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Old 12-02-2019, 07:57 AM   #1
Mike/NY
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Default Rebuilding a 1939 fuel pump

When swapping a new membrane in a 1939 fuel pump does it require to be pretensioned before tightening the screws? This is what is done eg. to a Volkswagen pump so the membrane is not distorted and pump works better. I believe it is not necessary to do so in an early Ford V8 pump. My membrane in a nos pump was completely melted due to modern fuel.

I plan to use an Antique Auto Parts Cellar membrane but the owner Tom wants ot know which membrane, does ayone have a part number for him?
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Old 12-02-2019, 10:38 AM   #2
flatjack9
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Default Re: Rebuilding a 1939 fuel pump

Not necessary.
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Old 12-02-2019, 06:19 PM   #3
Terry,OH
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Default Re: Rebuilding a 1939 fuel pump

Maybe not necessary but Fords rebuilding Service Bulletin calls for the diaphragm to be assembled with all the screws loose and the diaphragm extended then tighten all screws.
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Old 12-02-2019, 09:31 PM   #4
Charlie ny
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Default Re: Rebuilding a 1939 fuel pump

Mike,
Tell Tom you want the six screw AC style diaphragm, with a .250 center hole, 2 1/2" dia. The only diaphragm Ford used from 1932 thru 1950. Specify Viton.

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Old 12-03-2019, 01:30 AM   #5
Mike/NY
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Default Re: Rebuilding a 1939 fuel pump

Thanks guys, this answers all my questions.
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Old 12-03-2019, 12:40 PM   #6
Mike/NY
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Default Re: Rebuilding a 1939 fuel pump

This is what Tom says:

When the fuel pump is re-assembled, the directions tell you to operate the rocker arm to it's full travel in order to draw the diaphragm down into the casting. THEN the bolt circle lines up and the screws are tightened to hold the diaphragm down in it's flexed position. This allows the diaphragm to flap up and down moving as the sail on a boat does- not stretching. That gives the diaphragm the longest mechanical life.
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Old 12-03-2019, 01:08 PM   #7
Charlie ny
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Default Re: Rebuilding a 1939 fuel pump

Mike,
Before you do the rocker arm thing be sure to apply a little grease to the slot
that engages the arm.

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Old 12-03-2019, 01:11 PM   #8
Mart
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Default Re: Rebuilding a 1939 fuel pump

Thanks for mentioning this. I'd never thought or heard of it before.

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Old 12-03-2019, 05:37 PM   #9
jake197000
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Default Re: Rebuilding a 1939 fuel pump

ive pretensioned every fuel pump ive ever done.no problems.notsaying it matters,just whats happened
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Old 12-04-2019, 04:17 AM   #10
Mike/NY
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Default Re: Rebuilding a 1939 fuel pump

I did not pretension mine just now when I swapped the diaphragm but might do so before I start the 39 Conv.

Charlie ny, which slot do you mean? I did put grease on the slot where the actuating arm goes in and also to the slot the arm attaches to the diaphragm arm. Some instructions say to apply the pump bottom with plenty of grease around spring and arm?

I had a weird noise/rattle come from the engine last spring, I posted a thread about it. Never found out what is was and it went away after some driving, right about then the fuel pump started leaking. My guess is that that since the diaphragm failed (turned into soft black mush, leaked alot to the lower part of the pump and then to the intake but still worked pumping enough fuel to run the car), maybe the rattle came from the diaphragm being too loose and having no resistance? The rattle seemed to come from the intake area and somebody suggested a loose fuel pump actuating arm/bracket. But a loose diaphragm might well cause a rattle?
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Old 12-04-2019, 07:52 AM   #11
slowforty
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Default Re: Rebuilding a 1939 fuel pump

A loose diaphragm could cause someone with a rattle. Just ask your significant other. (sorry)
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