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March 2009 4x4 Truck Tech Questions - Tech Line

Posted in How To: Tech Qa on March 1, 2008
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Wants To Lighten Her Load With Heavier Tires
Question: I just bought a new Jeep Wrangler Rubicon and plan to add a lift kit and either 35- or 37-inch tires to it. With what I see advertised, I am going to need a new spare-tire holder of some type for the larger tire. Now here is the problem. I am a girl. OK, girls also buy Jeeps-but I am just a bit over 5 feet tall and weigh about 110 pounds. While recently at a tire store searching for what tire I wanted, I found that I could barely pick up that size of a tire and know that I never could pick it up when mounted to a rim. If I should get a flat tire, I think I could get it mounted on the vehicle's axle, but no way am I going to be able to lift it off or put it back on the spare-tire holder. Do you have any suggestions on how to do this, or would it be OK just to use the factory spare tire? Besides that, four tires and rims are a lot less expensive than five.
Marsha Mason
Los Angeles, CA

Answer: Yep, you sure are right, those 37-inch tires are rightly heavy and expensive. I run 37s on my own Jeep, and at 6 feet and 190 pounds, I have a very difficult time with my spare. In fact, my spare, just for that reason, is usually a 6.00x16 at 30 inches tall. What do I do if I get a flat? Hope that I don't!

OK, I carry one of ARB's tire-repair kits ( and a PowerTank ( and hopefully can do a trail fix to get me back and not have to use the spare. I have Detroit Lockers front and rear, so it's really important that the rear tires are equal height. Up front I have locking hubs, so I can turn out one hub and mount the small tire on that side and get back with three-wheel drive if necessary.

You're going to ask how I get the larger tire back on the tire holder should I need my spare? Hopefully, I am with some other people, or if alone I plan to hide it someplace and call in a favor from one of my much stronger buddies to come and get it.

So the answer is yes, you can run a smaller tire on either axle of your Rubicon as long as the axle is not locked up. I would suggest you go through the painful motions of swapping a front tire to the back if you should get a rear flat, and drive in two-wheel drive as much as possible and hope that you have some strong friends to do the work for you.

There is one other idea that I just came across a few days ago. I happened to see a press release for a Rubicon spare-tire holder that not only swings out for tailgate access, but will also fold down. It's one of those "why didn't I think of that" ideas. The company that makes it is Olympic 4x4 Products ( The company also has a new line of "high-end" Smuggler front and rear bumpers for the '07-'09 JKs that offer several advantages over what is presently on the market. The tire carrier and bumpers will be on the market the first of the year, or about the time this is published.

Wants To Convert IFS Toyota To Solid Axle
Question: On my '93 Toyota pickup, are there kits to swap to a straight axle, or does it come with an axle so I don't have to find one?
Wayne Donaghey
Cato, NY

Answer: All Pro Off Road (951/658-7077,, is just one of the places that comes to mind when I think of solid front axle conversion kits, and the company has a kit to fit the '89-'95 Toyota pickups. However, they do not come with an axle, which you will need to source locally. Even if you could talk them into supplying you with an axle, the shipping cost from the shop in California to your home in New York would negate any benefits gained due to the high freight charges.

Just for fun, I Googled "Toyota solid front axle conversion" and got, well, a lot more hits than I would ever have time to look at on the subject. You just might want to do the same, as I found some pretty good information.

Air Intakes: Good For More Power?
Question: I have a '92 Chevy pickup with a throttle-body injection system that I am looking for more power from. I have installed headers and a new exhaust system, which helped some, but was wondering if an air cleaner like a K&N unit would make any difference.
Peter Marsh
Geneva, IN

Answer: Yes, I would think so, but there is also something else that you can do. Some time ago, a buddy of mine installed a throttle-body spacer from Airaid/PowerAid (888/876-8984,, along with an air-cleaner base from a company called Alcone Engineering (505/247-4480,

While throttle-body spacers don't always show improvements on some engines, it seems to on this one by two ways: First, by increasing the size of the intake manifold's plenum area; and second, the threadlike pattern within the bore is designed to spin the fuel/air mixture, keeping the fuel droplets better suspended. The air-cleaner base from PowerAid is quite unique in that it's more of an airbox than just a flat bottom plate. It features a large velocity stack and tuning vane that accelerates and smooths the airflow. And yes, you can combine it with a K&N filter.

Fixes For Leaky Model 20 Rear
Question: The Model 20 rearend on my '83 Scrambler keeps leaking on the passenger side. I have replaced it three times in seven months at Off Road Warehouse. Can you help me please?
Bob Rasimas
San Diego, CA

Answer: First off, there are actually two seals used in the AMC Model 20 axle: An inner seal that is pressed into the housing, and an outer seal that is held in place by the backing-plate bolts. Several things could be causing the leak. The first one that comes to mind is wear to the axleshaft. If there is a wear groove in the axleshaft, or any roughness where the seal rides, then it will destroy the seal in a short time. The solution is to either replace the axleshaft or slide what is commonly referred to as a "speedy sleeve" over the damaged area. This is nothing more than a very thin metal sleeve that is sized for a press fit on the shaft and offers a smooth surface for the seal to ride on. They are available at just about any auto parts or bearing supply house.

It also could be that the end play on the axleshafts (adjusted from the driver side with shims) is excessive, allowing the axleshaft to move back and forth and damaging the seal.

Then there is the possibility that the axleshaft is bent. If so, it would move inside the tube in an elliptical orbit and quickly damage the seal. Checking for a bent axleshaft is pretty easy if you have some way to support the axle at the end of the spline and out at the bearing. Then all you have to do is put an indicator of some type at about the middle of the shaft, rotate it, and check the amount of runout. A lathe works great for this. Sometimes, if you have a sharp-enough eye, you can just take a good look at the shaft as you rotate it.

The worst case is that you have a bent axletube, which is not uncommon on the AMC Model 20. This would cause the axleshaft to put more of a load on one side of the seal than the other, resulting in a leak.

Checking for a bent tube is a bit more difficult. Usually what you have to do is pull the axle down to a bare housing, and then with special bearing blocks, run a long straight shaft the complete length of the housing from end to end and check the alignment. Another way, while not as accurate but a bit simpler, is to pull both axleshafts out and clamp onto each housing end a truly straight length of angle steel that is about 5 or more feet long. You will put one piece of metal on each side of the housing clamped or bolted to the brake flange so it's about centered, then measure from the housing along each piece of angle to a given point on each one out towards the ends. With both pieces of angle being on the same plane, the housing is straight if they are exactly parallel to each other. This is easily checked by measuring between each of the marks made on the angle iron. For example, if on one end the distance measures 60 inches and the other measures 59 inches, then you know your housing is bent. I would clamp the angle to the housing in several different locations in order to determine if it's bent up and down or front to rear. Naturally, it's important that both pieces of angle are straight and true.

Oh, and be sure to check a factory service manual for the proper way to tighten the axle nut that holds the flange in place. There is a specific procedure that is very important to follow.

Blocks Vs. Shocks: What Fits Where
Question: I have an '89 Chevy fullsize Blazer with a 5-inch block in the back. Will shocks from the same-year Blazer that has a 3-inch block fit mine?

Answer: That is kind of a "yes, no, or maybe" question. No, it will not work if the shock was originally sized properly for extended and collapsed length. Most likely it will be 2 inches too short and will not allow the suspension to drop down its full amount. OK, maybe you can live with that, but it's really not a good idea to let the shock be the suspension stop, either in an extended or compressed position. This can lead to bent and broken shock shafts and ripped-out mounts.

How to check for the proper length? Take both shocks off, block the front wheels so the vehicle cannot move, and then jack up the rear of the vehicle by the bumper until both rear tires are totally off the ground. Now measure the distance between the upper and lower shock mounts. Might want to add an inch or more as a fudge factor for when the vehicle is at full articulation-that is, one wheel up with the axle on the bumpstop and the other fully dropped, as it may be a bit further. This is the extended length that the shock needs to be.

Set the vehicle back on the ground and measure the distance between the two shock mounts. Write this number down. Measure the distance between the bumpstop and the axle, keeping in mind that the bumpstop will compress. How much is your guess, but guess more, rather than less. Now subtract that number from the first number you wrote down and this gives you your compressed length for the shock. It's not going to be exact, but most likely close enough. Most of the lift kit companies and/or shock manufacturers have charts that show the various lengths available.

What I usually do when building a vehicle takes a bit more time but is a lot more accurate. If it has coil springs, I put the vehicle on jackstands, remove the coil, and cycle the suspension with a floor jack to get my measurements. If it has leaf springs, I take a main leaf only and install it. That way, it's again easy to cycle the suspension with a floor jack. On a spring-over axle suspension you have to add a block to the thickness of the remaining spring leaves that you plan to use in between the axle and the main leaf in order to get the proper measurements.

Oh, and a quick check to see if you got the compression length right is to take a small zip-tie and put it on the shock shaft, right next to the body of the shock. As the suspension cycles, the zip-tie will move and then stay at the furthest compression point.

Land Rover Disco Oil Leaks
Question: I have a '99 Land Rover Discovery with the 4.0L V-8 engine. It now has about 120,000 miles on it and an oil leak that seems to be coming from the rear of the engine. There is not a Land Rover dealer near me, so perhaps you could be kind enough to tell me where this leak is coming from, and if I can fix it myself or have it repaired by a local shop.
Mike Allen
Casper, WY

Answer: I don't get many Land Rover questions and I find them pretty hard to answer due to my inexperience with them. However, in this case I think that I have an answer that you are not going to be very happy with. The leak could be coming from lots of sources, and hopefully it's nothing more than a leaking valve-cover gasket. That would be good news.

The bad news is that most likely the oil is coming from a leaking cam bore plug or a cam oil-galley plug. It's a common problem with these engines, and yours has most likely been leaking for quite some time and it's now getting worse. It's an easy 30 minutes or so fix using the proper sealant. I would recommend using Loctite No. 243. Doesn't sound so bad, right? Well, the problem is that the transmission, bellhousing, and flywheel have to be removed to get to these plugs, which is a major job.

Best Auto-Tranny Swap For CJ-7?
Question: I have an '85 CJ-7 with a Warner T-5 manual transmission, in place of which I would like to swap in an automatic trans. The Jeep has a 258 six, Dana 300 transfer case, Dana 30 front, and AMC 20 rear axles. What would be the best affordable auto trans that will bolt in? The Jeep is used for mild off-roading and has 32-inch tires on it.
Matthew Krzesniak
Chicago, IL

Answer: Jeep offered the three-speed Chrysler-built TorqueFlite automatic transmission as an option. This would be the simplest and most affordable trans to use. However, you just can't use any TorqueFlite. It has to come out of a CJ with the Dana 300 transfer case. One reason for this is that the transmission's mounting face has the proper Jeep bolt pattern and the rear has the proper adapter to the transfer case. My guess is that you're going to have to do a bit of searching to find one.

Another way to go that is quite a bit more expensive is to use one of GM's 700R4 four-speed automatic transmissions. Actually, this is a much better trans in that it not only offers you a much lower First gear (3.08:1 vs. 2.74:1), but the added value of an Overdrive Fourth gear. The drawback to this is that you will need two adapters: one for the trans to engine, and the other for the trans to the transfer case. Novak Conversions ( has the engine-to-trans adapter (PN 437 AMC-1), and the trans-to-transfer-case adapter (PN 137).

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