pull the rear cover to drain. There should be a fill plug on the rear cover, right about in the middle, a bit to the driver side. Fill to the bottom of that plug. Online manual says it holds 16 pints.

http://chevy.oldcarmanualproject.com/shop/1955truck2/55ctsm0457.htm


Mike
1955 Chevy 6400 ex-flatbed (no bed now!) sold September 2023
In the Stovebolt Gallery
1958 Chevy 6400 flatbed W/dump
In the Stovebolt Gallery
1959 Chevy Suburban Owned for almost 20 years, Daily Driver -- sold May 2016
In the Stovebolt Gallery

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