Just rebuilt a 1956 tbird 312. This 1956 312 has a dist with a dual vacuum advance. I tested it before we put it on the engine and it held vacuum(This is the only test I knew of). When we got the engine started, for the first time, the engine run very rough at idle and was hard to keep running. We unscrewed the advance lines(both) at the dist and capped off the lines. The engine ran very, very smooth. It seems that the vacuum advance must be the problem. Do you have any thought on this, and if mine is bad do you know where I could buy one?
Dual vacuum advance problem
- Thread starter cjc56
- Start date
Both hold a vacuum so I don't think the the advance is the problem after all. I have checked the lines to be sure they are attached properly. I have also checked the vacuum coming off the base of the carb and the vac coming from the upper portion of the carb( this is where the large camber of the advance is connected). At idle the vac from the upper carb is approx 10. the vac coming off the base of the carb is 20. This engine has just been rebuilt. I also have another issue in that the marks on the pulley are quite a distance from the timing cover pointer. Looking at the pulley the pointer is at 10:00 clock while the timing marks on the pulley are showing up around 8:00 clock when hit with the timing light. Engine starts right up and idles fine except a little rough. Also new petronic in the dist. Any thought what might be wrong?
the crank pulley is made in two pieces with a rubber liner between the two pieces, the rubber liner becomes hard and lets the outer part of the pulley slip on the inner pulley and throws the timing marks way off, there used to be a company that rebuilt them, but I don't know if they are still in business, and as far as I know there should be no or very little vacuum on the advance part of the distributor at idle
fordy_nine
Senior Member
One of the names for harmonic damper rebuilders was "Damper Dudes". I don't know if they are still around.......Bob L
rick55
Senior Member
I would think the engine would run very rough with timing that far out. It may still start depending whether it was advanced or retarded.
The timing mark is on the damper ring and can slip on a y block engine.
Time your engine with a vacuum gauge or by ear. By vacuum rotate the distributor to get best vacuum and then turn it back to reduce the vacuum reading by 1" of vacuum. By ear adjust the distributor to get the fastest idle and then back it back til you hear the engine note change. This takes a lot of practice to get this method right.
Remarking your damper will not solve your problem as the ring may slip again.
First of all: Ford3, neither chamber is for retard!! Both are for advance! Cjc56, is the carb original? These vacuum only distributors MUST use the right carb, which has special internal passages to increase vacuum as RPM increases. If you have a '57 or later carb or an aftermarket carb or a carb from another brand vehicle, you will have vacuum present at idle (as you mention) and therefore will have full advance at idle which explains the rough running and smoothing out with lines disconnected.
Ford used this design distributor from'49 ('48 pickups, I believe) thru '56 and added the second chamber and line in '56 to better control the advance on 4 barrel carbs. You should have either the Holley 'teapot' carb or the Carter WCFB, both specially designed to work with the vacuum advance only distributor.
Use a timing light to compare where the timing marks are at idle with the lines disconnected (as the factory says) and with the lines connected. If the marks go to full advance, you have the wrong carb or the lines are hooked up wrong at the carb (neither line goes to the intake manifold). Since it idles smooth with the lines off, I don't think your timing marks are too far off. Get this advance thing sorted out first.
Ford used this design distributor from'49 ('48 pickups, I believe) thru '56 and added the second chamber and line in '56 to better control the advance on 4 barrel carbs. You should have either the Holley 'teapot' carb or the Carter WCFB, both specially designed to work with the vacuum advance only distributor.
Use a timing light to compare where the timing marks are at idle with the lines disconnected (as the factory says) and with the lines connected. If the marks go to full advance, you have the wrong carb or the lines are hooked up wrong at the carb (neither line goes to the intake manifold). Since it idles smooth with the lines off, I don't think your timing marks are too far off. Get this advance thing sorted out first.
dmsfrr
Well-known member
The timing mark on a '55/'57 T-Bird is on the back of the belt pulley and cannot shift. T-Birds use a different style crank pulley than other Y-block Fords. Two pictures below.
If the damper ring has slipped it won't affect the timing marks, BUT if any damper ring is slipping it can come off and cause significant damage, and needs to be replaced or rebuilt.
http://damperdoctor.com/
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dmsfrr
Well-known member
Double check that the rotor is pointing where it should be when the timing marks are lined up w/ cyl 1 @ TDC of the compression stroke, or maybe? that your plug wires are one place off around the dist cap and/or your timing light isn't really reading off of cyl. #1.
Dominic Hide
Member
Is this a newly rebuilt distributor or is it untouched since before the engine rebuild? If newly rebuilt or at least one that you have never used before then I think the cam lobes have been installed out of phase with the rotor. To check remove the rotor and note the position of the flat on the shaft in relation to the lobes on the cam. It should line up with a high point. If it is not centered or if it is lined up with one of the flats on the cam then you would get the kind of situations that you are experiencing.
Check this link to compare your situation
http://www.jalopyjournal.com/forum/...iming-disaster-need-help.383175/#post-4160410
Check this link to compare your situation
http://www.jalopyjournal.com/forum/...iming-disaster-need-help.383175/#post-4160410
dmsfrr
Well-known member
I could have been sleeping at 2am but instead I copied the pictures here, from the link above, to make them easier to see.
As per Dominic Hide's post ....
The left pic shows the flat spot of the shaft for the rotor, correctly aligned with a lobe high point. The other pic shows it incorrectly aligned with a flat spot between the lobes.
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scicala
Well-known member
Great advice 40 Deluxe. I do differ with one thing you said. You mentioned that neither of the vacuum lines from the vacuum advance unit go to the intake manifold. I agree that neither line is physically attached to the intake manifold, however one line does got to the brass fitting at the base of the carb, which is the same as direct manifold vacuum.
Sal
TedEaton
Senior Member
Are you dealing with the original Teapot carb or a newer style of carb? If you still have the Teapot, then check that the primary throttle blades are positioned below the ported vacuum port at idle. If the blades are positioned too high, then double check for vacuum leaks, too much blade opening in the secondary bores, or the timing is simply too far retarded at idle.
dmsfrr
Well-known member
There's a really good description of how the Load-o-Matic distributors work at the bottom of the 1st page of of this linked thread....
http://www.fordbarn.com/forum/showthread.php?t=155756
http://www.fordbarn.com/forum/showthread.php?t=155756
It has to do with the vacuum generated by the engine or in the case of a Sun Distributor Tester how much vacuum is used to check the vacuum advance.
On a 57 Y that has both centrifugal advance and vacuum advance the vacuum is not set as precise as on the 56 Y which only uses small amounts of vacuum. That applies to all Load O Matic style dizzies regardless of the # of cylinders.
A couple of examples would be:
On a 56 312 Y, all advance is Vacuum
At 300 Distributor RPM: Advance would be 0 - 1/2 degrees at .16 Inches of vacuum. Note that is "point" 16.
At 400 Distributor RPM: Advance would be 0-1 degrees at .29 Inches vacuum.
On up at 800 RPM: 5-1/2 - 6-1/2 degrees at Inches vacuum: .88
at 1200 RPM: 8-1/2 - 9-1/2 degrees at Inches vacuum: 1.27
at 1600 RPM: 11 - 12 degrees at Inches vacuum: 1.73
at 2000 RPM: 13 - 14-1/2 degrees at Inches vacuum: 2.19
Very little vacuum is need to advance the breaker plate.
Now a 57 312 Y Vacuum Advance only is set at a constant Dizzy RPM of 1000. Centrifugal of course changes as RPM changes.
With the Sun DT at 1,000 Distributor RPM.
There will be 0-1 degrees of advance 5 inches of vacuum.
There will be 5-7 degrees of advance 10 inches of vacuum.
There will be 11-13 degrees of advance 15 inches of vacuum.
There will be 11-13 degrees of advance 20 inches of vacuum.
Note the profound difference. The 56 advance is 13 at 2.19 inches and the 57 is 13 at 15 inches. Those are all stock Shop Manual #'s. Depending on the dizzy - springs, washers or an allen wrench can be used to adjust or curve the vacuum advance.
Here is a pic of the Vacuum gauge on the DT 506 and also a Sun Manometer.
Note how the Vacuum gauge is marked off up to 6 inches and then note the Manometer is much more accurate for just the 2 inches shown in the pic. It is not impossible to set the vacuum advance - adjust the springs - on the LoadOs with just the vacuum gauge but the Manometer allows it to be more precise. Hard to do on a running engine with a standard vacuum gauge.
Manometers are filled with water, mercury, or "Sun Manometer Fluid". Depending on the specific gravity of the fluid determines how the Manometer is calibrated and how tall it is. Water is 1 and Mercury is 13.56.
HTH and does not take the thread too far off course but it does address the original question pertaining to the distributor and why pure manifold vacuum should not be used with a LoadO dizzy.
Jim
woodboatwayne
New member
had same problem, bought new dizzy for $139 @ local parts store, blocked off vacuum
fitting on rear of carb, connected vac advance on dizzy to front vac connection. Adjusted timing by ear. Now runs like a scalded dog (292 standards)
fitting on rear of carb, connected vac advance on dizzy to front vac connection. Adjusted timing by ear. Now runs like a scalded dog (292 standards)
woodboatwayne
New member
should have said later 292 dizzy w/single vac fitting
Scicala, I just checked back here and saw this post. Are you sure that fitting at the base of the carb connects to manifold vacuum? Because if it does, you will have full advance at idle and it will idle very rough, plus likely ping real bad at low speeds due to the excessive advance. And at full throttle manifold vacuum drops to zero so all your advance goes away and so does most of the power. I think you will find that this fitting has internal passages that go the venturi for the vacuum. Airflow through the venturi creates a vacuum signal for the advance.