I was told by the mechanic that I needed to have the knockouts replaced so that they can give me a full front end alignment (62,000 mi). My cam is off by 1.7 degrees. I notice that the vehicle pulls to the right a bit. The car has had prior alignments and nobody has mention anything about these knockouts. The showed me a picture of what they might look like and tell me that they are riveted on. Well, I looked at my front wheels and see that it appears that there is a bolt and nut in the assembly in the front and back of the arm. I told him I'd bring it back tomorrow to have him take it out. But does it sound like someone has already replaced the knockouts? It's a different person doing the alignment now. Is there any diagram or picture on the net that I can download to see?
Knockouts aren't usally replaced, they are knocked out and left out. The front and rear set of forks/prongs that hold the upper A-Arm have slots in them, you losen the nut, then turn the bolt and the whole assembly will slide in/out in that slot(the bolt is really a small cam). BUT, and a big BUT, GM puts small plates in the slot to force the bolt to a particlar location, essentially making the slot a hole, with the thinking that the assembly process is so exact, that if you put the setting in the same place on each truck, they will be right. And they are right, and it makes things easier for them in assembly, as they don't have to align the truck at the factory, it's aligned properly simply through assembly. So, down the road when things get sloppy or bent slightly, those plates need to be "knocked-out" (hence people call them knockouts) allowing for proper alignment to be reached. Without taking out the knockouts, only toe can be adjusted. Caster and camber cannot be adjusted without removing at least one set of knockouts. Sometimes the knock-outs come out easy, and sometimes it's a bitch. It seems to be its a function of how/where the vehicles been driven, dirt roads, snow/salt seem to weld those things in there. Some shops rob people on this procedure, some don't, what do they want to do the knockouts? No shop, I know of, includes removing the knockouts in thier regular alignment price. Some will charge a flat fee, some will simply charge by the hour. What type of truck is it? I believe they stopped these knockouts on the newer GMT800's (99-current) and they were only used on the GMT400's ('88-'98 trucks). The 1500's seem to be worse than the 3500 or 2500HD.
Another tip on aligning these trucks or any vehicle, with the knock-outs out of course, first try to hit the targets for individual caster and camber then adjusting them so that you minimize the amount of deviation from the target cross-caster and cross-camber; in otherwords, if necessary, sacrifice the individual corner targets to attain the proper cross-alignment target.
jack the truck up by the frame. remove the nuts holding the upper A-arm, slide the bolt out (may need to relieve tension with a jack under the lower control arm). Now, you will see the hole/slot on the head side of the bolt you just removed. Take an air hammer and zap it out. May take up to 1 minute to do this and STAY ON THE TAB - do not hammer on the A-arm. If you don't have an air hammer, then get a large drift punch and large hammer and start pounding away. This should be done with the tire removed, as sometimes it's a real bear to get the control arm to line back up after it's apart. Easier with a 1/2 ton since the parts aren't as heavy.
Put everything back together and repeat for the other side. Simple procedure. Make sure everything is blocked up well, so nothing comes crashing down on you. We don't want to see anyone get hurt.
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