Fragged Five-Speed
Q My AX-5 is grinding and needs to be rebuilt or replaced. What do you suggest?
A The AX-5 found behind 2.5L four-cylinder engines is OK at best. However, I can't see myself ever rebuilding one, so it's hard to recommend my readers do the same. Instead, I'd look into replacing the little 5-speed with an AX-15 from a 4.0L TJ or XJ with an Advance Adapters conversion kit. You'll also need to replace the input gear on the NP231 t-case to convert from the AX-5's 21-spline output gear to the AX-15's 23-spline gear.
Another option if most of your driving involves hardcore wheeling is to swap in an SM420 using a 60-degree V-6 bellhousing from a GM Camaro, S-10, or Blazer. The GM bellhousing will allow the SM420 to bolt up to the 2.5L. I'd use the factory GM slave cylinder, clutch fork, and throwout bearing. You'll need a conversion pilot bushing for the SM420's 0.590-inch pilot tip and a 10-spline clutch disc. Or, if you don't want to scrounge junkyard parts, you can use a Novak Adapters PN B150GM to bolt the tranny to the engine. There are several different types of adapters available to convert the SM420 to the Dana 300/NP231 pattern t-case. Although you'll lose the overdrive, if you do a lot of off-roading, the 7.05:1 First gear of the SM420 offers a huge increase in slow speed gearing compared with the AX-5's 3.93:1 First gear.
Steer Clear Rear
Q I've got a Dana 20 rear axle and want to build it for off-roading with big tires. What do you suggest?
A For starters, a Dana 20 is a transfer case used in late '60s to late '70s Jeep vehicles. A Model 20 is a rear axle put in fullsize Jeeps and CJs from the mid-'70s until the early '90s.
There's really nothing wrong with the Model 20 that came in fullsize Jeeps. These axles used heavier axle tubes and good 1-piece axleshafts.
While the CJ Model 20 used the same 8.875-inch ring gear and 29-spline carrier as the fullsize Jeep, these axles have relatively weak axle tubes that are prone to flexing and bending with heavy use. Furthermore, the casting where the tube enters the centersection is comparably weak and has been known to crack and fail. Finally, the CJs were given a horrendous 2-piece axleshaft setup that used a nut and Woodruff key to attach the hub to the shaft. In the field, the nut could back off and/or the Woodruff key could shear, effectively ruining your day.
Although there are a number of 1-piece conversion shaft kits on the market, it's really a waste of money if heavy wheeling is in the axle's future. Because of the tube flex, axle seal life is shortened, leading to leaks. And centersection cracks and bent tubes are likely with big tires and heavy off-road use.
I'd fully recommend adding some 1-piece conversion shafts and hitting mild trails with 31- or 32-inch tires and a limited slip. But if you're thinking of punishing your CJ Model 20 off-road with 33s or larger tires, I'd put my money into a Dana 44, Ford 9-inch, Dana 60, or some other beefy axle swap.
No Stink Link
Q What's with the high cost of TJ/JK lift kits? It's just a couple springs and some bushing ends welded onto some tubing, right?
A Aside from all the money the company is trying to recoup from its research, development, and design stages when producing a quality suspension system, a surprising amount of steel goes into a good setup.
It's old news by now, but the price of steel has pretty much doubled over the past couple years. And most of the name-brand suspension companies don't skimp on the quality or quantity of steel they spec for use in their springs and links. Skimping on spring materials and manufacturing will result in a suspension that sags after the first or second time off-road. Likewise, skimping on the control arm tubing thickness, diameter, and material can result in bent control arms. This can be true even if the arms aren't dragged over rocks. The control arms, especially the lower arms, have to contend with some crazy forces. And because of leverage, the longer the arm, the more force is exerted on the tubing. That's why you see long arm suspension systems that use heavy-wall tubing on the lower control arms. It's pretty standard for 0.188-wall and even 0.250-wall tubing to be used since 0.120-wall and thinner can fold.