XK140 SU fuel pump more audible than usual

My XK140 fuel pump began making considerably more sound while out on a drive. Idling at stops it is now audible whereas before (the previous 20 years ~ 10K mi) it could only be heard (ignition on) before start. It is an original style square body SU with solid lines in & out and rubber isolator mounts. The ticking is at normal intervals and there doesn’t seem to be any reduction in fuel supply, performance is as it has been. The sound difference is as though is has been mounted without the rubber isolators which are in perfect condition. In the past I have rebuilt and repaired many of these pumps but never had a noise such as this. Any suggestions from those of you out there with greater expertise on this subject? Thanks.

Just a guess, but what would happen if say the spring broke and the diaphragm or its iron bit now hits the housing directly?

David, yes it’s something internal, instead of the pleasant tick,tick,tick it is more of a knock, knock, knock. I can’t say for sure when it started, I had it out for a 40 minute drive 20 of which was freeway speeds (70 - 80 mph) when I came to a stop is when I heard it and when I started out on the drive it sounded normal. A broken spring I believe would severely limit fuel volume so it may have occurred during the high speed run, the remainder of the drive was slower speeds so less fuel demand. I’ll have to do a volume test before I take it apart. Regards, Jim.

I can’t remember but is the pump mounted on rubber bushings. If so one or more may be loose or missing. I do know the pump requires a separate ground wire.

Pat, yes the pump is isolated from the frame with rubber mounts which are all intact and you are correct it does have a grounding lead from the pump body to the chassis. Regards, Jim

Hi Jim you could also check that the hard fuel lines aren’t touching the sructure somwhere and transmitting the sound.

Where it passes through the chassis rail there should be a rubber grommet on both sides.

Randall, the mounting of the pump and lines are factory original, nothing has changed physically to account for the increase of sound from the pump. Thanks.

Rob, both grommets are present and the line passing through doesn’t actually touch either one, the first contact between the line and frame rail is ~ 1 foot further forward where it is held in place by the correct clip. The arraignment on a 140 is different from the pictures you provided but the basic idea is the same. Thanks for that suggestion, regards, Jim

Just got to eliminate all possibilities.

Randall Botha

I guess you’re left with taking it apart and having a look at the brass donut rollers, unless somebody has substituted the plastic spider to center the diaphragm. Can’t think what else would make a noise.

Rob, that is undoubtedly where I am headed. I purchased this pump 20 some years ago from SNG a new (remanufactured?) electronic conversion +ground unit which a has worked flawlessly for the ~10K I have driven so far. A recent spirited drive after the noise increase showed no sign of fuel supply deficiency so it is just a matter of the increase of sound that concerns me for reliability in the long term. Thank you Rob and all for your comments and suggestions. Regards, Jim.