I was looking at RockAuto's upper control arm shafts. They list a problem solver "OFFSET" shaft for the front upper control arms to increase positive caster. Has anyone tried using these shafts? Any problems at the alignment shop adjusting the settings? Thanks.

 

I believe you are referring to +camber instead of +caster. I was looking at them recently - I am rebuilding my entire suspension system (front & back). I suspect it's a simple matter of the degree of thickness/taper contained w/in the center shaft as opposed to OE. I'm replacing most of my new front suspension components w/ Moog Problem Solver components. I like the quality of their components and others on this site have posted great comments regarding Moog components. Since my center shafts are in great condition, I elected not to order new center shafts (w/ or w/o an increase in +camber) and instead use the OE center shafts and I'll make any adjustments to increase +camber w/ shims, instead. With caster & toe set appropriately, it should be a simple matter of adding additional shims to the center shafts to increase +camber.

There is a plethora of really good threads related to increasing +camber. Good stuff.

https://classicoldsmobile.com/forums...archid=5013098

 

I've never figured out how the offset shafts increase caster. As Norm correctly points out, they do increase camber, but that's not something that's needed. To increase caster you need to angle the upper shaft relative to the frame bracket so that the upper ball joint is moved rearward. An equal offset at both ends of the shaft doesn't do this.

Typically the 1960s GM upper control arms don't provide enough adjustment to allow a meaningful change to caster angle, and even if you could get the shafts adjusted that way, they move inward so much that the inboard ends of the upper arms hit the exhaust manifolds or headers, especially if you have a BBO. Now, if someone would make an offset shaft with only one end offset, THAT would be fantastic for increasing caster.

 

While mostly used for frame issues, the amount of offset is the amount of camber and caster you can gain or lose depending on which way the shaft is facing. The offset is usually around 5/32 worth of shims or 1.25-1.5* positive camber and or caster.

 

Think this through. You change caster by creating a differential in the amount of shim between the front and rear shim locations. The only way to increase available caster is to offset ONE side. If you offset both sides (which is what these shafts do) they you still have the same amount of shim available, so there is no difference in the amount of differential you can create.

 

I have, your control arm mounting point is moved either in or out approximately 5/32 just with the shaft and no shims depending on whether its mounted facing out or in. That is the gain or loss with the offset shaft for camber and caster combined.
Picture for reference:

 

And how does that change CASTER?

 

I believe I understand what both of you (Joe & Eric) are stating and IMO, the one piece which is missing but which Joe eluded to is the degree of offset of the center shaft itself.

Several manufacturers sell center shafts to increase or decrease caster. I'm not 100% certain why they do, but they do. IMO, you can adjust caster (- or +) by simply adding or subtracting shims from either the front or the rear of the center shaft. Once you have the appropriate caster established for the vehicle in question, it then becomes rudimentary to increase or decrease camber by applying or removing the exact same thickness of shims from both the front and the rear of the center shaft after caster has been established - depending on whether you're going -camber or +camber. I suppose if a manufacturer sells a -caster center shaft and they mark the center shaft as "facing towards wheel", you could logically reverse the orientation of the center shaft to produce a +caster, instead. I mean, to me anyways, it sounds like no biggie. As Eric stated, I think if you had a center shaft frame mount which was bent or offset (by an accident or some other means), purchasing one of these types center shafts might be in order; or, for specific style cars where it's known they need more -caster or +caster these type center shafts might be appropriate. I'm still left with the notion that adjusting for caster (either - or +) simply indicates more or less thickness (distance) on either the front of the center shaft or the rear of the center shaft.

I don't embark on aligning vehicles everyday and it's not something which remains as a sticky in my cerebral cortex; but, every single time I need to review caster, camber & toe - I always resort back to this guy who created, IMO, the absolute best video(s) of removing and installing control arms anywhere; and, this gentleman's video on the demonstration of caster, camber and toe is the absolute best visualization I have seen anywhere. I will be performing this exact method in a couple weeks after reinstalling my entire front end. The only delta I would suggest over his method is to, instead, use a 8' or 10' straight 2"x4" or an 8' x 10' straight solid piece of pipe to adjust toe.

 

The reason why you want to increase caster over the stock setting is to improve road feel and handling. Increased caster improves stability, but at the expense of higher steering force. When manual steering was still an option, GM kept caster settings below 2 deg to keep steering force manageable. Modern cars that only have power steering run 5-7 deg of caster. This is one of the reasons why newer cars feel better to drive. The design of the A-body front suspension does not allow you to increase it to those settings, and the offset shaft with both sides offset in the same direction do NOTHING to help this.