I wanted to provide good clean fuel to my efi project and to be sure I had fuel at any angle I might find myself at. I looked into all the different options for accumulators and decided that like everything else on my bronco, half the fun is making it myself. So off to the parts store I went. I started with looking at remote oil filter brackets and ended up with the Fram HPK2 with a Fram P4105 filter. This thing looks like it would hold well over a quart of fuel in the event my tank pickup tube sucked air. I fill the accumulator with a carter lp pump mounted near the tank and my hp is the airtex E2000.

Once I got home I looked at the way it worked and layed out how I wanted my hoses to route. I was using braided lines and AN fittings so I had lots of options. The input and output bungs were 1/2 npt so I ordered 2 adapters for each one to step me down to a 6AN fitting. I also used a 6″ piece of 1/4 npt threaded pipe for the pickup tube. A 2″ brass pipe with 1/8 npt threads on each end and a 6AN fuel gauge adapter was used for the fuel rail return and accumulator overflow back to the tank.

Look at the bracket assembly and locate a spot to drill and tap for the return. Make sure to drill to the inside of the seal area. Tap just far enough in with the 1/8 npt tap that the threads will seal but not so far as to have the pipe extend through the bracket. Attach the fuel gauge adapter to the top. I used teflon tape for all these connections. If you do use it, make sure that none is extending past the end of the threads where it can come apart and get into the fuel system.

Now install the steel threaded piece that the filter threads on to. I coated the threads with lock-tight prior to installing it. Next you need to tap the inside of this for the 6″ 1/4 npt pipe that will be the pickup tube. Once this was tapped I used some teflon tape and threaded in my pickup tube. To get the correct depth for your filter, insert a dowel into the bottom of the filter and put a straight edge across the gasket. Mark the dowel and transfer the measurement to the pickup tube. I subtracted a 1/4 inch to account for gasket squish and so the tube didn’t bottom out in the filter.

I decided to mount mine on the frame in front of the spring hanger. I would have located it up in the engine bay but just could not find the space. I bent up a skid plate to keep the filter protected. To prime the system, Disconnect the hp pump and run just the lp pump until you hear fuel flow back into the tank. This will provide the hp pump with fuel so it doesn’t cavitate and burn up trying to prime.

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The use of racing “billet” fuel doors has become a popular upgrade to both street and off-road vehicles. There are two versions of the billet fuel door available for the Early Bronco. The first is a large billet “door” that covers a recessed stock fuel cap. A great tech article on this style of door is available on Jim Price’s website (luvmybronco.classicbroncos.com). The other alternative is an actual billet door and funnel mounted to the fender.This tech article will guide you through the installation of the Mocal Aero 300 fuel filler door for the main and auxiliary tanks on 73′-76′ Bronco’s. This racing quality British made door is used as standard equipment on the McClaren, Ferrari, and Jaguar. The forged aluminum cap sits in a pressed aluminum flange sealed with a fuel resistant o-ring. Cap and flange are polished and anodized silver (colors available as special order). Caps are supplied with nuts, bolts, and fiber gasket. Locking version includes two keys. I used the locking version with matching keys for both doors (available upon request). Non-locking doors are also available at a lower cost.

To start the install, first remove the left rear wheel. It will make the install much easier. Unclamp and remove the main and overflow hoses between the filler tubes and the tanks. Now remove the three retaining screws at the filler neck and the retaining bolt at the bottom of the fender. The filler tube should now drop out through the bottom of the rear fender.

Next use a metal burr bit to slightly ream out the existing filler hole to fit the larger Aero Filler neck. Be careful not to cut past the existing screw holes. It will not take much, so test fit as you cut.

After reaming out the hole to fit the Aero filler, mark your mounting holes. With one hole positioned at twelve o’clock, the ten, two, and six o’clock holes will almost align perfectly. Drill out the 12, 4, and 8 o’clock holes first, then just mark and ream out the existing holes as seen in the photo.

Now take out your trusty sawzall with a long metal bit and notch out the ¾” inside fender lip to allow the 90deg hose room to fit back into the fender well. Be careful not to cut through the fender while you are notching out the back plate.

Once you cut two to three notches, hammer the lip up flush with the fender well top.

Now you can install the Aero 300 funnels in the fender. Do not fully tighten down the bolts at this time. Take your stock filler tubes, at this time, and prep them for final installation. As you can see in the picture, the main filler tube is cut right after the weld of the upper and lower section. The auxiliary tube is cut a little lower down the neck. You will need to cut 1 ” off the 90deg hose that you will attach to the main filler tube. Note: If you own a 66′-72′ the overflow tube attaches higher on the filler neck. You will need to cut the hose more or move the overflow tubes further down.

If you wish to vent your system, you will need to install ports into your filler tubes. I used ¼ ” barbed to 1/8 ” threaded npt brass fittings. I drilled an 11/32″ hole just to the right of the overflow tube on the main filler and just to the left of the overflow on the auxiliary tube. These locations will allow the tubes clearance in the fender wells. I reamed the hole out enough to thread the fitting into the tube. After screwing the brass fittings in, I used some JB Weld to secure the fittings a little better to the tube.

After installing the vent fittings, finish the assembly of your filler tubes. It is a tight fit, but the 90deg elbows will go over the filler tubes. A little soap solution will help. Be careful and wear gloves to prevent slicing your fingers on the filler tube. You should be able to slide the elbow down the tube approximately 1½” inches, almost to the top of the overflow tube, by working it back and forth. If you can’t get it to go, slightly notch the top of the filler tube in 4 places and bend in slightly. Tighten down with 2 ½” hose clamps. Attach 3ft of 7/32″ vacuum hose to the auxiliary pipe and about 1ft of hose to the main pipe.

You will find the Aero 300 filler neck has a two step barbed end. The first step is appx. 2″ and the second set of barbs are 2 1/4″ O.D.. The 90deg elbow (1 13/16″ I.D.) will not go over the second set of barbs without notching the rubber elbow about ¼” in four to six spots around the edge of the elbow. Due to the aero mounting bolts, the rubber elbow will not slide all the way on the barbed base.

It’s now time to reinstall the stock filler tubes. Slide a second loose hose clamp on the elbow to use on the aero 300 fitting. Carefully slide the tube up the inside fender into the notch you cut earlier in the fender well. If the 90deg. elbow does not align up correctly remove the filler tube and adjust the elbow to the right direction. This should be about in line with the overflow tube on the main and slightly to the right of the auxiliary. Coat the elbow and aero fitting with some soap solution and work the elbow on to the aero fitting mounted in the fender. You can now fully tighten down the allen screws on the Aero 300 door and firm up and clamp the elbow to the main fitting.

Before clamping the lower pipe support back in, connect new main fuel and overflow hoses. I found both hoses by the foot at my local NAPA store. The main hose is 1 ¾” I.D. and the overflow is 19/32″ I.D.

Now route both vent tubes over the aero filler necks to a ¼” plastic barbed “Y”. I connected the “Y” to a ¼” plastic fuel filter to catch any slosh or overflow. The output of the fuel filter runs over the rear side marker lamp, down the rear fender and out the back of the car. I also attached a check valve in the end of the vent hose to prevent debris or water from entering the hose. Make sure the vent does not exit around an exhaust pipe.

I have found the aero doors to work fine in daily use. You will notice that you have to feed the gasoline pump handle fully into the elbow or gas will slosh back out of the neck. Also stop filling after the pump handle kicks off the first time. Do not top off repeatedly or you will flood the filter and vent hose. I am looking into fabricating an attaching chain, (similar to what boats use) so that I won’t accidentally leave a $90.00 gas cap at the gas station.

Questions? Email John@edgecomb.netTech article by John Edgecomb (edge4)

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Overall I’m very happy with the tank. It’s a high quality product from a trusted vendor, installation was very easy and the unique design maximizes fuel capacity while still keeping the tank away from the rocks. Scroll down for installation instructions as provided by Chuck at B.C. Broncos. I’ve added some photos and tips (my comments in gray) that should help make installation a snap.

Remove the stock tank:

1. It’s always a good idea to liberally spray all tank and skid plate mounting bolts with penetrating oil 1-2 days before you begin the removal process.
2. Move the Bronco to a flat and level area and block the front wheels.
3. Remove the negative battery cable from the battery. If you’re one of those people that normally skips this step, just do it! You’ll be dealing with gas fumes and the last thing you need is to accidentally bump some wire causing an ignition spark.
4. Drain the main tank by either siphoning into an approved gas container or by running the tank dry.
5. If necessary, raise the rear of the Bronco to have adequate height to remove and install the rear gas tank. Support the Bronco’s frame on jack stands as necessary. With my 3.5″ suspension lift it would have been possible to install the tank without jacking up the rear end. However, taking the rear tires off made it much easier to access the frame.
6. Disconnect the fuel filler hose and any vent hoses, EFI return hoses or any emission hoses that may be present on the side of the fuel tank.
   I highly recommend ordering B.C. Broncos filler hose kit when you order the tank. After years of use both the filler and vent hoses will probably need to be cut off and you won’t be able to reuse them.
7. Disconnect the fuel gauge sending unit wire at the rear of the fuel tank.
8. Disconnect and plug the fuel line at the fuel gauge sending unit at the rear of the fuel tank.
9. Support the rear fuel tank with a scrap piece of plywood and a floor jack at approximately the center of the tank bottom.
10. Loosen the nuts securing the tank mounting strap(s) and swing the strap down. Disengage the strap’s “T” end from the frame and remove the strap.
11. Lower the fuel tank and disconnect the vent hose at the top of the tank.
12. Lower and remove the fuel tank.
13. Remove the 4 stock tank brackets from the frame.

B.C. Broncos Tank Installation:

1. Slide the special Unistrut nuts (with the nylon insert facing out) into the Unistrut rails.
2. Insert a provided mounting bolt through the tank-mounting tab and secure the tab to the tank’s Unistrut nuts (finger tight only). Orient the mounting tabs so the flat part of the mounting tab is up and against the frame rail/cross member.
   
3. Support the new fuel tank on a floor jack using a scrap piece of plywood to protect the finish and distribute the load across the bottom of the tank.
   
4. Carefully raise the fuel tank so the fuel line and vent/return lines can be connected.
5. Connect the 3/8″ fuel line and the 5/16″ return/vent lines using hose clamps. Note: If the return/vent lines are not needed connect the two tank nipples with a short length of 5/16″ hose and secure the ends with hose clamps. (see photo on the right)
   
6. A piece of cork or old inner tube (NON porous material) can be cut and placed on the upper four corners of the fuel tank if the tank will be mounted touching the underside of the body. I found that shock mount bushings fit perfectly between the tank and body. They give just enough clearance to avoid rubbing the tank on the bed.
   
7. Position the forward edge of the fuel tank against the forward frame cross member.
8. Raise the tank into position. Slide the side mounting tabs up to make contact with the frame rails. Slide the forward mounting tabs up to make contact with the frame cross member.
9. Position the tank to the frame rails so the gap is even on both sides.
10. Locate the tank’s forward mounting tabs over the existing holes in the forward frame cross member.
    See the photos above for a trick to mark the frame hole location in the mounting tabs. Draw a cross on the frame, extending the lines in all directions from the hole. Then when you slide the mounting tab up against the frame you can mark the center of the lines and this will be where you drill into the mounting tab.
    
11. Locate, then center punch and drill a 7/16″ hole in each forward mounting tab.
12. Insert 7/16″ bolts up through the fuel tank’s forward mounting tabs and through the forward frame cross member. Secure with 3/8″ nut and washer only finger tight at this point.
    
13. Locate, then center punch and drill through the tank’s side mounting tabs and through the bottom of the frame rail using a 7/16″ drill bit.
    I chose to use the existing oval holes in the frame rather than drill new ones. If you do this be sure to use an extra large washer on the backside of the hole.
    
14. Using an approximately 2′ length of stranded wire (speaker wire or equivalent), insert the wire up through the fuel tank’s side mounting tab and frame and out through the end of the frame rail at the rear of the Bronco. This is a good trick for getting bolts into hard to reach places. The wire is simply a tool to help you pull the bolt through. It isn’t for grounding or anything.
15. Twist the wire strands around the provided 3/8″ bolt. Carefully fish the bolt though the end of the frame rail and down through the holes drilled in step 14.
16. Secure with provided 3/8″ nut and washer only finger tight at this point.
17. Raise the tank into its final mounting position.
18. Tighten the mounting tab to the Unistrut bolts and to the frame mounting hardware. NOTE: It is highly recommended that the mounting tabs be tack welded at the points where there mounting tabs come in contact with the Unistrut. Both the bolts and tack welding will secure the tank. by grinding the tack welds the tank can be repositioned.
    CAUTION: DO NOT OVER HEAT AND MELT THE NYLON INSERTS IN THE UNISTRUT NUTS DURING THE TACH WELDING PROCESS. To avoid overheating I only tach welded one area at a time and had a spray bottle of water handy. After each weld I sprayed the area down to quickly cool off the weld and avoid melting the nylon inserts.
19. Check all mounting hardware for tightness.
20. Remove the supporting floor jack.
21. Reconnect and secure the fuel filler hose, fuel line(s), vent hoses, EFI return hoses and any emission hoses.
    
22. Reconnect the fuel gauge sender unit wire.
23. If used, remove the jack stands and lower the Bronco.
24. Fill the tank and check for leaks. If you’ve double checked all your hose connections you shouldn’t have any leaks. However, if you do it’s easier (and safer) to deal with them in your garage than at the gas station. Have a few gallons of gas to put into your tank before going down to the station.
25. Reattach the negative battery cable.

Other photos of the tank and hardware:

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