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July 2012 Your Jeep Tech Questions

Rear Driveshaft
Verne Simons
| Senior Editor, Jp
Posted July 1, 2012

Your Tech Questions Answered

Jp’s Opinion Angle
I am going to be installing a Wagoneer Dana 44 front axle and a Honda Passport Dana 44 rear axle in my ’91 YJ. My question is, how do you determine the angle of the rear axle? The Rough Country lift that I will be installing already has angle shims attached to the springs, but I will need to weld perches on the axles and would like to know how to set the angles. I am also installing a Rugged Ridge slip yoke eliminator.
Craig Warner
Mason City, IA

Assuming your slip yoke eliminator will require a double cardan (or CV) rear drive-shaft, you basically want the pinion of the rear axle aimed just about 1-degree under the driveshaft angle. That will compensate for pinion climb under acceleration and should place the pinion directly in line with the rear driveshaft. If you’re not using a CV rear shaft, match the pinion angle to the angle of the T-case rear output yoke.

To set the pinion angle, assemble the new axle on the new spring perches and leaf springs (without the shims) mounted to the Jeep with the shackles you plan on using. Longer or shorter shackles will change the pinion angle a little. Center the axle under the Jeep side-to-side and tighten the U-bolts just enough to keep everything in place. To set the pinion angle, allow the full weight of the vehicle to rest on the tires and bounce the suspension a couple times to get it to settle. Then, use a floor jack to move the pinion up or a rubber hammer to move the pinion down. The U-bolts need to be tight enough to support the Jeep but loose enough for you to be able to rotate the axle. Basically you want an imaginary line passing through the axis of the rear pinion (or perpendicular to the axis of the axle u-joint) to be aimed one to two degrees below directly at the rear output of the T-case. Once you have set this angle you can check to see that the axle is still centered and then tack weld the new spring perches to the axle. Then, support the Jeep and disassemble the suspension enough so you can finish welding the perches to the axle. Once driving, as you accelerate your Jeep the pinion will go up a degree or two and should be just about perfectly in line with the rear of the transfer case and thus vibration free.

I Have a Gas Problem
If I remove the catalytic converter from my ’97 Wrangler and install a test pipe, what effect would I have on the engine’s performance? And, would I have any warning lights on the dash as the catalytic converter has an O2 sensor attached?

If you remove an O2 sensor your Jeeps OBDII system will throw a code, and your engine may suffer from a loss of performance and mileage since the engine’s computer gets info on how to run from the exhaust gasses. Ew! Removal of a catalytic converter from your exhaust system may allow a tiny increase in horsepower at the top of your engine’s rpm range, but it will also probably cause a drop in your max torque at a lower RPMs (which is generally more important than high rpm horsepower to a Jeep being used off-road, or driven on-road the way most people drive on the road). This loss in torque will probably be more noticeable than any gain in high-RPM horsepower). Modern catalytic converters actually flow pretty well and don’t really limit power through the rpm range that much.

I wouldn’t remove it if I were you. If not just for the reasons above, it is also illegal in many areas around the U.S. and can carry stiff fines if you are caught. It also can make selling your vehicle more difficult, as the new owner won’t want to have to pay for the cat to be replaced or worry about any emissions standards they may have to meet.

If it is rattling, then it may need to be replaced, in which case you can either have it replaced at an exhaust shop or do it yourself if you are experienced with exhaust work. You can get a new replacement cat for your Jeep for $100 to $250. These will either be weld-in, clamp-in, or maybe bolt-in.

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