Pre 1941 Distributor Mod. for Improved Advance?

[ibshane]

37 Ford 78 V8 85

I was looking around online and saw a distributor rebuiler that offers a modification that improves the timing adavance on pre-1941 Flathead V8 Distributors.
So..., does this mod convert my 1937 vacuum advance, to a post 1940 mechanical advance?

http://www.classicparts4cars.com/193...dification.htm

[JSeery]

What is a 1937 vacuum advance, never heard of that? The early Ford distributors were all mechanical advance with a vacuum brake. From Bubba's Ignition site:

The most misunderstood part of a 1942-1948 Crab style distributor is the "vacuum brake" called by many a vacuum advance , with that not really being a correct name.
The vacuum piston is hooked to manifold vacuum and has a piston with leather wear washer glued to the end. This leather washer drags on a advance ring inside the distributor causing the timing to slightly retard when vacuum is lower than spring setting.
This should always be used even when the vacuum is not hooked up as it steadies the spark advance.

[Seth Swoboda]

Perhaps you are referring to the use of 11A weights in a pre 1940 distributor?

[ibshane]

Sorry guys..., I'm brand new to these rigs.
I just figured a vacuum line going to the distributor would be a vacuum advance??
That's why I ask the smart guys!

JSerry: Just so I understand correctly. If I did the advance mod.
Nothing changes in regards to the vacuum brake?

Thanks for your help!

[Seth Swoboda]

The modification that place is referring to is the use of the 1941 11A distributor weights.

[JSeery]

Sponsored Links (Register now to hide all advertisements)

I wouldn't think so, they are just changing out some of the later (crab distributor) for the earlier parts. They both use the same vacuum brake setup.

[40 Deluxe]

We were all "brand new to these rigs" at one time! Just be careful where you get your advice!! Get some manuals from that time period, either Ford repair manuals, or something like MOTOR manuals. Most are available as reprints and explain how distributors, carburetors, generators, etc. operate and how to repair. DO NOT listen to your buddies or some "old timer"! So often they don't know what they are talking about, to be blunt!
There are a lot of 'urban myths' in the old Ford world!

[JSeery]

Might take a look at Bubb's Ignitions site, lot of good information there. He will most likely post on this thread in the near future.

[ibshane]

I appreciate the advice.

Thanks guys!

[rotorwrench]

The 11A advance assembly was the replacement part for all the old ones after it came out in 1941. It gives a bit more advance than the earlier unit and is a direct replacement.

The vacuum brake system applies some braking force to the rotating advance disc assembly when the manifold pressure rises (vacuum decreases) during higher engine load situations. It is a different mechanical design than the more modern vacuum advance diaphragm in a can but it affects the same change on the ignition timing.

[35fordtn]

The 11A weights provide roughly 8 degrees extra of total advance and they advance just off of idle. The are indeed a improvement. The only thing that requires change in a 78- prefix distributor to convert to a 11A, is the weight, shaft and weight index plate. They all have centrifugal mechanical advance. The vacuum line is for the vacuum brake, which works nearly the opposite of a vacuum advance..

IMO with today's fuels I prefer the vacuum brake to be adjusted all the way out, unless the weight springs are too weak. In this case I would turn one in just enough to be certain on the sun Machine that the advance goes back to zero at idle.

[Hoop]

Very interesting comments.

The helmet and crab distributors are a centrifugal/vacuum design. This means that both the weights and vacuum are used to produce the desired advance.

Yes, part of the design is a vacuum brake ... however it is used to regulate or "fine tune" the advance created by the weights.

The braking pressure is provided by the spring. The vacuum relieves the spring pressure thereby increasing the advance ... vacuum advance. If you were driving on a level road at a steady, set rpm, encountered a downgrade, kept the rpm steady ... you would have to "lift" on the throttle ... vacuum applied to the "vacuum brake" would increase ... the spark would advance (depending on the rpm.)

Vacuum "adjusts" the drag on the brake thereby increasing or decreasing spark advance.

The design must be considered a "system" in which the role of the vacuum brake is part of an overall spark advance mechanism.

The design cannot be accurately described as either solely vacuum advance or solely centrifugal. It is a combination.

[BUBBAS IGNITION]

Very little difference in the 11A and model 68, both have approx 11 degrees or 22 degrees engine advance. All of the ford flathead distributors work very well with new parts and adjustments etc...... The small diameter distributor cam used with todays modern contacts and a good coil condensor combo is pretty hard to beat.

[pooch]

Is a smaller diameter cam available to fit a crab ?

Does this mean that with a modern coil/condensor, we can run single points?

[BUBBAS IGNITION]

Originally Posted by pooch

Is a smaller diameter cam available to fit a crab ?

Does this mean that with a modern coil/condensor, we can run single points?

NO the crab needs the dual set up and works very well. The dual points allow adjustment for case timing (intial ) and overlaping dwell ( coil build up) . There would be NO advantage to running a single set in this example....