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By SurfMerc - 15 Years Ago
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Been trouble shooting a rough idle, low performance problem for a long while on my 312 in a 56 Merc with stock distributor. I hooked up a dwell, RPM.volt meter and noticed that the dwell increases as I throttle the carb. Is this indicating a bad distributor? Also, The volt meter is reading 7 volts. What should this reading be and is 7 a low reading? Thank You - AR
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By GREENBIRD56 - 15 Years Ago
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It is most likely wear of the bushing allowing the clearance between the cam and points to change. As the internal bushing wears there can be increasing movement both up and down and side to side. Where is the 7 volts taken? After the ballast resistor or before?
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By SurfMerc - 15 Years Ago
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Volt meter had one wire at the distributor side terminal of the coil and the other to ground. Thanks AR
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By GREENBIRD56 - 15 Years Ago
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Not too bad then - that test point is on the "down side" of the wiring harness, ignition switch, ballast resistor, coil primary .......plenty of rsistance ahead of your test point to drop the Voltage. 
You probably have the "Load-O-Matic" distributor that looks like this under the cap? It delivers spark advance based on vacuum / air flow through the venturi orfice of the carb. If you have any leaks or stopages in that system - or a bad vacuum cannister on the dizzy - it can (and will) result in performance loss /over-heating / etc. The two visible upper springs and the "straight base points" are other ID clues. If you have a bad bushing in the old distributor, it might be to your advantage to try out a "new" rebuilt from one of the auto supply houses. Ask for a distributor for a 1964 light truck with a 292.
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By Y block Billy - 15 Years Ago
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If you do get a later distributor you will have to update the manifold and carb to match.
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By oldcarmark - 15 Years Ago
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Y-Block Bill! Even adding just the later distributor will make a big difference in the way it runs.I did change my distributor before I changed carb and manifold and really noticed an improvement in performance.You do need to find a source of manifold vacuum as you cant use the outlet on the stock carb.
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By paul2748 - 15 Years Ago
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If I remember correctly, Ted said in another thread that you can use the vacuum from the front of the carb for a later (57) distributor. The 56 has vacuum points at the front (ported??) and one at the rear (full, manifold, vacuum) which served the wipers, distributor and power brakes. Do I remember correctly?
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By oldcarmark - 15 Years Ago
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You cant use the one that worked with the stock distributor because its controlled by a "spark advance " valve in the carb.
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By SurfMerc - 15 Years Ago
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Your right! The original Carter thats on the engine has a vacuum port in the front that has a spark control valve that goes to the primary vacuum diaphragm on the distributor. At the rear of the Carter has a manifold vacuum source with a brass block that has two ports. One port goes to the secondary vacuum diaphragm on the distributor while the other goes to one of the vacuum assist on the fuel pump. Thanks for all the input - AR
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By GREENBIRD56 - 15 Years Ago
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Don't avoid the use of the later mechanical advance style distributor on account of a lack of a "ported" vacuum source on the carb - it can and will work just fine. Tuning is slightly different with the live manifold vacuum at idle (versus the ported) but the system will behave just fine on the road. When the throttle opens, the behavioral differences mostly disappear.......but the torque advantage of the mechanical advance version at lower levels of rpm is hard to overlook. There are some articles (provided by our Mustang enthusiast brethren) that show the differences and similarities of the Autolite and Motorcraft versions of the Ford distributor - but not really much is found about the earlier "Load-O-Matic". You could re-bush it if parts are available and get everything back to original - it will just take a bit of effort. http://www.mustangmonthly.com/techarticles/mump_0904_how_to_rebuild__autolite_motorcraft_distributors/index.html http://www.mustangmonthly.com/techarticles/mump_0702_ford_mustang_distributor_rebuild/photo_17.html
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By DANIEL TINDER - 15 Years Ago
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[quote][b]GREENBIRD56 (9/21/2010
"the torque advantage of the mechanical advance version at lower levels of rpm is hard to overlook".
Steve,
While I agree the later mechanical advance distributors deliver superior performance (quicker advance/not slowed by restrictive vacuum passages), I still wonder whether the Loadomatic's higher allowable initial advance setting (no throttle activated retard with centrifugal) might cancel much of that advantage if tuning was truly maximized?
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By GREENBIRD56 - 15 Years Ago
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Daniel - Isn't the dual diaphragm "Load-O-Matic" the one we were discussing? By mechanical means the two canisters are tied together and in a manner of speaking "summed". One of the two vacuum cans is hooked to manifold vacuum and I believe it then provides "auto retard" by dropping out when the throttle opens. The other can runs off the venturi effect at the throat - measuring air speed into the intake. The Load-O-matic distributor technology (purely vacuum based) was abandoned by Ford in 1956 - probably for good reasons ..... maintenance difficulties would be high on that list I'd imagine. It can be made to work (run an engine) - it just has some problems.
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By PF Arcand - 15 Years Ago
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Steve; Re the Load -O-Matic distributors, a small correction, they were abandoned "after" 1956.
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By oldcarmark - 15 Years Ago
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Actually as I recall they used the loadomatics on the 144-250 6 cylinders through the 60's.Stopped using them on the V-8 after 56.
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By DANIEL TINDER - 15 Years Ago
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[quote][b]GREENBIRD56 (9/21/2010) "maintenance difficulties would be high on that list"
Steve,
Was just referring to to the typical comments about improved acceleration after a switch to '57 & up distributor ("like removing 500 lbs. from the trunk"). By the time most get around to that swap, which often includes a carb. upgrade BTW, the Loadomatic is worn out and badly tuned. The same increase in performance can usually be accomplished by rebuilding & speed tuning on a Sun machine! Balancing the Loadomatic springs, and tuning a hot curve IS indeed difficult. That, and the added slower advance (vacuum restriction) was likely reason enough to make it obsolete.
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By oldcarmark - 15 Years Ago
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Actually Daniel I have to disagree with part of your statement.I simply switched to the later distributor and noticed a definite improvement in driveability.My loado was not worn out.I did this about 2 months prior to installing a Holley 390 and the "B manifold.Adding the later carb and manifold is the next step to improving the way it runs.Äs far as tuning the distributor that time and money is better spent tuning the later distributor as far as I am concerned.Just my opinion.
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By DANIEL TINDER - 15 Years Ago
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Mark,
Just going by my own experience. Original Loadomatic with 60K on it, probably only had points service since new (regular bushing lube unlikely), but still running fine. After pro rebuild & setup, got the "500 lbs. removed from the trunk" effect.
Have a spare Loadomatic that I will eventually rebuild also, but WILL invest the setup time to satisfy curiosity before installing a tuned Mallory, for definitive A/B comparison test of both units in max tune.
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