Fuel pump diaphragm

Just contacted a rubber supplier and was told Buna-n (Nitrile)is very resistant to fuel and used by the military. Also a lot less costly

McMaster-Carr says Viton is resistant to Fuel, doesn't say what kind of fuel. My comment was that Buna-N is not. Viton is also very expensive and because of that is probably not what dia. suppliers are using.
CORDially Mike

I have die stamped diaphrams for six hole AC & Stewart Warner fuel pumps that I have used successfully in my own cars for seven + years with no problem. I do not know what kind of rubber they are, as I buy them from a supplier. The price is $15 each.

I'm no chemist but I found this regarding resistance to gasoline. It looks Viton is more resistant to fuel than buna-n, but neither is great when you add alcohol.

www.pspglobal.com/viton-selecting.html

www.robinsonrubber.com/pdfs/NitrileRubber.pdf

Mike, is viton resistant to ethanol alcohol (crummy modern gas) as well?

Buna-N rubber is not resistant to fuel but Viton rubber is.
CORDially Mike

Steve:
Good job. Sounds like you are in business with your fuel system.
Regards,
Steve S.

I took off the pump as you suggested and re-tightened the top cover with the lever in, still nothing. Took it off again and completely apart, blew through all the lines, turns out the little fiber inlet valve was stuck. Put everything back together and now can clearly hear the sucking sound as I move the lever with my hand. Thanks for you suggestions, I guess you just have to keep trying things to you figure it out.

Steve:
Your cam lobe should be fine with that low mileage on it so the pump is the culprit. I would take it back off the car, disassemble it and check everything. Here are a couple of other things to try if you haven't already done them.

1) When replacing the top cover of the pump, you should start all the screws about three turns and then push the lever all the way in and hold it there while tightening the screws the rest of the way. This procedure is outlined in the factory service manual. Without doing this, the new diaphragm is too tight and restricts the movement of the lever stroke.

2) Don't use too thick of a gasket when mounting the pump to the engine block. Thin cork is OK as it compresses. Too thick of a gasket cuts down on the effectiveness of the cam lobe.

Regards,
Steve S.

The car was running about 5 years ago when it was parked. It had a bunch of old gas in the lines and tank which I have cleaned/blown out. The only thing I did was replace the diaphragm, it looked clean inside when I took the cover off, no gunk built up inside, and the arm moved the piston up and down well. Could be the cam lobe but the car only has 53K miles on it, so I kind of doubt it. I'm going to try a few other things, may have to take the pump back off and check it, I appreciate your offer to loan me the spare pump, and if I can't figure it out I may have to take you up on it.
Thanks

Hello Steve:
Was the car running on the fuel pump before you took it off for the rebuild? If so, then you have done something wrong on the rebuild. If not, then you need to check the fuel pump lobe on your cam shaft. It could be worn to the point that it won't properly cycle the pump. Another thing, did you resurface the shoe that contacts the cam lobe when you rebuilt the pump? If so, you may have removed just enough metal to prevent proper pump action. When working properly, the sediment bowl on the pump should start to fill with gas in just a few revolutions of the engine at cranking speed. I have a spare pump that I rebuilt and test ran on my 1932 model. I would loan it to you to try on your car.
Regards,
Steve Stevens

Got the new diaphragm in and put the pump back on, but still no gas coming through. I sucked some gas up to the pump inlet line with a hand pump, so I know the line's not clogged. Turned it over several times, for 10-20 seconds, but nothing comes into the bowl. None of the valves in the pump appeared clogged, but can they go bad? I primed it a little by putting some gas in the outlet opening, carb inlet, and the pump inlet.
Thanks

I won't be there this year, but thanks. I ordered a sheet yesterday and they usually get things to me in a day or two.
Thanks again

Are you coming to Auburn for the reunion? I could bring a peice for you.

Thanks, I'll get a piece of that and give it a try

I have used 1/16" reinforced Buna-N sheet, and it works great. You can get it at McMaster Carr, part # 1890T12

www.mcmaster.com/#1890t12/=8lrajb

Good luck! Joel

I took the pump off 1931 8-98A today and the diaphragm is dry and cracked (a little). I tried to hand pump some gas first and it was dry as a bone inside when I opened it. Can I get a diaphragm for this, do I need to make one (what to use?), or send the pump somewhere for a re-build? Not interested in putting on an electric pump.
Thanks