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Old 01-19-2020, 01:40 PM   #13
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Join Date: May 2010
Posts: 3,918
Default Re: Distributor vacuum brake question

There a lot of disagreement as to the purpose of the vac brake . Most very untrue.

Heres what actually happens in slow motion : ( assuming vac brake is properly adjusted) You can see this action on a distributor machine .

Engine off = no vacuum , piston is spring loaded down to the spark ring . Leather is pushed against ring.
Engine cranking = very low vac piston is still forced inward , causing a slight timing retard. ( desired)
Engine starts, manifold vacuum is increased ( above spring tension) piston moves off the ring allowing some advance as engine is now running.
Then driving down the road hitting a large hill etc vac again drops allowing the leather to again drag making the spark retard slightly..

I actually have this somewhere in a old ford training manual, will look it up as time goes on.
If it Makes Spark, we do it !!!!
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