Send your Gearhead questions to:
- Off-Road Adventures, Gearhead Dept.
- 610 West Walnut Street
- Compton, CA 90220
or email them to:
You CAD!
I’m curious about the vacuum shift motor assembly on the front of YJs. I have a ’91 YJ and wanted to know if it’s possible to run a locker and still drive on the street. While in 2wd, doesn’t this vacuum operated shift motor disconnect the right axle, unlocking the front driveline. Can I run a locker if it’s working properly?
Jeff, Palos Verdes, CA — Via e-mail
The device you refer to is called a Center Axle Disconnect, or CAD. It has appeared on many vehicles and usually with unit-bearing hubs (called “Live Spindle” hubs). When uncoupled, as you say, the right axle is disconnected from the carrier. The left axle still turns the side and spider gears, but like when you jack your vehicle up in the air and spin one wheel, it doesn’t turn the driveshaft. Most times. On occasion, usually cold days, the thickness of the oil is enough to let the diff gears spin the carrier and thus drive the ring, pinion and driveshaft. When you put in an automatic locker or a limited slip, the same thing happens. Everything inside will be driven by that left wheel and the driveshaft will be spinning. Often this creates vibration because the front driveshaft angle is usually not optimal for high speed running, especially if you have a lift. There are several cures for this. You can run an on-demand locker like the ARB Air Locker, Ox Locker, Eaton E-Locker or Auburn Ected. These lockers are all totally open until the driver hits the switch to lock them up. This is an OK solution that brings you back to something like the stock situation, but I don’t like the idea that parts of my expensive locker are being churned and worn as I drive. The better solution is to install Warn’s locking hub conversion. This allows you to unlock the wheels right at the hubs, just like in the good old days. An added benefit, should you choose to do it, would be to eliminate the two-piece right inner shaft. Replace it with a single piece unit from an XJ with full-time 4wd, which is stronger. You can remove the CAD and put a plate over the hole, or just remove the inner parts and leave the housing.
Three for MPG
I own and 2004 Jeep TJ “X” with the 4.0L, automatic and 3.73 rearend. I recently installed a 3 1/2 inch Rubicon Express lift and 33” BFG M/Ts. When I did this my mileage dropped from 18 to 10 mpg and gas is not cheap here in SoCal!
Chris, California — Via e-mail
I have a 2001 Ford Ranger 4.0L V6, 33x12.50-15 Goodyear M/Ts and I am only getting about 12.5 mpg. Can you make any recommendations?
Roger, Al Udeid Air Base, Qatar — Via e-mail
I have a ’99 Z71 Silverado regular cab, short bed stepside with a 4.8L and a 3-inch body lift with 33” SSRs and currently gets 13.8 mpg. I want to ditch the body lift and go to a 6-inch Skyjacker lift with 35s. How will this effect my gas mileage.
Kyle Pipkin, Jacksonville, Florida
Yep, we all understand the bind the recent gas prices have put on our paychecks. First off, the lifts and tires are going to eat a certain amount of your fuel economy no matter what you do because of increased rolling resistance and the loss of aerodynamics. How much is somewhat variable, but based on my experience probably an average of about 10 percent. You guys all share one problem and that’s a gearing mismatch. In general terms, you need 3.73 gears for 31s, 4.10 gears for 33 inch tires and 4.56 gears to run 35s. That puts you back to a reasonable overall ratio close to stock where your engine is not grunting all the time. With the right gears, you’ll be back to near stock mpg, minus that irretrievable 10 percent.
Towing With a Rubicon
I have a 2000 TJ Sport with lots of mods, but I’m thinking about upgrading to a Rubicon. The main reason is the Dana 44 because I tow a ski boat in the summer. Is the Rubi better at towing than the Sport TJ?
Scott Dillman — Via e-mail
Stock for stock, the Rubicon is probably a better tow rig because of its lower gears and the Dana 44 you mentioned, though Jeep rates them the same at 2,000 pounds. Even better would be the new Wrangler Unlimited. The long wheelbase Unlimited has a standard rear D44 and is rated to tow 3,500 pounds. If you want, there is a new Rubicon version that will be available later in ’05. The long wheelbase really adds to towing stability and probably has more to do with the unrated tow rating than anything else
Jeep 4.0L — One Foot in the Grave?
I’ve been thinking of buying a new Jeep Wrangler for a few years now. The last time I took my old CJ-7 in for service, I was told that Jeep was going to stop using the I-6 engine in Wranglers and go with the same V-6 that comes in the Liberty. Have you heard anything about this? The I-6 is a good engine. I don’t think I’d want a Wrangler with the V-6.
Tom Ryan — Via e-mail
According to insiders, we’re going to see a heavily revised Wrangler late in 2006 as a 2007 model. It’s reasonable that Jeep would mount the 3.7L V-6 and possibly even have a V-8 option (the 4.7L). Nobody will ever say the old 4.0L is anything but a great engine, and it will go down in history as one of the best. Still, the 3.7L is a good engine, too, making more power and the same torque as the 4.0L inline, while delivering better fuel economy and lower emissions. Ultimately, for Jeep, it comes down to consolidating engine production and emissions. The old 4.0L is used only in the Wrangler these days, which increases production costs. Also, with emission regulations getting even more stringent, it becomes difficult to keep the old 4.0L in compliance. Buy your Wrangler soon or buy a used one later — or learn to like the 3.7L V-6.