Help me understand ...

[Mean_Green]

Tire store was able to get the alignment in enough to meet specs, but they told me something I didn't understand.

Something about a knockout that had never been removed to be able to adjust the caster and camber. My non-mechanical mind doesn't understand why that would be necessary in the field and not taken care of during production and assembly.

 

[wjburken]

I believe this thread from GMT400 discusses what you are talking about.

OBS Upper Control Arm Alignment Knockouts-Whats The Story?

After you knock them out...Are new, different shaped washers and/or bolts needed, to allow proper front-end alignment? Or can the original nuts, bolts & washers be used? Thanks

www.gmt400.com

 

[Mean_Green]

I believe this thread from GMT400 discusses what you are talking about.

OBS Upper Control Arm Alignment Knockouts-Whats The Story?

After you knock them out...Are new, different shaped washers and/or bolts needed, to allow proper front-end alignment? Or can the original nuts, bolts & washers be used? Thanks

www.gmt400.com

Well, no, that doesn't really help at all:

"Sorry i don't have any pics"

 

[Mean_Green]

This is at least a better explanation, but I still can't see any pictures.

OBS Camber/Caster Knock-outs - how to tell if you have them.

This info is borrowed from fullsizechevy.com. I searched for an info here, but came up empty. What the knockouts are: When the OBS trucks left the line, you couldn't adjust the camber or caster because the upper control arm mounts were fixed. On side of each mounting point had a circular...

www.gmt400.com

 

[wjburken]

This is at least a better explanation, but I still can't see any pictures.

OBS Camber/Caster Knock-outs - how to tell if you have them.

This info is borrowed from fullsizechevy.com. I searched for an info here, but came up empty. What the knockouts are: When the OBS trucks left the line, you couldn't adjust the camber or caster because the upper control arm mounts were fixed. On side of each mounting point had a circular...

www.gmt400.com

A quick search for GM OBS Caster Knockout yielded this picture. Does this help?

 

[OR VietVet]

There are knockout slots on upper control arm adjustment cams, that allow an alignment shop to make finite camber and caster adjustments. The "knockouts" are there for adjustments that are made after the truck gets mileage on it and the bushings settle and therefore adjustments/settings change. When the truck goes down the assembly line everything is centered and assembled faster and easier with it all together. When it is time for an alignment and adjustments are out of spec, then the camber/caster adjustments cannot be made unless the knockouts are removed and cam kits installed.

In @wjburken pic above, once the knockout is removed and the egg shape cam kits are installed, the cams rotate and rub against the tabs and allow the upper control arm to move in and out and hold in place when tightened.

The alignment shops will charge extra to remove the upper control arm bolts, knock the tabs out and then install the egg shaped cams and then they stay there for the future alignment adjustments.

The age of your truck indicates that alignment techs that aligned before were lazy and did not want to do the extra work. They "set the toe and let it go". The current alignment tech is doing what should have been done a long time ago.