939 Battery Box Upgrade on 809 - Steel Soldiers::Military Vehicles Supersite

MyothersanM1 · 12-07-2011, 02:00

I have had my eye on a 939-series upgrade battery box for sometime now. I thought it would be a nice to modify one these boxes for use on M818 (all 809 series trucks should be able to use this mod). Well, I came upon a rather affordable kit locally with benefit of no shipping costs. I spent a little over a third of what I have been seeing these kits selling for.

Using only two batteries for my truck, the bottom compartment could be used for extra storage. I feel it has a cleaner look that the standard 809-series battery set-up. The box and side steps fit perfectly between the fender and fuel tank. The fender does become an integral part of the installation…more on that later.

The kit includes the steel box, two plastic battery boxes w/ hold-downs, two 45-degree frame brackets (which will become fodder for mounting modifications), eight battery cables of varying lengths (eight according to packing list…my kit had nine) and a small bucket load of hardware (to include bus bars, retention cables and a bunch of NBW’s). In fact, the only things you don’t get are battery terminals and j-bolts.

I am going to chronicle my installation in the next several postings. Mind you, it is a simple install. BUT, the kit was designed for a different vehicle. So, some drilling, cutting and welding were required. I will post the full instruction sheet to include the packing list provided with the kit,

MyothersanM1 · 12-07-2011, 02:07

Obviously, the first thing is to remove was the original battery box set-up. Everything goes down to the frame…the only thing left are the battery cables; hot lead, the 12VDC accessory lead and the ground lead.

I flipped the steel box on its head to loosely mount the frame brackets. Here’s where things start to change. The 809 cab sits lower to the frame than the 939. This calls for the frame brackets to attach to the frame on the long leg and short legs support the steel box. The brackets have identical holes drilled in them. On the short leg, I used the outer most hole as the pilot. Match up the back hole, mark and drill (see pics. for details). Drill a fairly good size hole…it makes it easier to mount later.
Note: The steel box mounts to the inner holes on the brackets.

While the brackets are dry fitted to the steel box. I measured the inside distance of the frame brackets for proper frame mounting. I was an even 13”.

I then moved on to the frame prep and mounting of the brackets. The top three holes of the brackets long leg are used. The front bracket can use one existing hole from the old bracket. The other two had to be drilled. I measured 13” from the rear edge of the front bracket and mark. Measured and marked holes for drilling…use a helper to hold the bracket for more accurate marking. I drilled the holes for the rear bracket and mounted both brackets. I then dry fitted the steel box onto the brackets to get a good look of the new set up.

MyothersanM1 · 12-07-2011, 02:12

The two 45-degree support bracket would not work with the 809 install as provided. The box hangs lower in relation to the frame for these brackets to be effective. Here was where the thinking really began.

The front bracket is flat and the rear has approximately 1 ½” lip along its edge. Using the flat bracket, I made a span bracket laying it across the side steps and marked for cutting. I cut the bracket and drilled holes to match existing holes the bottom step. The lower step is already drilled out, but the top is not. I marked 1” in and 1” down and drilled the top step. The bracket was drilled to match. The span bracket was bolted onto the steps using the hardware provided in the kit.

MyothersanM1 · 12-07-2011, 02:15

I decided to use the fender rear support arm to hold up the front of the steel box. I removed the two inner bolts on the fender support bracket, dry fitted the steel box and marked the box for drilling. I drilled for 3/8” bolts then mounted the box to the frame brackets. For stand off between the fender and steel box, I slipped two flat washers and a ½” shaft collar over each bolt and tightened it all up. Make sure to install the fender bolts prior to final frame bracket attachment.

MyothersanM1 · 12-07-2011, 02:22

After bolting up to the frame brackets and fender support arm, the box felt a little flimsy when I stood on the step. I decided I would modify the rear angle bracket and attach it the span bracket between the two steps. With the help of my neighbor, we cut the lip off of the rear angle bracket. I wanted to keep the lip for strength and rigidity, but it was to wide to fit between the steps and the fuel tank.

The good news was the existing the frame holes for the original frame brackets matched the holes on the rear angle bracket, so that all stayed. I dry fitted the angle bracket the frame and marked where it met the span bracket on the steps. Both brackets were then removed, welded together and overburden removed. We ended up giving the new bracket a good sanding and cleaning. I primed and repainted the new bracket.

For ease of installation, I removed the top side step from the steel box. I loosely bolted the top step to the new rear support bracket. The top side step was bolted loosely back in its place on the steel box, the rear support bracket to the bottom step and to the frame. Everything was snugged up. I climbed up the steps and it was solid as rock.

The frame attachment is now complete. Everything else pretty much follows the instruction sheet minus the items unique to 939-series trucks.

Note: I removed the steel box door for (1) to sand and repaint and (2) ease of installation. If you choose to remove the door, bare in mind it is a little difficult to reattach once the steel box is installed. So, give a little leeway to assemble the door prior to tightening everything up.

MyothersanM1 · 12-07-2011, 02:27

The box upgrade actually looks better on my truck than I imagined. It is a little different procedure climbing into the cab, but it all works.

The plastic battery boxes are easier to remove than the original set up. There are steel cables that retain the plastic boxes when pulled out to make maintenance easier. I am using the bottom box to store my slave cables.

There are bus bars provided in the kit, which attach to the back of the top compartment. All electrical connections are routed through these bus bars. This makes complete battery removal much easier…no messing around with battery terminals. Using the multitude of cables provided, I replaced the majority of all the older cables. However, I did reuse the existing terminals.

I have a NATO slave connector kit on order and I have to compltet the 12VDC accessory attachment. Those will be the icing on the cake.

I hope I have been thorough enough describing this project. Feel free to contact me if you are endeavoring in this mod and have any questions.

Thanks for viewing this post.

wsucougarx · 12-07-2011, 03:03

Ingenius! Great looking install. I want one of these kits

cranetruck · 12-07-2011, 03:24

Nice job! I like the tilt feature.
There must be different versions of the M939 series battery boxes, I have a box (junk) that was installed under the passenger seat for four batteries from a '96 M925.

islandguydon · 12-07-2011, 04:01

I aspire to have a battery box like yours. Please let me know if any more of those kits come up and are available. I like the extra storage vault, good place for the slave cables and the like.

You get 1 REP point and 2 Thumbs up from me for your perseverance and ingenuity for a job well done.

motorolanut · 12-07-2011, 04:04

Wow awesome mod thanks for the pics and tutorial.