operation, assuming they are topped up of course.

regards, Richard

Evening Richard,
I did check the operation of the shock absorbers when I dropped the axle for wedge fitting. Did this by disconnecting the drop arm and manually tested that their was resistance to upward and downward force.
Maybe not very scientific but there was what seemed like an equal resisitance.