Vacuum and Mechanical Advance Differences?
#1741696
01/29/15 04:11 PM
01/29/15 04:11 PM
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Joined: Nov 2006
Posts: 356 NE
moparpoolman
OP
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OP
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Posts: 356
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With a 1972 400, What's the difference IF any between the Vacuum and Mechanical advance on a 4spd vs. auto. Also is there any difference with 2bbl vs 4bbl? Thanks
Last edited by moparts; 01/30/15 02:39 PM.
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Re: Vacuum Advance Differences?
[Re: moparpoolman]
#1741699
01/29/15 09:22 PM
01/29/15 09:22 PM
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Joined: Nov 2006
Posts: 356 NE
moparpoolman
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OP
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NE
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Quote:
With a 1972 400, What's the difference IF any between the Vacuum advance on a 4spd vs. auto. Also is there any difference with 2bbl vs 4bbl? Thanks
Also would like to add that I'm interested if there are differences in the original 1972 distributors with vac advance, not newer replacement distributors? Thanks
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Re: Vacuum Advance Differences?
[Re: D_C]
#1741700
01/29/15 09:25 PM
01/29/15 09:25 PM
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Joined: Jul 2008
Posts: 259 Khemi, Stygia
Mebsuta
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Khemi, Stygia
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I think some are fixed, and if you go in there with hex key, can puncture the diaphragm if you are not careful.
68 Roadrunner. 383 4-spd. Beat up.
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Re: Vacuum Advance Differences?
[Re: Mebsuta]
#1741701
01/29/15 09:42 PM
01/29/15 09:42 PM
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Joined: Jun 2008
Posts: 3,916 usa
lewtot184
master
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master
Joined: Jun 2008
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usa
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Quote:
I think some are fixed, and if you go in there with hex key, can puncture the diaphragm if you are not careful.
adjusting the spring pressure on the diaphragm won't puncture the diaphragm. i do it all he time.
the real difference i've noticed in the canisters is the amount of degrees that are in them. the number of degrees in the canister is stamped on the arm that connects to the plate. they range from 7 degrees to 10 degrees (distributor degrees). i have noticed the lower degree canistrs having a slightly weaker spring.
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Re: Vacuum Advance Differences?
[Re: moparpoolman]
#1741702
01/29/15 09:46 PM
01/29/15 09:46 PM
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Joined: Feb 2010
Posts: 1,645 Phila. Pa.
Mattax
top fuel
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top fuel
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
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Quote:
With a 1972 400, What's the difference IF any between the Vacuum advance on a 4spd vs. auto. Also is there any difference with 2bbl vs 4bbl? Thanks
If you have a '72 FSM it will have the specs for both. You will then know if they were supposed to be the same or not.
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Re: Vacuum Advance Differences?
[Re: RJS]
#1741704
01/30/15 12:18 AM
01/30/15 12:18 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Lincoln Nebraska
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The electronic one retards when it is energized by the emission controls (same deal as the O tdc timing). Are you wondering about the differences or is your can shot & you are wanting to replace it? If so I'd suggest a regular (non electric) one and CCW with the 3/32" allen wrench slows the curve (doesn't change the total the can offers which is as said the number stamped on the arm) by requiring more vac for the same amt (deg) of advance. You can file the notch in the arm for more advance and epoxy strips of feeler gauge with JB weld on the back of the can to limit the arms' travel into the can to limit the total (either way as needed). I would set the initial then the total (initial+slots/no can) then springs then hookup/adj the can and (A) you want to stay just under the pinging point on your hottest/driest day at a steady (high vac) rpm such as an interstate cruise at or above the RPM where the springs are maxed out (full mech/vac adv) by altering the arms' travel then (B) with the allen wrench let the can come in as fast as possible staying just under the pinging point on your hottest/driest (most likely to ping) day in everyday driving under varying vac levels. alot of work but alot of gain to be had
live every 24 hour block of time like it's your last day on earth
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Re: Vacuum Advance Differences?
[Re: moparpoolman]
#1741706
01/30/15 12:55 AM
01/30/15 12:55 AM
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Joined: Jan 2003
Posts: 6,232 JERSEY
RJS
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JERSEY
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The distributor for your Road Runner is going to look the same 2 bbl or 4bbl. The auto and 4 speed is going to also look the same except for the large vacuum can on 4 speed that I posted already.
Here is a 400 4bbl. auto distributor: Ron
Last edited by RJS; 01/30/15 12:59 AM.
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Re: Vacuum Advance Differences?
[Re: moparpoolman]
#1741709
01/30/15 01:22 AM
01/30/15 01:22 AM
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Joined: Feb 2010
Posts: 18,493 Granite Bay CA
Kern Dog
Striving for excellence
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Striving for excellence
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Granite Bay CA
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Quote:
That's a nice engine pic. But that distributor is a 1974. Are the internals of a 1974 the same as a 1972?
He is right, that IS a beautiful view!
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Re: Vacuum Advance Differences?
[Re: moparpoolman]
#1741711
01/30/15 11:07 AM
01/30/15 11:07 AM
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Joined: Feb 2010
Posts: 1,645 Phila. Pa.
Mattax
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Quote:
What I'm trying to figure out is if All the 1972 Distrbutors are all physically the same and maybe different internally(springs or weights) and if they all have same or different vac. adv. units (physically or internally). I have a 1972 400 4bbl auto and am Looking for an original Distributor. Do I need to buy one just for that application or can I buy a 2bbl or a 4spd one and make internal changes if they are different.
For the distributor to perform to spec, rather than just look correct, your odds are best if you can get hold one specifically for your '72 400 4 bbl auto. However, if you have access to a distributor tester, or are willing to spend some time testing on engine with a timing light, you can modify the internals to meet spec.
It will be hard to find the replacement springs by part number - although can try. Even more true for the top shaft-slot plate. So it comes down to tweaking what you have, taking parts from other applications or doner distributors and so forth. A standard, all mechanical vacuum advance will be not so hard as a pretty good range is still available new.
First thing to do is get a hold of a '72 shop book and write down the specs. Then look for all other applications with the same specs. A '72 parts book will reveal if the vacuum pod, springs etc were used for other applications that year. Then you can look at other years and if you post up, some of us can help by looking at other years.
In addition to the spring rate and advance slots (mechanical advance allowed), adjustments can be made to the initial spring force by turning the spring posts. The /6 folks know this, but everyone else seems to be unaware of it. On the secondary side this will change the point when the long loop engages.
Not many books on how dizzy's work. Some tech info here on the 'new' 1961 Chrysler built distributor http://www.imperialclub.org/Repair/Lit/Master/136/index.htm
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Re: Vacuum Advance Differences?
[Re: moparpoolman]
#1741713
02/02/15 02:00 AM
02/02/15 02:00 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,041
Lincoln Nebraska
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I'd go ahead & get the one listed for your app (# on the arm) & adj it with the allen wrench to come in just under the pinging point (which can be anywhere in the slope as your eng/gas/elevation/driving style etc are different from the next guy with the exact same setup) if you want to get it spot on. bottom line NO pinging allowed under any circumstances, You stay fairly close to the line but never over it
live every 24 hour block of time like it's your last day on earth
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