Fuel Pump rebuild 1973 911T

steve meltzer · 03-24-2025, 02:00 PM

The electric fuel pump on my '73 911 T motor is leaking. The pump actually works fine, but it's leaking and I suspect that the O-rings of which there are three, need to be replaced. Does anyone know the size or source for getting these O-rings? It looks like trying to find them will be a nightmare, although I did see one post where the rebuilder found them at his FLAPS. I find it hard to believe that O'Reilly will have this, though I admit I haven't looked anything yet. Perhaps there is someone who actually does the rebuilds that I might contact you. steve

stownsen914 · 03-24-2025, 03:34 PM

I don’t have the exact info you are seeking, but I went through a similar exercise a few years ago with a Bosch fuel pump out of an older Mercedes, which is similar in design to the ones in Porsches . No rebuild kits were available. I took apart the pump, measured the orings, and ordered some from McMaster Carr. And voila, I had a leak free pump again.

I’m pretty sure there are threads on here about rebuilding the early Bosch pumps, you may find more specific info there.

steve meltzer · 03-25-2025, 05:48 AM

A little tricky to measure the size of the O-rings, but I came to the same conclusion you did and will order from them shortly. Thanks again, Steve.

stownsen914 · 03-25-2025, 08:54 AM

You're right that measuring orings is a little tricky. The cross section was the easier part to measure. Just check in a few places, keeping in mind that an old oring is probably squished in one dimension.

For the diameter, the large oring that is the diameter of the pump body is the harder one to measure. You can put it on a flat surface and do your best to measure a few different places circumferentially while taking care to not distort/compress the oring while measuring.

Doing those two things got me close enough to figure out which size orings I needed. It may also be possible to measure the groove in the pump where the oring goes to validate your measurements.

steve meltzer · 03-25-2025, 10:30 AM

I measured the cross-section several times using a pair of calipers. Using the calipers to measure the ID was difficult dammit, but the measurements I got correlated pretty well with what I got laying the O-ring on top of a flat metal measuring stick. I actually ordered O-rings on either side of what I believe to be correct ones, and hope that McMaster-Carr has a generous return policy! Thanks again. stebve

BimPorDuc · BimPorDuc's Garage

You might try contacting Apple Rubber Products or Zatkoff Seals and Packings. They both specialize in O-Rings. McMaster is just a catalog supply house. Zatkoff stocks metric o-rings which is likely what's in that Bosch pump. You might also see if the seal is available in Viton. It's much more chemically resistant than typical rubber.

BTW I hear the newer "correct" pumps aren't as reliable as the older ones. Some people upgrade to a Pierburg pump with the same pressure and flow capacity for CIS.

BimPorDuc · BimPorDuc's Garage

You might try contacting Apple Rubber Products or Zatkoff Seals and Packings. They both specialize in O-Rings. McMaster is just a catalog supply house. Zatkoff stocks metric o-rings which is likely what's in that Bosch pump. You might also see if the seal is available in Viton. It's much more chemically resistant than typical rubber.

BTW I hear the newer "correct" pumps aren't as reliable as the older ones. Some people upgrade to a Pierburg pump with the same pressure and flow capacity for CIS.

steve meltzer · 03-26-2025, 05:22 AM

@BimPorDuc thanx for the info. Lemme file that away to use if the Viton ones i ordered don't work. steve

E Sully · E Sully's Garage

If you decide to follow through make sure the o-rings are rated for E10 fuel. I also wondered if the original was round and looked square from years in place or was a square cross section o-ring. I took a leaking one apart but decided against trying a rebuild myself. I was worried about re-crimping the housing and getting good seals at it's rated pressure.
Also, the one by the electrical connector seems tough to get to since the wire connections seem to be staked.
I would say to either convert to one of the newer pumps with a hose and fitting change, or send out the original for rebuild.
Fuel Injection Corp. is highly rated.
https://fuelinjectioncorp.com/products/fuel-pumps/

steve meltzer · 03-26-2025, 12:34 PM

I decided that I will return the O-rings to McMaster-Carr
and my way to the post office to send my now dissembled fuel pump to fuel injection Corp. thanks again, Steve

gamin · 03-26-2025, 01:39 PM

Good move. I had 2 early Bosch pumps done by Fuel Injection Corp, Livermore CA, I think. I received 2 beautiful pumps. Looked better than new. One has been running in the '70 for many years. One of the best outfits that I have worked with in 50+ years.

Quickstep192 · Quickstep192's Garage

Check your fuel lines. I had the same problem a while back. I discovered that my fuel lines were also unserviceable and should have been replaced.

I ended up getting an RS tank and putting a Bosch inline pump up front. The tank+pump were less costly than a replacement Porsche pump.

steve meltzer · 03-26-2025, 03:25 PM

Thanks guys! I feel better already! s

stownsen914 · 03-27-2025, 04:08 AM

Viton seals will be the best bet for fuel resistance. Rebuilding these isn’t hard but a good rebuilder can no doubt get the job done.

HarryD · 03-27-2025, 08:54 AM

Just curious. How does the cost of the rebuild compare to the universal Bosch replacement pump (~$90) plus, if needed, a custom line from Len (~$175)?

rowingone · rowingone's Garage

I was not happy with Fuel Injection Corp. I sent my original 1972 fuel pump to them to rebuild and they sent a new one instead . . they did send my original case back after I complained but I wanted my pump rebuilt . . not a new non original one.

steve meltzer · 03-27-2025, 12:12 PM

The correct three port fuel pump for my car (69E with 73 T motor) cost about $1000 new. Clearly the cheapest route was to replace the O-rings, but I decided to let Fuel Injection Corp. fix it at $475. I hope it was the best decision. It certainly was not the cheapest. I was not interested in plumbing things for a universal pump. Steve

HarryD · 03-27-2025, 03:33 PM

Quote:

Originally Posted by steve meltzer

The correct three port fuel pump for my car (69E with 73 T motor) cost about $1000 new. Clearly the cheapest route was to replace the O-rings, but I decided to let Fuel Injection Corp. fix it at $475. I hope it was the best decision. It certainly was not the cheapest. I was not interested in plumbing things for a universal pump. Steve

Hope it turns out ok.

I replaced my failed pump with the Bosch unit and the custom Len line. If you have a lift or can get the car up a few feet, it was not hard.

stownsen914 · 03-28-2025, 07:01 AM

If you don’t care about original, it is possible to adapt a modern fuel pump to an early 911, as long as your fuel system has a return line to the tank. I know MFI cars do, not sure about carbed. Keep in mind that for MFI the pump needs to be happy working at 1 atm / 15 psi. Carb pumps often are rated for 10 psi or less.

The third port on the early Bosch pumps is to allow for over-pressure relief, I assume in case of fuel line blockage. The third port goes to a tee in the fuel return line. It’s possible to use a standard two port pump as long as it is rated for the correct pressure - the MFI fuel filter stand has a check valve in the return circuit that acts as a simple pressure regulator to keep pressure at 1 atm.

steve meltzer · 03-28-2025, 10:53 AM

thanx for all of the info! s