Thanks Tim,
I was unaware of a band type brake on an SM420.
Of the three I have and the countless others I've seen all have the double shoe.
I (incorrectly) assumed they were all the same.

What I've read about and never seen is supposedly some AD school buses used a "Tru-Stop" brake on the transmission, which I think is a disc brake, so far I haven't spotted one, but check under every AD bus I see.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-