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totally random question military trailer related


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So I'm asking this question here even though I asked it in the military equipment forum I am in as well, just because there is so much random knowledge and experience out there you never know where you might get an answer or even just an idea. 

Here are a couple pictures for those that don't know what I am talking about.  

Here is the dolly by itself (M720)  (this picture is from a couple weeks ago, my truck but someone else's dolly.  We were picking up a shelter back behind the barn here and there wasn't room for a larger truck to get in there)  (and no, I'm not the fat guy on the right)


Here is what it looks like with the shelter (S280) mounted on it for transport.  Could be towed with 2.5 ton or larger truck with air brakes.  This one is a 5 ton.



(if nothing else it's a couple of pictures to show off a few of our local rigs :) )


It uses air over hydraulic for the brakes, and the 2 halves of the dolly are independent systems.


So I'm currently buying an M720 shelter dolly. I've been reading up, and can't find anywhere that anyone that has done an electric brake conversion with one of these.

I do not have an air brake capable vehicle to tow it with, so looking at what are my possible options.

it looks like there are primarily 2 possible ways to do a conversion.
way 1 is buying 2 separate electric over hydraulic actuators, and install one on each the front half and rear halves of the dolly.
While this is the simplest method, it's also pretty spendy (looks like parts would be over $1500 for 2 actuators) and also the problem that I do not know if a standard trailer brake controller is able to power 2 actuators at the same time. If not it adds a lot more parts and gets stupid. Up side is it is 100% reversible no problem.

Way 1.5 would be just put brakes on the front dolly set and have no brakes for the rear. Wouldn't be an issue with a larger tow vehicle, especially if I wasn't loading the shelter dolly up at max.

Way 2 is the one I'm considering to be better from a complexity standpoint is to get the spindles replaced with modern trailer spindles. Would require new hubs and drums, as well as backing plates as well. Not sure on cost as I have no idea what a shop would charge to replace 4 spindles, but I'd imagine in the end would probably cost around the same as the electric over hydraulic. I also can't use the current backing plate flange on there as it is 6 bolt, modern electric brakes use either 4 or 5 bolt backing plates (I could probably drill holes in the backing plate, but that requires a little more precision to center the holes properly than I currently have available to do)

Plus sides with this one are parts have been standardized for a long time, and I don't expect the industry to change them any time soon. after the conversion parts would be readily available at any trailer parts store.

Down sides, I can see several. One is the fact that is is non-reversible. I suppose I could take parts off of a second dolly to repair it, and there seem to be plenty of these out there. main downside for me is I would have to either change to a different bolt pattern for the wheels, or the actual axle capacity would be lower.
I'll explain that last one. The spindles for 3500 lb axles have matching hubs with the 5 on 5.5 bolt pattern that the dolly currently has. 2 axles like this = 7k lbs. This is about 1k lbs lower than the current rating. Other spindle would be for the 5k and 7k axles, but the hubs only come in 6 and 8 bolt lug patterns.

(and before anyone starts arguing that it's only a 3 ton dolly set and that 2 3500 would be fine, like everything else it's rated for 3 tons of load. The dolly itself weighs just over 2k lbs, with 3 tons of load that's an actual weight of just over 8k lbs, or 4 tons)

I'm sort of leaning towards the 3500 lb spindles because I don't see myself ever putting 4300 lbs worth of crap into an S280 shelter (empty weight around 1650, at 7k lbs total weight I'd still have over 3k lbs of available load). I'm primarily looking at it as a possible camping shelter, though using it as a portable tool room isn't out of the question, which could get heavy. I could also use the current wheels with the 3500 lb spindles.
On the other hand if I go with 5k spindles, I could bump up to 8 lug hubs. This gives me greater braking capacity (3500 lb use 10 inch drums, 5k uses 12 inch, it currently has 11 inch which hasn't be used for decades apparently other than military) With the 8 lug wheels I could, in theory, put HMMWV tires on it (in theory a lightly loaded M720 with S280 is still within the HMMWV towing capacity) which would increase ground clearance, make it so I have to carry fewer spare tires, but also make it so I have to have the shelter jacked up in order to hook up and detach the shelter. Also not sure if there would actually be enough clearance for the larger tires, but other sizes of 8 lug wheels/tires are readily available.

(to answer another possible question, the hubs it comes with cross reference to WWII era Bantam T3 trailer and also front axle on jeeps of that era. The spindle is straight, not a stepped down configuration that takes a larger diameter bearing on the inside and smaller diameter outer bearing. Both inner and outer bearings use the same part number)

I've also toyed with the idea that maybe a sleeve could be machined to fit over the existing spindle to match it to the 5k spindle profile. i theory it shouldn't change the weight capacity of the existing spindle, and still reversible. Would have to modify either the brake backing plate or mount for backing plate to match this.

Does anyone have any thoughts about this? I would greatly prefer constructive thoughts and reasons to go along with those thoughts, as opposed to just flat out telling me it's crazy or won't work.

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