[kmckmc]

Alignment Problem. How to adjust LEFT castor on 968



Is this a simple task?



How to adjust the CASTOR on a 968. Just by loosening those 2 bolts on castor block? Somehow this 968's LEFT side (front wheel center to rear wheel center's distance is shorter by 1cm, compared to the RIGHT side) has slight alignment issue. The mechanic could not get the castor value within the standard spec.



Please help.

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[flash]

It is done at the caster block, located at the rear of the control arm.

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[kmckmc]

I got a printout for today's alignment.



Front:

Castor: Before Alignment Left = 2.22degree; Right = 2.78degree

After Alignment Left = 2.10degree; Right = 2.65degree

(standard range: +2.5degree to +3.27degree)



Note: The change of value is entirely due to the adjustment of camber. This mechanic has no idea that castor can be adjusted earlier today, and he did not touch the castor block. And you can see that Left Castor value is out of range. The mechanic will attempt to adjust the castor block's screw in two days.



=======



Camber: Before Alignment Left = -2.28degree; Right = -2.12degree

After Alignment Left = -2.26degree; Right = -2.07degree

(standard range: -0.17degree to +0.17degree)



Note: This mechanic told me that old cars having more than -2.0 degree camber is not uncommon. Is this true for 968? Both sides' camber are way out of range.





What could I do now?

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[Cloud9...68]

Being off by a centimeter sounds like an awful lot. Is there that much castor adjustment available?



Edit: Post #3 came across while I was typing my response. Looking at the castor expressed in degrees, I can see how a small change is castor angle can translate to a large changed in the distances the OP describes in his first post. I'll shut up now, as this is a topic I'm not terribly knowledgeable about, but am looking forward to learning more about.

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[flash]

first off, i would seek out a different alignment guy. i would take it to either west end in gardena (the best), or lucent in west l.a. (second best)



that being said, that much camber is a LOT. there is no reason you should not be able to get below -1 degree, unless you have lowered the car too far (more than 1.25", which would put the roll center below ground anyway)



if you're up for a drive, you can pop over here and i can take a look at it, though i won't be able to fix it. i'm about an hour from you

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[Cloud9...68]

Question - My understanding is that the maximum caster is achieved when the tab pointing outward, parallel to the ground. Is this correct? Thanks.

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[kmckmc]

How about that RAYBESTOS, RAYBESTOS 616-1048 kit? Alignment Camber Bolt Kit.







Who has tried it with success? This particular set 616-1048 is said to be able to adjust Plus or Minus 2-1/2 Degree.

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[JWahlsten]

The kit above is for camber not caster. The caster is adjusted with the eccentric at the rear of the a-arms. Adjusting the eccentric changes the fore-aft vertical of the strut by altering the placement of the aft mount of the a-arm.



I don't have the car with me in the Middle East, but if I remember right putting the tab all the way outside is max and all the way inside is min caster. More caster = more stable, but heavier steering effort.



The adjustment is accomplished with part number 14 with 13 being the caster block. You can see how adjusting the eccentric changes the position of the ball joint and therefore changes the angle of the strut.

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[Cloud9...68]

Joel,



Thanks for the explanation. So, rotating the eccentric bolt #14 in the diagram effectively "tilts" the control arm by moving the rear pivot point at the caster block up or down. To generate positive caster, the eccntric would have to be turned such that the rear pivot point is low relative to the front pivot point, which is represented by the front A-arm bushing, which is item 12 in the diagram. I'm not remembering what the tab is connected to (it isn't shown in any diagrams I've found) - I'll have to look on my car. But I have heard from several sources that having the tab pointed outboard generates the maximum amount of positive caster.

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[flash]

i think it depends on which way the tab is installed, and which side of the car. i think they can be flipped, which would make it possible for either one to go the other way. i'll be under the car next week and take a look.

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[Eric_Oz_S2]

[quote name='Cloud9...68' timestamp='1373559093' post='145525']

Joel,



Thanks for the explanation. So, rotating the eccentric bolt #14 in the diagram effectively "tilts" the control arm by moving the rear pivot point at the caster block up or down. To generate positive caster, the eccntric would have to be turned such that the rear pivot point is low relative to the front pivot point, which is represented by the front A-arm bushing, which is item 12 in the diagram. I'm not remembering what the tab is connected to (it isn't shown in any diagrams I've found) - I'll have to look on my car. But I have heard from several sources that having the tab pointed outboard generates the maximum amount of positive caster.

[/quote]



Correct - tab out is max caster. This moves the control arm forward therefore increasing the "rake" of the strut (ie increases caster).

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[Cloud9...68]

[quote name='Eric_Oz_S2' timestamp='1373691493' post='145573']



Correct - tab out is max caster. This moves the control arm forward therefore increasing the "rake" of the strut (ie increases caster).

[/quote]

Ah - so the eccentric moves the control arm fore-and-aft, not up-and-down.

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[JWahlsten]

Correct. It changes inclination of the strut by moving it fore and aft.

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[Cloud9...68]

Thanks - I took a look at my right one (the left side of the car is next to the garage wall, making it a little harder to get to), and the tab is pointing outward, so I should be getting maximum caster, which is what I specified. I trust the shop I took it to, and I put the suspension back on myself, being very careful to keep the parts on their correct sides. I would have expected a but more self-centering feel than I'm getting, but then there are a lot of factors that could influence this, including camber, ride height, wheel width, etc., all of which have changed. And as I said, it's been so long since I drove the car that I won't swear that the degree of self-centering is any different that before all the mods.

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[flash]

a lot of guys will set a car up with toe out, so as to improve turn in. on some cars this works, and it works on this one for autocross, but it makes a mess of the car at speeds above what you see in autocross. set toe to zero for track setup



too much negative camber is also an issue. a lot of guys put in too much negative camber, thinking it will flatten out the inside tire, but in reality it puts the outside tire on its corner, which in turn increases roll and increases the load on the inside tire, which increases the heat on it, and ends up costing them net contact patch area, as well as grip under load. even for a full-on track car, i wouldn't set it up with more than 2 degrees negative camber at any corner

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[Eric_Oz_S2]

Ideal camber depends on a lot of things. Roll stiffness, tyre choice, etc. As an example, twin groove tyres need about -3.5 camber. R specs -2.5 to -3.0. This will also vary with roll stiffness.

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[kmckmc]

I think I got it!









The Left Castor value currently is 2.10degree. And the castor tab is "Tab In". It looks like "Tab In" to me.



I suppose if the Tab were to be moved to "Tab Out", the Left Castor value should increase.



==========

Castor: Before Alignment Left = 2.22degree; Right = 2.78degree

After Alignment Left = 2.10degree; Right = 2.65degree

(standard range: +2.5degree to +3.27degree)

==========

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[Cloud9...68]

You are correct - my tabs point completely outward, or parallel to the ground, so yes, you have room to increase your caster by turning the eccentric so that the tab points outward. How is the tab on the right side of your car?

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[JWahlsten]

Like Flash said, I am running zero toe and even caster side to side. I have -2.0 degrees of camber set in the front and could use more, but I think it will be a trade off. My car rolls too much even with the M030 bars and M030 struts. No my car isn't an M030 car, but I do have the suspension. I would like to get 300 lbs of rate in the front and matching in the rear. I figure a 120 lb spring in addition to the torsion bars will be about right.



I'm debating Motons like on Cloud's and my turbo, or Flash's set up. I think both would work very well, That being said it's pretty good the way it is now with track rubber on it, I am just losing some wear on the outside of the tires due to the body roll and a lack of negative camber.



For the OP you certainly have a LOT more caster available to you looking at where the tab is currently... Look up alignment settings in the search and you will find some good suggestions on the forum. I set my caster equal side to side, but for the street you may want to try the unequal settings Flash uses.

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[flash]

re: camber - yeah i see it all the time. people get bad information and don't do any testing, and set their camber too high in an attempt to save tires or reduce understeer. it's exactly the wrong approach. unfortunately racing rules often preclude the right approach.



re: caster - in california, most of our roads are crowned to drain to the right, so setting caster to correct that makes driving straight easier. in other areas, this may not be the case, or it may even be backwards.



as for "tab in or tab out" i still need to get under the car and see if that tab can be installed backwards. i think it can, which can make tab in max caster.

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