Running Crab Distributor without vacum

[Mr 42]

As i said in the heading what happens if you run the crab distributor without the vacum brake connected.
Will the rubber on the piston wear out? or?
Is it OK or not?

Question 2: Where does the vacum source connect originaly?

[Henry/Kokomo]

Q1: The timing will not advance as intended.
Q2: Different years connect at different places but all are on the intake manifold.

[Bruce Lancaster]

If you just disconnect and leve parts in there, you get the full throttle curve but not the longer cruise curve...it runs with the brake on. Waste of power and gas potentially.
If you gut it and disconnect the vac, you get longest form of curve. Possible too rapid advance at full throttle.
Howitworks: Centrifugal advace produces the most advance Ford thought usable (and they were pretty much right)...brake drags on advance at full throttle opening to slow down advance to full throttle specs, BUT this is not on-off. It is a continuum that varies with adjustment on that bolt sticking out...
On modern gas, you will probably be fine with adjust mostly out, leaving only light brake drag.
There is ABSOLUTELY ZERO advantage to disconnecting. Do it thus: Turn or rplace leather, 90 turn is usually fine.
Turn adjust bolt out all the way BY HAND, tighten maybe 1 1/2 turn to keep a very slight drag, and try some full throttle accel in high gear. If no pinging or very light pinging, you are done. If it pings...unlikely...tighten down the adjuster a bit and retest.

Vac source is manifold.

[Mart]

I've heard of people saying to remove the plunger, but I'm tending towards what Bruce is saying, very light drag from the plunger.
This is my thinking: More modern distributers have return springs which oppose the centrifugal weights. The Old Ford ones do not, the drag of the plunger resists the pull of the weights.
So, Does anyone run with the plunger completely removed? Or is this bad advice?

Just for the record, I run with the plunger lightly applied and the vacuum hooked up.

Mart.

[51FordCustom]

Sorry if this doesn't apply or if you already know, but I have a '51 Ford 8BA and for years I ran around getting only about 14mpg until one day an old flathead guy told me to check the vacuum advance. When I did I found that it was not connected. After connecting it my mpg went up to 17-18mpg. So I guess I am just agreeing with the advice of Bruce L. in saying it doesn't do any good to run around with it disconnected.

[Mr 42]

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Ok Thanks,
I just wondered since I wanted to start it up for the first time and maybe do some driving to check out gearbox/brakes etc.

And since the distributor is NORS i did not want to destroy anything.

I backed of the spring full, and still got some drag, on the disc.

Some one has mounted a 1/2" bolt in the hole in the manifold.

Does the crab Distributor work on "normal" manifold vacum?

The 8ba needs the special holley carb port, to work.

Maybe i can drill a hole in the bolt and use it as a vacum source.

[bobscogin]

Originally Posted by Mr 42

Does the crab Distributor work on "normal" manifold vacum?

Bruce already posted the answer, but yes. Manifold vacuum.

Bob

[Gumpy]

Manifold vacuum is best to get the full power out of your engine tried both and 1CM ran better in all ranges....a ford 94 carb is good also...

[V8 Bob]

Originally Posted by 51FordCustom

Sorry if this doesn't apply or if you already know, but I have a '51 Ford 8BA and for years I ran around getting only about 14mpg until one day an old flathead guy told me to check the vacuum advance. When I did I found that it was not connected. After connecting it my mpg went up to 17-18mpg. So I guess I am just agreeing with the advice of Bruce L. in saying it doesn't do any good to run around with it disconnected.

The late '48-'53 loadomatic distributors have NO mechanical advance, only vacuum, so, if disconnected, will only result in 2 degrees BTDC crank timing, if the pointer and pulley dot are aligned, and the correct 27 degrees point dwell.

[rotorwrench]

Just to add: 8BA/8CM Load-A-Matic is no real comparison the the crab types. The crab types work relatively well and the Load-A-Matic barely worked when new. The carb source Load-A-Matic uses venturi vacuum from two locations internally to make it almost work. The old crab types use the straight manifold vacuum and will work for all kinds of engine combinations including multiple carbs.

[ken ct]

Originally Posted by Mr 42

As i said in the heading what happens if you run the crab distributor without the vacum brake connected.
Will the rubber on the piston wear out? or?
Is it OK or not? PS its not rubber,its leather and i have brand new ones. ken ct.

Question 2: Where does the vacum source connect originaly?

Intake manifold. ken ct.

[Enbloc]

I to was unsure about connecting the vacuum brake.

In the end I removed mine completey. I think this is a must if you chose not to use it otherwise the vacuum brake is constantly on fully, totally messing up the advance curve in the process. The vacuum holds the brake off not on.

My reasoning for not using it was all the Ford literature I read on them talks about it being an aid to stop detonation (Pinging) when using poor fuel.
A piece I read even talked about adjusting it on the road if you developed detonation after filling up with a poor tank of gas.

Thats my take on it. Whether its right or wrong my car runs great without but I haven't run it with the brake to compare. But reading posts in this thread about gas milege increases when reconnected has intrigued me.

[gavin m]

I also removed the vacuum brake when i fitted a crab dizzy to my 21 stud. Seems to run great without it.

[BUBBAS IGNITION]

I have ran a ton of thee crabs on a test machine and can offer some testing info.

With the piston and spring removed the spark advance will jump all over the place and will not remain steady or do the same thing twice.

As Bruce stated above i would suggest leaving the piston, leather and spring in place and adjusting for a slight drag on the retard ring at all times.

OR better yet make it functional ( for you single carbs guys) and allow it to work like Henry wanted it to.

[Lowsquire]

hmm.
I have mine disconnected from vacuum but have the piston and spring still in there, and almost backed right off (as bubba says)
If I read it right, higher vacuum will pull the plunger up away from the ring, and more advance will ensue (under cruise conditions).Then if you nail it, vacuum drops, the plunger drags more on the ring and the timing retards a little. I feel like as I accelerate my car needs more advance, not less....Never pings under load, and static timing is set at about 8degrees advanced at idle, and with a timing light seems to hit around low thirties when revved to about three grand.(i marked the pulley at TDC and 10,20,30 when I built the engine) I feel like the engine could take more timing advance than stock (its a ported and twincarbed 99A with headers, a mildish cam .40 over) anyone have any reccomendations ?

[flatjack9]

Originally Posted by BUBBAS IGNITION

I have ran a ton of thee crabs on a test machine and can offer some testing info.

With the piston and spring removed the spark advance will jump all over the place and will not remain steady or do the same thing twice.

As Bruce stated above i would suggest leaving the piston, leather and spring in place and adjusting for a slight drag on the retard ring at all times.

OR better yet make it functional ( for you single carbs guys) and allow it to work like Henry wanted it to.

So when running under part throttle (high vacuum), the plunger is drawn away from the plate. Are you saying that we can expect to have an errant spark under these conditions?

[Enbloc]

Originally Posted by BUBBAS IGNITION

As Bruce stated above i would suggest leaving the piston, leather and spring in place and adjusting for a slight drag on the retard ring at all times.

Would this be with the vacuum connected or disconnected?

[BUBBAS IGNITION]

Originally Posted by flatjack9

So when running under part throttle (high vacuum), the plunger is drawn away from the plate. Are you saying that we can expect to have an errant spark under these conditions?

I guess errant is a good term , when the piston is all the way out the spark isnt very steady, like it is with a slight drag on the leather.
If you look at the drive slot ( not a tight fit) and the mechanism that just the way it is, so a slight drag is preferred i would think. Kinda keeps the clearances
tightened up.

[Mr 42]

Just for the record, i backed of the piston so there was a slight drag.
And fired it up. Im planning to fix the vacum source later on.


It still need some tuning but it started up OK

https://www.youtube.com/watch?v=Set0o8e1Y6E

[Mart]

Cool, Lars, obviously what was stopping that from running right was a lack of tattoo's.

Nice vid.

Mart.