Manifold Failure
Weak link: 4.0L exhaust manifold
Models affected: '87-'01
What happens: Sad but true, these manifolds have a penchant for cracking. For whatever reason, Jeep never resolved the problem, and it continued throughout the XJ's life. NAXJA member Andrew Fecko notes that the cracks are always above the O2 sensor, which can cause the sensor to read a lean condition, thereby causing the ECU to increase the fuel mixture, which can affect mileage.
Strong fix: Don't bother trying to fix the stock manifold, because it will just crack again. It's no surprise that almost every aftermarket exhaust manufacturer offers a header for these engines. We've installed a number of them over the years, and one we really liked was the Borla unit. It fit perfectly, is constructed of T-304 stainless, and includes a new gasket and all associated hardware.
Contact: Borla Performance Industries, 877/462-6752, www.borla.com
Box Stress
Weak link: Frame around steering box
Models affected: '84-'01
What happens: Tough trails and bigger tires put stress on the steering box, which often results in cracks in the quasi-frame around the box. For obvious reasons, frame cracking of any kind is unacceptable.
Strong fix: A quick and easy fix is to brace the steering box using a brace like this one from T and J Performance. One end clamps on the steering box, while the other end attaches at the sway-bar mounting point. Installation requires drilling one hole. The kit also includes a spacer for the other sway-bar mount.
Contact: T and J Performance, 714/633-0991, www.tandjperformance.com
Weak Axles
Weak link: Dana 35 axles
Models affected: Many '84-'01
What happens: The Dana 35 non-C-clip rear axle was used on some '84-'89 XJs, and the Dana 35 C-clip rear axle was used on some '90-'01 XJs. They had several things in common, including 27-spline, 1.18-inch axleshafts; a 7.58-inch ring gear, 2.62-inch-diameter axletubes, and the urge to break frequently.
Strong fix: Obviously, ditching these axles is the accepted formula. Many 'wheelers install a Dana 44 or a Ford 8.8 axle, and either will hold up well on rigs fitted with up to 35-inch tires. Another good choice is a late-model Chrysler 8 1/4-inch axle because it has 29-spline, 1.21-inch axleshafts and larger 3-inch-diameter axletubes. This axle can be found under some '97-'01 XJs. If you just can't bear to part with your Dana 35 axle, one of the companies offering upgrades to make 'em last is Randy's Ring & Pinion. Randy's offers the Ultimate 35 kit that includes two Yukon heavy-duty alloy 30-spline axleshafts, carrier bearings, studs, axle bearings, and shims. Further, you can choose kits that include a Detroit, Ox, or ARB locker.
Contact: Randy's Ring & Pinion, 866/245-2316, www.ringpinion.com
Breaking Brackets
Weak link: Motor-mount block brackets
Models affected: All 4.0L
What happens: XJ owners who use their 4.0L-powered rigs hard are reporting that the block bracket-the piece that bolts to the engine and serves as the connection point for the motor mount-can break off. When this happens, the block itself can be damaged. Sometimes the bolts will loosen and break; other times, the bolts will simply shear off.
Strong fix: The folks at Mountain Off Road Enterprises have addressed this nasty problem with their brand-new Bombproof Block Brackets. The secret to their strength is that they more than double the number of mounting bolts by utilizing seven to eight threaded, unused holes in the 4.0L's block per mount. This is a huge improvement over the stock three-hole mounting system per mount. Currently they offer mounts for the '91-'96 4.0L engine, with other applications coming soon.
Contact: Mountain Off Road Enterprises, 970/625-0500, www.mountainoffroad.com
Seat Failure
Weak link: Front seats
Models affected: All
What happens: XJ front seats use a stamped metal framework that is spot-welded together. Occasionally these spot welds will break. The result is that the seat will often lean rearward and crooked.
Strong fix: One option is to hit the salvage yard and procure a pair of seats from a comparable XJ. Dan McKeag at Burnsville Off Road says that a better option is to install a pair of seats from a '99-'04 Grand Cherokee. These seats are way more comfortable because they are contoured and of better quality overall. They will bolt directly to the XJ seat tracks.
Contact: Burnsville Off Road
Broken Housings
Weak link: Stock taillights
Models affected: All
What happens: The mounting location and plastic construction of the taillights make them vulnerable to off-highway damage.
Strong fix: Rusty's Off-Road Products makes a professional-grade solution in the form of a beefy steel taillight kit. Available in two styles covering the '84-'96 and the '97-'01 models, they were developed using computer-aided design, and they're laser-cut and computer formed. Two holes are pre-cut into the housings, allowing fitment of 4-inch rubber flush-mounted lights. The top hole is for the brake/taillight, and the lower hole is for the backup light. Kits are available as housings only or with lights and/or wiring harness.
Contact: Rusty's Off-Road Products, 256/442-0607, www.rustysoffroad.com
Transmission Trouble
Weak link: AW4 automatic transmission
Models affected: '87-'01
What happens: Actually, this light- to medium-duty Aisin-Warner transmission isn't a bad unit overall, though XJ owners report varying experiences. Our research has found that it does harbor two peculiarities. First, it generates an excessive amount of heat, which as we all know is the number one killer of transmissions. Second, the Transmission Control Unit (TCU) won't allow you to lock the transmission in First or Second gear, which is very aggravating off-highway.
Strong fix: To bring the temperature down, install a transmission cooler like the SuperCooler from B&M Racing and Performance Products. The SuperCooler is constructed of 100 percent aluminum and uses embossed plates sandwiched together to create one of the most efficient oil cooling devices available. One of the things we like about the SuperCooler is that it's designed with a unique bypass feature that allows a controlled amount of ATF to bypass the stacked plate core when the fluid is cold. For those in cold climates, this guards against lube system failure. Solving the shifting issue is a bit more complicated. Fortunately, NAXJA member Dion Fotinakes has devised a way to override the TCU on '87-'96 AW4s, which allows for full manual control. The instructions are too lengthy to print here, so we've printed his instructions in their entirety on fourwheeler.com.
Contact: B&M Racing & Performance Products, 818/882-6422, www.bmracing.com (cooler); www.fourwheeler.com (solenoid modification instructions)