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

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

    A lot of people on here ask about the knockouts and if they have them or not. I don't know if this has been covered here or not, but if it has I guess this will just disappear in a few days.
    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 knock-outs:


    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.
    Last edited by Shwa Kid; 01-13-2013, 11:25 PM. Reason: Misleading info clearified
    -Pat

    "I drive it like I built it.... poorly."

  • #2
    Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

    Good write up/pics. Some people have complained about how hard they are to remove. Mine were easy as pie. I used a small hammer and a flat head screwdriver to remove mine. :lol:
    -Grant

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    • #3
      Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

      Mine were that easy too.
      SSSHHHHHHH! I'm on a secret mission!

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      • #4
        Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

        Need to check mine. I've had two seperate shops say they could not get my truck aligned right and i "might need" camber bolts. Well I paid for new bolts but tires still wear bad on outside on both sides of truck. I'll check mine, could be the problem. Knock outs!

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        • #5
          Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

          Ya, I hate how vague the shop near me was. "You might need the knock-outs punched out." "Ok, how much $$?" "Uh...". Now that I see what all is needed, I'll do it myself, and drive the 1mi to the shop for an alignment right away.
          1999 Chevrolet K2500, Crew Cab, Short Box, 4L80E, 454 ci, 3.73 rear 14b FF 10.5"
          Working on my own custom tune with EFI Live.

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          • #6
            Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

            My shops didnt even refer to the knock outs! They said maybe the frame was bent.(could be, truck was wrecked before I bought it)

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            • #7
              Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

              Without going outside and looking at mine, I do remember that my 94 K1500 does not have a stamped/formed UCA. It is made from a solid round bar. Therefor I guess I don't have this issue. My front end guy has never mentioned anything about him not being able to align the castor/camber. Is this unique to K models?

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              • #8
                Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                It's not a part of the control arm, it's part of the mounting pocket for it on the frame. Your 4x4, and even 2WD models from 8600GVWR up, have tubular-appearing arms which are actually forged solid pieces. Doesn't make any difference in regards to the knockouts. The reason your guy hasn't mentioned them - yet - it's not required to remove these for an alignment, until the amount of adjustability exceeds a range where the knockouts need to be removed in order to attain further adjustment. It'll get there one day.

                Richard

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                • #9
                  Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                  Thanks. Good to know.

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                  • #10
                    Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                    looks like that control arm needs a good sandblast and some new paint. :lol:
                    O2 GMC RCSB 4.8L V8 AUTO 3.73's
                    rebuilt/beefed up 4L60E(at 43,000miles)

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                    • #11
                      Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                      Originally posted by NEUMANNZZ View Post
                      looks like that control arm needs a good sandblast and some new paint. :lol:
                      I removed most of the rust, not on top of the priority list right now.
                      -Pat

                      "I drive it like I built it.... poorly."

                      Comment


                      • #12
                        Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                        Originally posted by Shwa Kid View Post
                        I removed most of the rust, not on top of the priority list right now.
                        Slacker. :read:








                        I will admit that it took me as long to clean/prep/prime/paint my control arms as it did to do the rest of the front end rebuild. :lol:
                        -Grant

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                        • #13
                          Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                          LOL I was admiring your control arms in your build thread... I should have taken pics of the other side, they're painted :LOL: Part of my time crunch in getting my truck back together, that side didn't get painted, it looks bad but it's functional.
                          -Pat

                          "I drive it like I built it.... poorly."

                          Comment


                          • #14
                            Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                            Originally posted by Shwa Kid View Post
                            LOL I was admiring your control arms in your build thread... I should have taken pics of the other side, they're painted :LOL: Part of my time crunch in getting my truck back together, that side didn't get painted, it looks bad but it's functional.


                            I know where you're coming from. My frame got sprayed off with brake cleaner and coated with one heavy coat of semi-gloss black. :lol: It won't last long, but I can always re-do it later and it looks fine for now.
                            -Grant

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                            • #15
                              Re: OBS Camber/Caster Knock-outs - how to tell if you have them.

                              I just looked at my step side and it appears that mine have already been done (looks like cam bolts). Good thing, too. The alignment shop wanted double the price if they weren't done. I was gonna tell them they better just index the wheel, straighten out the toe, and leave everything else the hell alone :lol:

                              - 1993 C1500 - 5.3L/4L60E Swap - 3/5 Hotchkis - '96 Interior - Tuned by EPS -
                              - 2013 Camaro 1SS/1LE - Borla - 1" Eibach Drop - Roto Fab Intake - Katzkins Interior -

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