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 hole, and the other was slotted. This allowed the factory workers to just slide the bolts in without doing a full alignment, they were close enough to spec. Provisions were made to allow for future camber/caster adjustment and these were known as "knock-outs". Basically all they were was an area that could be punched out around the circular UCA mounting hole to elongate it to a slot, allowing the UCA to be moved inward/outward. Seeing as the camber and caster weren't adjustable from the factory, a hardened bolt was used to hold the UCA rather than a cam bolt. To adjust the camber/caster or OBS trucks, you must remove the knock-outs and install the cam bolts (GM calls this "Camber and Caster adjustment kit No.15538596")

The easiest way to tell if your truck still has the knock-outs in tact is to check and see if you have hardened bolts holding your UCA's in or if they are cam bolts. If you have the cam bolts installed, that means the camber/caster has been adjusted on the truck and the knockouts have been removed. - This is not definitive to confirm they have been removed as the PO could have done a number of things, it should confirm only if they have NOT been removed.

The most definite way to check if your truck has the knock-outs still is to remove the UCA and visually check for them. To do this, jack up the vehicle and SUPPORT IT ON THE LOWER CONTROL ARM. This is very important as it keeps the tension on the spring but relieves the load from the upper control arm. You can now remove the upper control arm bolts and look at the holes to check if they are round or slotted. Only 2 of the 4 holes on each UCA will be round, these being the front holes of each mount. Here is what a knock-out that has not been removed should look like, in this picture you can also see the outline of the knockout, which will be removed. First picture is the knockouts on my 89, the second is G9M3C's on his 93, as you can see, they're slightly different.


To remove the knock-out, use your pick of removal tool and hammer it out. (I used a punch and chisel, but an air chisel would work well too.) *EDIT* I just found out that there is actually a tool made for doing this, it uses a threaded rod through the UCA mount that you can tighten against the knock-outs and eventually break them off. */EDIT*Here's what a completely removed knock-out should look like. You man need to file the edges a little to allow for proper cam-bolt actuation. Also note that sometimes the knock-outs don't come out all in one piece and are only partially removed. Make sure the whole knock-out is removed for full alignment potential.

Here are the removed knockouts:

Before you re-install your UCA, install the cam bolts and ensure full travel, just to be sure there aren't any hang-ups.

For reference, here is a picture of a UCA with just the bolts, the way it came from the factory and a picture of the cam bolts installed.


You shouldn't need to remove your fenders like I did, but I decided in favor of it for the space and because I had to gap them anyways.

If you have any questions, ask away.

*Edit Jan 13/13
Here's a quote of mwall from page two, added it here because this post is misleading/wrong with regards to using the existance of cam bolts to determine if the knock outs have been removed. (My info was specific to 88-90)

"1988-1990 GM CK trucks came from the factory with straight bolts and had spot welded washers over the adjustment slots. In 1991 GM updated the CK trucks with greaseable ball joints and they came from the factory with cam bolts installed but the adjustment slots were indented and the "knockouts" needed to be removed for adjustment. When dealer inspecting brand new 1991 and newer trucks I remember that many came from the factory with the driver side cams straight up and the passenger side cams straight down. Starting in 1996, GM didn't indent the adjustment slots as well as on the previous trucks so to make them easier to remove (in their opinion), they slotted the knockouts from the factory which made them bend and tear during removal with the GM special tool knockout remover making a die grinder neccesary many times."

Link to the original thread on fsc:
http://www.fullsizechevy.com/forum/...ter-knock-outs-how-tell-if-you-have-them.html


I have to check my truck in the morning since I need an alignment.

And again, this is gathered info from another forum. I'm not claiming it as mine, and give all of the credit to them!

...bringing a good thread forward into modern society...

My '88 K1500, and my '97 K2500 both have cam bolts, and both have NOT had the knock-outs removed. Same goes for the '94 K1500 I robbed front suspension parts from to repair my '88.

Far as I'm concerned, the presence of cam bolts indicates NOTHING.

Only way to tell is back a nut off and look. I have seen several with cam bolts and the knockouts still in place myself.

if you never alter or change the ride height from standard, you will most probably never need to install the aftermarket offset camber bolts in question. people that lower their C-1500's need them, for example. very common.

I have the knockout tool. It did a nice job with it. Whether it's worth it versus knocking them out with a punch, dunno, but I didn't have to clean up any rough edges.

It's obviously a one-time use thing (unless I get another truck), so if anyone wants it, shoot me a PM.

Mike

Any pics of what the tool looks like? I just checked my 97 GMC Sierra since I'm doing ball joints and tie rod ends. i'm not doing control arm bushings yet anyway but my knockouts are still present. It has cam bolts but the knockouts aren't "knocked out". I'm also installing some energy suspension spring spaces that will slightly lift the front end, so I dont know where my camber will end up. All the aligments this truck has had until now have just been toe adjustments I guess. I'll have to look at some of the old paperwork my dad gave me with the truck. I've got receipts and printouts for a couple aligments if I remember correctly.

I need that tool now im removing my so called knock outs on my 95 c1500 and they are a *****. I think gm forgot to perforate mine all the way. I made a tool but the threads ripped off the tool. About to start grinding.

So if I'm lifting only with a body lift and spindles but not changing the actual geometry of the control arms, do I still need to knock out the knockouts?

Aelfred-cyning said:

So if I'm lifting only with a body lift and spindles but not changing the actual geometry of the control arms, do I still need to knock out the knockouts?

Click to expand...

Two ways to know:

1. Take it to an alignment shop when the rest of the work is done, see if the alignment angles are appropriate. If camber or caster isn't, you need the knockouts removed.

2. Drive the truck while watching for tire wear. Tires wearing evenly, no steering problems, good-as-is. If the tires wear unevenly, or there's a steering/handling issue, you're back to #1.

Realistically, if you're doing a lift-and-steering knuckles; you might as well mark the position of the eccentrics, then remove the knockouts, do all the steering work, put the control arms back on with the eccentrics in the EXACT same position as before, and just expect to align the vehicle afterwards. Maybe you get lucky.