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SU Fuel Pump ReBuild

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DenverMGB

DenverMGB

Freshman Member
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1979 MGB - SU fuel pump model AZX1307

The fuel pump stopped running and was leaking around the diaphragm so I decided to go for a minor rebuild - gaskets & points - using a kit from Victoria British. The kit includes a replacement diode so I need to get the old one off but it's red-wire tag is under what looks like a pair of lead washers loced on to the bolt that sticks up from the bakelite. I can't shift those washers without hacking them off with a sharp knife. If I do that, what do I replace them with? Does anyone have experince with these pumps and could offer some advice on how to replace the diode? Anything else I should be wary of?

Thanks!
 
Check the diode/resistor assembly for any burned or melted areas on the periphery. If there are no signs of the assembly having any damage, then there is no reason to replace it and I would suggest that the original one be left in place. If there is damage to the assembly, then you will need to replace it. There is only one lead washer used under the power terminal nut (which is dished on the under side). If you need to replace the diode/resistor assembly, you will need to have the washer, but the cost of having one shipped from V/B. E-mail me at SUfuelpumps@donobi.net and I can sell you one and the only shipping cost will be a $0.42 stamp.
Cheers,
 
You west coast guys keep *funny* hours... :jester:

DenverMGB: Dave is an old hand at these pumps. Follow his advice, you're in expert hands.
 
My pump seems to have given up the ghost. It pumps when I tap it, but only once or twice. I have opened it up, and all looks well.

I am wondering if the diode could be the problem. Now, I don't exactly understand what the diode does, so I could be shooting in the dark, so please excuse my ignorance. :smile:
 
1965_MGB,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]It pumps when I tap it, but only once or twice[/QUOTE]

So, OK... Was the pump connected to the fuel lines (in and out) when you checked it?

Were you having a fuel starvation problem that caused you to look at the pump?

When I suspect a fuel problem, I disconnected the fuel line at the carbs, inserted the line into a bottle and turned the key. Fuel should flow and the pump should merrily tick away since no pressure is established.

As you already know, the pump only pumps (ticks) when the line pressure drops below the designed pressure... So, when you first turn the key it will 'tick,tick,tick' and then go quiet. When you drive the car the pump will pump (tick) as long as there is a need to re-pressurize the fuel line as the fuel flows into your carbs..

If all of the seals and the diaphram looks good and if the procedure above works, then perhaps the problem may not be the pump.
 
Ron, tapping a diode won't make it work again if it's damaged. It's also there to protect components and isn't actively involved in pump operation.

Based on what you're describing it is very likely that you have problems with the contact points inside the Bakelite cover mentioned above. I'm sure Dave will check back and post the correct solution but I would suggest removing the cover and drawing fine sand paper through the pump's contact points followed by pulling a bit of clean paper between them to remove any debris. If the points are still close to being in adjustment, cleaning with fine sandpaper is likely to restore your pump to operation.

Edit: Two "Rons" posting in a row.
As an addendum to my post, follow Ronzet's suggestion to confirm the fuel lines are open and capable of pumping before sanding the points as I suggested. As he mentioned, the pump will only "tick" when it can move fuel.
 
Ron (1965_MGB) - The diode/resistor assembly is there to suppress arcing at the points (note: it suppresses the arcing, not eliminate it). Having to tap the pump to get it to run is normally an indication that the points are worn or dirty or both. Ronzet's suggestion of checking the flow to the carburetors is good, once the pump is operating properly and Doug Lawson's suggestion to clean the points with some 400 grit sand paper is the place to start (you may have to do some minor disassembly to get the lower points cleaned. contact me at SUfuelpumps@donobi.net for instructions. Also see the article Fuel Delivery Troubleshooting Guide under the SU Fuel Pump Articles section of my web site at: https://homepages.donobi.net/sufuelpumps/
Cheers,
 
I once traveled the length of Alligator Alley with a suddenly intermittant SU pump... thumping the bulkhead with a two pound granite ROCK to keep it ticking over...

Just why did I HAVE a two pound granite rock aboard, you ask?? As a WHEEL CHOCK! To substitute for th' missing handbrake cable, of course.

Twenty minutes of knobblin' with some #600 wet-or-dry in the in-law's driveway in Miami and all was fine again.

Ahhh, youth. :jester:
 
DenverMGB,

I just gotta say this.... Your Avatar is, well, whew, I dunno, it's, well, ahhh.. interesting, no it's unique, no it's just plan scary... :jester:
 
Hi all, thanks for the quick responses (even the hijackers!). Sorry I didn't wait up for Dave's post - I'm not that far west!

In order....

I checked the diode and resistor package and all looks fine, like new, so I'll leave it in for now. I can bench test the pump when I'm done so it won't be too late to change it out. Thanks for the offer of the washer. Considering what I paid VB for handling AND shipping on top, to get the kit here before the weekend, 42 cents is a bargain!

The avatar is called "Mona Bean" coz I have a passing resemblance to Rowan Atkinson aka Mr Bean - not to the Mona Lisa!
 
I once drove home from my sister's house at night while holding a wooden toothpick in the melted toggle switch for the headlights to stay on. It was only about 15 miles, but boy were my fingers cramped up when I got home.

*not on topic, just trying to one-up Doc's story. :devilgrin:
 
My three 'dead at the side of the road' experiences have all been SU pump related, and all had to do with dirty points...the last one, some crud had slipped down under the front point's 'spring' and prevented it from releasing the rear point... little electrical cleaner and tapping, as well as regular clean (have since used 400 grit paper) worked like a charm!!!!

Oh wait...i once was dead at the side of the road with a broken rocker...[censored]..and it only lasted 56 years....you just don't get em like you used to??????
 
Sorry for the hijack on this one. I probably should have started a new thread, but it just happened that I was trying to empty my (now rusted through) fuel tank, and the pump was being no help emptying it.

Thanks to all for helping with the problems I am having. I now return you to the original thread starter. :smile:
 
Thank you! I'm back with a freshly rebuilt pump, just itching to plug it in and hear it click.

A couple of points (ouch!) to note for anyone about to attempt this for the first time....

The kit from VB (part 3-2058, page 116) is a genuine SU part but does not include everything you might need. No diode but a varistor instead; has the lead washer (see above); only 1 o-ring for the in/outlet banjos (if you pump has them, you'll need 2); only 2 fibre washers (4 needed if your pump doesn't use o-rings).

The instructions talk about an armature guide plate but the kit doesn't have anything like that. In the end I decided the 5 figure-8 shaped bits of plastic need to be crammed into the underside of the diaphragm to keep it central. Like a guide.
 
You haven't put power to it yet? You have more patience than I do... I would have powered it up immediately.

GB, I had forgotten that you're in Ontario. I just made my travel plans for Niagara Falls. We'll be up your way in 3 weeks.
 
Work, work and more work I'm afraid. Still not done with Friday.... I should have time tomorrow, depending on the "Honey-Do" list of course. :smirk:
 
Good luck, when I rebuilt mine, with the help of David D. I bench tested it with Marvel Mystery oil, which is a pretty low viscosity stuff and not overly combustable (like gas is for instance), of course with some hoses to pick up the fluid and deposit it in the same container so it could run continuously, in my case a two cup pyrex measuriung cup, but anything will do.

Turned it on and off a few times, left it running in the garage while I watched a little TV (you want it to run maybe for hours as you go down the highway) turned it on and off to make sure it would start after stop.

After a few hours of running an a few dozen starts and stops figured it was OK to put it on the car, no problems.

Good luck


Greg
 
DenverMGB said:
Thank you! I'm back with a freshly rebuilt pump, just itching to plug it in and hear it click.

A couple of points (ouch!) to note for anyone about to attempt this for the first time....

The kit from VB (part 3-2058, page 116) is a genuine SU part but does not include everything you might need. No diode but a varistor instead; has the lead washer (see above); only 1 o-ring for the in/outlet banjos (if you pump has them, you'll need 2); only 2 fibre washers (4 needed if your pump doesn't use o-rings).

The instructions talk about an armature guide plate but the kit doesn't have anything like that. In the end I decided the 5 figure-8 shaped bits of plastic need to be crammed into the underside of the diaphragm to keep it central. Like a guide.
Click to expand...

A varistor or a TVS is the more modern replacement for the diode/resistor assembly and is not polarity sensitive. If you need the 'O' ring, I would call V/B and tell them that you were shorted on 'O' ring - same thing for the fiber washers (they are not a locally procurable part like the 'O' ring is). You can get away with reusing the fiber washers, but not the 'O' ring. for future reference, the 'O' ring is a standard 2-117 (or just 117). "The 5 figure-8 shaped bits of plastic" are the present day replacement for the centering plate and they do a better job than the old centering plate, just make sure that the diaphragm is adjusted correctly (using the old centering plate temporarily) before putting the figure 8 pieces in place. The figure 8 pieces make the diaphragm very difficult to turn and can cause the diaphragm to leak if you pull it around by the fabric. If the V/B kit didn't include an assembly and adjustment procedure and you don't have good, updated procedure, e-mail me at SUfuelpumps@donoi.net and I'll send you one. If the pump is not adjusted correctly, it won't run or will run but not at full efficiency.
Cheers,
 
Thanks for the advice Dave,my pump has 4 fiber washers so I had to re-use 2 -- good to hear that's OK. It also had the figure-8 pieces so I wonder if it's been rebuild in the past - old fiber washers with new 8's?

I followed the adjustment instructions in the SU box of bits. It says to screw the diaphragm in until the rocker doesn't throw over, then back off until it just does then back off a further 2/3rds of a turn. I pushed it in and out before and after I fitted the 8's and it seems to move freely.


glemon said:
Good luck, when I rebuilt mine, with the help of David D. I bench tested it with Marvel Mystery oil, which is a pretty low viscosity stuff and not overly combustable (like gas is for instance), of course with some hoses to pick up the fluid and deposit it in the same container so it could run continuously, in my case a two cup pyrex measuriung cup, but anything will do.
Click to expand...

I was going to use the petrol I drained from the tank for the bench test but now that you mention it, that might not be a good idea. What on earth is "Marvel Mystery Oil"? Canola is probably a bit viscous for the test I think.
 
MMM is an old brand name, the stuff can be had from most good parts houses in gallon cans. It's great stuff for many things: Lube for dirlling, air tool lube, damper oil in SU and Zed-S carbs ( :wink: ), additive to crankcase for upper cylinder bits, tooth brushing... oh, on second thought mebbe that'd be a bit much.

But it has many applications. Light oil, red in colour. Great stuff. :thumbsup:
 
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