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Thread: Fuel Sending Unit Restoration/Rebuild - Factory Carb Applications

  1. #1
    all the CFI are belong to me
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    Default Fuel Sending Unit Restoration/Rebuild - Factory Carb Applications

    Recommended reading:

    Thread: kishy's 1983 Grand Marquis 2dr
    Reply #34, 2020-05-21. I removed the fuel sending unit to install a new float on it, and discovered that the inside of the tank and the sending unit itself were very rusty and needed attention. Good photos for reference.
    http://www.grandmarq.net/vb/showthre...l=1#post842997

    Thread: Sending Unit, Carb Applications (internet finds)
    Whole thread is useful, but Reply #22 shows the two different (yet oddly the same) NOS sending units I purchased and now have.
    http://www.grandmarq.net/vb/showthre...l=1#post856505

    The scenario:
    My 83 Grand Marquis was factory built with a carb 302. This means the car was assembled using the carburetor fuel tank: the rear-facing fuel pump hole seen on FI cars is not present. The fuel gauge sender which fits into the 2" hole on the front of the tank also features a fuel pickup tube. This is a returnless system so there is only one fuel line fitting.

    The problem:
    Initially, the vehicle had an inoperative fuel gauge, and fuel drainback issues.
    Upon removal of the sending unit to install a new float, I discovered the tank and sending unit were thoroughly rusted, due to the car having been parked for a long time with an empty tank.
    The sending unit rheostat is operational and installing a new float would have corrected the gauge concern.
    However, the fuel line fitting (external to the tank) has rust holes through it, and the steel is very thin in areas.
    The rust holes through the fuel line fitting did create an external leak, however because this fuel system is a suction system (pump on engine, not in tank), the leak that was occurring was air coming in, rather than fuel going out. Hence the drainback issue. It also would have leaked fuel out if the fuel level were high enough, but it seems just by chance it never was for long enough to happen.
    Further repair/refurbishment was required. I preferred the option of finding a replacement part if possible.

    Steps taken so far:
    I acquired a 1983 carb Town Car for parts, which had a new condition fuel tank and an original but decent-seeming-condition sending unit that would work for my needs.
    I installed the replacement fuel tank which corrected the rusty tank concern.
    The 83TC sending unit required repair (fuel line fitting), which I successfully did, and I then installed the part.
    After filling the tank, it was discovered that the 83TC sending unit has a fuel leak through a rust hole in the round mounting plate.
    I attempted to mitigate this by using JB Weld Steelstik putty to fill and enclose the rust hole, however, fuel leaks around the JB Weld product.
    I purchased two NOS sending units that turned out to both be the wrong resistance range (one for Lincoln with digital cluster, one for 90-91 carb box).

    Current state:
    The car is parked with a low fuel level.
    The 83TC sending unit remains installed in the car at present. It will leak if the fuel level is at the sending unit height or above.
    The 83GM sending unit is on my workbench. It was thoroughly de-rusted and sandblasted. It has flash-rusted over much of its surface area again but this is easily dealt with.

    Options to move forward:
    1. Re-repair the leak on the 83TC sending unit and continue using it in the 83GM car.
    2. Repair the 83GM sending unit. Preferably, this would be done in a way that adds material to the whole part, thickening and stengthening it. The metal thickness is significantly compromised.
    3. Modify an EFI version of the fuel gauge sender to function for this purpose.
    4. Locate the correct part, in adequate condition.
    5. Modify one of the NOS parts already on-hand to be suitable for this application.


    Notes about these options:
    1. When I repaired the fuel line fitting on that part, the method I used created a fuel bottleneck from normally 5/16 down to approximately 1/4" due to the repair method I used on the fuel line fitting. This may or may not be an issue. Other than this concern, I like the idea of this option quite a bit. It is also worth considering that removing the JB Weld might destroy more of the thin steel encased within. It is unclear to me if metal joining techniques hotter than simple soldering are practical because the adjacent electrical connector is plastic.

    2. It might not make sense to do this. Repairing the fuel line fitting will result in the same concern as above. Maybe some form of electroplating could be done to the rest of the part to improve metal strength concerns and ward off future corrosion.

    3. I have spares of the EFI parts so this is definitely an option
    A. Modify an OE design part: the 5/16" tubing that forms the structure of the part can be extended down to the bottom of the tank, and the plug soldered into it through the mounting plate can be removed. Attaching an external fuel line fitting to the existing 5/16" tubing will create the same concern as #1 though.
    B. Second method, which could also be applied to a reproduction part: use a bulkhead fitting to get the fuel through the mounting plate. Build a pickup tube which attaches to the bulkhead fitting.

    4. At this point, I have low confidence in ever finding the correct part, used, in condition good enough to use without the same issues I'm already trying to get past. And NOS is an expensive proposition.

    5. The NOS parts I have, specifically the 90-91 carb part, can be altered to meet the need. The fuel return line fitting will need to be sealed off, and the rheostat will need to be swapped with one of the correct resistance range. A complicating factor is that the rheostat mounts "backwards" between this part and the ones the correct rheostat will need to come from, which might create the need for breaking the mounting piece off and spot welding (not within my abilities).

    This thread serves to gather input as well as eventually show my progress.
    I will work on supplying additional photos but the above-referenced threads have some good ones already.
    Last edited by kishy; 09-18-2021 at 03:07 PM.

    Current driver: 85 CS
    Currently owned, parked: 83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 Ranger +trlr | 86 GM | 88 TC | 91 GM POTM 12/2017
    Gone: 97 CV | 83 TC
    Junkyards

  2. #2
    I'm an air-conditioned gypsy gadget73's Avatar
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    I'd be tempted to repair the leak with solder. Need to use acid flux to make that happen but its otherwise not that different from any other form of soldering. If you have one of those massive branding iron looking things you might be able to use that, but more likely this is a torch sort of repair. Wrap the sending unit in a wet towel to control heat there and try to limit the time spent with the torch.

    Elecctroplating can be done but the amount of metal it adds is insignificant. I don't think it would ultimately fix the problem. The usual material that isn't too difficult to DIY at home is copper, and that could possibly introduce a whole extra concern with galvanic corrosion. Off the top of my head I don't know what gives up to what in a copper to steel combo but it might eventually cause the tank to rot where they touch.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  3. #3
    all the CFI are belong to me
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    Detail shots of the post-Evaporust, post-sandblasting 83GM sending unit in reply 72 of the 83GM thread: http://www.grandmarq.net/vb/showthre...l=1#post848424
    It is maybe not as thin as I was thinking, except in a few key spots.

    New ones comparing 83GM original item against the NOS 90-91 carb part:






    I think this better illustrates what I mean by "mounts backwards". A spot welder is indeed required to rearrange the part into the required configuration, but it can be done.
    The NOS item does have some minor rust which I'd want to take care of.



    Regardless of what direction I go, I've been made aware of "cold galvanizing spray", essentially spraypaint containing a zinc coating that is supposed to do a decent job at corrosion resistance and should be gasoline-safe. I'm sort of thinking that I can just fix the fuel line fitting on the 83GM part, remove all rust, then paint the whole thing with the zinc spray, and maybe that'll do it.

    Soldering to fill the hole on the 83TC part (currently installed in 83GM vehicle) is probably a viable choice, and ultimately I want to fix both parts regardless of what solution ends up going into the car. I'd either be using a small butane torch or, if going more into brazing temperature range, propane plus oxygen. I don't think I need or want it that hot though.

    Current driver: 85 CS
    Currently owned, parked: 83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 Ranger +trlr | 86 GM | 88 TC | 91 GM POTM 12/2017
    Gone: 97 CV | 83 TC
    Junkyards

  4. #4
    I'm an air-conditioned gypsy gadget73's Avatar
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    Its thin, you should be able to soft solder it with just a propane or butane torch. Could braze or silver solder it with MAPP or acetylene, shouldn't need the oxy- part. If you do it'll likely want the smallest tip you can find to not just blow through the steel.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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