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March 1998 Nuts & Bolts

Posted in How To on March 1, 1998 Comment (0)
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Photographers: The 4-Wheel & Off-Road Files

A Different Spin
I have a '95 Toyota 4Runner with the 3.0L V-6, five-speed tranny, stock gears, and rear posi. With 90,000 miles on it, I am preparing to change the clutch. Some friends told me to replace the flywheel with a heavier unit, supposedly to get more torque at lower rpm. I have always thought that lighter is better, so what is your spin on this debate?
Steve Harron
Houston, TX

This is one of those questions where the answer depends on how you use your truck. A heavier-than-stock flywheel will not actually produce more torque at lower rpm, but the extra inertia created will keep the flywheel spinning longer for a given amount of power input, or torque retention. For instance, if you're driving up a long grade and have to shift down before the engine bogs out, a heavier flywheel will keep the truck moving longer due to the increased inertia of the flywheel, or momentum of movement. The only drawback is the extra initial power needed to get the heavier flywheel up to speed; it will take more throttle input and gas to get it going. In addition, the heavier flywheel weight will reduce throttle response, so acceleration from a stop will diminish. Jim Sickles at Downey Off Road (Dept. 4WOR, 10001 S. Pioneer Blvd., Sante Fe Springs, CA 90670, 562/949-9494) specializes in Toyotas and offers a heavier flywheel for 4Runners that need it. According to Sickles, the additional 9 pounds of flywheel weight increases torque inertia for positive clutch engagement without bogging down the motor. This really helps when larger tires are added, and also reduces stalling during slow-speed crawls.

Getting Engaged
Iwas out 'wheeling in my '96 Chevy K1500 pickup and was halfway across a boulder-strewn stream when I got stuck. Even though I had the transfer case lever in four-wheel-drive low range for several miles, I noticed that only the rear tires were spinning. Is there a problem with these trucks, or am I the only one? How can I fix it?
Gregg Morin
Mesa, AZ

All '87-'97 IFS GM 4x4s use thermally activated axle disconnect devices to engage the front tires. When the transfer case is engaged, an electric switch closes, which sends electricity to a thermal unit on the front axle. As the thermal unit heats up it expands and forces a dog clutch onto the axleshaft that engages the front axle. If this unit fails to operate, the front driveshaft spins but power isn't transferred to the wheels and you get stuck. While GM has improved its thermal actuators, aftermarket companies offer replacement actuators that operate with either cable, vacuum, or electric shift. Warn Industries (Dept. 4WOR, 12900 SE Capps Rd., Clackamas, OR 97015, 800/543-9276) offers a vacuum-operated replacement actuator that screws into the same hole as the factory unit. By hooking up a few wires and hoses a much more reliable engagement is afforded, without the need to drill holes or pull cables. Another option is the electric-shift style from Rancho (800/GO RANCHO), which also replaces the thermal actuator. The Rancho unit is basically a big electric solenoid that replaces the factory style and plugs into the factory harness.

Scouting Around
I've been looking for a manual for my '67 International Scout 800 Half Cab, which I bought for 100 bucks. No one seems to have a manual, and I can't even figure out which of the two four-cylinder engines used is in my Scout. Is there a place that knows this stuff and has parts for my truck?
Patrick Bryan
State College, PA

Lucky for you, we do know about Scouts and a source for all your goodies: Giddum' Up Scout (Dept. 4WOR, 3625 N. Stone Ave., Colorado Springs, CO 80907, 719/632-8294). International Harvester is a mysterious breed to most auto parts stores, so going to a specialist is the best thing to do. Giddum' Up Scout has a complete line of service manuals, and the 1,000-page version for your rig will teach you everything you need to know. As far as which engine you have, the 152ci four-cylinder was used through the '66, while the 196ci was introduced in the '67. This means either engine could be in your Scout, depending on its build date. From the outside, the two engines are virtually identical. The 152 was basically an International 304 engine cut in half, and the 196 was a 392 done the same way. Since the four- and eight-cylinder models share similar internal parts, the smaller engine has a smaller bore. But rather than disassemble the engine to identify it, Rod Phillips of Giddum' Up Scout recommends looking at its serial number. On the driver side of the engine at the front of the block is a machined surface facing sideways, about 3 inches high and 1 inch wide. Underneath the actual serial number are some numbers that indicate the type and size of the engine, with 4-152 indicating the 152 and 4-196 signifying the larger 196.

Flippin' It
Instead of using blocks to raise the rear of my K20 Chevy pickup, I've thought about reversing the spring shackles to gain height. However, it appears that the pinion angle will be rotated upward a great deal and might cause a problem. Also, will this shackle flip affect wheelhop or axle wrap?
James Bauer
Juneau, AK

Flipping your shackles from tension style to compression type will add about 6 inches of lift. Since the rear of the springs will be lower in relation to the front pivot end, the springs will sit at an angle that will indeed point the pinion upward. But since the angle of the U-joint at the transfer case will increase, the extra tilt may help reduce driveline vibration. Even so, the axlehousing can be rotated back to its original position by using degree shims under the spring pads, although cutting the pads off and repositioning them correctly is a better alternative. Theoretically, the axle or spring wrap problem would be the same, since the stock springs would be retained. We haven't heard of anyone experiencing worse wrap due to this conversion. If you experience excessive wrap, using stiffer springs, add-a-leaves, or any of the numerous aftermarket traction devices available may alleviate the problem.

Driveline Vibration
I recently purchased a four-door '95 Jeep Cherokee Sport. So far I've lifted the Jeep with a ProComp 3-inch front suspension kit and Rancho rear leaves with 1-inch blocks. Since then I have experienced a lot of rear driveline vibration. To fix it, I tried shimming the rearend, lengthening the driveshaft, and dropping the transmission 1 inch. This helped a lot but didn't completely solve the problem. The driveline angles have been checked and are within three quarters of a degree of each other at the U-joints.

W1 = Path of first u-joint. W2 = Path of second u-joint.

The vibrations occur between 20 and 25 mph and between 35 and 45 mph under load. I have heard that a CV-style driveshaft might solve this problem. Will it?
Jeff Malfatti
San Ramon, CA

Any time you troubleshoot something on your rig, first try each solution individually. For instance, you say you shimmed the rearend, lengthened the driveshaft, and dropped the tranny. Did you do this all at the same time, or did you add the shims and try it, yank the shims and try the new driveshaft, and then yank it and lower the tranny? Did you try these fixes in different combinations (tranny and shims, tranny and 'shaft, and so on)? By trying all the remedies at once, you may have "overfixed" your problem.

Fig. 3 Proper Geometry for CV Joint Driveline

We didn't have a vibration problem on our lifted Cherokee, and the driveshafts were totally stock. We have heard that lifted Cherokees with stock driveshafts can develop some wobble in the rear slip yoke after some miles are put on it, but we suspect that wouldn't cause vibration under load as you described, and it shouldn't be a problem if you lengthened the driveshaft.

Fig. 4 Proper Geometry for a Conventional Two-Joint Driveline (Centerline of differential pinion and transmission are parallel)

Furthermore, we certainly wouldn't lower the transfer case at 3 inches of lift. All the off-the-shelf T-case lowering kits we've seen drop the 'case by angling it down at the back. That alone can cause vibration, since it loads the motor mounts differently. In extreme cases, it may even upset the angle of the front driveshaft. If your Cherokee has an NV231 (NP231) 'case instead of the NV242, then you can use one of the several aftermarket short-extension housing kits that allow you to install a longer rear driveshaft. This shouldn't be needed on your Cherokee, but see "Instant Superhero," Dec. '96, for more info.

For more ideas, we called Tom Wood at Six States Distributors (Dept. 4WOR, 1112 W. 3300 S., Ogden, UT 84401, 800/453-2022). He felt that your problem could be torsional vibration. As a U-joint rotates, it moves through an elliptical path, which causes the surface speed of the driveline to increase or decrease twice per revolution. If the second U-joint angle is equal to the first, it will speed up as the first slows, allowing smooth operation of the driveshaft. If the angles aren't equal, or if the U-joints are out of phase, vibration can occur (see fig. 1 and 2). Wood says a CV-style driveshaft will remedy your problem if our other suggestions don't. If you go with a CV, we'd put the T-case back to its stock position before you begin.

The proper setup for a CV-style driveshaft is such that a straight line can be drawn from the pinion centerline up through the centerline of the driveshaft (see fig. 3) while the vehicle is moving. Remember that the pinion climbs upward under power, so we usually set the pinion a degree or two down from perfectly inline with the 'shaft while the 4x4 is at rest. Still, the pinion angle may need to be angled upward from stock, and if so, Six States recommends adding enough extra gear lube to fill up the rearend to the center of the pinion bearing.

If you're going to stick with a regular U-jointed driveshaft, Figure 4 will serve as a reminder that the T-case and pinion must be parallel to each other (or have equal and opposite angles that cancel each other out) to eliminate vibration. Any custom driveshafts you need can be obtained via mail-order from Six States.

Fig. 2 Cardan or Universal Joint at 30-degree Driveshaft Angle (One revolution)

Cosine of Angle = Maximum Velocity
Driving Velocity
(Min. and max. percents are not reciprocal numbers)

Samurai Lift
Please help! I have a stock Suzuki Samurai, and I want to make it the ultimate rockcrawling rig but still have it perform reasonably well on the highway. I want to mount 30-inch BFG Mud-Terrains on it. What's the best way to fit these tires? Should I use a suspension lift, a body lift, or cutout fenders with stock springs? I'm not sure I want to hack the body, so if the cutout fenders would be best, what's the second best option? Dirk Suchy
via e-mail

Have you heard of Calmini Products (Dept. 4WOR, 6600-B McDivitt Dr., Bakersfield, CA 93313, 800/345-3305)? The staff eats, sleeps, and breathes Suzuki stuff. Owner Steve Kramer said that a 3-inch suspension lift will mount 30s nicely. He suggested heavy-duty shackles for rockcrawling, 'cause your stock ones will eventually get mangled.

You said that you want "the ultimate" rockcrawler. The term "ultimate" is pretty subjective. Ultimate for an easy bolt-on buildup of a Samurai might mean a step up to 31- or 32-inch tires using 3 inches or more of suspension lift, plus a 2-inch body lift.

Even with 30s, you may want lower gears in the axles; Calmini recommends 4.56s with the 30s or 5.43s with the 32s. Also consider Calmini's low gearset for the T-case. It reduces the low range from 2.27:1 to 4.16:1, and high range is also a bit lower for on-road power.

Odd Problem
Ihave a '71 Jeep CJ-5 with a Buick 225ci V-6 engine. Unfortunately, it doesn't run very well. I was wondering what I can do to improve the ignition system. Does anyone fiddle with these old beasts, or should I change from the points-type distributor to an electronic one? Also, how difficult is it to convert the front Dana 27 axle to the later Dana 30, and is that a good idea?
Greg Miller
Cornland, IL

The Buick mill used in the CJ-5s has an odd-fire design, so named because of the uneven firing order of the cylinders. Even when it is running properly, the engine sorta sounds like a V-8 trying to make up its mind about which cylinders to fire. The uneven design was a result of taking a 300ci Buick V-8 and essentially lopping off the rear two cylinders and rearranging the backside. If you look inside the distributor, you'll see that the rotor tip has a tail on it because even though the contacts on the cap are evenly spaced, the firing pulses need to occur at uneven intervals. You'll also notice on the distributor that the lobes the point block rubs against are a combination of short peaks and long lobes, also needed for the engine to fire properly. This is important because every drop-in electronic ignition we've ever seen has evenly spaced lobes for picking up the firing impulses. As a result, the engine will run poorly and won't rev worth a darn. But there is one worthwhile modification for your engine, which is installing an HEI factory electronic-ignition distributor from a '75-'76 Buick odd-fire 231ci V-6. This distributor interchanges with your standard unit and greatly increases the spark energy and reliability of the ignition system. The larger diameters of the base and cap require grinding down the intake manifold where the right front intake bolt is, and a special button-head bolt from the 231ci engine needs to be used for clearance.

As far as the axle swap, a Dana 30 from a CJ will fit on your rig just fine because the leaf spring spacing is the same as on the Dana 27. You'll need to use larger U-bolts and spring plates since the tube diameter is larger, and the shock mounts will need to be reworked because they will be in the way if you use a disc-brake Dana 30. The driveshaft U-joints are also different, so this would be the time to upgrade to the larger Dana 30 joints to strengthen the driveshaft. Don't forget to match the ratio of the rear axle, which should be either 4.88 or 3.73 for your model year. The brake hoses might also need to be modified.

To Drive or Not to Drive
My '87 Suzuki Samurai had a terrible vibration in the rear end that drove me crazy until I figured out the slip joint and splines on the rear shaft were shot. Now that I have the shaft in the shop for repair, I want to drive the Suzi on just the front axle, but I've been told doing so will mess up the frontend. Is this true or should I just drive it for a while?
Cristian Carvallo
Oahu, HI

Except for full-time or all-wheel-drive systems designed for street use, most standard transfer cases come with stern warnings against driving them on the street in four-wheel drive. This is because the front and rear driveshafts are locked together in four-wheel drive, and in normal road driving all four tires end up rotating at slightly different speed when turning corners, which causes drivetrain windup. In dirt, this stress is usually dissipated by the tires scuffing the ground. But on dry, hard surfaces, like pavement, the tires won't skid and eventually something will break. Our last tech story on the NP231 case used in Jeeps and Chevys ("Beefing the 231 Transfer Case," Feb. '98) showed what happens in that situation and how to prevent it. However, with the rear driveshaft off, the rear spins freely, just like disengaging locking hubs on the front. The frontend will operate like a front-wheel-drive car, with slightly different handling characteristics. For that reason, you should be cautious when driving, but there's no reason why the frontend or the transfer case should get damaged or worn if the rear driveshaft is removed.

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: Nuts & Bolts, 4-Wheel & Off-Road, 6420 Wilshire Blvd., Los Angeles, CA 90048-5515, fax 213/782-2704, e-mail quinnelc@petersenpub.com.

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