Correct finish on C2 rear spring center bolt

[Joe R.]

I just finished rebuilding my 67 9-leaf spring with the Quanta gray paint and the GM liners. My question is, what is the correct finish for the single bolt and nut that hold the leaves together?

Sorry to bother you guys with such a small detail, but I'd like to get the entire assembly correct.

[mike mccagh]

Re: Correct finish on C2 rear spring center bolt

natural "black phosphate" appearing finish. available at most spring shops. mike

[Joe L.]

Re: Correct finish on C2 rear spring center bolt

Joe----

As Mike indicated, the bolt was black phosphate. However, no part of the bolt is visible after installation. The bolt was crudely "chopped off" below the nut after the spring was assembled. The "chopped off", bottom portion of the bolt was then "natural" steel and rusted, of course.

Also, most replacement center bolts, including those available from GM, have a head which is too long. You will need to grind it down so that the thickness of the head is the same as the old bolt. It's very important that this bolt head fit completely into the countersink in the differential cover.

[Joe R.]

Re: Correct finish on C2 rear spring center bolt

Hi Joe:

So the bolt is black phosphate, but what about the nut? Is it natural? I agree that the bolt is almost completely obscured, but the nut is in plain view.

By the way, I learned about the too-tall head on the bolt from earlier postings here. On my car the previous owner had installed a spring with such a bolt, and I think it contributed to bending the spring plate when the spring was installed. I ground off the bolt that I used in my rebuilt spring.

[Joe L.]

Re: Correct finish on C2 rear spring center bolt

Joe-----

I'm not sure of finish on the nut. I think that it was plain steel but I'm not 100% sure.

[Howard W.]

Re: Correct finish on C2 rear spring center bolt

If you want to restore the old bolt to a close to Black Phosphate finish. heat the bolt with a tourch then dip it in used motor oil. the older the better make sure you use a container that won't melt the oil will get very hot.

[Joe R.]

Re: Correct finish on C2 rear spring center bolt

Thanks Joe. In the absence of any other feedback, I decided to use a natural finish on the nut.

[Franz E.]

Re: Correct finish on C2 rear spring center bolt

Chevrolet engineering released part number 3850839 for the standard nine leaf spring and specified center bolt part number 3731381 located on chart drawing 3739568 along with corresponding nut part number 103025. The retaining nut is a "Standard GM Fastener" and is located in GM's "Standards Book" section "E" page E-1.121 and is noted as follows: 5/16-24 plain finish.

[Joe R.]

Re: Correct finish on C2 rear spring center bolt

Thanks Franz. I guess that settles it!