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Each of the front brake drums has a spring around the circumference of the drum. The rear drums do not have springs. What is the function of the springs on the front?
Steve
Steve
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Re: 63 front brake drum
It's supposed to attenuate or elimiate brake squeak. It's never been clear to me if all drums were supposed to have springs. It's possible that the requirement came and went over time.
I had enough springs from both my original and OE replacement J-65 drums to put one on all four. Also, I think there are two types - one a "flat" wire and the other a conventional round section wire.
It's not a judging issue as far as I know as the springs cannot be seen during the judging process.
Duke -
Thanks. *NM*
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They don't appear in the AIM because the
drum and spring were delivered as an ASSEMBLY. You will find them in Gr 5.810 in old parts books and they were used front and rear.Comment
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Re: 63 front brake drum
Duke,
For what it's worth............every "big" car I've seen with the metallic brake option had the flat wire wound damper springs on the drums. ('61-'63) The drums themselves carry a different casting number and part number as well. I've seen both types of springs on standard brake shoe cars.
.....Just another tidbit for the memory bank.
Verne.Comment
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Re: 63 front brake drum
Base and J-65 drums are the same castings, but multiple casting numbers were used in production and later service drums. The J-65 drums' friction surface was machined to a finer finish so they carried different part numbers.
As far as I know both base and J-65 had (or should have had the springs), but their presence seems to be hit or miss. One or two were missing from my original drums. The replacement J-65 drums I bought from GM did not all have springs, but between the two sets I ended up with four springs and installed them on the car.
DukeComment
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Re: 63 front brake drum
Duke,
I suppose it's possible the "big" cars also used multiple casting numbers in production (those were the drums I was referring to). I had assumed the different castings I've seen on metallic equipped cars were actually a different iron content to hold up to the higher heat generated. That was just a guess. Yes, it's been my understanding the metallic brake drums were finished to a 2 micron surface flatness.
Mainly, I was offering a field observation of the flat wire wound springs showing up on those drums, which perhaps might indicate those springs were selected specifically for the metallic brake drums.
I don't have my books in front of me now to see if both kinds of springs were offered as service parts.
VerneComment
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Re: 63 front brake drum
The '63 Corvette Shop Manual calls for metallic brake drums to be honed to a 20 microinch finish, but I don't know the process to achieve this.
Anyone know?
My Corvette P&A catalogs from the mid to late seventies only call out one drum spring part number, 3694290, all '53 to '67 [?] except HD and Sp.H/Per., which I assume refers to the HD brake packages for C1 and C2. The quantity per car is "as required", which raises questions about their utilization over the years.
Since only one part number is listed, I am currently assuming that the flat wire and round wire springs are the same p/n and interchangeable.
I've been informally gathering data on drum brake systems (except HD), but have little to go on other than anecdotal evidence from drum brake Corvette owners. Since most of the details of drum brake systems cannot be seen during the judging process data such as drum casting numbers and drum springs are not observable. As a result there is little data to go on.
One theory I have is that the drum spring was developed as squeal fix, and may have only been a field service fix in the early days, but I have never heard of a TSB on the issue. It's also possible that the springs were added to production and then removed and added back again. The inconsistent appearance of these springs on both production and service drums leads me to believe that there were multiple changes in drum spring useage over the years that Corvettes had drum brakes.
DukeComment
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Re: 63 front brake drum
Could these springs also have been used for heat dissipation purposes for the drum?
Just curious.
Chuck 32205Comment
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Re: 63 front brake drum
No. The springs have no apparent effect on drum thermal capacity or heat transfer. As far as I know they were there only to attentuate/damp the high frequency drum vibration that we hear as brake squeak or squeal.
DukeComment
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The finish is done on a Brake lathe.
Just had a set done for a Corvair with metallic brakes. Much smoother that a regular turn job.Comment
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Re: The finish is done on a Brake lathe.
What kind of tool or stone is required to achieve the specified 20 microinch finish?
DukeComment
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Re: The finish is done on a Brake lathe.
I can't tell you that. I believe it to be different than the standard tool. I used to think they just slowed the feed speed but I don't believe that is correct. I do know there are different tools for different finishes.Comment
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Re: The finish is done on a Brake lathe.
Duke,
Just found the website for the Ammco brake drum lathe and they show a pic of the grinding attachment that was used for metallic brake applications. It's primary use was for drums that had hot spots that were too hard for the cutting tool to remove. The grinding attachment/motor is 4th in the list, #4850 and shows a pic of the attachment that mounted in place of the conventional cutting tool.
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Re: The finish is done on a Brake lathe.
Mike,
I too had a set of drums ground for metallic linings for my '62. The guy went to his book to look up the application and spec, then picked one bit and made a slow pass, then picked a different bit, set the speed even slower and made a final pass. The finish was like a mirror when done.
But like Duke, I can't envision how it was done in mass production to that finish. If you do the math, 20 microinches (20 millionths of an inch) is actually about 0.5um (microns). I can't imagine that technology existed back then. Now if they confused microinches with microns, 20 microns is a little less than .001" (25.4 microns = .001"). That would be more believable for the time.
Verne.Comment
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