Clear coat yellowing????

[Brandon Metzger]

I am in the middle of a frame off on my '72BB. I am looking at protecting my half shafts, drive shafts, and posi rear end. I know this topic has been talked about a lot but I find the archivale searc a bit difficult to navigate, so please forgive me if this is to much of a repeat.

Since the the shafts and differential are left natural and I am sandblasting them I am and looking for a way to preserve them. My questions revolves around the clear coat. I believe, from reading many of the post, that there isn't a realy good way of preserving them which is why I am looking at the clear coat.

How long does it take for clear coat to yellow? Why does it yellow? Is there a way to prevent this or slow the process? Is there a clear coat that would not yellow?

Thank you much,
Brandon

[Terry F.]

Re: Clear coat yellowing????

It is really hard to restore original half shafts and drive shafts to give them the original look (gray smooth steel with glueish/brown/yellow discoloration at the end where the u-joint sections were electric welded on). They may have had a part number stenciled on them also. A lot of the drive shafts did from recollection of picture I have seen and some NOS I have looked at. I am not sure about the half shafts.

Sand blasting leaves a sandblasted look. I would sooner acid dip or glass bead, acid dip being my preference. You might want to protect the area that fits the u-joint. Places that do metal plating will do it for you. If the shafts are not pitted they will look good.

If you are trying to clean them up and protect them, you can sand blast them. You can clear coat and that will help keep them from rusting. Yellowing to me is not that big a deal since it isn't original anyways and it is better than rust. I have had success with coating things with spot clean in a can and then wiping it down before it dries. I do that a couple times and it leaves it a nice dull that you can see the original color of steel through and you can't tell it has anything on it. I have never noticed it to yellow (maybe I wiped it all off :0). You can also coat them with cosmoline. I like this stuff called LP3. Comes in a spray can and leaves a slightly sticky residue like cosmoline. Just the way I do things sometimes. I am sure others have some ways of there own also. I like to make things look natural and original as best as possible. I heard you can get your shafts restored now at Quanta. I recall reading that recently.

Take care, Terry

[Mark #28455]

weren't big block half shafts shot blasted?

If the big block shafts were originally shot blasted then they would no longer have the heat affected zone from the welding. In fact, you could just take them to a machine shop that blasts engine parts and "restore" them, couldn't you?

Mark

[Terry F.]

Re: weren't big block half shafts shot blasted?

Good question, I don't know. I only seem to recall discoloration from the heat near the welds. Joe might no. He probably has NOS stuff like that laying around. It is probably in the archives also.

Shot blasting would relieve some of the stress though.

Ask Dick, he would know I am sure.

Terry

[Dick W.]

Re: weren't big block half shafts shot blasted?

Original big block half shafts were shot peened (steel shot blasted) to relieve stress. Once the shaft corrodes it is hard to tell that it was done.

[Brandon Metzger]

Re: weren't big block half shafts shot blasted?

Ok guys, we stepped into an are that I have no knowledge of.

What is shot peened and what does it me to me on restoring these parts? What sort of places do this if I want to get them done again or do I pick a paint that is colored correctly and paint them.

All the best,
Brandon

[Terry F.]

Re: weren't big block half shafts shot blasted?

I believe you would be hard pressed to tell the differance after sand blasting and shot peening. The end result would be a blasting of the surface of the metal.

The judging manual does not mention the shot peening. It does say there was discoloration near the weld joints though. So, I wonder if this discoloration was seen only on small block cars and not big block, or was it seen on both?

Call you local machine shop and they would know who could perform the task. I believe it is a process of blasting the surface of the metal with hard steel pelets with compressed air. It relieves tension in the metal and makes it less likely to shatter or crack at the welds or in the casting, etc. I am sure there are others that can talk more about it.

Later, Terry

[Terry F.]

Re: weren't big block half shafts shot blasted?

So, would this process remove the appearance of the heat markings on the half shafts and drive shaft?

Thanks, Terry

[John H.]

Re: weren't big block half shafts shot blasted?

Shot-peening is done in a heavy steel cabinet, with the parts either hung or placed on steel grating, and after closing the very heavy door, the parts are impacted by millions of tiny steel balls driven at extremely high velocity by air pressure. This process relieves surface stresses and dramatically improves durability. The balls get smaller and smaller as the cabinet is operated, and eventually disappear through the cabinet's vacuum system, requiring regular addition of new charges of steel balls. No, you can't duplicate the process at home

[Terry F.]

Re: weren't big block half shafts shot blasted?

I didn't mean to imply that sandblasting is the same as shot peening. Just that if the half shaft had been stress reliefed in the past and has become all rusty, sandblasting or glass beading would probably give the item the same appearance as when it left the shot peening cabinet. Thanks for the explanation on shot peening. Terry

[Mark #28455]

now used to clean blocks too

My prior machine shop used an oven to incinerate the gunk on engine parts. They were then placed in a shot blast cabinet to remove the ash deposits and were finally placed in a tumbler to remove the shot. Was told it is a new politically correct way to clean parts without the toxic waste from a hot tank.

Go figure!
Mark