Your Tech Questions Answered
I’ve received a few questions about the AxleTech 4000 axles that were mentioned in our feature article, “U.S. Military Spotter’s Guide,” (Mar. ’13). Jeff Armfield, director of global product line management for AxleTech International, was nice enough to give me a bit more information and tips on the new heavyweight military axles.
In terms of sheer strength out of the box, Armfield said, “At 1,500 pounds apiece with diff locks, ABS, CTIS (central tire inflation system), and a load capacity of 20,000 pounds, I can’t imagine a vehicle for the average off-roader would come close to breaking one.” Another area of interest has been the massive disc brakes, to which Armfield responded, “I would strip off the brakes and do a conversion to hydraulic-disc brakes in a second. The 4000 Series typically carry air-actuated discs or drums that are A) overkill from a performance perspective and B) heavy. The rotors or drums clock in at nearly 100 pounds apiece. The calipers are 30-40 pounds apiece. And the air system required to actuate is complicated and heavy as well.”
Armfield was nice enough to offer answers and advice to anyone who has questions or needs help from a technical or vehicle interface perspective. Feel free to shoot me your questions at firstname.lastname@example.org and I will compile another batch of Q&A for the gentleman in the know!
Q I’ve been a fan of your magazine since before I was old enough to drive. I especially enjoy the overland and expedition travel articles. I hope that since the rest of the world finally seems to be catching on that this is a great way to wheel, those articles will become more frequent. I realize that for some people wheeling consists only of rockcrawling, desert racing, and/or mud running. But trail riding and camping, getting from point A to point B, and enjoying the journey has always been my favorite way to wheel. Perhaps it is because one of my other favorite pastimes is backpacking, and overlanding is a lot like backpacking with a 4x4!
I do have a technical question for you. Does anyone make replacement gearset for the 2½-ton Rockwell axles? If not, why not? They’re a great and nearly indestructible axle, but the standard 6.72:1 ratio is a little low for some projects. Any information you can provide would be greatly appreciated!
Jeremy Lee Armour
A The 2½-ton Rockwell is a great axle, but it isn’t for everyone. In terms of a different gearset, Ouverson Engineering & Machine (www.ouversonusa.com) offers one that replaces the upper pinion and ring gear. The company’s heavy-duty gearset provides the Rockwell with a final ratio of 4.90:1.
Q I have an ’01 Ram 1500 with a 5-inch lift and experience front driveshaft vibrations. What is the best fix for my problem?
A Anytime you have a driveline vibration, start simple and work your way up from there. The basics include making sure the driveshaft U-joints are in good shape, and if the driveline is equipped with a CV (constant velocity) joint, that it is not worn. While you have the driveline out and have determined that all parts are in good working order, have it balanced by a certified driveline shop. A bent or out of balance ’shaft can create a steady driveline vibration and potentially damage surrounding parts.
If you find that the driveshaft is not the source of the problem, start looking at your front differential and transfer case outputs. A worn pinion bearing and/or transfer case output bearing can contribute to a driveline vibration. Also, if your driveline was the problem, be sure to check for extensive slop or play in the aforementioned outputs. If you don’t have a driveline shop nearby, Tom Woods (www.4xshaft.com) and J.E. Reel (www.reeldriveline.com) are both reputable driveline companies that offer custom and O.E. replacement driveshafts that can be shipped anywhere in the USA.
Q I am building a custom Jeep and want to know the best way to go about making it watertight. I am installing a snorkel, but want to make sure the rest of the Jeep is sealed properly as well.
A Water can be more damaging to your 4x4 than years of crawling over massive boulders. Remember, just a few ounces of H20 can destroy your engine if ingested! Since water has a tendency of seeping in just about everywhere, you have to be extra vigilant to seal your rig accordingly. Installing a snorkel is a step in the right direction. The next important purchase will be a few tubes of RTV silicone. The RTV should be used virtually anywhere that there isn’t a gasket or where the seal is less than effective—places such as your distributer cap, air-inlet junctions, vacuum hoses, oil caps, and even dipsticks if you plan on seriously submerging your rig. Marine application dipsticks are also worth looking into.
If your Jeep has a mechanical engine fan, swap it to electric. Once you convert the fan, route a bypass switch that will allow you to easily disengage it. While I prefer mechanical fans in most scenarios, in deep water crossings they can be pulled into the radiator and cause significant damage. Your Jeeps wiring and computer are also extremely susceptible to damage. Sealing your ECM or placing it inside of the vehicle will be crucial. Companies like Painless Performance (www.painlesswiring.com) offer an assortment of waterproof electronics and controls.
Routing your Jeep’s breathers to a high location (differential, transfer case, etc.) is another safe way to keep water out. If frequent water passage is a necessity, more extreme fixtures such as a high-mounted custom exhaust are worth the investment. Lastly, use common sense. Your Jeep isn’t a boat, and isn’t made to be submerged completely in water. Quick dips and crossings are fine, but any sustained period can lead to serious environmental and vehicle damage.
Q Is there an easy way to figure out the size on those metric tires that all the OEMs seem to be running these days? I don’t understand why they won’t just label the tires in inches in the first place!
A I too am generally annoyed at the metric tire stamping. To examine a metric tire, let’s start at the beginning. You’ve likely noticed that the tire size begins with either an LT or P. The LT stands for light truck. P is for passenger vehicle. Those are the easy basics. The first point of confusion often comes at the last number. For example; on a LT305/70R17, the R stands for radial tire and the 17 references the rims diameter in inches. Why they use an inch measurement for the rim size, but not the rest of the tire, is odd, I know.
Now let us examine the 305/70 portion of the tire. The 305 number represents the tires section-width, while 70 marks the tires aspect ratio. Both numbers are in millimeters. The smaller number is simply a percentage of the tires width. In this case the width is 305mm and the height is 70 percent of that. To calculate this you multiply 305 x 0.70, this nets you 213.5mm. But wait, there’s more!
Since 213.5mm is the measurement from the outside of the rim to the top of the tires tread, you must double the number to get the tire’s actual height. In this case we have 427mm. To convert from millimeters to inches you divide X number by 25.4. For our example tire, that equates to 427mm divided by 25.4, which equates to 16.81 inches. Lastly, we add the diameter of the wheel (17 inches). So our 305/70R17 is roughly the equivalent of a 34-inch-tall tire (33.81) that’s 12 inches wide. Would it have been easier to just say 34x12 on the tire? Why, yes. Yes, it would have! Thankfully, there are plenty of conversion calculators online to do the math quickly for you.
Q I am looking for a lift kit for my ’74 Toyota FJ40 Land Cruiser. The original springs and shocks are completely worn out, so I would prefer a kit that replaces both. I don’t really want to lift it too high, as it still needs to be able to fit inside of my garage.
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