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January 1999 Your Jeep

Posted in How To on January 1, 1999
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Contributors: David Freiburger

Tiring Tire Tips
I own an '80 Jeep CJ-5 that has manual steering, 31-inch Goodyear tires in front, and 32-inch BFGs in back. The 31s are easier to steer, and the setup seems ideal for my daily driving and casual off-road needs. However, in your Feb. '97 Letters department you state that having different size tires will not change the axle gear ratio, and thus all four tires will spin at the same rpm. Does this mean that equal stress is applied to the axles and gears, even with the differences in tire diameter? So far I've had good luck, but I sure don't want anything to break.
Brendan Wiese
Cincinnati, Ohio

True, the tires will spin at the same rpm with a 50/50-split transfer case and the same axle ratios. With taller tires on the rear and shorter tires on the front, however, the distance traveled by the tread of each tire is different, and that causes unequal stress on the drivetrain when in four-wheel drive. This is called drivetrain windup. In the dirt it's usually dissipated by the slipping of the tires, but on pavement, in four-wheel drive it can actually cause the vehicle to stop moving if the traction is greater than the power input (and nothing breaks).

In your situation, the difference is almost negligible. The 1-inch difference in diameter works out to be next to nothing in circumference, and in the dirt such a small amount will be absorbed through slippage. On the street you should be in two-wheel drive anyway, so tire size is not a factor as far as drivetrain components are concerned. However, the rule still applies: All four tires should be the same diameter and have the same tread for best performance and longevity. And don't forget that tire measurements can vary among manufacturers by as much as 2 inches. You may actually have the same size tires without realizing it.

Axle I.D.
I have a '52 Jeep M38-A1 with stock axles, and I want to put lockers in them. No one I've called knows what I have, and there aren't any tags on the axles. I also need to know the ratio and the biggest tires I can put on the stock 15x7 rims.
Name withheld
via e-mail

The military M38-A1 Jeep is basically the same as the civilian CJ-5, which began production in 1954. They share the same axles: a Dana 25 front and a Dana 44 rear. If they're the stock axles they have open differentials with 5.38 gears and 10-spline axles.

The easiest way to install lockers is to use Lock-Rights from Powertrax (Dept. 4WOR, 245 Fischer Ave., Bldg. B-4, Costa Mesa, CA 92626, 714/545-7400) to replace the spider gears inside the open differential case. On the other hand, some M38-A1s were Marine Corps issue and were equipped with Dana's Powr-Lok limited-slip differentials. If your axles have Powr-Loks or any other nonopen differential, then the Lock-Right can't be installed into the existing differential.

Now for your tire-size question. The stock M38-A1s used 7.50-16s on 16x7 wheels, and 30x9.50-15s will usually fit if the Jeep hasn't been lifted. Using lockers with tires any bigger may lead to axle breakage.

While the front axleshafts can't be upgraded easily, there are many options for the rearend. The Dana 44 was also made in a 19-spline version, and though the diameter of the shafts is about the same, they're stronger than the 10-spline axles and interchangeable with them. What's more, a Detroit Locker from Tractech (Dept. JP, 11445 Stephans Dr., Warren, MI, 48090 810/759-3850) is also available for this setup, as is a full-floating axle kit from 4 Wheel Parts Wholesalers (Dept. JP, 14100 S. Kingsley, Gardena, CA 90249, 310/323-5337). But if you plan to buy new axleshafts (whether full-floating or stock 19-spline) and a Detroit, you might as well go for 30-spline units. They're much stronger than the 10- or 19-spline ones, and the locker is the same price. Both Summer Brothers (Dept. JP, 530 S. Mountain Ave., Ontario, CA 91762, 909/986-2041) and Moser Engineering (Dept. JP,1616 N. Franklin St., Portland, IN 47371, 219/726-6689) have 30-spline flanged axleshafts, and 4 Wheel Parts Wholesalers can also supply you with a 30-spline full-float kit.

First Jeep
I'm in the market to buy my first 4x4 and plan to get a Jeep Wrangler. I'd like your recommendations for what type of standard features I should select. I plan to use this vehicle as my primary transportation (10 miles round trip to work) and for camping and mild four-wheeling on the weekends. I don't plan to tow with it.

What do I want in the following categories, and what are the pros and cons of each?
• Power or manual steering
• Four-speed or five-speed trans
• Six-cylinder or eight-cylinder
• Air conditioning or not
• Cloth top or hardtop
• Any type of optional brakes
• Size and type of tires
• Size and type of wheels (alloy, chrome, or painted)
Thanks for your help.
Mike Harrison
O'Fallon, Missouri

Wow! Those are hefty questions. We decided to answer them because so many of you are just getting into four-wheeling, and the Wrangler is a popular first 4x4. We're assuming you're looking for a used one since that's the thrifty approach, though our advice will apply to the '97 or '98 Wrangler in most cases. If money is no object and you're deciding between a used '87-'95 leaf-sprung Wrangler YJ and a '97 coil-sprung Wrangler TJ, we'd go with the '97 due to the vastly improved ride.

Your first concern is power versus manual steering. At one time there was a Base trim level that made it possible to order a six-cylinder with manual steering, but we haven't seen many of them. Since around 1994 only the four-cylinder versions had manual steering (with power optional). In any case, we consider power steering a desirable option for easier steering as the tire sidewalls push on obstacles during trail maneuvers. On the pavement, manual steering is not objectionable with a near-stock Wrangler.

As for transmissions, your choice is not between a four-speed or a five-speed trans, but between a three-speed automatic and a five-speed manual. All four-cylinders had manual transmissions until the '94 model year when the automatic was made optional. The automatic trannies are best for a first-time four-wheeler who's learning to negotiate trail challenges, but they sap a lot of power-especially from the four-cylinder. Even though the early Peugeot-built five-speeds were problematic, we'd stick with the manual trans for performance, simplicity, and overdrive.

You question choosing a six-cylinder or a V-8, but a V-8 has never been available in a Wrangler. The '87-'91 Wranglers have carbureted 258ci AMC inline-sixes or 2.5L AMC four-cylinders. The later Wranglers have injected 4.0L sixes or 2.5L four-bangers. Either six-cylinder is preferable to the four for power, but we'd always opt for the improved power of the injected 4.0L. A four-cylinder may be tolerable for your brief commute, and it will be good for low-speed trail crawling (partially because four-cylinder models have 4.11 axle gears versus the 3.07s or 3.54s with the six). However, you'll tire of the 2.5L's lack of power for sand, mud, and highways, and a six will always have better resale value.

Air conditioning or not? Hardtop or soft? Those depend on your personal preference. With no top, the A/C is near useless and only adds complications with hardware and ducting. If you want to run a top, the hard version will be quieter and more weatherproof. It will make the vehicle more top-heavy, but that shouldn't be a concern if you leave the Jeep at stock height. If you want a hardtop, it's cheaper to buy a Jeep with one installed than it is to buy a used top later. And you can always install an aftermarket soft top.

There aren't many Wrangler brake options. In fact, they all have power-assisted 11-inch front discs and either 9- or 10-inch rear drums. This works OK with stock or slightly upsized tires. Four-wheel antilock became available in 1993, but it's an option we wouldn't choose.

Finally, what size and type of tires do you want and which rims should you use? The largest tires that will fit on a stock Wrangler are typical 31-inchers, and they fit best when mounted on 15x8 or 15x7 rims with backspacing around 4 7/8 or 4 1/2. Wheels with 4-inch backspacing will stick the tires too far out from under the fenders. For mild trail use, we'd pick medium-aggressive mud treads such as BFGoodrich Mud-Terrains, Goodyear Wrangler MTs, or Dunlop Mud Rovers. If you can't tolerate a bit of tire noise, use all-terrains. And for the type of mild 'wheeling you plan, wheel design and material can be based on your appearance preference.

Oil-Pump Jelly
I'm currently rebuilding the 304 V-8 in my '79 CJ-5. I bought a Haynes manual for the rebuild, and the oil-pump section says to pack the pump with petroleum jelly to prime it. Isn't there a better way to do this? Also, does anyone sell a new oil-pickup tube for my engine? My local Dodge dealer says they're no longer available, and my old one is shot.
Bart Wilson
Hartford, Kentucky

Packing your pump with petroleum jelly is a time-honored tradition that works surprisingly well. Because the pump is located in the front timing cover on your AMC engine, far from the actual pickup point in the pan, the goo between the gerotor gears helps create the suction needed to draw the oil up into the engine without risking massive oil starvation on initial start-up. The petroleum jelly quickly dissolves in the regular oil, but some builders feel better about using cam assembly lube or even STP or similar products. Just make sure the stuff is thick enough that it won't run out of the pump before you're ready to fire the engine.

By the way, we'd prime the oiling system by spinning the oil pump with a special tool that's spun with a drill motor-the oil pump tool is available from most mail-order speed shops. This ensures that oil will reach the entire engine before you crank it over for the first time.

As far as the oil pickup goes, you need a new parts person at your local dealership. At press time, the oil pickup tube and screen assembly were still available for about $16 from Chrysler under PN J3216049. Federal-Mogul also makes a screen and pickup assembly for the AMC V-8s. It's PN 224-14161 and available at almost any quality auto parts store. The same pickup can be found in a wrecking yard on a 360 or 401 engine, but most yards won't pull off the oil pan to get at a $2 part. Milodon (Dept. JP, 20716 Plummer St., Chatsworth, CA 91311, 818/407-5436) also makes an extended pickup (PN 18400) for its deep-sump AMC V-8 oil pan.

I have a '76 J-10 pickup with a full-time transfer case. I want to swap in a Dana 20 transfer case and a four-speed transmission from a '74 J-10. Is this possible? If so, what parts will I need? What sort of complications might I run into?
Jim Stivers
Port Orchard, Washington

Since these pickups came with both of those drivetrain options, this swap is certainly possible but not as easy as it may seem. Since you wrote that your current T-case is full-time, it should be the Borg-Warner Quadra-Trac used during that era. That means it's coupled to an automatic transmission, the TH400. Therefore, you'll need the entire clutch system for your manual transmission, including the clutch pedal and linkage under the dash as well as the flywheel to match your engine, the clutch assembly, and the bellhousing-and the bellhousing isn't the same as a CJ's or a three-speed J-truck's. And don't forget all the little bolts and brackets not included with your current auto tranny.

Hopefully, you still have the donor vehicle 'cause there's more. The crossmember is a little different, and so is the tranny mount, but a bit of drilling and fabricating can solve that since it will need to be moved forward on the frame anyway. And unless you have custom exhaust, the hanger bracket will also need to be modified.

Inside the cab, you'll need to remove the shift selector from the steering column unless you really want to confuse your friends, and the low-range lever under the driver seat will also need to go away if your truck is so equipped. The factory floor plate from the '74 makes a nice swap for a clean installation, but hacking up the original to allow the trans and T-case shifters to poke through also works. Disconnect the Emergency Drive vacuum actuator knob in the glovebox, and make sure you plug the hose that runs to the intake manifold to prevent vacuum leaks.

So much for the easy part. The front driveshaft needs to be modified for a regular yoke instead of a CV joint, or you can change the transfer case's yoke. The driveshaft needs to be shortened anyway. And once you see that the rear driveshaft needs to be lengthened, you'll realize the Quadra-Trac had the rear output inline with the front output-both off to the passenger side. The Dana 20 drives straight rearward from the centerline of the engine, so the stock rear axle assemblies were offset or center-set to match the different transfer cases. If you have a longbed pickup, you may have enough length to run the driveshaft sideways to the old rearend, but then you'll have to deal with the vibration possibilities from weird driveline angles. If you have the donor truck, swapping rearends is better, but make sure the gear ratio is the same as your frontend's. Or swap in the donor front axle to match ratios, but remember that a '74 may have drum brakes since discs were an option that year.

Had enough?

Don't Do It
My father has a '67 Jeep CJ-5, and when he puts the transfer case in four-wheel drive, the Jeep won't move. Is the problem in the differential or the transfer case? Also, what is the best suspension lift and gear ratio for this Jeep to run 39-inch tires on 14-inch rims? Finally, the Jeep has a Buick 225 V-6 engine that's in good shape, but will that be enough of an engine for the tires?
Chuck Holtorf
Clallam Bay, Washington

Your dad's CJ-5 should have a single-lever Dana Model 18 transfer case. If the Jeep will move in two-wheel drive but not four-wheel drive, it's probably not a differential problem. But you didn't mention if the drivetrain is binding up and stalling the engine, or if the transmission is acting like it's in Neutral. It's more likely that the shifter is only clicking the transfer case into the Neutral position.

More importantly, forget about big tires and wide wheels on this poor little Jeep, unless you plan to replace the axles with ones from a 1-ton truck. The stock Dana Model 27 front and Dana 44 rear are way too light to handle that type of stress, and the axle gears would have to be in the 6.16 range, which isn't available for your front axle. And stopping with the factory 10-inch manual brakes? Better leave a lot of room between you and the garage wall. In addition, no one makes a lift that would accommodate tires that big on an early CJ. While something in the range of 4 inches of lift and 33-inch tires is at least feasible, even that will take its toll on the weak transmission, which is probably a Borg-Warner T-86 or T-14. When matched to oversized tires and a heavy foot, neither gearbox has a great reputation for strength or durability.

You do have a great 'wheeling engine for the 4x4 in stock form, but it'll be seriously underpowered if you saddle it with big tires. The Buick V-6 has lots of torque for off-highway use and is a favorite among knowledgeable Jeepers.

Submission information:
Questions should be as brief and concise as possible. We will answer as many letters as possible each month, but due to the large volume of mail, we cannot send personal replies. Letters are subject to editing for length, as space permits. Always check state regulations before modifying a vehicle with pollution controls or one that will be driven on the street. Write to: Your Jeep, Jp, 6420 Wilshire Blvd., Los Angeles, CA 90048-5515, fax 213/782-2704, e-mail

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