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Single vs dual diaphragm distributor 72 Q Code
Guys apologies for the basic question.....

I want to order the correct vacuum lines from Marti http://www.martiauto.com/reproducedparts.cfm

There are two sets shown for my car a 72 Q Code. How can I tell if my car has the single or dual diaphragm distributor please? I do not have Ram Air (in fact I don;t believe Ram Air was offered as an option on the 72 Q code.


Nigel B

1972 Mach 1 Cobra Jet 4 speed

Dual diaphragm has a vaccum port both at the front and rear of the advance unit...

[Image: 4871f7e8-77d4-45de-b076-6f01c8d29980.jpg]

Single diaphragm only has one vacuum port at the front...

[Image: dva1_2.823.jpg]

Usually when I see a dual diaphragm it is on a 4 speed car
Not positive that is the rule though

Ohio Mustang Supply

[Image: oms_sig_banner.jpg]
You guys are so helpful. Thank you. I'll see if I can check tonight. My car is in the workshop getting the clutch replaced and the flywheel skimmed.

Nigel B

1972 Mach 1 Cobra Jet 4 speed

you might need to pop off the air cleaner to get a good look making sure there is or isn't a rear vacuum line.
stock would be a dual and is for smog, but you will get more performance from a single.
I've got a dual on my car. I found the coolant actuated vacuum tree which switches the distributor between advance and retard to be worthless. Bypassed the whole thing and just run a vac advance to the distributor. Plugged the rest.

[Image: FE177109-A1-C8-4-A6-C-9224-AACCFD66-C3-C9.png]

Rick Bombard
1971 Grabber Green Mach 1 351C 4V
2013 Race Red California Special Convertible
1973 Medium Copper Metallic Convertible 302 4V     SOLD
1953 F-100 SOLD
The coolant actuated vacuum tree to the distributor is designed to aid in cold engine starts. The Vacuum came from the manifold port, since vacuum from the carburetor was very low during higher rpm's.The timing was advanced on the distributor to accommodate the higher RPM's to get the engine warmed up. Once the coolant, carburetor, and engine reached optimal operating temperatures, it switched back to vacuum port on the carburetor, releasing the vacuum on the diaphragm, allowing the vacuum advance to operate on Carburetor vacuum.

Agree on doing away with the dual vacuum.

I do not know about the 72 but my 73 came with a dual it is 351, 4-V, 4 speed. One of the first things I changed on my car was to put Ford's conversion to a centrifugal advance dual point distributor on. The kit came with a new guts for the dist. that included several sets of weights and springs to tune the advance. It also required that you change the center cam because the position of the points had to be raised in order to get the mechanical guts in the dist..
I always pulled the dist. out and set the points using a dial indicator on the bench. I did not have any way of tuning the distributor back then but seat of the pants. I played with the springs and weights and looked at the timing at different RPM levels. My brain cells with that info have long since died off since I did that in the spring of 73.
The vacuum advance diaphragm is still on the distributor but the arm going to the plate in the dist. is cut off so it does nothing.
I will have to see if the box with the kit is stuck on a shelf in the garage to get a part number. Might still be some on a Ford shelf somewhere. Anyone have a parts book to look it up?

When a man is in the woods and talks and no women are there is he still wrong??
Thanks everyone. I checked my car last night that is in the shop and yes it has the dual diaphragm as several of you suspected.

The guy working on the car (Jeff Schrembi at Oval Repairs in Livonia MI) knows his stuff re older Mustangs, and was surprised that my car still had the points step up inside the distributor and wondered why I hadn't changed over to Pertronix. Apparently you don't have to do any non reversible work so can always revert back, just install the new innards in the distributor.

I had a quick read on here and can see several people have changed over, some things to watch out for etc. But what I have works today, and I know will need maintenance in the future. I think I need to do some more reading to form a better opinion. As usual I'm finding the help I get on this forum amazing. Thanks all.

Nigel B

1972 Mach 1 Cobra Jet 4 speed

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