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March 1999 Nuts & Bolts

Posted in How To on March 1, 1999
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Curing the Shakes
I have an '87 Toyota truck with oversize tires. At certain speeds, the front end starts shaking and the steering wheel moves back and forth at the same time. What can be done to correct this?
Bradenton, FL

Front-end shimmy can be caused by several things. Your first step is to make sure the truck is properly aligned. If the alignment has been thrown off (which can easily happen when off-roading), it can cause the truck to shake as you've described. You should also inspect all the steering components for wear or damage and replace them as necessary. An out-of-balance tire can create the same symptoms, so have the tires balanced (this should be done periodically because the balance changes as the tires wear) or try rotating the rears to the front to see if that helps. The wheel bearings should also be inspected and repacked.

If all of these parts check out, the problem is likely being caused by the knuckle (also called kingpin) bearings in the frontend. Solid-axle Toyotas have a closed-knuckle design that use these bearings as pivot points instead of the ball joints used in most domestic open-knuckle frontends. Just like any other bearings on your 4x4, the knuckle bearings must be periodically serviced or they become loose, and, if neglected for too long, they can be destroyed. The solution is to purchase a complete knuckle rebuild kit from Randy's Ring and Pinion, (Dept. 4WOR, 11630 Airport Rd., Ste. 300, Everett, WA 98204, 888/324-9091). The kit contains OE parts and has everything needed to service both knuckles, including the wheel seals, inner axle seals, knuckle bearings and races, knuckle bearing preload shims, gaskets, and wiper kits, which include the felt and rubber outer seals for the knuckle balls. It retails for $108.33 at the time of publication and fits '79-'85 Toyota trucks and 4Runners as well as '75-'90 Land Cruisers.

Servicing the knuckles on your Toy takes some time (probably a day working at a leisurely pace), but it's fairly easy. The exact procedure is outlined in the factory service manual, but the process basically requires completely disassembling the knuckles, which includes removing the locking hub, wheel bearings, spindle, and knuckle, then cleaning everything, replacing all the seals (included with the rebuild kit), repacking the bearings and Birfield joints with fresh grease, and putting everything back together. The knuckle bearings are located under caps above and below each knuckle. It's a good idea to replace the bearings if the truck has seen a lot of miles or off-road use, but if you're looking to save some time and money, you can reuse the original bearings as long as they're in good shape. The only tricky part to using the original bearings is keeping track of all the shims located under each cap. These shims set the preload on the bearings, and mixing them up can cause damage as well as lots of shimmy. If you haven't mixed up the bearings or replaced them, there's normally no need to readjust the preload unless you lose track of how many shims go with each cap or suspect the preload was off. If you do replace the bearings, the preload must be reset using the simple procedure outlined in the manual. It's also important to use the proper torque spec (71 lb-ft) on the bearing caps to ensure the preload is correct. Overall, it's a messy job, but once you're finished, the shimmy should be gone.

Lifting Leaves
I want to lift my '84 K5 Blazer 2-3 inches, but I can't decide whether to use add-a-leaves or purchase new leaf springs. The Blazer sees a lot of mud and ditches, so which is better for my needs? Add-a-leaves are cheaper, but I'd like to know the pros and cons of both.
Damon Owens
via e-mail

Add-a-leaves will generally lend you 1-2 inches of lift while almost anything is possible with leaf springs. Either will work fine for the type of four-wheeling you do most. However, while add-a-leaves are cheaper than new lift springs, there are other factors you should consider before you buy.

An add-a-leaf's primary purpose is to increase the spring rate or load-carrying capacity of the leaf spring, and the modest amount of lift is really a side benefit. When you increase a spring's load-carrying capacity with an add-a-leaf, you also increase its resistance to compress and deflect, so ride quality suffers when the truck is unloaded. Therefore, installing add-a-leaves at all four corners will make your Blazer's ride much stiffer than it was originally unless it spends most of its time fully loaded.

Most aftermarket lift springs are designed to retain the truck's stock ride quality but have a more positive arch to gain lift. Although in reality most lift springs have slightly more spring rate than stock, the change in ride quality is much less drastic compared to using a set of add-a-leaves. Although this isn't as much of a concern with mud-bogging, aftermarket leaf springs will yield much more suspension flex than add-a-leaves in the original spring packs.

The bottom line is that for your off-road needs, either one will work. If the truck spends most of its time off road and in the mud, and you're on a tight budget, then go for add-a-leaves. But if it's used on the street and you're concerned about ride quality, spend the extra money for a regular lift kit. Besides, if you shop around you'll find that an inexpensive lift kit that uses blocks in the rear will only set you back about one more Franklin than a set of add-a-leaves.

Needs More Rubber
I have a stock '78 Ford Bronco with 31x10.50-15s on 15x8 rims. I want to upgrade to 33x12.50s. I've heard that I can put 33s on my truck without a lift or any other modifications, but I've also read that 33s require a 2-inch lift. In addition, I've been told that putting on tires that are 2 or more inches larger than stock requires a gear swap. I'm almost to the point of exploding. To prevent innards from covering my magazine, please tell me what I can do.
Jeff Cookman
via e-mail

We'd hate to see innards covering any issue of this magazine, but the only true answer is that it depends. It's been our experience that 33x12.50-15s mounted on a set of 15x8 wheels fit just fine under your truck with no lift and only superficial rubbing on the inside of the rear inner fenderwells when the truck is really twisted up. However, the tire's actual diameter on those wheels was only 32 inches, and the wheels had 3 5/8-inch backspacing. Since these tires just barely fit, it's quite possible that a different tire and wheel combination may rub. Our advice would be to stick with standard offset wheels and shop for tires that have a diameter of no more that 33 inches when mounted on those rims (most tires with an advertised height of 33 inches will be shorter, but some may be slightly taller until they've worn a little so be careful). If you're in doubt or extremely concerned about rubbing, go ahead and install the 2-inch lift, which can be inexpensive for your truck if coil spacers are used in front and blocks are used in the rear.

As far as the gear change goes, that's another judgment call. The general rule of changing gears when tire height increases more than 2 inches is correct, but we see rigs every day running larger-than-stock tires with original gearing and the owners are perfectly happy. Be prepared for a slight decrease in acceleration performance and gas mileage if the gearing is left alone, but with the minor increase you propose none of those drawbacks should be significant for your truck.

Trash the 20?
Ihave a '76 Jeep CJ-7 with a Chevy 283 V-8, an NP435 tranny, and a Dana 20 transfer case. The rearend is a Model 20 with 3.54 gears and semifloating tapered two-piece axles. I don't do any extreme rockcrawling, but I do spend a lot of time in the mountains and am concerned about strength and reliability. I would like to change the gears to 4.10s and install a locker in the rear, but should I spend the money upgrading the Model 20 or swap in a Ford 9-inch? If a 9-inch is the way to go, is there one that doesn't require cutting or custom fabrication?
Ron Gale
via e-mail

The Model 20 rear axle used in Jeeps has a reputation for being weak, mostly because AMC used two-piece axleshafts in them that are prone to failure. However, there are plenty of parts available to make it significantly stronger than stock, and the cost of the upgrades may be cheaper than a complete axle swap.

There is no stock Ford 9-inch that will bolt directly in place of the Jeep Model 20, so unless you possess the skills to modify an axle assembly yourself, the only option is to purchase an axle assembly from a company that specializes in building custom axles such as Currie Enterprises (Dept. 4WOR, 1480 N. Tustin Ave., Anaheim, CA 92807, 714/528-6957). Currie can build a 9-inch front- or rearend with just about any combination of gear ratio, differential, and axleshafts you can think of, and the right combination will be stronger than the most beefed-up Model 20. However, since your four-wheeling isn't extreme and you want to avoid custom parts, your best bet may be to upgrade the 20 instead.

The first items that need beefing on a Model 20 are the axleshafts. Moser Engineering (Dept. 4WOR, 102 Performance Dr., Portland, IN 47371, 219/726-6689) and others manufacture one-piece heat-treated alloy axleshafts that are significantly stronger than the two-piece design, and they bolt directly in place of the originals. For even more beef, Warn (Dept. 4WOR, 12900 SE Capps Rd., Clackamas, OR 97015-8903, 800/543-9276) makes an affordable kit that converts the Model 20 to a full-floating design and comes with axleshafts that carry a lifetime warranty. A full-floating design is stronger than a semifloating one because the weight of the vehicle is carried by the axlehousing instead of the axleshaft, which reduces strain on the shafts. This design also enables the vehicle to be driven (with a locker) or towed should an axleshaft break, and since the full-floating kit includes special lockout hubs that disengage the rear tires from the rest of the driveline, the Jeep can be more easily flat-towed.

Another weak point on the Model 20 is the stock open carrier. Several traction-aiding differentials are available for the 20, including an ARB Air Locker, a Trac-Lok, and a Detroit locker. Since the carrier is weak, we would recommend using a differential that completely replaces the carrier (such as the ones listed) rather than one that retains it. For gearing, the ratio you propose is available in addition to 4.56s. Buying a quality gearset will also help ensure additional strength and reliability. Any of these modifications will provide a significant strength improvement over stock, and all of them put together should provide more than enough strength for your needs with minimal hassle.

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 323/782-2704, e-mail

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