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Discussion Topic:
Fuel Pump Push Rod
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Dolman |
07-28-2011 @ 7:01 PM
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New Member
Posts: 177
Joined: Dec 2010
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I finally have a fuel pump that works but only produces 5 inches of vacuum installed. It produces 10 inches on the bench. Suspect a worn push rod. What is the procedure to pull the rod to measure it? Engine is a '34 V8.
This message was edited by Dolman on 7-28-11 @ 7:41 PM
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supereal |
07-28-2011 @ 9:43 PM
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Senior
Posts: 6819
Joined: Oct 2009
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Be sure you have the correct push rod if you have changed it. The rod for an aluminum intake. Is different from the cast iron rod. To pull the rod, remove the fuel pump stand and simply pull the rod up and out. It isn't unusual to get more vacuum when pumping the arm by hand on the bench because the motion of the rod doesn't work the pump to the extent that you do by hand. A fuel pump can be good inside, but lack stroke if the arm pivot is worn.
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TomO |
07-29-2011 @ 7:09 AM
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Senior
Posts: 7271
Joined: Oct 2009
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I like to check the push rod by measuring the travel. It should be about 1/4". Low vacuum can also be caused by leaking input valves or a stretched diaphragm. The new Airtex pumps that I checked last year would only hold 5" of vacuum, but would produce 10" on the car. I don't like them because the cup is so flimsy that it is hard to get it in place on the push rod.
Tom
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supereal |
07-29-2011 @ 9:59 AM
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Senior
Posts: 6819
Joined: Oct 2009
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In addition, some of the new replacement pumps have an "improved" linkage that doesn't seem to me to be of much benefit, unless I missed something. Like Tom, I find the rod cup to be flimsy, and the pump is best installed by pulling the stand, attaching the pump, and then setting it down on the rod. I usually put some heavy grease on the cup to hold it in the correct position as I lower it. If the cup isn't properly seated on the rod, the stroke, if any, will be greatly reduced.
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Dolman |
07-29-2011 @ 12:35 PM
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New Member
Posts: 177
Joined: Dec 2010
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I tried pulling up on the rod but something is preventing it from lifting all the way out. It comes up about 1/2 inch before it hits the resistance. Electrons are my friends but this hard mechanical stuff is alien. Bear with me MG, I am not using this forum as a plaything
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MG |
07-29-2011 @ 12:45 PM
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Posts: 1263
Joined: Nov 2009
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Nice shot.....
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35ragtop |
07-29-2011 @ 1:39 PM
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Member
Posts: 57
Joined: Aug 2010
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Hi Dolman,I had this experience with my 35. I found upon removing the inlet manifold that the metal tube ( there has to be a proper name for it ) had been installed on the wrong side of the manifold. ie it had been inserted into the inlet manifold from the underside instead of the top. This prevented the push rod from coming all the way out. The car ran fine like this with no problems.Interesting! 35ragtop
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Dolman |
07-29-2011 @ 2:01 PM
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New Member
Posts: 177
Joined: Dec 2010
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35ragtop, my '34 pickup was running fine too until the fuel pump and right distributor cap went toes up. I definitely want to measure the push rod but considering your experience it sounds like major surgery to correct the installation. (My brother would tell me I didn't have a big enough hammer.) Here's hoping that Supereal, TomO, or Stroker, to name a few of the guys that have been down the road and back with flatheads, will come up with a simple solution.
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shogun1940 |
07-29-2011 @ 2:37 PM
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Member
Posts: 464
Joined: Feb 2010
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the cam lobe determines how high the push rod goes up and down so check that first
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37RAGTOPMAN |
07-29-2011 @ 5:49 PM
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Senior
Posts: 1970
Joined: Oct 2009
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Here is some info you might need, the FUEL PUMP push rod length 48-9400-A 8.872 CAST IRON INTAKE 8 7/8 48-9400-B 7.872 ALUMINUM INTAKE 7 7/8 out of the GREEN FORD PARTS BOOK, my 3cents 37RAGTOPMAN
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