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NCC Forum Home Page -> NCC - Projects and Updates -> If I add or remove shims to change the caster, is there general method to use to adjust the toe in?
Post Info TOPIC: If I add or remove shims to change the caster, is there general method to use to adjust the toe in?
jim larson


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If I add or remove shims to change the caster, is there general method to use to adjust the toe in?
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I have recently found out that I have to much caster for bias ply tires. I guess it causes the car to dart and have less stability at higher speeds.

 I have 3.0 on the right and 2.6 on the left according to the print out I received when I had the alignment done a couple of years ago..  In the 66 service manual it says removing 1/32 of a shim will reduce the caster by 1/4 of a degree.  So if I remove 8/32 on the right and 6/32 on the left the caster will be approximately 1.0 and 1.1 respectively; with the recommendation being both 1.0 right and left for a SS car with PS.

If I remove and add shims, the toe-in also has to be adjusted.  I was wondering if there was a way to determine what fractional part of a turn I have to rotate the adjustment sleeve on the tie rod to compensate for say a removal of a 1/8" (1 degree) shim?  Like remove 1/8" shim equal 1 rotation of the adjustment sleeve.  Anyone have an idea?

Or should I just rotate the sleeve so that the sleeve exposes 1/16" more of the tie rod on each side of the sleeve for a removal of a 1/8" shim?  



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Jim L

Lake City
John D


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Maybe our "resident" alignment and handling expert (Derek) will chime in, but in lieu of his reply this is what I did when aligning my car...

Lock the steering wheel straight ahead with some rope down to the brake pedal.

I built a simple trammel rod with adjustable (but lock-able) outriggers out of a length of 1"x1" pine. The outriggers had a small finishing nail driven through them. I made a mark on the front & back of the front tires in the center of the tread, as near as possible to the horizontal center (through the hub fore & aft). Then literally sticking nails into the mark, locking it down, then measuring - then move the rig to the other side and compare.

Tape measure toe-in.
Just adjust both side tie-rod adjusters equally.



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John D. - St. Louis Park, MN.

1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
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Back in Black


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Or you could stop by my house in Rochester and we could measure/adjust using toe plates.

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Keith - Rochester, MN

1970 El Camino SS 396 L78

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Seems like a good shake down drive to me.

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Kevin

Northwestern Ohio
jim larson


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Back in Black wrote:

Or you could stop by my house in Rochester and we could measure/adjust using toe plates.

 Thanks for the offer Keith.  I just came in from the garage and use an improvised method from John's method.  It measured 1/4" more in the back then in the front, so I think I will call it good, unless there appear to be excessive wear on the outside of the tires., then I will be calling for help.  I think you are only about 30 miles from Lake City.



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Jim L

Lake City
Lost in the 60s


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jim larson wrote:
Back in Black wrote:

Or you could stop by my house in Rochester and we could measure/adjust using toe plates.

 Thanks for the offer Keith.  I just came in from the garage and use an improvised method from John's method.  It measured 1/4" more in the back then in the front, so I think I will call it good, unless there appear to be excessive wear on the outside of the tires., then I will be calling for help.  I think you are only about 30 miles from Lake City.

 1/4" toe is too much, especially if you are running radial tires. 1/8" would be better. I'm thinking you will scrub the tires off rather quickly where you are at.



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Mitch D.   River Falls, WI

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1966 Chevelle SS 396 M20

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jim larson


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Lost in the 60s wrote:

 

 1/4" toe is too much, especially if you are running radial tires. 1/8" would be better. I'm thinking you will scrub the tires off rather quickly where you are at.

Thanks Mitch.  I am running bias tires.   The manual says 1/8" - 1/4".  What is confusing to me, is that when they do the alignment at the shop I think they are actually using the wheel rim and not the tire ( thinking you could actually have the tire removed and just do the alignment with the rim).  In using John's method that uses the outside of the tire.  The ratio of the wheel to the tire is 14:27 ( with the tires I am using) or about 1:2, so if the toe in measure at the outside of the tire diameter is 1/4".  And  the toe in at the wheel/rim would be about 1/8"?  I also tried to measure this and it was about 1/8 at the rim.  Then what about if the rim has some run-in/run-out.  I see the manual says 1/8" is OK for a rim.

The service manual doesn't say wether to toe-in is at the rim or at the outside of the tie.  Maybe the computer at the alignment shop make an adjustment for the outside of the tire toe-in or maybe not.  This is all kind of confusing. I would think that  if you remove just shims from the rear pivot shaft attachment points there should be a mathematica formula that tells you how much the toe-in changes.



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Jim L

Lake City
jim larson


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Well I did a little math.  According to the print out on my last alignment the toe in angle on each side should be between 0.13 and 0.33 degrees, which converts to between approximately 1/32"and 1/16" on each side when using a 27" diameter tire.  This would be a total of between 1/16" and 1/8" total toe-in.

Well the print-out does not designate if this is the specification for a radial or a bias ply tire.  My best guess would be radial tire.

My old 66 service manual mentions 1/8" to 1/4", which I would assume would be the total toe-in for a bias ply tire for the standard tire, which would have a diameter of about 27".  So I think I should shoot for 1/8" using the old 66 service manual.  Which means I have to reduce the angle that I have now from  about 54 degrees to 27 degree.  That would mean increasing the length of each tie-rod about 0.030"

 



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Jim L

Lake City
Derek69SS


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I agree with Mitch, 1/4" is a bit too much toe.

Toe in ads stability, but of course causes tire wear...

I've never driven a car on bias tires, so I can't offer much help regarding them.

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Derek Kiefer - Mantorville, MN

69 Malibu Pro-Touring stroker LS1-383/T56 - 69 SS396-325/3spd project
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