power brake unit in trans

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If you haven’t done it already, order Pierce-Arrow Society Service Bulletin 1974-1 which is a reprint of an eight page document titled “The Stewart-Warner Braking System”. Also, Service Bulletin 1983-6 contains a reprint of a Radco Automotive Review article from October 1933 titled “Service and Adjustment of Stewart-Warner Power Brakes on Pierce-Arrow Cars”. Both of these have a wealth of good information. Now to your question about lubricant. Use a straight mineral gear oil. At the time SAE 90 was recommended for winter and SAE 160 for summer. It is very important not to use a hypoid gear oil as this has a bad effect on the linings in the power brake unit. Quoting from the Radco document, ” The power unit is in the same compartment with the free wheeling element and is suitably lubricated by oil from the transmission”. By filling the transmission the gear oil will also fill the power brake and free wheeling.

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