C2 Offset Control Arm Shaft

[George C.]

After removing the old bushings and shafts from the control arms of my 1965 Roadster, I noticed the upper shaft on the right side has an offset to it. The part number indicates that it may not be the original part. The part number is 6318-F. The left side is part number 5820483 GM22. After checking in the catalogs I found one supplier who advertises an offset upper control arm shaft. Can anyone tell me what this offset shaft does or why I might want one? Is there any chance this is original, I can't find any information in the AIM or the service manual. I found reconditioned shafts in the Paragon catalog and plan to buy one unless there is some value in the offset part.

Thanks as always,

George

#36809

[Terry M.]

Re: C2 Offset Control Arm Shaft *TL*

Offset upper control arm shafts are installed to allow sufficient space to install shims when the frame has been bent. Time, big blocks and corrosion will allow the upper suspension mounting points to settle inward. An offset control arm can move the upper control arm out enough to allow the car to be aligned without pulling the upper mounting points back out. Lowering springs will sometimes require offset shafts to compensate for the different ride height, and some racers will install them because they effectively lengthen the upper control arm - but in those cases both sides are usually changed at the same time. Worst case - a front end encounter of the striking kind can also be compensated with an offset arm.
These are definitely not installed at St. Louis.
You might consider having the frame measured before you invest a lot of time and effort in it. Frames can generally be pulled back into proper dimensions, but that work might damage a fresh finish.

[George C.]

Re: C2 Offset Control Arm Shaft

Terry,

Thank you for the response, although I guess that isn't what I was hoping to hear. I am heading for the garage to take some measurements and see what I can find. The existing shim setup is two one eighth shims at all four locations plus a one sixteenth shim at the rear right location. Once again a lesson on cars with no history.

George

#36809

[George C.]

Re: C2 Offset Control Arm Shaft

Terry,

I measured between the center hole in the front cross member and both front and rear control arm mounting bolts on each side. I also measured to the control arm mounting bracket itself. I can not find any difference that would seem to warrant an offset control arm shaft, all measurements are within 1/32nd of an inch.

The shaft was also mounted with the offset facing in. If I read your post correctly you mentioned this could have been done to effectively lengthen the control arm, but the way it was installed I think the result was a shorter control arm length.

I think I will replace it with an origainal when I find one, and figure that the part was what someone could find when repairing whatever damage there was.

If anyone has other suggestions of checks I could make please let me know.

Thanks again,

George

[Terry M.]

Re: C2 Offset Control Arm Shaft *TL*

George,
I mentioned positioning the offset arm to make the upper control arm effectively longer because that is the usual mode of installation to compensate for the normal sagging of the front crossmember and/or a reduced spring height. If you have installed new front springs you may have eliminated the original need. Unfortunately, you will know for sure only when you have the car aligned - after it is all together. Best of luck. I can't think of any other suggestions.