Why is the fuel pump leaking?

[ttraut@unlockit]

I put the rear of my 69RR on jack stands to remove the gear case; the rear was jacked up about 9" off the ground.

This morning, I noticed the fuel pump leaking -- a drop every 30 seconds or so. While it's tough to tell, it LOOKS like it's leaking around the bottom rubber gasket (see picture).

It's a new fuel pump on a newly rebuilt with about 15 hours of running time on it. I have never had a leak.

After finishing my rear-end work, I took the car back down off the jacks; sitting level again, there's no leak.

Could tilting the car up cause the fuel pump to leak? Why?

Thanks, Terry

[pishta]

Yes, it is clear that the orientation is causing the fuel leak. I would check the fittings as the pump pulls fuel and the leak looks like it may be coming from that fitting. That is an NPT fitting going into the pump body, right?

[ttraut@unlockit]

Pishta,

Thanks for the quick reply. You said, "orientation is causing the fuel leak." Do you mean the orientation of the car? If so, why would that cause the leak? I thought the fuel system was pretty self-contained/enclosed. In fact, my thought is that I could stand the car on it's nose and the carb bowls may empty and I might lose gas from the gas tank vent, but that would be it.

Now regarding fittings, you are most likely right since I put the stuff together That IS a NPT fitting on the fuel pump. I had to use two connectors to get the hose to the pump. Both were silicon sealed and tightened.

The big puzzle is why does it leak when tilted and not leak when not tilted? is there no gas at those joints when not tilted? And why doesn't it leak when running?

Thanks in advance; I'm trying to learn how all this stuff works and appreciate your insights!

Terry

[pishta]

Here is a test, or a question. How high is the fuel level in the tank in inches off the ground, then how high is the fuel pump inlet? (assuming the car is level/normally sitting). If the fuel level is higher in the tank, then naturally it is going to seek its own level on the other end, the fuel pump end. Inside the fuel pump, there are 2 (or 3) check valves, in opposite directions. It takes a force to unseat the inlet check valve, either vacuum, or pressure (both are present) If the pressure of the fuel column (remenber it is measures in inches, the higher ther fuel level the stronger the pressure)) can overcome the inlet check valve, the fuel pump will flood but it probably will not overcome the outlet check valve. The additional pressure in the pump body may be just enough to weep fuel out of a normally low pressure gasket/fitting. Those pumps are easy to R/R and the fittings are also eazy enough to seal once the problem is found. The leak will also drip at its lowest point, so it may be leaking out somewhere else. Good luck. A static leak in an automatic trans will leak if parked, but will not leak once the car is running (like a selector shaft seal) because the fluid level is normally lower than the seal.

[ttraut@unlockit]

Time for some rework --- stuff I'm good at! I'll check out the connections this weekend. (After I drop the tranny and replace the wrong sized pilot bushing in the engine!!!! YIPES!)

Thanks, Pishta!

Terry

[charger_dan]

terry,
i think pishta's right on the money. most likely a fitting that needs
a little attention. if there's one thing i can add: when tightening those
npt fittings, go easy -- it's not difficult to tighten them just a bit
too much and crack the pump body at the fitting. this was a le$$on
i learned first hand.
good luck
dan

[ttraut@unlockit]

I'm just closing up this thread even though it's several months old.

It WAS a fitting issue. I had used flare and NPT fittings together (I forget which was which). I now have a dripless connection using the same type fittings (I think flare...)

Thanks!

Terry

[pishta]

wow, I remember that whole thread...Good