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zKars

Weakness Revealed in the GMB and Spectra Mechanic Fuel pumps

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    Just for grins, I checked a new equivalent Spectra pump for a 510  that I have in stock. Popped it’s cap and it’s assembled right.

    I just put an electric pump in this Z, so I’m going to get the owner to run it with the fuse pulled for as long as he can stand it, and let the “fixed” mechanical run and see if it quits again. Easy to get back on the road if it does with a simple fuse insertion.

    At this point, knowing this pump can run at full pressure and flowrate after having failed, the only other failure mode might be heat related where maybe the check valve flaps stop sealing well after a period of time, then re-form and work again after they cool off?? The main diaphragm is just fine, 

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    I took the top off of a Delphi. It is not a confirmed failed pump. It was assembled how you said it should be.

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    2 hours ago, SteveJ said:

    I took the top off of a Delphi. It is not a confirmed failed pump. It was assembled how you said it should be.

    Was there reason to believe it was giving problems before? Is it new?

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    24 minutes ago, zKars said:

    Was there reason to believe it was giving problems before? Is it new?

    It is new. I replaced the original factory fuel pump on another person's car with the Delphi. The car ran well at first but then had some performance issues that indicate a lack of fuel. I replaced the Delphi with another fuel pump I removed from my own car (and was operating fine when removed) a few years ago, looking to see if that was the cause. I have been eliminating one thing after another on that car, and I might actually put the Delphi back on in case the other fuel pump is a contributing issue.

    At the risk of threadjacking I have already

    1. Cut apart a fuel filter to look for debris. It was pristine.
    2. Checked the oil in the carburetors (and replaced a piston damper that came apart when the clip at the bottom came off)
    3. Adjusted the front float when I discovered there was almost no fuel in the bowl
    4. Rebalanced the carburetors. (It was so far out of balance it was only running on the rear carburetor. Don't ask me how it EVER ran well like that.)

    Now I plan to

    1. Look for air leaks around the throttle shafts and intake manifold.
    2. Monitor fuel pressure to see if it drops 
    3. Inspect the banjo filters
    4. Disassemble/clean the needle valves
    5. Re-install the Delphi pump

    Not necessarily in that order. So, I figured I would inspect the fuel pump based upon this thread before I re-install.

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    Here lies the culprit in my recent swap. Either the return spring is faulty or the rubber diaphragm in the check valve is faulty. I reinstalled the originals and she ran like a top3CB2FC6E-7613-4D5C-A4BA-F9D20FD8419C.jpeg

    Edited by Trnelson

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    11 hours ago, Trnelson said:

    Here lies the culprit in my recent swap. Either the return spring is faulty or the rubber diaphragm in the check valve is faulty. I reinstalled the originals and she ran like a top3CB2FC6E-7613-4D5C-A4BA-F9D20FD8419C.jpeg

    That’s something I haven’t seen before. That’s an OEM check valve isn’t it?  If you poke the valve disk, can you get that disk to reseat or is it deformed and stuck like that?

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    So I rebuilt a hand full of stock ones, I got some datsun pumps off ebay for a different model. Then swapped the guts.  Worked perfectly.  

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    51 minutes ago, duffymahoney said:

    So I rebuilt a hand full of stock ones, I got some datsun pumps off ebay for a different model. Then swapped the guts.  Worked perfectly.  

    I just did the same. Rebuilt an old Nikki with parts from a new 510 Nikki. Pretty simple after you do the first one. Had a new GMB and opened it up. The check valves looked different so didn’t use them. 

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    9 hours ago, zKars said:

    That’s something I haven’t seen before. That’s an OEM check valve isn’t it?  If you poke the valve disk, can you get that disk to reseat or is it deformed and stuck like that?

    That is the check valve from the GMB that I cannibalized, made it about 20 miles. I tried to reseat the rubber but it kept flipping back up. It gives me concern about the quality of the main rubber Diaphragm. 

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    That’s excellent feedback. Good to know that check valves are a problem too. 

    \Sorry I mistook it for an OEM. I’ve never dug one out of the body. With those stamped in valves, how did you get it stay in after you removed it?

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    2 hours ago, zKars said:

    That’s excellent feedback. Good to know that check valves are a problem too. 

    \Sorry I mistook it for an OEM. I’ve never dug one out of the body. With those stamped in valves, how did you get it stay in after you removed it?

    I was using the GMB as a parts donor for my KD pump. I ground out the “nubs” to get the check valves and installed them in the KD pump using the screws and plate. The sizes of both the the valves and squared o-rings were/are a perfect fit. There just seems to be aa issue with the rubber portion of the check valves. I hope they can figure it out because it’s a great way to keep the original housing with new internals. 

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    It may very well be that my one example of the cap on 90 degrees out is a total one-off anomaly and the real culprit is the check valves as I initially expected. More evidence to gather for sure. 

     Keep them cards and letters coming.

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    Ah the wonders of Rock Auto. My three GMB fuel pumps came in today already. (ordered Monday, Fed Ex cheap delivery)

    I am sad to report that the top caps on all three of these were assembled correctly. 

    So what can we learn from this.

    Is it only Spectra pumps that have these issues?

    Was the one incorrectly assembled Spectra I encountered a total one off?

    I sent the customer home this morning with his Spectra working flawlessly and instructions on how to pop the fuse back in the new electric pump circuit when (and if) it fails. 

    It seems we are back to check valve shaming for the time being.

     

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    Interesting thread! Especially as my Aussie (spectra looking) pump started to play up at the weekend and intermittently pumped well then dry filter time. It’s been on the car for under 4k miles!!!

     

    Fortunately I had the 43 year old original pump and a small socket set in the spare wheel well so I swapped it out on the side of the road. Then I proceeded to carry on with my 3 hour round trip journey and even terrorised a Mustang having a go and not thinking my car was a fair bit quicker ;). Just love that modified L28! And in all of this the old pump didn’t miss a beat!! I only replaced it previously so that the engine bay looked new/ tidy

    When I put the L28 in. Waste of money by the looks of it.

     

    I will take it apart at some point and upload photos.

     

     

     

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    Thought I would see if the original check valves could be reused, so the first one is an old used valve, middle four are all the bits when taken apart and the last one is one cleaned up, disc flipped around for a new surface and seat buffed up. IMGP2156.jpg

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