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MG TD TF 1500 - Fuel pump help required.

Hello all. I have just gotten a new diaphram and gasket for my TD fuel pump. SU #AUA150. The pump was functioning properly but developed a fuel leak at the diaphram, and body gasket. On disassembly the body gasket was "rotten", and the diaphram was deteriorated to the point of leaking. I got a new diaphram and gasket from Moss, disassembled and cleaned the pump, points and valves. Reassembled, and all looked great.

Pump does not work, it refuses to cycle. Coil is good and the diaphram was set to point rock-over and backed off 2/3 of a turn. With the body removed and the brass alignment washers removed it will work. Put back together... no go.

What am I missing here? Help appreciated.
C.R. Tyrell

I suspect that Mr. David DuBois will chime in here with his extensive experience in this area. I spent a good deal of time trying to renew my fuel pump a couple of weeks ago. I never did succeed in getting it to work properly. I eventually discovered that the bakelite points platform was cracked due to over tightening of the mounting screws. I honestly don't know if I was the culprit or if it was a DPO. I am not overly impressed with the lack of support under those screws as it is easy to crack the piece. So, I am in need of a new bakelite piece if anyone has one available.

I wonder if you failed to use the match stick under the points with the pump energized before tightening the diaphragm in place. I think if you miss this step then the diaphragm is unable to flex enough to pump. This is speculation on my part, as I have not yet gotten my pump to work even though I have become quite expert at tearing it apart and reassembling it in every conceivable incorrect manner.

Wishing you better luck than I have had to date!

Kirk Trigg TD24953

Both of you send them to Dave, and have him rebuilt them as solid state pumps. Worth the money every day - do you really want a failed pump by the side of the road?

Tom Lange
MGT Repair
t lange

Tom the pump I am replacing the diaphram is a spare. To date the other pumps in my cars are working flawlessly. Only other pump I had trouble with was one with the electronic circuit board. Never had a problem using the ones with points. I clean the points as a matter of regular service every spring. Kirk, I did shim the diaphram when tightening the screws. The only thing that I can see is that the rod on the diaphram may be in some way jamming in the pump. Bakelite is all in good condition as are the points and holders.

This is becoming a personal challenge. Dave Dubois has helped me in the past and I use his articles to help with this. This is the third pump I have rebuilt and the others work fine.

Is the Moss part somehow different than the original?
C.R. Tyrell

"This is becoming a personal challenge. Dave Dubois has helped me in the past and I use his articles to help with this. This is the third pump I have rebuilt and the others work fine."

I fully agree with the personal challenge part. I have read Dave's articles and posts on this board with great interest for the past two years now. I may well end up with one of his solid state units in the end. But, since I am nowhere near the completion stage of my project, I'm gaining some sort of satisfaction from trying to understand all I can about this car. Even when I fail miserably, I find myself enjoying the process. I will readily admit that there are many areas of this restoration that would be better and more cheaply performed by others. As I get a little closer to the finish line I will most likely use their services more and more. But, for now, I continue blissfully on in my ignorance and occasional frustration.


Kirk Trigg TD24953

i like the points pump too. i did install an arc suppressing transistor across the points. i also carry a bit of hose and a rubber stopper with tube and a blood pressure bulb for air pump as bud i think..o this forum..between the pump and the standby air pump you are never stuck by the side of the road. regards, tom
tom peterson

Just send to to Dave Du boos. For the money you will be satisfied. He has done several for me and will likely do more.100%

Brian Warmuth

Sorry about my chubby fingers on the last post!

Oh my! I've got several issues in one thread. I'll start with Tom first - Remove the transistor! The only thing you will accomplish with that is to trade one problem for another. The points have to have a bit of arcing when they open to burn the film off them that develops over time. With the transistor in place, all arcing at the points is eliminated and there is nothing to keep the film from building up, which will stop the pump cold. If you don't want to go to a solid state pump, put a diode (preferably a TVS diode) across the points (or across the coil). And yes, I know, I probably wrote the article you used to install the transistor, but that was my first attempt to eliminate burned points - it did that, but caused the filming problem.

Kirk - The broken pedestal is a very common failure - one has to have a calibrated hand to keep from breaking them (I've broken my share). You can get a new pedestal from Victoria British E-mail me at and I'll send you the P/N. The new one is constructed differently, with support around the mounting screw holes.

CR - I suspect that you have the wrong diaphragm for your pump. The AUA 150 is a high pressure pump and uses a different diaphragm than the AUA 25, which is a low pressure pump and what is shown in the catalogs. The two diaphragms are not interchangeable. If you will send me a picture of the top of the diaphragm (where the spindle is) and the bottom of the coil housing, I can tell you if that is the problem.

Do you still have the all electronic pump? If so, I can probably help you get that running too. Remind me of that when you send the pictures. Cheers - Dave
David DuBois


You have mail.


Kirk Trigg TD24953

I have given up on SU fuel pumps and now fit modern electric fuel pumps to my cars especially when the pump is under the car and not seen. My F2 Magna is a case in point, in that case I have routed rubber fuel hose through the original SU Fuel Lifter (which, I am told, were troublesome). They "rattle" away but are inaudible once the engine starts and I have found them 100% reliable.
Barry Bahnisch

Thanks Dave. I will send you some pictures of the two diaphragms and the bottom of the coil housing. I suspect if it is a high pressure pump the original was replaced at one time with this one. The electronic pump I had has been returned and I am awaiting a replacement. The car it is going on is undergoing restoration. (MGA).
C.R. Tyrell

hello dave, my is a TVS diode per our conversation prior to the work..i am obviously not a sparks guy. thanks again. regards, tom.
tom peterson

"I have given up on SU fuel pumps and now fit modern electric fuel pumps"

I am not sure why the inference that SU pumps are old fashioned (Outdated?) when when the Facet pumps operate basically the same way a SU pump does, or why Fuel Flow in New Zealand goes to such great lengths to produce a pump that copies all the operational characteristics of the SU pumps. The SU pumps are impulse pumps and share the same operational characteristics of any other impulse pump.

"the original SU Fuel Lifter" That would be the old Pertolift style fuel pump, which is in fact is outdated and no longer manufactured. That pump worked by pulling fuel from the tank into a holding chamber, which then fed the fuel to the carburetors via gravity. That was about one step up from the high mounted fuel tank in the first American Model T Fords, which depended entirely on gravity to get the fuel from the tank to the carburetors. That resulted in having to back those cars uphill. Cheers - Dave
David DuBois

A few years ago, I sent my pump to dave and never looked back! Best thing I ever did.
Bob McLeod TD 5618

I have tried the electronic conversion and have had no long term success. The one su factory electronic pump
was 100% reliable. The point driven pumps on all my british cars occasionally require point filing(or replace) and readjusting, but you can see it coming and do at the side of the road if you ignore the warning.
Even though I gave up on the solid state mod, I can still get out of the house by telling my sweetie "I gotta go fix my fuel pump"! Really.
Besides, it's fun to watch the sparks... Only one minor fire in 30 years. Safety Fast!
cj schmit

This thread was discussed between 27/07/2013 and 29/07/2013

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