The Ford Barn

Mike/NY · 12-02-2019, 07:57 AM

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?

flatjack9 · 12-02-2019, 10:38 AM

Not necessary.

Terry,OH · 12-02-2019, 06:19 PM

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.

Charlie ny · 12-02-2019, 09:31 PM

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.

Charlie ny

Mike/NY · 12-03-2019, 01:30 AM

Thanks guys, this answers all my questions.

Mike/NY · 12-03-2019, 12:40 PM

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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.

Charlie ny · 12-03-2019, 01:08 PM

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

Charlie ny

Mart · 12-03-2019, 01:11 PM

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

Mart.

jake197000 · 12-03-2019, 05:37 PM

ive pretensioned every fuel pump ive ever done.no problems.notsaying it matters,just whats happened

Mike/NY · 12-04-2019, 04:17 AM

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?

slowforty · 12-04-2019, 07:52 AM

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

12-02-2019, 07:57 AM	#1
Mike/NY Member Join Date: May 2010 Posts: 57	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?

12-02-2019, 10:38 AM	#2
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,526	Re: Rebuilding a 1939 fuel pump Not necessary.

12-02-2019, 06:19 PM	#3
Terry,OH Senior Member Join Date: May 2010 Posts: 4,750	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.

12-02-2019, 09:31 PM	#4
Charlie ny BANNED Join Date: May 2010 Posts: 3,019	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. Charlie ny

12-03-2019, 01:30 AM	#5
Mike/NY Member Join Date: May 2010 Posts: 57	Re: Rebuilding a 1939 fuel pump Thanks guys, this answers all my questions.

12-03-2019, 12:40 PM	#6
Mike/NY Member Join Date: May 2010 Posts: 57	Re: Rebuilding a 1939 fuel pump Sponsored Links (Register now to hide all advertisements) 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.

12-03-2019, 01:08 PM	#7
Charlie ny BANNED Join Date: May 2010 Posts: 3,019	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. Charlie ny

12-03-2019, 01:11 PM	#8
Mart Senior Member Join Date: May 2010 Location: Solihull, England. Posts: 8,749	Re: Rebuilding a 1939 fuel pump Thanks for mentioning this. I'd never thought or heard of it before. Mart.

12-03-2019, 05:37 PM	#9
jake197000 Senior Member Join Date: Sep 2010 Posts: 349	Re: Rebuilding a 1939 fuel pump ive pretensioned every fuel pump ive ever done.no problems.notsaying it matters,just whats happened

12-04-2019, 04:17 AM	#10
Mike/NY Member Join Date: May 2010 Posts: 57	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?

12-04-2019, 07:52 AM	#11
slowforty Senior Member Join Date: May 2010 Location: Tinley Park Ill Posts: 1,060	Re: Rebuilding a 1939 fuel pump A loose diaphragm could cause someone with a rattle. Just ask your significant other. (sorry)