TJ Tech

By: Tim Mulverhill

New England Four Wheelers, Inc. are known for the variety of vehicle brands, types, and stages of development. Early Broncos, FJ-40 Landcruisers, Scouts, ‘Zuks and Jeeps of every SWB model can be found at club events. As newer people join the club they frequently bring newer vehicles. The ‘new’ Jeep TJ Wrangler is becoming a common sight on the New England trails after making the scene in late ’96. There are a few built up TJ’s in the club, and those looking to buy and build one can learn from their mistakes. I get asked a lot of questions about tire size, lockers, axles, etc. at events and rides - hell, even at the deli. I’ve compiled a list of the most common questions with answers based on personal and club experience:

Tires

A stock TJ can fit 31X10.50 tires without a lift. This will work on the trail as well as the street. Jeep designed the TJ for this size tire, but the weenie attorneys at Chrysler made them sell with a 30” max. They will fit on the original factory 8” mag rims, but not the stamped 7”. If you are getting new rims, get 15X8 with 4.5” backspacing and tires will not rub. This number worked for my 31’s, 33’s, and still holds true with my 35X12.50’s. Steering stops will need a 5 minute adjustment.

I started off with BFG AT’s. They were great on street and good on trail - lousy in mud. I drove 1-½ seasons on them before going to BFG MT’s. These are a good tire for New England , but somewhat susceptible to sidewall puncture. I lost two last year.

Most hardcore guys run Swampers, Boggers, and the new MT Baja Claws. These are heavy-duty tires with thick, puncture resistant sidewalls. The problem is they’re heavy. The stock TJ front axle will eventually break with 35-36” Swampers or equivalent tires. Lambert did it, but he was smart enough to have spare axles and tools when his axle finally broke. The BFG’s or Swamper TSL’s are better for D30 axles.

A hint for anyone running 33’s - you can get away with using a 33X9.50 spare if you use 33X12.50’s. It’s lighter and more compact, yet will still get you off the trail.

Lifts

A 4” lift will get you 33” - 35” tires depending on actual tire diameter. For trail use a 4” spring lift & a 1” body lift will work for 35-36” tires. A 1-2” body or coil spring spacer lift will work for 31-32” tires.

For better articulation get a lift with adjustable control arms, a necessity for adjusting pinion angles on higher lifts.

Axles

TJ’s come with Dana 30 front axles and either a Dana 35C or 44 in the rear. The 44 is the preferred axle of the two. The front D30 is a full time 4wd axle, that is it has no disconnects. Warn makes a locking hub kit for the front but for our applications you would do well to stay away from it: It is a light duty design using a Bronco II hub. It isn’t designed for use with a locker or tires over 33”. A number of club members have had problems with them failing. If you want hubs in the front go to a D44 front axle.

The factory D44 axleshafts can be upgraded with Warn heavy-duty shafts. Steve Ballou actually twisted the splines on his factory shafts, so it might not be a bad idea. Similar HD shafts are also available for the front.

D35C owners that are still waiting for something bad to happen should either swap in a D44 or reinforce the 35C. C-clip eliminator kits and heavier shafts are a start, but the $$ is probably better put towards a ’44 from a TJ or early XJ. Rick Boiros is a good local contact for these stock axles, and Todd Landers might have a few also

Custom axle options include Dana 44’s, Dana 60’s, or Ford 9” differentials. Jim Lambert has the 9” rear in his ’96 and a custom ’44 in the front. Steve Ballou has a 44/44 combination. A Dana 60 for a stock TJ driveline is overkill. Beefier is better when it comes to resisting breakage, but the weight and reduced ground clearance will eventually become an issue.

When upgrading axles you will have the opportunity to switch to the CJ' s 5 on 5-½-bolt pattern (TJ’s come 5 on 4 ½). This gives you a much bigger selection of HD parts and brakes options.

Lockers

I started out with a factory Trak-Lok limited slip in the D44 rear and it worked very well. At 20K miles I went to a Lock Right in the rear and a Detroit Tru-Trac limited slip in the front. I noticed a big difference with the full locker in the back, but the limited slip didn’t help much up front. The Tru-Trac needed more RPM’s to engage than those we develop at rockcrawling speeds. It may have helped in mud or snow, but it didn’t pull me up any ledges.

TJ front axles are constantly turning - there is no way to disconnect them except at the transfer case. This means you can’t put a full locker in the front axle without affecting steering and stressing the front driveline. Limited slips are an option, but with the trails we run you’ll probably wind up doing what I did: Install an ARB air locker. The ARB can be turned off for the street, and engaged with the flick of a switch for an obstacle. There are a few downsides - they cost more than other options, but are cheaper than having to upgrade in the future like I did. The compressor can fail, either through electrical fault or by losing an air line. A spare line is cheap and easy to carry. Hardcore drivers of dedicated trail rigs prefer full lockers, but they have the advantage of locking hubs and trailers. Almost every TJ is still a daily driver pulling double duty, and for this the ARB is the clear choice.

By running a mechanical locker in the back, even if the compressor fails you’ll still have one locked axle.

Safety

Ask me what happens to a TJ when it goes to inverted flight. When it is all over damages can cost a lot, but there are ways to minimize: Get a set of soft doors, at $250 for a pair they are a bargain compared to $900 for a factory full hard door (1). Run a bikini top, weather permitting - soft tops are pricey, factory or not ($500+), and factory hard tops cost thousands.

Get a roll cage. A few companies make them that bolt in. MORE has one that can be tied into the frame. Have someone in the club weld it together, it will be stronger. Have a bar welded across the two rear hoops of the factory ‘sport bar’. When my TJ went over the two hoops were pushed together and kinked the tub. This bar will prevent this.

Having a rollcage will allow you to drop the windshield. In factory form the windshield and support bars are a part of the safety equipment that protect the occupants. In a slow roll they perform very well but are destroyed in the process. With a ‘cage' the windshield can be dropped without compromising safety. That windshield frame costs $700 without glass, molding, or paint. Having it down is a good idea.

That should save you five or six grand depending on the severity of your disaster. Tow Hooks - a club requirement. Easy installation up front, but without a trailer receiver or aftermarket bumper out back mounting can be tricky. DO NOT bolt a hook to a factory bumper. The bumper will bend and the hook will tear out. I mounted mine to the side of the frame rail using one existing hole in the frame and drilling one other. Worked great for years until I got shackles installed.

Gears

Very early TJ’s came with ridiculous 3.07 axle gears. 3.55 and 4.11’s became available for 6 and 4 cyl. models respectively. A 3.73 option is now available for TJ’s with the factory Trak-Lok.

As soon as tire size is increased gearing is affected. Go to 31” tires and acceleration is not as snappy. Go to 33’s and forget about using overdrive on the highway. Changing the axle gears will compensate for this and help reduce your low range on the trail. 31” Tires - 3.55 gears - I didn’t change anything as it wasn’t too noticeable. 33” Tires - Time to switch to 4.11 gears - this brought performance and speedometer back to factory feel. 35” Tires - Had to go to 4.56 gears, still a little off - like when I went to 31’s.

If I had to do it all again I’d have gone straight to 4.56 gears and enjoyed the extra low range on the trail. 4.56 is as low as you should go with a D30 axle - the gears have less metal due to differential size constraints and therefore make the gears weaker. 4.88 is the next size but would be vulnerable to breakage. If you want to go lower you’ll need a custom 44 or 9” front axle.

Armor

The TJ has a number of vulnerable spots. Fortunately the aftermarket has items available to address these problems:

Engine - the oilpan sump on 6 cyl. TJ’ is very low and exposed. At the Catskill Jambo in ’98 the local Jeep dealership ran out of pans and started banging out the bent ones and siliconing them back up. Tomken and Skid Row make engine skidplates for TJ’s. The Skid Row is much heavier and what I’d get though my Tomken has held up for 3 years now. It’s bent and twisted, but that’s what it’s there for.

Gas Tank - Notoriously low on TJ’s, especially the 19-gallon variety. Factory skidplate is a joke, tank is plastic. Tomken and a few other manufacturers make tank skidplates that can take the beating they will get.

Steering Box - Out in the breeze on TJ’s. Leaf sprung Jeeps of the CJ/YJ variety get box protection from the driver’s side spring. Not so on the coil sprung TJ (hey Dad, what’s a spring shackle?). Tomken, Terraflex, Turbo City all make a $50 plate that protects this vital part.

Transfer Case - After 2 years my factory X-fer case skidplate/crossmember was whooped. It was bent and gouged so badly that it couldn’t be re-installed after I had some work done. Terraflex makes a ‘Belly Up’ skidplate for TJ’s that raises everything up for an extra 2-4” of ground clearance. A number of other assemblies need modifications for this to work, but the plate is HD and the clearance is fantastic. It requires a NP231 short shaft kit, 1” body lift, and it has a spacer to lift the motor ½”. Driveline angles are extreme with a 4” spring lift and require a new rear driveshaft.

Rocker Panels - Boulder bars, Rock Rails, whatever the name they’ll save your sheetmetal.

Quarter Panels - Off Your Rocker steel corner guards will save your ass-end. I’ve seen vehicles suspended by rocks or Hi-Lifts on these without damage. Don’t waste your time on aluminum ones.

Bumpers - the factory ones are very lightweight. The first thing you should do with a TJ when it comes off the dealers lot is pull the stupid plastic end pieces off of the bumpers. They’ll get torn off and squashed soon enough anyway. There are more options on bumpers than anything else. Everybody makes them with all sorts of options in any size. Early (pre ’98) TJ’s can use YJ and CJ bumpers, the bolt holes all line up. Later models need to drill holes.

Tire Carriers - You’ll need one if you supersize your tires. That factory carrier will eventually tear out of the tailgate with a super heavy tire.

Shocks

TJ’s with flexy suspensions need to invert their rear shocks. Axle & suspension travel will dent the reservoirs of res. down shocks. Rubicon Express makes a kit for this.

Spares

Things to Bring: D30 axleshafts, serpentine fan/alternator belt, U-joints (especially for steep rear d-shaft angles), D35 axle parts, fuses. This is in addition to all of the regular items you should have and listed in a previous tech column.

Transfer Case

TJ’s use the NP231 case. This is a chain driven aluminum cased unit for medium duty applications. It can be built up for HD use or replaced outright.

Buildup options include short shaft kits, 2WD low, and low-low range gearsets. The tailshaft kit allows the use of a longer rear driveshaft and eliminates the slip-yoke weak link. The low range gearset is available from Terra and makes a huge difference on the trail. It only affects gearing in 4 Low, leaving street gearing the same. These mods will leave you with the NP231’s weak point, the chain drive. Advantages are the lightweight and small size of the unit.

If you want to do away with the chain drive an Atlas II transfer case will give you low gears, longer driveshaft, 2wd low range, and a beefy case. Disadvantages are weight and size of the case. Jim Lambert needed a 1.5 or 2” body lift to clear his Atlas and a custom skidplate need to be fabricated.

Both options will run the same in cost within a few hundred dollars of each other. The advantage of the NP231 build is that it can be done in stages.

Engine Mods

With emissions regs and warranty constraints being what they are, there isn’t much that can be done to a TJ motor right away. One simple mod is to remove the airbox, cut the intake tube at the appropriate spot, and install a K&N air filter. This raises the intake over the top of the engine and increases power and fuel economy. The computer doesn’t complain either.

Some people swapped in a cat-back exhaust for power, but I couldn’t justify that until the factory one needs replacing. I’m still waiting after 3 ½ years.

There are headers and power chips for more power, but in all the time I’ve had it, a lack of engine power has never been a problem. The $$ is better spent on the rest of the driveline.

Exterior Mods

Some people have problems finding a spot to mount a CB antenna. There are more choices now than there were when my Jeep was new. Companies make brackets that fit behind the tailights or on the windshield hinges. The hinge bracket will interfere with folding the windshield and will lay the antennas down horizontally.

My original solution on my almost-stock TJ was to drill & mount a standard aluminum CB ‘L’ bracket to the spare tire carrier behind the tire - very neat and out of the way. Also very free.

Going to soft or no doors means relocating mirrors. The Sun brackets are popular, but they rust after a few months. The passenger side bracket is worthless with a door installed and is usually omitted.

If you still have side steps remove them before the trail does.

There are a ton of things I’ve either skipped, missed, forgot, or just don’t know about. I hope this summary helps anyone thinking of building up a TJ for trail riding. These are just observations I’ve made from experience. Hopefully they’ll save you some time and money. They perform very well from the factory, and with a little help can tackle some of the harder trails in our area. If you want to ask anyone about their buildup try to get a hold of Jim Lambert, Steve Ballou, Ben McCarthy, or myself.

Tim Mulverhill

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