60mm brake variations

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bil brown
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60mm brake variations

#1 Post by bil brown » Sat Jun 26, 2021 3:36 pm

Here are 3 different 60mm front brakes......left 356 Carrera.......550........RSK. The later RS60 drum was a cut down version of the longer-finned RSK, having its fins machined down to clear the new 15" wheels.
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Joris Koning
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Re: 60mm brake variations

#2 Post by Joris Koning » Sat Jun 26, 2021 4:14 pm

Bill,

What kind of shoes have you encountered on these brakes? Looks like the early 60 front shoes were steel before moving to the aluminium shoes.
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Re: 60mm brake variations

#3 Post by bil brown » Sat Jun 26, 2021 4:34 pm

Joris......the shoes shown were not with any of these drums. Yes, I have had the early steel shoes, but my first encounter with the alloy shoes was with my old 62 Carrera Coupe with lots of GT stuff. I have a pic somewhere of some alloy shoes having 356A part numbers.....and some with 695 356B part numbers.
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Re: 60mm brake variations

#4 Post by bil brown » Sat Jun 26, 2021 4:45 pm

Here`s a pic of 3 alloy shoes, 2 with different part numbers. The third shoe with no markings seemed to be a different alloy.....did they ever make a magnesium shoe? I think some of the later 718 Spyders may have had mag backing plates?? There might be a service bulletin denoting the steel to alloy shoe changeover.......I`m guessin 58/59ish.....since there is a 356A part number and a B number.
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Harlan Halsey
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Re: 60mm brake variations

#5 Post by Harlan Halsey » Sun Jun 27, 2021 5:52 am

I only have the steel shoes: Single central web with brake spring pins (Which keep the brake springs close to the backing plate) Special low coefficient of friction linings from Carbotech, but not the standard Carbotech material. No Idea what was original on my "59 nor do I care.

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Re: 60mm brake variations

#6 Post by Martin Benade » Sun Jun 27, 2021 9:16 am

By your description those linings work poorly? Wouldn’t it be worthwhile to put something good in?
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Re: 60mm brake variations

#7 Post by Harlan Halsey » Mon Jun 28, 2021 4:08 am

I have no experience with the original lining material. Carbotech carbon fiber was the hot setup in the 1970s and it worked as advertised, but it wore, and wore the steel drum lining badly, about .010" per race weekend. I measured shoe and drum wear after every race for a number of years. As you probably know, drum brake function is complicated, depending as it does on friction and servo action. Servo action depends on the angle and position of the thrust surface on the end of the shoe and the stop. (Of course everyone who relines 356 brake shoes is careful to retain the original shape of that end.) There are a number of SAE papers on the subject from the American car drum brake era, but nothing directly applicable to the 356 drum brakes. So Chuck Forge modeled the 356 brakes in a Lotus 123 spread sheet. The results were eye opening. Of course we knew that the shape of the ends of the brake shoe were important, but there's also an optimal coefficient of friction. And the Carbotech material, while it worked well for disk brake pads, had too high a coefficient for drum brakes. So Forge got Carbotech to find a source of lower coefficient material, and we had them line our drum brake shoes with that. The new material worked well, didn't fade any worse than the carbon fiber stuff, and didn't wear the steel linings. Besides my Carrera, the Von Neumann car had those linings in it.

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Re: 60mm brake variations

#8 Post by Justin Rio » Mon Jun 28, 2021 4:46 pm

Hey Bill,

They did make a Magnesium shoe to go along with these later magnesium RS60/61 drums
540 5566.jpg
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Has the shaved fins as you described. This drum is shot; not quite as resilient as Aluminum.
540 4898.jpg
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Magnesium shoes. I'm sure the part number is unique to these.

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Re: 60mm brake variations

#9 Post by bil brown » Mon Jun 28, 2021 4:50 pm

Justin........those shoes you show have the same 695 part number as one of the shoes I show earlier
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Re: 60mm brake variations

#10 Post by Joris Koning » Tue Jun 29, 2021 12:55 am

There were also magnesium backing plates. Not sure if these were only for the F1 and F2 cars or also used on late spyders.
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Re: 60mm brake variations

#11 Post by Harlan Halsey » Tue Jun 29, 2021 1:44 am

Joris,
Those mag backing plates don't seem to have the B type rain grooves although the period would seem to be right. How much do they weigh? (Unless they were stored submerged under oil, mag parts from the 60s are not usable today.)

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Re: 60mm brake variations

#12 Post by Mike Smith » Tue Jun 29, 2021 4:02 am

Early Steel Shoes with Original Asbestos (?) Linings

Note the Adjustment Instructions
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Re: 60mm brake variations

#13 Post by Joris Koning » Tue Jun 29, 2021 4:06 am

If anybody has some of the shoes shown by Mike I would be interested for my '56
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Re: 60mm brake variations

#14 Post by Harlan Halsey » Mon Jul 19, 2021 8:41 am

Joris,
It occurred to me that if a set is not forthcoming, it wouldn't be too hard to fabricate a set. They are just sheet steel with a turned spring attachment pin.

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Re: 60mm brake variations

#15 Post by Dick Roth » Thu Sep 02, 2021 1:38 pm

Those magnesium backing plates were a work of art. Carl Thompson at Vasek's place had a brand new set that I contemplated putting on my RSK, but ended up sticking with what I had. Boy were they beauties...
The other thing that occasionally gets lost in these technical discussions about the parts themselves it's just how incredibly effective those brakes on the RSK were. You could absolutely stand on them with maximum pressure time after time, and they never degraded or lost their ability to perform. One hears about brake fade and other problems associated with drum brakes of the 50s on race cars, and how the superiority of discs changed everything (true!), but it was not a problem on properly prepared brakes of a Porsche Spyder.

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