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1954 Cadillac fuel pump

Started by Zanderg12, May 21, 2021, 07:53:17 PM

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Zanderg12

I have a 1954 Cadillac devile and I'm having problems with the mechanical fuel pump,I put a new one on,and the fuel push rod is moving but the fuel pump isn't pumping any gas from a bottle,if anyone knows anything or any fixes for this .

J. Gomez

Quote from: Zanderg12 on May 21, 2021, 07:53:17 PM
I have a 1954 Cadillac devile and I'm having problems with the mechanical fuel pump,I put a new one on,and the fuel push rod is moving but the fuel pump isn't pumping any gas from a bottle,if anyone knows anything or any fixes for this .

A few questions;   ???

Do you have the correct fuel pump rod, is yours still the OEM?
Is the rod moving freely up and down with no binding during the full crank rotation?
Did you have the same condition with the old fuel pump?

When you installed the new fuel pump you should feel the rod pressing the fuel pump rocker arm even with the rod all the way down. The fuel pump rocker arm should be about 1/3 pushed with the rod down and just about full pushed when the rod is all the way up.

Good luck..!
J. Gomez
CLC #23082

Lexi

Agree with Jose's points. In addition, ensure that you do not have a "strainer nut" air leak. That refers to the large (7/8" I think) bolt head on top of your fuel pump. If that is not tight & is leaking air, your fuel pump's efficiency will drop as air will be sucked in. This nut may still be tight but gasket is no good and can leak air. My new pump leaked air from that spot when new. Note: You won't see fuel leaking from there if a problem but air being sucked in at that location can cause your pump to fail.

If you have a vacuum gauge; Vacuum test at idle with the gauge at pump INLET side. Disconnect line here and fit gauge to pump. Start car. A normally filled carb bowl will permit your car to run for at least a minute or more with the fuel pump disengaged. If your bowl is empty as pump not filling, you can fill the carb manually through the vent tube. Run car and observe gauge. Normal minimum vacuum should be 10 - 13 inches, I believe for your type of Cadillac pump.

Pressure test at OUTLET side of fuel pump. The reading on your vacuum gauge should be 5.5 psi with engine running at idle, (4 - 6.5 I believe is the considered spread for that year of Caddy fuel pump). I believe there is a separate section to read this on your vacuum gauge dial. Hope this helps you. Clay/Lexi

P.S. 1. Fuel pump rod should be 7.1425" - 7.1475" and travel the required distance to properly activate the pump.

P.S. 2. I have been told that if you bench tested the pump's lever and pushed it too far, you may negatively impact the pump's diaphragm. Have not done or checked on this myself, but mention for what its worth. Makes sense as maximum push rod travel is only about 1/4 inch. So if the pump permits one to over exceed that threshold limit, that cannot be good for the pump.

James Landi

"I have a 1954 Cadillac devile and I'm having problems with the mechanical fuel pump,I put a new one on,and the fuel push rod is moving but the fuel pump isn't pumping any gas from a bottle,if anyone knows anything or any fixes for this ."

One more consideration:   pack some grease into the pump's cavity to ensure that the pivot is well lubricated.  In the original GM pump of that era, a zerk fitting for greasing was included in the design.  With out the grease, the pivot for the "drive arm" wears out, the arm loosens and the pump pressure eventually fails. 

D. Mailan

I agree with everyones comments above. My dad and I have owned several 56, 58, 59, 60, and 66 Cadillacs and have had many issues with reproduction mechanical fuel pumps. Many times you will be driving on the freeway and the car will drive fine. Once you pull off and get on to the streets, the car will sputter and the fuel bowl will be empty. After countless times replacing reproduction fuel pumps, we found the culprit of the problem one day driving back home in our 1960 Cadillac. From this day on we have never had a fuel pump issue on any of our cars since. I suggest that you take off the top of the fuel pump and check if the valves inside are sitting correctly. Sometimes they will come out of their place when the car warms up and cause the fuel pump to pump less fuel or none at all. Another thing to check is if your fuel pump arm is sitting on top of the pushrod. Like said above by the others, make sure you don't have a strainer leak. A loose strainer nut will definitely cause fuel pump issues. Even if barely loose, it will cause the fuel pump to lose a lot of suction. Our 1956 Eldorado had an issue where the reproduction fuel pump was barely pumping fuel but just enough to keep the level in the glass filter about a quarter full. After tightening the strainer nut which was only barely loose, the fuel filter bowl became full. 

Good luck!

Michael Petti

A  fix for reproduction fuel pumps are to use Locktight to cement  the check valves in position. I used 242 which is the fuel resistant stuff. Another fix is to replace the self tapping screws holding the two halves together with nuts, lock washers and bolts or at least put lock washers on the screws you have if they are long enough. The originals tend to back out causing air leaks.
Add these to the suggestions above.

fishnjim

If it's the combo fuel/vacuum, then it can leak more places.   My parts list calls for this in '54.

I don't know what's wrong with the manufacturers, I've contacted them, but apparently not interested. since they're selling many pumps.   I rebuilt the combo on my "P" without problems, but they actuate direct off the cam.   
All the push rod type pumps in my opinion from back in the day, eventually had issues.   It's just a consequence of the design.   That's why they got rid of the pushrod design.   I'm changing to mine electric.   Just a few more hours of tubing and wire hook up and I'm hoping to not have to deal with this again.   But is it ever that easy with these '50s era?

I'd definitely prime the pump before I operate it, as they have little suction so once air locked they won't operate.   They require many rpms so they won't deliver much if you try to manually pump it.  Mine worked fine after a new fuel line and until I had the motor rebuilt the, I've been through 3-4 new pumps since without success.   Unfortunately I threw out the old pump.
I'd suggest to rebuild the OEM one, if you still have, with ethanol resistant parts.   
I had na electric pump I took off the car when I got it.   I use it to transfer gas.   I tried it this time and was not pumping.   I disassembled and the diaphragm was mush.   So that "new" gas is nasty.