Classic Mustangs List Archive

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Mail From: (email redacted) (email redacted)

I've been rebuilding and detailing the rear in my '69 Mach 1 and wanted to
make sure the brakes that came off were the correct size. They were 10" x
2".

I've seen in catalogs that for 428 cars, they list 10" x 2.5". I tried to
determine the width based on Ford's literature. It says "Brakes: 10.0 in.
drums, lining area 173.3 sq. in." Is this the total area for 4 drum
brakes?
What is the correct width for my car?


Jeff Kennard... (email redacted)
'69 Mach I SCJ

This read-only message was archived from a public mail list.
Mail From: Eric F. Riggert (email redacted)

> I've been rebuilding and detailing the rear in my '69 Mach 1 and wanted to
> make sure the brakes that came off were the correct size. They were 10" x
> 2".

I don't know if those are 'correct' or not. But follow my calculation
below:

> I've seen in catalogs that for 428 cars, they list 10" x 2.5". I tried to
> determine the width based on Ford's literature. It says "Brakes: 10.0 in.
> drums, lining area 173.3 sq. in." Is this the total area for 4 drum
> brakes?

The total SWEPT area of the rear brakes could be calculated as the area
of the inside surface of the drum, which is:

2 x pi x radius x width, or 2 x 3.14 x 5 x 2 (the width of your drums).
= 62.83 sq. inches.

If you multiply by 2 (for both back brakes?), you end up with 125.66 sq.
inches, far short of the number you quote from the Ford lit.

Interestingly, if you do the same calculation with 2.75" width 10" dia.
drums, you get:

2xpixrxwx2 = 172.78 sq. inches. (about .3% error from your source).

Is it possible that you should be looking for either 2.75" wide rear
drums, or perhaps 3" wide rear drums with 2.75" wide brake shoes?

> What is the correct width for my car?

I can't say for sure, Jeff, but Jeff Speegle or John Dettori will almost
certainly know. I have kept myself entertained for a few moments with
this speculation though... Thanks!

Regards,
Eric Riggert, '66 Mustang GT, '88 LX 5.0, '94 Cobra, SCOASCC, SMA
(email redacted)