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April 2005 4x4 Tech Questions - Tech Line

Willie Worthy | Writer
Posted April 1, 2005

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Techline
Four Wheeler
6420 Wilshire Blvd.
Los Angeles, CA 90048-5515.

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Question: I have a bone-stock '92 Jeep Cherokee 4x4 with the 4.0L straight-six, automatic, with the axles atop the leaf springs. I want to give it at least a 4-inch lift and add 33-inch tires, or possibly a 6-inch lift and 35s. I also want to upgrade the stock limited-slip differentials for better traction. I'll be using it mainly for light hauling and towing, as well as playing on the weekends. What type of lift, suspension upgrade, differential conversion, and gear ratio do you recommend? Keep in mind, I do not want to experience high rpm while driving on the highway and I don't really want to spend a fortune on this project.
Bryce K. Tubb
Imperial, CA

Editor: Gosh, Bryce, perhaps you had better take a look at your Cherokee a bit closer. Yes, the rear suspension does use leaf springs, but they're mounted above the rear axle. Up front you will find coil springs between the axle and unibody subframe.

To clear 33s with a 4-inch suspension lift, you will need to do a bit of fender trimming along with some large fender flares such as those from Bushwacker; 35s definitely require the 6-inch lift, along with the trimming of sheetmetal.

There are a lot of good suspension kits on the market that will work, but I would really suggest that you go with one of what is referred to as a "long-arm kit." By relocating the pickup points for the front suspension control arms further away from the axle, you're able to greatly improve the suspension geometry. Take a look at your stock suspension control arms. Note that they are pretty much parallel to the frame. Visualize what happens when a wheel moves upward. The arc of travel is upward and rearward. Now with a lift kit installed, the arms are no longer parallel to the ground but are pointed at a downward angle towards the axle. The arc of travel has thus changed. That means in order for the wheel to rise over an obstacle, it must move forward as it's moving upward. In one way, maybe this is good as it puts more pressure on the tire for better traction in low-speed rockcrawling situations. However, a very low percentage of the time are we in such a situation. The vast majority of the time, the suspension's job is to follow the terrain and enhance ride quality.

Any lift over about 3 1/2 inches puts the suspension arms at such a steep angle that much more shock load is transferred to the body instead of being absorbed by the springs and shocks. This can lead to very poor ride quality. On a long-arm system, the rearward mounting point greatly reduces this angle.

Another thing you're going to need is a slip-yoke eliminator kit for the transfer case. This is also known as a "short shaft kit." What this does in effect is to give you a rear driveshaft that's several inches longer with a slip joint within the shaft, not within the transfer case as it presently is. The longer shaft again means less angularity, which offers less chance of the U-joints binding under full downward travel.

You're going to have to definitely upgrade your present rearend if it's the Dana 35. It's just not strong enough for 33- to 35-inch tires. A Dana 44 from a Jeep Comanche pickup is a basic bolt-in with a change of the spring pad location. The 8.8 from a Ford Ranger is also a good choice. There are some narrow Ford 9-inchers around, but a bit on the scarce side.

If you have the 8 1/4-inch Chrysler rearend with 27-spline axles, these can be updated to 29-spline shafts with a differential change. Factory posi-tractions just don't do it off-road, so look into the numerous true locking differentials available.

Now, doesn't a 3 1/2-inch lift with 31-inch-tall tires look a lot better financially?

Question: I own an '00 Chevy Silverado 1500. The front end is really low compared to the rear. A friend told me to adjust the torsion bars. I have also seen this done on TV (they were adding a 6-inch lift kit, which I'm told is illegal in my state). Is this advisable, and how would I do it?
Scott
via e-mail

Editor: We get this question a lot. You can adjust the torsion bars up, but it is supposed to sit lower in the front so that the truck will sit level when it has a load in it. Otherwise, with a load it will be tail-down. You need some special tools to adjust the torsion bars up, and while it will raise the ride height, the ride will suffer as there will be very little wheel downtravel. If you really want to get the front up so it sits level, consider a 2-inch lift kit and skip the rear blocks.

Question: I have an '04 Toyota Tundra four-door model with the TRD package. I'm interested in leveling the front end or lifting the truck 2 to 3 inches only. I don't need the performance lift kits, but manufacturers are telling me it's unsafe to use the spacer kits and they recommend coilovers only to lift the truck. Which do you recommend and why? There is a big price difference between the two!
Frank Pimentel
Brawley, CA

Editor: This is one that I wasn't sure of, so I went to Jim Cole VP of Cage OffRoad (www.cageoffroad.com), who commented:

"I'm not really up on Toyota TRDs like I am with Fords, but they are approximately 2 inches higher than the standard Toys are from the factory. Basically, most lift kits will only lift the vehicle the amount over stock height of normal non-TRD-equipped Toyotas. So the amount of lift is minimal for the amount of money. As far as I know, this is not a problem, and I do know of several people (and have personally talked with them) who have done such lifts, but I have not done one myself to 100-percent verify this info. By adding a spacer kit with the all-important differential drop (actually, most rotate the front axle), there should be no reason why it will not level up the front of the vehicle. Again, the diff must be rotated or else there will be angle issues with the CV shafts. Most companies shy away from lifting TRDs due to the fact that its lift systems do not provide the stated amount of lift on the vehicle.

"In regards to coilovers versus spacers, there is no difference in the angle the shafts ride at if both lift types are done properly with appropriate differential drop spacers and both systems provide the same amount of lift."

Question: My Chevy pickup has this strange vibration when I let up off the gas and go into "coast" mode. It only seems to happen at lower engine speeds, let's say under 1,500 rpm. At no other time is there a vibration. Trying to eliminate the problem, I've had the tires rebalanced, swapped tires with a friend, checked the driveshafts, U-joints, and even had the rear shaft rebalanced. I've checked all the suspension components and even changed the rear pinion angle, none of which has solved the problem.

The truck is an '00 model with the 4L60 E transmission, 5.3L V-8, and 4.10 gears. Do you have any idea where else I should look to solve the problem?
John Maison
Colorado Springs, CO

Editor: It seems that you've done your homework in trying to solve the problem. It took me quite a bit of time to track this one down until I just happened to read a short piece in one of the trade journals. It seems that what is causing the problem is actually the torque-converter clutch locking up. This in turn sends engine torsional vibration into the rest of the drivetrain, resulting in the vibration that you feel.

The solution: Have your Chevrolet dealer program your truck's ECM. They should have a service bulletin that lists a chart with the correct calibration number needed.

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