Topic: how much change to caster from adjusting huts on strut rod

[Murf]

This is possibly a question that no one can answer .  How many degrees of caster change can be affected by turning the strut rod nuts a given number of turns?  In other words how many turns of the nuts on the strut rod would be needed to affect the caster setting one degree.  Suppose we shortened the effective length of the strut rod 3 complete turns - how much positive caster would be added? Anyone care to comment or know to figure out the ratio of adjustment length ( in number of turns of adjusting nuts) to change of caster measured in degrees? Your comments are encouraged along with sharing any experience you may have gained that applied to this situation. 

[Bob Gaines]

This is possibly a question that no one can answer .  How many degrees of caster change can be affected by turning the strut rod nuts a given number of turns?  In other words how many turns of the nuts on the strut rod would be needed to affect the caster setting one degree.  Suppose we shortened the effective length of the strut rod 3 complete turns - how much positive caster would be added? Anyone care to comment or know to figure out the ratio of adjustment length ( in number of turns of adjusting nuts) to change of caster measured in degrees? Your comments are encouraged along with sharing any experience you may have gained that applied to this situation.

My opinion is that you are wasting your time with this exercise. Alignment machines are best . I have used less sophisticated alignment tools designed to help with alignment at the race track but it wouldn't make sense to spending the money for one unless you are doing many multiple alignments and even then it will not produced as precise of a alignment.  It is one thing when eyeballing alignment adjustment when you change out strut rods ,control arms etc. just to get it to alignment shop. It is another thing to make adjustments meant to be permanent for driving . Unsophisticated alignment adjustment possibly puts you ,your car and others at risk IMO. 

[67gtasanjose]

Alignment is in essence, setting up the Geometry of the components "combined". Moving one setting usually affects the other settings.  Vintage Mustang Caster adjustments, can be altered much easier than most other vehicles,  WITHOUT also affecting other critical settings such as camber but I doubt it wouldn't also change the toe setting somewhat. I wouldn't personally do a Caster angle change without also rechecking the camber and toe. (I do alignments at my day job).

I would ask what the reasoning is for your query.
I concur with Mr Gaines statements.

[jwc66k]

Is there any mention of caster adjustments in the shop manual?
Jim

[Murf]

I agree with you, Bob! Just one of those questions that run through ones mind during a sleepless period late at night. My question is based simply from being curious about the relationship of movement measured in degrees vs. a unit of measure such as a fraction of an inch or a decimal equivalent of that fraction, such as putting a certain sized shim  - say a caster wedge adjustment shim in a straight axle will cause a known amount of change in the caster  (as in an older car where wedges are used to set front wheel caster and the camber is fixed by the axle itself).  And yes, we are fortunate that on our old Mustangs beginning in 1967 the camber and caster are pretty much independent from each other.   I also agree with everyone that shortening or lengthening the strut rods effective length will have some effect on the toe setting.  Let's see - how many degrees toe in are present with the specification of 1/8 inch toe in?  Is there no end???  Some modern front end alignment machines will measure in either degrees or fractions of either an inch or in MMs but - that is another question.