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Common Full Size Jeep Problem Solving

Posted in How To on August 1, 2012
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For whatever reason, XJ prices have suddenly shot upwards. Wranglers and CJs have always been kinda spendy. And odd-ball stuff like Willys pickups and wagons, FCs, and other models can prove frustrating to use on a daily basis unless you go swapping a bunch of major components. But don’t fret. Recently we’ve noticed a ton of AMC-era full-size Jeep pickups, Wagoneers, and Cherokees for sale at haul-it-away prices. Sure, nicer or restored versions fetch a premium, but if you’re willing to take on a project requiring some elbow grease, you can score large for little coin. So take some pointers from our ’78 Cherokee Chief, and don’t shy away the next time a full-size bargain jumps up and hits you squarely in the forehead.

Pumps, Pumps, and Pumps
Whether fuel, water, or oil, you’ve got to hook up some gauges and see what’s doing to ensure long life and proper performance. The AMC engine oil pump is a steel gear housed inside the aluminum timing chain cover. Over time, the gear can wear the cover and reduce oil pressure. You can shim the pump, but the real fix is to use a replacement timing chain cover like those from Bulltear, Crown, Proform, Omix-Ada, and others. The water pumps aren’t a common wear item, but it seems many FSJs suffer from overheating, so if your water pump is going bad, take the opportunity to upgrade to a Flow Kooler pump (PN 1781). They do make a difference.

The AMC fuel systems route the line up the side of the engine compartment and in front of the engine. To reduce vapor lock, the factory-carbureted applications run a return line from the pump all the way back to the tank. This diminishes vapor lock, but also bleeds off pressure, so unless your fuel pump is working perfectly, even a new replacement can deliver less than ideal pressure. Hook up a gauge and ensure you’ve got 6-7 psi fuel pressure at idle and with the engine revved.

Fuel System
Many FSJs are plagued by rusted or leaky fuel tanks and leaky or poorly working carburetors. Ours was no exception. In addition to a big hole punched in our fuel tank, ours had some leaky fuel hose that we replaced and a carb that needed a rebuild. The two-barrel Motorcraft 2100 or 2160 carb is easy to rebuild and even the Autolite 4300 four-barrel is doable for the average enthusiast. The factory carbs perform rather well off-road, so a rebuild isn’t wasted effort.

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The AMC exhaust manifolds used in most ’70s applications actually flow pretty well. The bummer is that the exhaust manifold gaskets blow out at the cylinder head and at the collector. And when you go to replace them, more times than not the collector studs strip the cast iron manifold or the manifold bolts snap off in the cylinder head. Also, for the Quadra-Trac-equipped vehicles, you need to do a bit of custom exhaust work to fit a standard oval performance muffler. The factory unit is a long, round-case muffler that fits next to the offset rear driveshaft. Our manifolds leaked everywhere and our muffler was rotted with holes in it.

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Tranny and Motor Mounts
To be honest, AMC didn’t exactly spec the best materials to create these vehicles. And most of the engines, transmissions, and T-cases leak at least a little. Most leak a lot. So, when you couple poor quality rubber that dry-rots and cracks easily with a good soaking in engine oil, ATF, and Quadra-Trac fluid, it’s a recipe for broken mounts. Oh, and don’t get us started on the Quadra-Trac T-case. Check our story “Quadra-Trac Rebuild,” (Jan. ’12) for more info on these cases.

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Interior Attention
For starters, the ’78-earlier trucks have pretty poor electrical systems and an ammeter that’s a ticking time bomb. Check “The Monkey Bus, Part 1,” (July ’11), or on for more info on the electrical system. The wiper switch tends to go bad, but BJ’s carries one that works. Ditto on the door locks—the spring inside the door that holds the lock up breaks and then the doors lock themselves when you slam them shut. Good for security, but not so good if you left your keys in the ignition. If you’ve got a tilt steering column, chances are it’s all loose and sloppy and good luck getting your A/C to work. If it does, you’ll be able to freeze meat on a summer day. If not, you’ll be logging into for replacing parts.

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We’ve already touched on the ammeter time bomb, but just in case you’re too lazy to check our web site for the whole story, you’ll want to do yourself a favor on ’78-earlier rigs and pull the gauge cluster. Disconnect the leads to the ammeter and connect them together, and then tape it off. That’ll prevent a meltdown. Also, check and lube your speedo cable to prevent it from snapping and killing your speedo. Finally, the three glass lenses in front of the gauge clusters can dislodge and fall partially down. You can crack open the cluster and use some Superglue or plastic modeling glue to pop ’em back in place.

While most of the factory gauges are pretty accurate when working, there’s no way to keep tabs on engine speed. We didn’t want to change the vintage vibe of our ‘70s interior, so we selected this Sunpro 33⁄8-inch Retro Tach (PN FZ88R) and mounted it on the included bracket over one of our non-functioning vent pulls. The half-sweep tach looks period-correct, and the green light almost perfectly matches the factory gauges at night.

Vacuum and Emissions
The ’71-’91 AMC-era vehicles have what seems like miles of vacuum lines controlling the analog switches for emissions devices, HVAC controls, the Quadra-Trac T-case, and a host of other gizmos. And by now, most of the factory hose is rotted and leaking. Heaven help you if you need emissions switches. Some are still available through vendors like BJ’s Off-Road or even you local auto parts store, but some are not. Simply replacing the dry-rotted vacuum lines will usually smooth out the idle and get vacuum-operated devices working properly again and allows you to trace malfunctioning thermal and timed emissions devices if your state requires it.

In addition to collapsed and dry-rotted vacuum lines, our ’78 had a cracked charcoal canister that was the source of a major vacuum leak. Since we couldn’t find a replacement for our year vehicle, we tried sealing the original with RTV. Ultimately, we logged onto and bought a canister (PN 53030500) for newer Jeep applications. We had to drill out the nipple for the carb bowl vent (at left—now disconnected and capped). Ported vacuum goes to the valve in middle, and the fuel tank vent to the nipple at right.

Our Cherokee tried to kill us one day when the master cylinder quit working just yards before a four-way stop. The early ’73-older vehicles relied on four-wheel drum brakes, but the ’74-newer got a very good front disc, rear drum setup almost identical to GM pickup and SUVs of the era. When working properly, it’s actually a really good braking system that stops well with larger-than-stock wheels and tires. We rebuilt our front and rear brakes and replaced our master cylinder with components from our local auto parts store. You also want to grab a vacuum pump with a gauge and verify your power booster doesn’t have a leak.

Even after a full system rebuild, we couldn’t get a decent pedal feel because our factory combination holdoff/proportioning valve/distribution block was toast. Rather than cut and flare the brittle brake lines for a universal part, we found a direct-fit replacement assembly (PN VML102) from Inline Tube. We also used the company’s wire lead (PN PR201) to splice into our factory brake light switch. Inline Tube also carries new hard lines, hoses, brake cables, and even fuel and exhaust components. The new Inline Tube part did the trick and now our SJ stops on a dime.


Lincoln Electric
Cleveland, OH 44117
Cleveland, OH 44135
Inline Tube
Shelby Township, MI 48315
Rock Auto
Madison, WI 53719
Suwanee, GA 30024
Bulltear Industries
Lindstrom, MN 55045
Dynomax Performance Exhaust
Monroe, MI
MTS Company
Dubuque, IA 52001
(800) 522-1622
Proform Parts
Roseville, MI
Crown Automotive Sales
Marshfield, MA 02050
Bj's Off-Road
Flow Kooler
Nostalgic Air Parts, Inc

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