C2 Leaf Spring Bolts

[Michael G.]

Re: C2 Leaf Spring Bolts

Ron, you may have seen such parts, but I think that they probably did not have the coatings you mention.

There was not a brown phos organic coating in use at GM throughout the whole C2-C3 era. If you are speaking of GM6174M or GM 6047M ( the common early phos organics), these finishes were dark black, usually with a wet oil dip. With age, they did not become brown, they developed red base-metal corrosion products.

Most likely, the "brown" parts are old phos & oil. That finish has minimum corrosion performance. After it sits for a while, it develops a brown hue from corrosion of the base metal. No 1960's era phos & oil part would survive this long, in any atmosphere, without some such slight discoloration from corrosion.

No 400-hour silver finish existed at GM until GM6111M, developed by Magni and first used at Olds, in production, about 1979. C2's (and most C3) could not have had such a finish.

The silver parts may be early 168 hour Dacromet, but I'm not sure if that was available before 1975.

[Ronald L.]

Re: C2 Leaf Spring Bolts

Michael, service parts were available well past 1982, early parts most likely phos & oil, later heavy zinc; the print will tell us what the spec and finish was, let's start there and end the speculation.

[Roger P.]

Re: C2 Leaf Spring Bolts

I installed the new 8" leaf spring bolts and adjusted the ride height. The black bolts look correct, and the ride is nice with the new spring cushions. I will give the cushions a few months to settle, and after checking the ride height again, I will cut off the bolt threads that extend below the Nylock nut to have it look aesthetically correct.

Roger (50141)

[John D.]

Re: C2 Leaf Spring Bolts

FWIW an old Restorer I have has an article on underbody finishes. For part number 3831585 it says "Natural Hot Forged Black-Gray to pickled and oiled". Is that consistent
with phosphate ?. Does anyone have a part number for a later service part ?

[Michael G.]

Re: C2 Leaf Spring Bolts

John, that description would tend to suggest that they were neither black oxide or phos & oil coated, but essentially plain oiled steel.

I agree with Ron, we probably need to find a print, so we can stop guessing

[Terry M.]

Re: C2 Leaf Spring Bolts

John, would you be kind enough to cite the issue and page. i want to grab that article for reference. Thanks.

[Joe L.]

Re: C2 Leaf Spring Bolts

FWIW an old Restorer I have has an article on underbody finishes. For part number 3831585 it says "Natural Hot Forged Black-Gray to pickled and oiled". Is that consistent
with phosphate ?. Does anyone have a part number for a later service part ?

John----


Yes, later SERVICE bolts were as follows:

GM #351592 (I THINK this bolt had the zinc finish)

GM #458982 (This bolt was definitely black phosphate)