Maxi Trac OBA system (2 Viewers)

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Jan 6, 2003
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Finally got around to installing an onboard air system on my FJ40. I've used a lot of portable compressors over the years, and while they all worked fine, I hated the whole process of getting it out, connecting it to the battery, airing up each tire, checking pressures, then packing it all away. With a low volume compressor it's easily a half hour or 45 minute procedure. It's tolerable if you only have to do it once each day, but if you're moving between different terrains or hopping on and off paved roads in between dirt roads, the whole thing become tiresome. Also, I'm pretty lazy and try to avoid extra work, so A. I don't air down when I should, or B. I don't air up when I need to. It's usually the former, I run a lot of dirt roads at street pressures if I don't think it's going to be too rough or too long just because I don't want to air up and down all the time. I usually avoid B because I don't have power steering on my FJ40 and steering at <15psi is really tiring and will wear you out quick.

The heart of the system is the Maxi-Trac 300LPM that was sold by Napa. At 10.3 cfm, it's faster than the ARB dual, but at the time is was also <$100. Looking back I should've bought 3 of them for spares. Now they're impossible to find, but other companies are selling rebranded versions for more $$$. Here it is compared to the Viair 88P and the Viair 300P. It's a monster of a compressor. It draws 90-100amps when running, so most people upgrade the thin wires feeding it.


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Had to make a custom mount to squeeze it in the engine compartment. I copied the design of the dual battery trays for the FJ40 that mount to the shock tower for support. As you can see it barely clears the air intake. There are a lot of videos and writeups on modding this compressor online, but the only 2 things I did was replacing the switch PCB with a heavy duty solenoid and increasing the output fittings to 1/4"NPT. Hidden behind the compressor is an air manifold which has all the connections, gauges, and pressure relief valve.

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One of the problems people have found with using a high volume compressor like this is the Schrader valves are the limiting factor, so you need to use a quad inflator or do something else to handle the flow. I did both. Otherwise when filling a tire, you end up creating a lot of backpressure on the compressor (not good) or you just don't take advantage of the speed. In my initial tests, filling up one tire took about half the time as filling up 4 tires, so a lot of the flow from the compressor was being restricted.

Since i already had a hollow tube bumper, I just converted it to an air tank. I tested it up to 120psi, but I have a pressure relief valve in the system to vent at around 60psi, and I normally don't pressurize to >40psi.

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For the control, I bought a cheap no-name compressor off of amazon so I could take the control board. Here it is during testing. It acts like a pressure switch, but on this one you can set the cutoff pressure and it will automatically turn of the compressor when it reaches the desired pressure. Just one less thing to deal with when airing up. All you really need from this system is the digital display with the buttons, the rest of the compressor and handle can be cutoff. For now I just tapped into the control board wiring with an external connector, then used the original air hose for the pressure sensing line. Eventually I'll hack it up and permanently mount it somewhere in the engine compartment or maybe inside the cabin.

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A lot of people use quad inflators with this compressor, but I didn't like the idea of dealing with a rats nest of hoses every time I wanted to air up. So I did the wifey air mod, which is essentially a quad inflate system but with quick disconnects at each corner. So instead of 50ft of hose, I have 4 short hoses that connect to the tires. It takes more time taking off the valve caps than connecting the hoses, so overall it's pretty quick.

For the final results. I can air up 33x10.5x15 tires from 0-30psi in under 5 minutes. Taking out the hoses, connecting them, and packing away is probably 2-3 minutes additional times, so overall it's still <10minutes total. Compared to the 30-45 minutes it used to take to air up, it's a major improvement.

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Well done, sir! One of these compressors are on my list of things to buy. I really need to start airing down when I go off road.
 

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