63 front brake drum

[Michael H.]

Re: The finish is done on a Brake lathe.

The actual process was done using a silicone carbide grinding wheel instead of a tool bit, or at least that's the way it was supposed to be done. The two leave a totally different finish if viewed close up. The machining process with a tool bit actually chips away at the material and leaves a rather jagged surface but the carbide wheel isn't a chipping process. I suppose if the drum cutting process were done as you described, slow feed and minimum cut, it could come colser to the correct ground surface.

I'm still looking for one of the small instruction sheets that came packaged with new met brake linings because that gave us the speed/feed for this operation and if I find it. I'll post it.

I noticed the link I posted earlier doesn't work when clicked on. May have to manually enter it into the address bar.

[Duke W.]

Re: The finish is done on a Brake lathe.

There are some "standard" procedures/tools/stones for obtaining a specified finish that are probably listed in books and a good machinist or manufacturing engineer might know some off the top of their head.

I double checked the spec on page 5-16 of the '63 Shop Manual and it is 20 microinches and mentions honing, which implies a final pass with a fine stone. I recall that the "20 microinch" is the root mean square of the surface deviations from the average, or something like that, but I'd have to go research through some books to find the definition. In any event, 20 microinches is a very ffine finish.

I'm not sure why metallic linings required such a fine finish, but I imagine it was required for proper bedding in of the linings. With use, especially hard use, the drum wear surface will score.

Though I never had a set of metallic brake drums refinished, I'm impressed that the drum turning equipment has a procedure in the documentation, especially nowadays, when those systems are 40 years old.

It was my experience that when the metallic linings wore out drum were was near the point where refinishing would result in a drum at the diameter limit, so I just replaced them.

Duke

[Verne Frantz]

Re: 63 front brake drum

Duke,
I did some digging too, and wanted to share what I found. I used a '63 P&A book (Oct. 1, '62 printing). My books are the "passenger" books, which also include all the Corvette applications. That book shows the same partnumber (3694290) as the later book of yours, as the only drum spring available. It's application was:
38-62 PASS, Corvette (exc. H.D. Brake/Susp.)
63 PASS. Corvette (exc. Sp/Per.)
32 3/4" free length.

This agrees almost 100% with your book, other than the breakdown between HD brake and Susp. I'm not sure why they would breakout suspension as a separate exclusion, unless they were referring to RPO Z-04 (police and taxi chassis package), which included the metallic brakes, so it breaks down to those brakes anyway.
Soooo, if it seems clear those springs were not serviced for the metallic brake option, I have to wonder why I've seen the flat wire wound springs on original metallic drums. As you say, it could have been something added later, but I haven't seen a TSB to that effect either. The originals I've seen sure look like they've been there since day one.
I also thought to check a separate Heavy Duty parts section in the front of my book, but the springs are not listed there either. So, with little else to go on at this point, I'd be inclined to agree with your theory that their use was "inconsistant". If they weren't serviced separately, one might think they were already on the drum. Now all we have to do is find someone who has an NOS metallic brake drum in the box (ha ha).
By the way, in the '80s, I bought some of those springs through my local Chevy dealer using that partnumber. The ones I received were the round wire style.

Verne

[Michael H.]

Re: Lemme try this link again....

Hope this works this time. These people list the drum grinding attachment for a standard brake drum lathe.

http://www.ammcoats.com/accessories/7Grinding%2CDressing.htm

http://www.ammcoats.com/accessories/7Grinding%2CDressing.htm

[Duke W.]

Re: 63 front brake drum

The reference to "exc. HD brakes/susp. Sp Hi Performance DO NOT refer to the RPO J-65 metallic brake option (686 on C1s) The reference to HD/brakes/susp for C1s in my book is likely due to the fact that they were bundled as a package. The reference to Sp. Hi Perf. for C2s is likely a reference to the Z-06/J-56 HD drum package.

Since these HD brake packages had larger drums the spring would not fit, and I suppose they didn't bother with a spring since these packages were expressly designed for racing so brake noise would not be expected to be an issue.

The references in the parts books can sometimes be cryptic and require a degree of interpretation, but it sounds like all base and metallic brake option drums should have the springs, but none on the HD brake packages.

Nevertheless, their actual appearance on original and service drums seems to be hit or miss.

Duke

[Joe S.]

Re: They don't appear in the AIM because the

I've been told by at least one owner of an original 63 that they were only on the front drums when delivered. ???




Joe's 63 FI Convertible