64 & 65 rear wheel brake cylinders

This is a curiosity question - I was looking at the parts catalog for '65 brake rear wheel cylinders (I don't need any part number references)
The '64 & '65 earlies with 3:36 rears take a smaller brake wheel cylinder (7/8" vs 1-1/16"). - Any educated guess why is that? Maybe four cylinder motors?

Just wondering...

What parts catalog was that? I have not seen that one.
all the rear ones I have seen had a 13/16 piston which is hard to find  and more than three times the price of the more common 7/8 rear wheel cylinder. I found the 7/8 one to work better for the disc/drum set up.
They used a 1 +1/8 for the front cylinder.

Many newer parts Catalogs have been know to have errors.
M1D

,,,,here is what I think,,,,,thats where the Early 65/Late 65 change came in April, 1965,,,,,the ones they called the Early 65 were leftover 1964 parts,,,,,,which were the 1st Chevy vans,,,,,just testing the van market and to see how their vans sold and worked and if that 64 model needed improvements,,,,so in April 65 they changed the body and brake system,,,,,and,,,,,them there SportVans got invented so they needed more efficient braking to protect the passengers,,,,,

1967 Catalogue

The 3.36 rear axle is the one seem to me as standing out - like I said just a curiosity question why would the other ratio rears use a different size.





FWIW - my '65 12 bolt rear appears to have the original cylinders @ 1-1/16"
Both the front & the rear right side have the same casting number.
Both the front & the rear left side have the same casting number.


(Casting P/N)

The higher gear rear ends use the larger 2 1/2" brake shoes,,,

It did get some 2-1/2" shoes, test install was lousy - I suspect the prior owner had 2" kit; the spring pins that go through the backing plate seem a tiny bit too short,

Stranger than dirt?