66 Control arm bolt finishes

[Dave K.]

I’m trying to determine the straight scoop on my 66 Corvette upper and lower control arm bolt finishes. First off, the judging manual (JM) says nothing about the upper control arm bolts and nuts, that clamp the shims in place. I believe that these bolts are 7/16 in., Grade 8. Secondly, the JM specifies that the lower control arm front bolts, fastening the CA to the frame and screwed into the nut blocks, are to be cad or zinc. I believe that these are 3/8 in., Grade 8 bolts. The rear bolt fastening the lower CA to the frame is to be black phosphate with a cad or zinc nut. This bolt is 9/16 in. The bolts and large flat washers used to tighten the CA bushings are not specified in the JM for the upper CA but I believe that these and the washers should be black phosphate. They are Grade 8 bolts. The JM specifies that the bushing bolts/washers are to be painted gloss black for the lower CA (same as the CA)which I have a hard time believing. I’m assuming that these should be the same as the upper CA bushing bolts/washers?

Regards,
Dave Kitch

[Gene M.]

Re: 66 Control arm bolt finishes

Dave, All the bolts (fine thread) are black phosphate as you stated. The hardware on the ends of the controll arm shafts was in place when the A-arm were painted less the ball joints. The likely hood of them not receiving any paint is remote. The bolts were tightened down after the car weight was lowered down to avoid twisting the bushing. Thus wrench impact marks are feasible. The studs on the frame securing the shims and pivot shafts are phosphate black again 7/16 fine thread till '66. The nuts were plain/grey phosphate or unfinished grade 8. The lower bolts are 7/16 fine threading into the twin nut (no finish) plate and are also black phosphate. You stated correctly the rear lower controll arm bolt as phosphate with plated nut. The washer on that bolt is a special serated type also black.

[Dave K.]

Re: 66 Control arm bolt finishes

Gene,

Thanks for the reply. Since there was some controversy regarding these finishes among some of my judging friends, I decided to look in Nolan Adam’s book , Vol. II, for pictures that might answer some questions. I found several pictures of mid year assembled car chassis bottom views where you can see some bolt finishes. I found another picture of a rolling chassis (front view) as it came down the assembly line at St. Louis. For the most part these pictures corroborate your opinion, except for the lower control arm front mounting bolts that thread into the twin nut plates. These bolts appear to be plated as stated in the judging manual (they could also be natural). Several of my friends are still of the opinion that the hardware on the ends of the control arm shafts were black or gray phosphate. I can’t tell from the Adam’s book photos whether they are black phosphate or black paint (control arm paint).

Regards,
Dave Kitch

[Gene M.]

Re: 66 Control arm bolt finishes

In almost all cases the grade 5 hardware is not plated. The industry standards were to use phosphate or black oxide to provide a limited rust preventive. Short lived as it was. Other situations had oil or no finish at all. Electro plating was generally not used on high graded hardware because it can cause the piece to become brittle if not heated afterwards. If I was to guess hardware appearing plated in the chassis photos (graded hardware)was oiled or bare steel. When taking your car apart check the threads that are not exposed and many times the answer as to finish can be found.