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| Why Do I want an EXAXT Axle? |
| Why? There are lots of reasons. Clearance. Strength. Cable-actuated selectable lockers. Coolness. And, there are other guys selling Unimog portal axles. But ask them if they have trail-tested (and street-tested) their designs? Have they done the homework to recommend the right ancillary components, such as master brake cylinders? At EXAXT, we sell what we build and test ourselves, so we know what there is to know about our product.
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| Why not Unimog 406 Axles? |
| Unimog 406/U900 axles are definitely stronger and newer than the Unimog model 404 axles we use. However, with those advantages come disadvantages. 406 series axles are far heavier (320kg/700lbs front, 280kg/620lbs rear, stripped) and more expensive. (A 406 axle weighs more than a Rockwell!) In addition, disk-brake 406 axles cannot use a rim size smaller the 20 inches (18 inch rotors) without virtually zero backspacing on the rims. Disk brake calipers have to be manually adjusted, and replacement pads are prohibitively expensive. Finally, it’s more difficult and expensive to remove the torque tube and mate the center section to a regular driveshaft. Still, if you want 406 axles (that are as close to unbreakable as anyone needs) or replacement parts, give us a call, we may be able to help. We've worked on them before and and can set you up with a bombproof design.
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| Why do disk brakes cost so much? |
| The disk brake kit is far more than simply a rotor and a caliper. We have to machine brand new Mog hub. Still, this is the strongest, safest disk brake conversion kit that we are aware of! The new hub changes to the common 8 on 6.5 inch bolt pattern so that commonly found rims can be used. The kit also includes the caliper mount adaptors, all the necessary hardware. When comparing prices, check to see if other disk brake kits are as complete.
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| I’ve heard Unimog 404 axle portals are weak, are they? |
| In an word, no. But nothing is unbreakable. The questions ar: How much strength do you need? How much do you value the increased odds of getting home without a break? We value it pretty high. That’s why we did the research before working with our first pair of Unimog differentials. Without exception, everyone who is familiar with these axles, including the portals, knows they are stronger than even a Dana 70. But that doesn’t mean they are unbreakable. Although we’ve now seen some pictures, we have yet to see one actually break. And we’ve done burnouts with our 44” tires on our test mule, which happens to have a strong big block under the hood. We also absolutely abused it at the Top Truck Challenge (spectators were expecting the axles to shrapnel!) And they continue to hold up just fine.
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| What if I need another axle ratio? |
| Unimog 404 axles come with one axle ratio: 7.56:1. 3.54:1 (either 25:7 or 39:11) is in the crown and pinion, 2.13:1 (32:15) is at the portal. What does that translate to? Without overdrive and 44” tires, expect to do roughly 4000rpm at 65 mph. If you have an overdrive, the RPM will drop accordingly. This is too much for some engines, but not all. And, it is possible to build a hybrid axle with a different center section (such as a Dana 44, Ford 9”, or Toyota). The Unimog selectable locker is lost, but if you are upgrading from existing axles, you may already have a locker that can be used. Please do not ask us about an alternate gear ratio. In our opinion, one cannot be designed without severely impacting the strength of the ring gear or requiring a significant redesign of the 3rd member.
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| I’ve heard the axles can’t handle highway speeds, is that correct? |
| Unimog axles were designed from factory to handle 39 to 41 inch tall tires. With those tires, the factory maximum sustained speed rating is 90kph (55mph). With 44 inch tall tires, that rating will convert to 100kph (62mph). There is a safety factor, and through our testing we haven’t come up with what we consider a true maximum speed rating so we continue to state the factory original speed rating. Disk brakes do help, though, since they allow more air to pass around the portal than drums, to help keep the portal cool.
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| These axles are different, what do I have to consider before buying a set for my 4x4? |
There are many items that need to be considered:
These, and other concerns, will determine whether a portal axle will work for you, and whether it will have to be a custom, hybrid axle. Feel free to contact us with any specific questions and concerns.
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| Do I need to narrow my Mog axles to fit my truck? |
| It really depends on your application. If your vehicle is a Jeep or a Toyota, then the axles will likely be narrowed. In these situations, a hybrid axle is probably ideal only because other concerns such as driveshaft lengths, angles, etc. often negate the use of the stock Mog center section. It also depends on what rims you choose to run. In many cases, a hybrid axle remains more cost-effective than narrowing a Unimog axle to retain the stock center section, anyway. We have not found any need to narrow these axles for full-size applications. Depending on the suspension and frame configuration, narrowing the axles can mean losing turning radius, which is something we wanted to avoid (as it is, our tires still occasionally rub at full lock). Concerned about center of gravity? Take a look at our test mule. It has been on side hills past 25 degrees and remains firmly planted on the ground. And it is taller than necessary. Still, we run with trucks taller than us which have conventional axles. Concerned about track width? We are too. So we chose to pick rims with an appropriate backspacing instead of narrowing the axle. It is simply a more cost-effective solution, and it retains a reasonable scrub radius. Our width measured from outside of tire to outside of tire, with 44x18.5” Dick Cepeks, is approximately 88 inches (inside to inside is approximately 54 inches), which is comparable to other trucks running this size tire. If this remains too wide for your application, a hybrid axle is still possible.
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| The rear differential is slightly offset, does that matter? |
| Under most all situations are rear offset differential is not a concern. The only concern is when the offset increases U-joint angles to an unacceptable degree. Even stock full-size Jeep Wagoneers came with a centered rear transfer case output and an offset rear differential. Why does this not matter? A U-joint doesn’t know or care which way is up! All it is concerned about is the angle at which it is running. Whether that angle is true to the ground or not is of no consequence. As long as U-joint angles remain in phase and are operated at correct angles, there should be no problems.
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| Can I run an unmodified steering axle in a rear application? |
| Some people do run unmodified steering axles in the rear, but we don’t think that this is the best idea. There are left and right gearsets in the portals. Under many circumstances, there is no reason to be concerned, but under high load, like climbing a waterfall, these gearsets should be on the correct side, or you risk blowing the portal. Why? These are heli-cut gears, and may load the portal housing when under high stress in the wrong direction. At least, it is relatively simple to switch the portals from side to side. We also believe that the front axle shafts are a bit too small for a rear application. They are some 70% smaller than the rear axle shafts. Again, for a light vehicle, there may never be a problem, but remember that these shafts were only intended to be used when 4wd is engaged on the Unimog, not in any 2wd application.
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| Why don’t you sell a pinion brake? |
A pinion brake may be cheaper, but it is seldom a good choice, particularly when you have a selectable locker. Concerns were:
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| What do I do for caster and camber? |
| Each vehicle will require different specifications so it is impossible to give one set of numbers that will work for all vehicles. However, we recommend starting with the factory specifications and fine-tuning from there. Remember, due to the portal design, relatively low caster numbers are ideal. Camber : 1.75 degrees |
| What oils do I use? How often should they be changed? |
| 90W gear oil is suitable, though we recommend a high quality synthetic gear oil, such as a 75w90. Differentials and portals should each be changed every 8000km/5000miles. The differential requires approximately 3.0 litres, each portal requires approximately 0.3 litres.
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| What kinds of tires can I run? |
There are actually two answers to this question:
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