31 Spoke Drum Question

Fredb_

Fredb_

Well-known member
Can anyone tell me what the usable specification would be on these 11" 1931 Model A spoke drums would be? I was told .040 and I was wondering if this is correct. Thanks.
 

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they are called rocky mountain drums . the slots are for cooling . cast iron also .
 
Thanks, yes I figured that information out with past research. I also found on this forum that .130" is the minimum thickness for cast drums. Any other information would be helpful. I have three of them with average wall thickness of .160" so I'm hoping they are good for use.
 
The Rocky Mountain brake reference is common, but incorrect. Spokes are not exposed, so extra cooling may also be a misconception. However the original inside diameter was 11", I would start being concerned when the inside diameter is much greater than 11.060 ID.
 
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I agree with darrylkmc on all points. Historians here may dispute this, but I believe this is Ford's first attempt at integrating the hub and drum into a single structural component leading to the wide five drums in '36. It's an elegant design solution but I doubt it has any substantial effect on cooling. It does have a significant advantage in reducing unsprung weight, however.
 
First off brake drums are measured by inside diameter, all of them..... the Model A brakes are an 11" diameter brake so the maximum usable diameter would be 11.060". It is not uncommon to see vintage cars use oversize drums (EG; 11.090") Secondly I do not believe that any Model A had these drum assemblies installed from the factory. These were manufactured for 1932, 1933 and possibly 1934 fords. As a side note I have a drum that looks identical but is for 12" brakes.
 
loowiloowi said:
First off brake drums are measured by inside diameter, all of them..... the Model A brakes are an 11" diameter brake so the maximum usable diameter would be 11.060". It is not uncommon to see vintage cars use oversize drums (EG; 11.090") Secondly I do not believe that any Model A had these drum assemblies installed from the factory. These were manufactured for 1932, 1933 and possibly 1934 fords. As a side note I have a drum that looks identical but is for 12" brakes.
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The 5 Spoke cast iron Front and cast iron smooth style Rear drums were introduced for production September 1931.
 
loowiloowi said:
First off brake drums are measured by inside diameter, all of them..... the Model A brakes are an 11" diameter brake so the maximum usable diameter would be 11.060". It is not uncommon to see vintage cars use oversize drums (EG; 11.090") Secondly I do not believe that any Model A had these drum assemblies installed from the factory. These were manufactured for 1932, 1933 and possibly 1934 fords. As a side note I have a drum that looks identical but is for 12" brakes.
Click to expand...

My late 31 Tudor, inserted firewall came new with the spoke front drums. The rears were standard looking cast iron. I put the front spoke drums on my 29 roadster in March 2013. Have fun modelAtony tony white Lafayette, LA
 
The 11 "Spoked" cast iron drums were installed on all Model A Fords beginning Sept. 1931. At the same time, cast iron (non spoked) drums were introduced on the rear of those cars. Ford used the same design, only in a 12: diameter on ALL 1932-1934 Fords.

The steel drums, made prior to Sept 1931, were .140 thick . The cast drums are much thicker.

These cast drums, while a HUGE improvement over the steel drums, were not a great casting, and wear out pretty quick. The rear original late 1931 cast drums crack very easy.Rarely due you find them in great condition. When you turn them they cut really easy, unlike the new cast drums, which are better casting
 
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