The 56 LOM DUAL DIAPHRAM vacuum advance is best for a LOM performance engine. It was designed expressly for this purpose.

It was HOLLEY's last attempt to save the system before going DUAL ADVANCE.

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So it not the best for high performance but it will work all my parts seem to function the two diaphragms seem ok and the carb has been rebuilt. It looks cool 

Excerpt from 1956 FORD SHOP MANUAL - LOAD-O-MATIC - Dual Diaphragm Advance  - 1956 4V Only

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That is all good information thank you 

55 Glass Top:
If you are preserving the original arrangement as a "survivor" restoration, the Load-O-Matic was the factory spark advance control and it has a matching carb. No such thing as "emission control" in that era. The two were a matched set. In order for the system to provide an increase in advance as rpm increases, there is a port in the carb that directly monitors the speed of air entering the engine. The faster the engine runs, the faster air must flow over the inlet venturi port - and vacuum in this "pitot tube" steadily increases. That vacuum causes the distributor vacuum pot to advance the spark proportionally to increases in rpm / air velocity in the carb throat. There were Ford systems that used this pot alone and didn't have the second - a very simple spark vs speed control. You disconnect the venturi vacuum line and set the engines initial timing with a light. Connect the line and the system goes "live" increasing above initial and then decreasing downward varying with inlet air speed changes. This amount is limited upward at some point - but you can see how it works.
The second pot piggybacked onto the distributor is reading manifold vacuum - when the engine starts and idles, this pot will quickly go to full travel. This adds a set amount of additional advance that sums onto the initial. So on a stock set-up with say 6º initial, this pot adds something like 10º right away (just a random guess). So now the started engine would be idling at 16º - and a smooth steady throttle increase in venturi air speed would then add an additional amount of spark timing up to its design limit. If the engine is accelerated, this fixed addition drops away with the instant decrease in manifold vacuum. So it responds to the potential of engine knock under load by essentially retarding the spark. The offset in advance helps control running temperature and gives better economy with a higher compression ratio engine.  

Very much simplified 




 
 Steve Metzger       Tucson, Arizona

One side of diaphram is for retard and one side is for advance.  The side closest to distributor goes to manifold vacuum 
and the other side goes to throttle vacuum. I think it makes the timing more responsive and the retard helps to reduce emission

The inner canister is SPARK CONTROL VALVE actuated. The outer canister is full manifold vacuum and provides a control over
excessive spark advance causing pre-ignition and/or full retard during de-acceleration (popping out exhaust).

If the canister is good, it is worth money to restoroers.

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Just looking on Ebay .Lots of  those Carcone 30-2808 57+  Distributors are back available. They were gone for awhile. Not available. Wonder if Carcone finally fixed the Problem of being 1/4" too short. anyone bought One recently?

  

That's the 56 loadomatic distributor, and it will only work with the correct 56 carb. Last year for the loadomatic on y blocks, then they went to more conventional units in 57. Unless it's a stock restoration, the 57 and later distributor will be what you need. Tons of info on the search function, but someone more knowledgeable will probably chime in.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

If i had to take a guess. One side of diaphram is for retard and one side is for advance.  The side closest to distributor goes to manifold vacuum 
and the other side goes to throttle vacuum. I think it makes the timing more responsive and the retard helps to reduce emissions. Just my guess. 

Located in Harford County Maryland 

Hello can someone tell me what is the purpose of two vacuum chambers on the distributor on my 292 since only one arm is attached to the plate. Thanks