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Answers to all your Jeep questions

Posted in How To: Tech Qa on January 14, 2016
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Persnickety AMC 20
I drive a ’86 Jeep CJ-7. It has a 2 1/2-inch Rough Country suspension lift and a 2-inch body lift that clears 31-inch tires. The running gear is stock. It has a 258ci inline-six, T-5 manual transmission, Dana 300 transfer case, Dana 30 front axle, and an AMC 20 rear axle. Three years ago, the driver side rear wheel hit a really large pothole at about 45-50 mph. Since then, I've had nothing but problems with that side of the AMC 20. Hitting the pothole destroyed the wheel bearing. I could hear metal-on-metal grinding immediately after I hit it. The bearing was replaced, but I still have problems with failing axle oil seals and wheel-bearing failures. I'm being told that nothing is bent. What could be the cause of these failures? Is the axle or axletube really bent, or is there some other terminal fault in the axle? As you can imagine, this is costing me money every time it happens so I'd like to fix it permanently.
Roy Winn
New York, NY

The AMC 20 rear axle found in the ’76-’86 CJs has been notoriously cantankerous, especially for those of us that lift our Jeeps and take them off-road. Even though the ring gear of the AMC 20 is nearly 9 inches in diameter, the rest of the assembly has more than its fair share of weaknesses. The axletubes are somewhat small in diameter and not especially thick, but worst of all are the axleshafts. The AMC 20 features a two-piece axleshaft design with a serrated and keyed ’shaft that fits into a serrated and keyed hub. Too much tire, torque, or abuse can cause the assembly to loosen. Typically the keyway and serrations strip out. Overall, the entire axleshaft assemblies and bearings are kinda persnickety. They require the exact amount of bearing preload, which is adjusted via shims. If there are bends in the axleshafts or the housing, the problems are exacerbated. For decades, the solution has been to replace the two-piece axleshafts with aftermarket flanged semi-floating axles. Not all of these kits are equal. Some of them still use a complicated shim pack for axle bearing preload. More expensive full-floating axle conversion kits were also available. These are a great option for anyone who will flat-tow the Jeep, although the kits are becoming more difficult to locate. Used full-float kits are the only option today. The good news is that companies like Alloy USA (alloyusa.com) and TEN Factory (tenfactory.com) offer complete one-piece chromoly axle kits for ’76-’86 CJ AMC 20 axles. However, if the housing is significantly bent, these ’shafts may not solve your problem. You should have the axlehousing inspected by a trusted and knowledgeable mechanic. Find a mechanic that is familiar with AMC 20 axles, their problems, and the aftermarket parts available to remedy them. Have the bearing pocket on the housing inspected thoroughly. If you drove on a damaged bearing for an extended period of time, the pocket on that side may no longer hold the bearing and axle properly.

XJ Issues
I wanted to give you guys an update on my ’01 XJ project. I've put a Rusty’s 4 1/2-inch long-arm suspension lift kit on it and then tried to cheap out by using spring shims and no slip-yoke eliminator kit. When I turn and then let go of the steering wheel it acts like a stopwatch, and the vibrations are like a 9.5-magnitude quake.

I recently had an Advanced Adapters slip-yoke eliminator kit and Rubicon Express double-cardon driveshaft installed, and then I installed Mickey Thompson 33x12.50 Baja ATZ-P3 tires mounted on Black Rock Viper silver wheels. I topped it off with Bushwacker flat-style flares. It drives like factory, but I have a shimmy from 28 to 35 mph. I cut off the spring perches on my 8 1/4-inch rearend, and with the full weight of the vehicle on the ground, I rotated the pinion in a straight line to the transfer case with the driveshaft on. The vibration is still there, but it’s been lowered to a 4.5 quake. Rusty’s said to shim it 4 degrees with the thick end facing forward. Any wisdom you can give me on this?
Calvin Splan
Via email

It sounds like you may be dealing with two unrelated issues. First, let’s concentrate on the steering problem. The Rusty’s Off-Road (rustysoffroad.com) long-arm conversion for the front XJ suspension allows for caster adjustment. Make sure the caster is set to the recommended angle, generally around 5 degrees positive caster. Next, you’ll need to inspect the tie rod ends, draglink ends, steering box, track bar ends, and ball joints for slop. The majority of steering shimmy problems stem from worn or loose track bar and steering draglink components, so give them an extra close inspection. You may also need to adjust tire air pressure to make sure that the tread surface is making full contact with the ground. Too much air in your tires for the weight of your vehicle can cause the tread surface to be crowned, this leads to wandering and can cause the shimmy you describe. The maximum psi molded into the sidewall of your tires is likely much too high for the weight of your XJ. Experiment with different tire air pressures until you get full-tread contact with the road surface. You will likely need a steering stabilizer of some sort to help control the tires. However, don’t simply install a steering stabilizer to mask the other problems caused by worn or parts or incorrect alignment. The stabilizer should be the last part to be added.

As for your driveshaft vibration, 4 1/2 inches is a considerable amount of lift on an XJ. Assuming you have the rear driveshaft angle correct, some of the vibration you are feeling could be coming from the front driveshaft. Unfortunately, there is no easy or cheap way to correct this. The design of your XJ front axle allows the entire axle assembly and front driveshaft to spin, even in two-wheel-drive. Correcting the front driveshaft angle by rotating the housing will alter the steering caster, causing handling issues. So that’s not an option. The simplest (albeit expensive) way to keep the front driveshaft from spinning on the highway is to install a front locking hub kit or swap the front axle out for one that has locking hubs. Alloy USA (alloyusa.com) offers a bolt-on locking hub conversion kit that fits your factory XJ Dana 30 front axle if you decide to go that route.

FC Overdrive
I own a green ’59 FC-150. I have two questions. I hope the first is an easy one. In your "Write Us" block in every issue, you ask for .TIF, .JPG or .EPS files but say you can’t use .pdf files. I’m a trained photographer, and I also own and operate a small commercial print shop and routinely use .pdf files in layouts I prepare for offset printing. What do I need to learn about images? I’m not arguing with you, but rather I’m curious about why you do not like .pdf images.

Now for the slightly harder question. Most FCs have the T-90 three-speed transmission and Dana 18 transfer case. I have come into possession of a Warn/Saturn overdrive. The unique nature of the linkages for FCs makes installation of the overdrive more complicated. Is there some sort of electrically operated engage/disengage control available? Do you have any experience with an Overdrive in an older Jeep that is operated electrically?
Dan Laity
Elmore, OH

Technically, we can use a .pdf image; however, it slows down our production process. With hundreds of images to push through the production system, we try and streamline it as much as possible. Tossing .pdf images in the mix is the equivalent of throwing a wrench in the spinning gears of the Jp machine. Besides, most modern enthusiast and hobby cameras produce .jpg images. There really is no need to send a .pdf.

As for the FC Overdrive, you have a couple of options. You could go down the path of trying to adapt an electrical solenoid of some sort to the back of your transfer case, or you could simply use a cable shifter. Herm The Overdrive Guy (hermtheoverdriveguy.com) offers many different Overdrive shifter kits for early Jeeps, including a cable-operated Overdrive shifter kit specifically for the FC-150 and FC-170. Another option would be to locate an old (hard to find) Borg-Warner R10 or Rancho electrically shifted Overdrive. These units bolt right in to replace the Spicer 18 rear output so they can only be used in two-wheel drive.

Shocking TJ
I have a shock question that I can't find a good answer to and thought Mr. All Knowing Jeep guy would know this off the top of his head. I have a ’98 TJ with a bastard 3-inch short-arm suspension lift. It has sway bar disconnects, aftermarket control arms, a dropped pitman arm, and a dropped track bar. It's no long-arm kit, but it flexes pretty well for a short-arm lift. I'm going to replace the crappy existing front shocks. It currently has Old Man Emu (OME) shock on the rear, and I love the ride they give. I can't find a front shock listing anywhere for the OME shocks. Quadratec lists only 2 to 2 1/2-inch lifts and 4 to 5-inch lift heights for OME shocks. My concern is that the shorter shocks will limit down travel and the longer ones may bottom out. Would you recommend one length over the other or go to another brand completely?
Ryan Light
Shellsburg, IA

Mixing and matching suspension system parts can cause lots of complications, including what you have found here with your shock lengths. There is always some compromise when piecing together your own suspension system. Don’t fret though, with a little research, there is almost always a solution, especially when it comes to fitting shocks. If you are happy with the length of the front shocks you have now, remove one of them and measure it at full extension and at full compression. I suspect the dimension will be very similar to the OME (arbusa.com) 2 to 2 1/2-inch-lift shocks. The OME extended-length shocks (PN 60047L and 60049L) are designed for 3 1/2 to 5 inches of lift and will require bumpstop extensions. If you don’t currently have bumpstop spacers and you don’t plan to install them, then you should stick with the shorter shocks.

Headlight Upgrades
I have a ’00 TJ. Is it possible to use a JK headlight assembly in my Jeep? How hard is this swap? I want better and brighter lights without spending $700.
Steve Gillmore
Via email

We all want brighter lights at night, but there are a few things to consider. Not all of the conversions available are for street use. Unfortunately, the JK headlight and grille assembly is quite a bit different than the TJ grille and headlight assembly. Is a swap like this possible? Of course, anything is possible, but it isn’t worth the cost or effort, because there are many other bright light options available that won’t set you back $700.

The ’97-’06 Jeep Wrangler has the same standard 7-inch round sealed beam headlights that most Jeeps have come with since 1946. For a quick and easy headlight swap that is about 20 percent brighter than stock, you can switch to Sylvania (sylvania.com) SilverStar sealed-beam headlights. These are a direct bolt-in replacement for your factory sealed-beam headlights. No additional wiring is required. The SilverStar lights and bulbs are available for many different applications and are completely street legal.

If you have a slightly bigger budget, you can do an H4 headlight conversion. Companies like Hella (hella.com) and Rampage Products (rampageproducts.com) offer H4 conversions for the 7-inch round headlights in the ’97-’06 Jeep TJ Wrangler. The street-legal kits utilize 60/55W bulbs. If you aren’t worried about street legality, the lights can make use of up to 130/90W H4 bulbs. Of course, with these you’ll also need to add a relay system to support the increased electrical demands.

If you are into LED lights and don’t mind spending a little more, companies such as J.W. Speaker (jwspeaker.com), Sylvania, and Truck-Lite (truck-lite.com) offer bolt-in LED headlight conversions. J.W. Speaker offers several different LED replacement headlights to choose from. The Sylvania Zevo replacement LED headlights provide a 6,200K color temperature, which is said to surpass most Xenon HID OEM light sources. Sylvania says the headlights work with your vehicle's existing socket and wiring and feature a shock-resistant design. The Zevo LED lamps are backed by a lifetime limited warranty and said to be good for more than 2,000 hours of operation. The Truck-Lite LED replacement lamps can be installed in any ’46-’06 Jeep with 7-inch-diameter round sealed beam headlights and are made in the USA. All of the LED conversions mentioned are completely street legal in all 50 states.

Pinky Broke I have a ’78 CJ-5 with a healthy 304ci V-8 that my family and I have enjoyed for the last 20 years so far. I was coming home the other day down some beautiful backroad when I rounded a corner to a freshly smoothed over gravel road. Without thinking, I had the instinct to have some sideways fun. As I was correcting the steering out of my rooster tail of dirt, my pinky finger got caught in the steering wheel (the holes in the hub) and snapped backwards. I busted it good! Any recommendations on a replacement steering wheel for a CJ that still retains the factory horn function in the wheel?
Jeremy Rendell
Via email

That makes me cringe just thinking about it. I always wondered what it would be like to get a finger stuck in a steering wheel like that, but never enough to actually try it. Anyway, Grant (grantproducts.com) offers numerous steering wheels and adapters for your Jeep and many other Jeep models. You’ll need to order the proper installation kit for your application for the horn to function properly. Apparently there are two different versions. One version has the horn tube at the 1 o’clock position and the other has it at the 11 o’clock position. Be sure you match up the correct adapter with the proper steering wheel series.

Quadra-Trac Limits
I have a ’79 Jeep Cherokee FSJ. It has a Dana 60 front axle and a GM 14-bolt rear axle, both with 4.56 gears. A TH400 automatic transmission is bolted up to the built AMC 360 V-8 and a factory Quadra-Trac transfer case. My Jeep is getting close to being done. I have one question for you: How much tire with the Quadra-Trac transfer case support when it’s shifted into part-time? I have 37-inch tires and a heavy foot. Will it last? I love Jp for all the info, but I would like to see more fullsize SJs.
Tom Stanly
Via email

Component durability questions are always a little hard to answer without knowing more about driving habits, the off-road terrain you plan to encounter, the condition of the component, and so on. However, in this case, you’ve made it a little easier. Look at it like this: You essentially have 1-ton drivetrain in your Jeep now. The Dana 60, GM 14-bolt, and TH400 are all 1-ton parts. And right in the middle of them you have put a fusible link. That’s not to say that the Quadra-Trac transfer case is junk, but even on its best day when brand new, it’s still a light-duty 1/2-ton component. Now, I suspect that your Quadra-Trac isn’t new, or even rebuilt. The chain in these transfer cases is one of the most wear-prone items. The fact that many people used the incorrect oil in most Quadra-Trac T-cases at some point in their life isn’t very reassuring. Also, there aren’t many top-quality U.S.-made chains available anymore. Once the chain wears and stretches to a certain point, it will rub a hole in the bottom of the transfer case and let the fluid out. As you can imagine, this eventually leads to catastrophic transfer case failure. The other problem is that the output shafts are relatively small in diameter and have coarse splines, identical in strength to a Spicer 18 or Dana 20, both of which are marginal under V-8 power in a heavy FSJ. This is even truer in an FSJ with 1-ton axles and 37-inch tires.

Having said all of that, can you make the Quadra-Trac live in your project? I actually think so, if you are careful with it, at least for a while if it is in good condition. Just keep in mind it is your Jeep’s weak point. Drain the fluid and refill the T-case with the correct Quadra-Trac oil. Crown (crownautomotive.net) manufactures the proper TCL-1 fluid for your transfer case. You’ll need 2-3 quarts without a low range and 3-4 quarts with a low range.

In the meantime, keep an eye out for a more heavy-duty transfer case and adapter. Consider a GM NP205. This big-boy transfer case will offer a straighter shot to your centered rear axle and can be adapted to your TH400 using a factory GM output shaft and adapter. Offroad Design (offroaddesign.com) offers rebuilt NP205 transfer cases and the correct adapters you’ll need to make the swap.

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