Crab distributor mechanical advance ?
 

Have "Ford Reconditioned" 21A crab distributor with a 11A mechanical advance unit. I assume the rebuilder just put together what they had on hand. Does the 21A & 11A have the same advance performance ? Any drawback to using that mechanism. Thank you Fordbarn.

Re: Crab distributor mechanical advance ?
 

The 11a is a better one, gives a few more degrees, and comes in a little earlier.

Re: Crab distributor mechanical advance ?
 

the 11A advance mechanism was used 1941-1948, assembled into the 1941 Helmet, the 1942 crab, and the 1946-8 squid. The basic parts were obviously assembled onto 2 different shafts for these jobs. The 11A parts also became the service replacements as the Model 68 and 78 distributors were rebuilt.
78 was capable of faster and slightly longer curve (as modified by brake adjustment) than earlier, and was part of evolutionary adaptation at Ford as the worst grades of gasoline disappeared from the market.
Advance had to be capable of coping with the worst gas out there and also with lazy drivers whol lugged their cars...the brake also helped dealers cope with these factors.