Joe Lucia C2 Control Arm Shaft Part #

**Joe L.** · May 19, 2003, 10:57 PM

Re: Joe Lucia C2 Control Arm Shaft Part #

George-----

The GM #3820483 upper control arm shaft was used in PRODUCTION for 1963 Corvettes and most, if not all, 1964 Corvettes. After 1964, it may have been used in PRODUCTION intermittently through about 1967 or 68. I believe that this is the shaft that has the square-cornered bosses for the frame retaining bolts.

In March, 1964, the 3820483 was discontinued from SERVICE and replaced by the GM #3845244. Actually, the latter part number is not a part number for the shaft, but rather the part number for a unit which includes bushings, retainers, and bolts. I do not know what the part number for the shaft, alone, was/is. However, this shaft is usually the one that has the rounded bosses for the frame retaining bolts. There is no part number stamped on these shafts that I have ever observed. This shaft was used on mid-year Corvettes not equipped with the square-cornered boss shafts. It was used on all Corvettes after about 1969. It is possible to have a Corvette which was originally equipped with both type shafts, one type on either side. The shafts were part of the a-arm assemblies as-delivered to St. Louis. Since I believe that both types were used intermittently and randomly in PRODUCTION for several years, it's very possible that both types ended up on some cars. The factory didn't necessarily install upper a-arms as "matched sets"; they used what was on the parts racks.

If you have an upper shaft with an off-set, that shaft was NOT installed at St. Louis. No such shafts were ever installed in PRODUCTION. Such shafts, although NEVER available from GM, were, however, installed in SERVICE in some cases to compensate for frame "spread" and/or collision damage in order to make front end alignment to specifications possible.

**George C.** · May 19, 2003, 11:14 PM

Re: Joe Lucia C2 Control Arm Shaft Part #

Joe,

Thanks for the quick response. You are correct about the square corners, in fact both shafts have that feature. Back to the garage, I found the "offset shaft" has the following part number barely visible, "1 6318 F", there may be a 4 in front of the F but this number is barely raised, not at all like the other part. I am not sure I inderstand the frame spread you mention, but I have measured everwhere I can and both sides seam equal. The alignment shims however were almost identical. Two 1/8 shims at all four locations, and one 1/16 at the rear of the side with the good shaft. I guess I will just opt for a used shaft with no part number and get back on the assembly route.

Thanks again,

George

**Joe L.** · May 20, 2003, 12:22 AM

Re: Joe Lucia C2 Control Arm Shaft Part #

George-----

The number which you described is not a GM number. However, it does fit with the fact that if it's offset, then it's not a GM piece. If you switch to a non-offset piece, you may find that you will have problems getting the car aligned properly. If the piece is, indeed, offset, then I'm pretty sure that's why it was installed. They'd really be no other reason to do it. The offset shafts are a specialty item which would be unlikely found just lying around.

"Frame spread" is a condition which Corvettes and other Chevrolets suffer from after long service. In this condition, the frame rails distort or "spread" after the continual "pounding" that the frame must endure. This is especially true of cars that are driven over rough roads at high speeds. When this condition gets to a certain point of distortion, all of the camber/caster adjustment which can be achieved by the shims gets "used up" and the car can no longer be aligned properly. In some cases, the frame is corrected by being "rolled" on a frame machine to "un-distort" it. Other times, offset shafts are installed to restore further adjustability in that way.

**Joe L.** · May 20, 2003, 05:35 PM

Addendum

George----

One other thing that I forgot to mention. I believe that the "square boss" upper control arm shafts may be cast iron (if so, likely of the nodular, ductile, or malleable varieties). Their configuration and marking implies this, but I'm going to need to carefully examine one at my next swap meet foray.

The "round boss" upper control arm shafts are forged steel.

**George C.** · May 21, 2003, 09:28 PM

Re: Addendum

Joe,

Thanks for the explanation of frame spread. Given your explanation I would think that this spread would cause the upper control arms to be moved inward towards the center of the car. This in turn, if I am thinking correctly would mean that an offset in the shaft would be used to push the upper control arm towards the outside of the car allowing for more camber adjustment.
The offset shaft in my car was installed so that the offset was toward the center of the car. I have no idea what this means but am open to suggestion. You are correct the shafts are cast not forged, my mistake. One more question, does the shaft turn on the metal sleeve in the bushings or just move with the flex in the bushing? I am trying to decide if I shoud paint the shafts where the bushings ride.

Thanks again,

George

**Joe L.** · May 21, 2003, 09:55 PM

Re: Addendum

George-----

The shaft doesn't turn, at all. However, the bushing rotates about the shaft by a small amount limited to that which the elastomer in the bushing "flexes". I would not paint the end of the shaft that goes through the bushing, although I don't really think that it would do any harm. I apply a very light coating of silicone grease to these ends.

**George C.** · May 25, 2003, 11:44 PM

Re: Addendum

Joe,

Thanks for the response, you are right the shaft is bolted down and doesn't move. I wasn't sure if the steel sleeve would rotate on the shaft, or if all movement is limited to the flex in the bushings.

Thanks again,

George

Joe Lucia C2 Control Arm Shaft Part #

Joe Lucia C2 Control Arm Shaft Part #

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