Gearing Gear
Our '98 Jeep has the AX-15 transmission, and it's making grinding noises and will not stay in First gear. The shop says it needs new synchronizers to fix it. Is this tranny worth the $1,000 it would take to fix it? Would we be better off finding a new one? Are there any six-speeds that would fit?
Hairy
Via e-mail
The new six-speed will work, but you'd need to use an Advance Adaptersharmonic-balancer kit to relocate the crank position sensor from the AX-15 bellhousing to the front of the engine.
However, the six-speed is more or less on par with the AX-15 strength-wise. I think $1,000 is fair for a complete rebuild of your AX-15, but that being said, I think it's a lot of money to dump into a transmission that lots of guys are removing for swaps. I'd look for a good used replacement that you can bolt in. Check www.craigslist.com and some off-road Web forums. You should be able to pick up a good used AX-15 for around $300-$400.
No Go
I've been looking online and asking all kinds of people questions on how to get more power out of the 2.4L in my '06 Wrangler, and I get a million different answers. Other than swapping gears and spending $4,000-$7,000 on a supercharger or turbo, is there any other way I can get at least 15-20 more horsepower out of my 2.4L for less than $1,000 so I can run 32-inch tires? I'd like to swap gears, but the dealer says it will void the warranty even if they did the swap.
Matther Colson
Via e-mail
You can't make that kind of power for that kind of money. A good rule of thumb for these 2.5L and 2.4L four-cylinder engines is to figure it costs $100 for each additional horsepower. Throw a $250 air intake on it and save your pennies for a set of 4.88s if you want 32s with decent performance.
Smiley Axle
I have a problem. I have an AMC Model 20 rear axle, and I like it. There I said it. Stop laughing! I can hear you! I'm wondering if you could do a short article on building an axle truss. (I can still hear you chuckling.) You know, the basics--to plate or not to plate? Do I weld it to the pumpkin? What should I use--square tube or DOM? Any help would be great once you guys stop making fun of my affliction.
Bryan Irons
British Columbia, Canada
Sorry, no article. I just don't want to perpetuate people trying to polish a turd. Here's why.
First, the FSJ AMC Model 20 found in Cherokees and Wagoneers is a good axle, but it has one-piece shafts and thick axletubes right from the factory. The CJ's Model 20, however, has the horrible two-piece shafts, thin tubes, and a spindly centersection. Even if you upgrade to one-piece shafts, you need to do a lot to prevent the tubes from bending. And there's always the possibility that the centersection will snap where the tube is pressed into it.
As for trussing, just the simple act of welding on a truss can warp and distort the housing to the point that you can notice it with the naked eye. When you weld, the area being worked on shrinks and contracts as it cools. When aftermarket or race shops weld trusses, they're relying on years of experience to know how much to prebend the housing so this warping will bring the housing back into shape. Trying to press a warped housing straight after it's been trussed is almost impossible.
That said, I'm sure you're going to try to truss your axle yourself anyway, so here are some tips. Unlike a Ford 9-inch, which requires the truss being run on the back of the housing (opposite the pinion), the AMC 20 needs a truss either on top of or on the bottom of the axle to keep it from turning into a U shape. You can use whichever tubing you want, but 1.5-inch, 0.120-wall DOM round tube would look a lot better. I'd bend the tube so the truss contacts the top (or bottom, depending on which side you're trussing) of the pumpkin, then extends out to the ends of the axletubes. Then I'd fashion some 1/8- or 1/16-inch plates to fill in the gaps, making allowances for U-bolts or spring perches. The plates could be hole-sawed anddimple-died for aesthetics, weight savings, and a little added strength. Check out www.race-dezert.com for photos of some prerunner trusses to get an idea. As you're welding the truss to the housing, try to use a relatively low heat and move the nozzle quickly across the work area; you're trying to avoid putting a lot of heat into the housing. This will help minimize warpage.