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JEEP TJ GEOMETRY, THRUST ANGLE, ALIGNMENT

I did multiple checks to make sure the first was accurate. And any time I adjusted something, I would go back and recheck the prior adjustments because they can and will be affected. The consensus seems to be that as long as any offset is within 1/8", you are where you need to be.

REQUIREMENTS:
This write-up assumes you already have a double cardan rear drive shaft or plan to order one after you take the measurement - in non-Rubicons, this will require a slip yoke eliminator (SYE). Not sure? If both drive shafts at the transfer case look the same (double u-joints), then you have a double cardan. Know that Rubicons come from the factory with a double cardan but will require a longer shaft. This write-up also assumes your TJ/LJ is already at it's desired suspension lift - that means coils are installed and you may be waiting to measure for shock and drive shaft length after most steps are complete. You will need eight adjustable aftermarket control arms to help get the best possible geometry. You will either need aftermarket fender flares or will have to remove/modify the OEM ones to maximize suspension travel. If you do not have adjustable track bars, you'll need a cutting wheel, welder, and tubing. Make sure you are working on a flat and level surface as this job depends on accuracy.

A double cardan is basically a stronger version of a CV joint and does not require a rubber boot. Some people use the terms interchangeably - they are not the same since CVs do not use u-joints.

TOOLS:
- All the normal stuff plus...
- Angle/Degree Finder
- Standard Bubble Level (magnetic is best)
- Plumb String (any string will work)
- Plumb Bobs or Heavy Nuts
- Magnet (that can hold up your plumb line)
- Long, Metal ruler (48"+)
- (2x) 3' Lengths of 1"-square metal tubing
- - (3' will only work for tires up to 35", so you may need longer)
- Quality Measuring Tape
- (4x) C-clamps
- (8x) Jack Stands (or at least four big ones for the frame and then use blocks and shims for the axles)
- Floor Jack
- Coil Spring Compressor (and an impact wrench/gun so you don't hate life)
- Torque Wrench
- Bright Colored Paint Pen
Important note: you are going to either need to modify (welding required) or replace both OEM track bars with aftermarket items. I replaced my front track bar and lengthened my stock rear track bar.


1) SETTING WHEEL BASE AND BUMP STOP: Remove any foam bump stops because they're not included in any measurement since they flatten. Poly bump stops may work but you might find that a different length is required at the end of this step. Measure the distances from the bottom of the bump stop shafts or the poly bump stops to the lower coil pads for both axles while the Jeep is sitting static (normal/weighted) and write them down - this is your "ride height". Now raise the chassis and place a tall jack stand near each of the four lower control arm brackets (LCA) on the frame. Remove the wheels, coils, track bars, shocks, and sway bars. Then support the axles at "ride height" relative to the supported chassis at the same distance you wrote down. Now raise the axles with a floor jack all the way up until the lower coil pad makes contact with the bump stop. If the bump stops aren't centered to the coil pad, lower the axles back down to the measured height. Make the distance adjustment with the LCAs and raise it back up to check again. This is your wheel base. Be aware that pairs of control arms will likely have different lengths for proper geometry due to slight frame imperfections.

Notice that your pinion angles will be changing. This is the angle of the u-joint yoke coming off the axle's differential (the pinion). For a double cardan drive shaft, you want the pinion yoke to be pointing at the yoke coming off the transfer case. Step #6 and #7 will fine tune pinion angles, so for now just quickly eye the pinion angles and adjust the UCAs to reduce making big changes later on. Just keep in mind that UCAs are for pinion angles only, so any adjustment you are making specifically for Setp #1 is done primarily with the LCAs.

Now reinstall the wheels to verify the clearance between the tire and wheel well at full bump/stuff. If the tires are making contact with the sheet metal, you will have to increase your bump stop. This does not mean longer foam bumpers since they are designed to flatten. This can include longer aftermarket bump stop shafts, bump stop shaft spacers, poly bump stops, and/or adding hockey pucks to the coil pads (very practical on the front axle). If you adjust the length of the bump stop, double-check to ensure it still makes contact with the center of the coil pad.

2) CENTERING THE REAR AXLE:  An adjustable track bar will help greatly with this, but I modified my stock bar and the aftermarket relocation bracket instead once I was finished with all other steps. Continuing from step #1, remove the wheels and reinstall the coils. Remove the jack stands holding the frame/chassis so only the axles are on stands - the chassis will sit at it's normal ride height like this. C-clamp one piece of the square tubing to the outer surface of each rear rotor. I used a level to make sure they were both vertical front-to-rear and left-to-right. Then I took a measurement between the outer edge of the frame rail and the square tubing and shifted the axle left or right until both sides were equal.

Adjust your aftermarket track bar to fit (do not bother tightening the large adjuster nut yet). Otherwise, use ratchet straps (be mindful not to pull diagonally) or jam wooden shims* in the recess of the track bar brackets to keep the axle where you want it throughout the process. Once everything is finished, you'll modify your stock track bar as a final step.

*Shim method: basically, this is temporarily "adding length" to the track bar to push the chassis to center it over the axle. You remove the track bar bolt at the bracket and then insert some sort of wedge or shim to counter the force of the chassis. This can be something that looks like a cheap wooden triangular door stop. The shim goes between the inside of the bracket and the end of the track bar joint. This offset will prevent you from re-installing the bolt, so you will want to zip-tie or bungee cord the end of the track bar into the bracket so it doesn't pop/drop out.

3) CENTERING THE FRONT AXLE: This is pretty much the method Mr. Blaine advises for accuracy. The plumb we are going to drop here should remain throughout the process, allowing you to reference back to it. As with the rear, an adjustable track bar will make things much easier, but isn't necessary as I lengthened mine once all steps were completed. First, measure between the front frame rails (I used the underside frame holes near the shocks and had to bend the lower steering line up a bit to keep my tape flat).

Since the harmonic balancer sits rearward compared to the frame holes, a trick I found to mark the balancer was to take a rectangular bar magnet and stick it to the balancer. I then stuck a razor blade to the magnet so it would extend out towards my tape measure. I moved/adjusted the magnet until the blade was centered to the midpoint between the frame holes, then marked the balancer with the paint pen:

You'll need three reference points to make an accurate alignment: 1) tie some string to a heavy nut and hang it from the mark on the balancer with the magnet; 2) now measure between the underside mounting bolts of the front bumper (where the bumper bolts to the frame) - find the center between these bolt heads and mark the underside of the bumper at this midpoint with the paint pen. 3) zip-tie the long metal rule between both sway bar lower mount tabs on the axle (you could also just use a piece of steel bar with the center marked between the tabs).

Now line up the bumper midpoint and the plumb string with one eye. Keeping your head still, look down to where the string is at on the metal rule - shift the axle until the string lines up with the midpoint on the ruler between the two sway bar mount tabs.

If you have an adjustable track bar, you can go ahead and get that mounted (but don't bother tightening the lockimg nut) - this will force the axle to stay where you put it as you work. However, as the steps progress, you'll want to go back and double-check that you're still centered. So leave the plumb line and the ruler in place because things may continue to change up here. If you don't have an adjustable track bar yet, you need to find a way to keep it centered through the remaimimg steps. For example, you may need to use a ratchet strap or place wooden shims in the recess of the track bar brackets to move it where you want it while you work on other areas. This has to be done without changing how the chassis's weight sits on the suspension (for instance, not being level because you're pushing/pulling diagonally). Once all steps are complete, you can cut/weld the stock track bar as I did until I purchased an aftermarket one.

4) THRUST ANGLE (Squaring the Rear Axle): Start this step with the coils in. Support both axles on jack stands with the weight of the chassis resting on the coils (do not support the frame/chassis with jack stands). Make sure the axles are level. With the rear wheels removed, clamp the square tubing to the outside surface of the rotor and double-check that the axle is still centered to the frame. Now check that the frame is level front-to-back and left-to-right - this doesn't matter for normal ride height, we just want it level now to use it as a reference point. If necessary, level the frame by jacking up a side or corner. I did my best to mark identical reference points near the end of either side of the rear axle shaft - these are where I will be placing the end of the tape measure. Butt the end of the tape to the paint pen mark and measure to the hole in the frame rail that is above the center of the transfer case skid plate. A zip-tie around the axle will work to anchor the tape at the axle mark if you don't have a helper.

If these measurements are off, you will need to adjust a lower control arm - remember, control arm pairs do not need to be equal in length. Make sure the axle has remained centered (square tubing clamped to rotors) and readjust if necessary. Now raise the rear axle up to the bump stops to ensure they are still centered at the coil pads, then return the axle to the jack stands.

5) SQUARE THE FRONT AXLE: One of the early mistakes I made was trying to square both the front axle and the rear axle to the frame. It just wasn't possible since these frame aren't absolutely perfect. The "compromise" is to square the rear axle to the frame (rear thrust angle takes precedence) then square the front axle to the rear axle. 

Make sure the front axle is still centered with the plumbed nut in Step 3. The zip-ties for the tape measure on the rear axle from Step #4 are a necessity here if you're by yourself. Plumb a string off each end of the front axle just behind the knuckles. These can be seen near the jack stands in the next picture...

Measure from the same rear axle points we used in Step #4 to these newly-plumbed strings. If taking this measurement without a helper, make this zip-tie snug to ensure accurate readings. Alternatively, you could use a plumb line to drop and mark a point to the floor near each axle end - this would also allow you to easily compare diagonal measurements for another double-check ...if the diagonal lengths are equal, your axles are square.

Make lower control arm (LCA) adjustments on the front axle until these rear-to-front measurements are equal. Make sure your front axle is still centered to the plumb line throughout. Double-check that the bump stops are still centered to the coil pads at full stuff.

Adjusting UCA Pairs: Before moving on to the next step, understand that the weight of the differentials will cause the axles to rotate/roll inward if they are set on the ground by themselves with the wheels attached. This can cause the axle's second UCA bracket location to kind of rotate a little more with only the first UCA bolted up - it's not a lot, but it is something easily remedied. This is especially important up front due to the offset differential putting most of the rotational mass on the driver UCA. If not accounted for, the caster could be different from one side to the other and there's potential for some axle bind. So, once in the final phase of determining the length of a pair of UCAs, only use the driver-side UCA and unbolt the passenger-side UCA from the axle. Tighten the installed driver-side UCA bolt at the frame and then simply jack the pinion up very slightly - just enough that the axle-side bolt slides in and out easily between the driver's axle bracket and UCA. With the passenger UCA mounted to the frame only, adjust the passenger arm out until its axle-side bolt easily "slip-fits" as well. This final UCA adjustment is done with the Jeep sitting static (wheels on, springs in, no jack stands). It is then a good idea to go back and recheck that axles are still centered and square. If either of those are off and you adjust them, you'll want to recheck the UCA slip-fit again.

6) REAR PINION ANGLE: Again, this write assumes you will be using a double cardan rear drive shaft - in non-Rubicons, this will require installation of a slip yoke eliminator kit (SYE). The Jeep should be sitting static (springs in, wheels on, and no jack stands) on a level floor. If you have a Rubicon or already have an aftermarket double cardan shaft, you can leave the shaft in and use a degree finder by comparing the angle of the drive shaft to the differential-side's u-joint rotated so that a flat spot is at 12 o'clock. Otherwise, remove the drive shaft and eye the rear differential so the pinion yoke points to the yoke on the back of the transfer case (this should already be the SYE). Assuming you need to tilt the pinion up, place a jack under the rear differential near the u-joint and lift just enough to allow you to disconnect the UCAs from the rear axle. Jack the pinion up a little until it looks like it is in line with the drive shaft and/or pointing at the transfer case yoke. Adjust and reinstall the UCAs.

Once adjusted, this is the time to take the measurement for a double cardan rear drive shaft and get that ordered (if you have a Rubicon, you will want one of longer length). Now is also a good time to measure for rear end shock length (collapsed and fully extended). Just keep in mind that you might be tweaking the pinion angle slightly while trying to eliminate driveline vibes. If the rear pinion angle is steep, you should consider an aftermarket differential cover with a higher fill hole.

Once the double cardan is installed, you should check for bind. Lift the frame and place it on four tall jack stands. Remove the wheels and droop the axle all the way down (are your brake lines long enough?) then all the way up, making sure the drive shaft doesn't bind when you spin it in these two positions. Again, recheck that the axle and bump stops are still centered (yes it sucks, but better to check now than to start the whole process over trying to track down a drivability issue). Some have reported that having the pinion slightly lower (1 to 2 degrees) than parallel netted better results. Later, test drive it and tweak it up or down to eliminate or reduce the vibes best you can, allowing you to get deeper into the RPMs before the vibes start. In taller lifts, it may be impossible to eliminate vibes entirely with the UCAs alone due to the TJ's short wheel base. Installing taller aftermarket engine mounts can help here (usually +1"), but too high may be detrimental to the front shaft angle. Lowering the transfer case's skid plate with washers/spacers will help the rear and front shafts. Basically, the steeper the shaft angle (the taller the lift), the more likely you are going to run into or worsen a vibe problem lower in your RPMs. A "workaround" on a manual transmission is to do the best you can and then just short shift before the vibes occur.

7) FRONT PINION ANGLE: Set the front pinion angle just like the rear, but know that this will affect your caster. The priority is pinion angle because this lessens abuse of drive shaft vibrations on the more expensive driveline. It is recommended to only use the driver-side UCA for this adjustment as it will hold the weight of the offset differential on it's own. Once you get the driver UCA in, slip-fit the passenger UCA in as described in Step #6.

At this point, you'll want to make sure you are actually getting full droop from the front axle. With the frame lifted on four tall jack stands with the wheels removed, drop the axle and check to see if the LCAs are making contact with the lower coil/shock bracket. If so, cut or grind a notch in the bracket to allow additional droop. After this is complete, it is a good time to measure for front end shock length (collapsed and fully extended).

When you start your test drives, you may feel a rumble (it can be subtle) that is referred to as driveline vibes. To determine which shaft is causing this, you can disconnect the front shaft at the differential and secure it out of the way (do not use 4WD) ...a much safer option is to remove it entirely. Or you could remove the rear axle instead and run in 4WD on the street to ensure the front is not the axle producing vibes under load from the transfer case. Apparently, there was an assembly issue within early 2004 Rubicons where a transfer case bearing was installed incorrectly - to check, disconnect the rear drive shaft at the transfer case, start the engine, and let it idle in gear (2WD only). Take a look at the rear drive shaft flange coming off the TC - if it isn't spinning concentrically, you will need to remove the case and have the bearing replaced.

Wheel Caster (and Shimmy/Wobble): Proper caster does help produce a more stable front end. During early test drives, I was thinking I was experiencing a caster-related shimmy at certain speeds. I mistakenly became obsessed with caster. However, I found that once I upgraded to the more robust Currie steering linkage and freshly balanced tires, my issue ceased entirely. I believe that the flimsy stock tie rod was not substantial enough to calm the vibrations between the larger tires - I imagine it was flexing like a strummed guitar string. After I got rid of the weak links in the front end, I went from being overly concerned with caster to barely giving it a thought since. I have a tall lift (at least +6.5" of suspension) with no issues, so my advice is to not worry too much about caster. But if you are not getting any vibes from the front and you're sure the rest is correct, you can try decreasing the pinion angle a little and retest. However, you may only be masking a weak component that could grenade at a later date. I did the research, so I might as well post what I have learned. Just know that nine times out of ten, it seems bad components (usually tires out of balance) are to blame for these problems and not caster.

The problem with dialing in the caster is that it is very difficult to measure on a TJ/LJ. There really aren't any good places to get an accurate reading. I've found putting sockets on castle nuts or getting readings off the underside of the bottom knuckle just aren't consistent. Here's  an easy way that references the differential cover (see the chart near the end - use Low Pinion). whatever way you choose, you likely won't be exact but you'll be close. Here's another option I came up with for measuring caster. 

The factory setting is somewhere around 7 degrees which is, of course, intended for stock tire sizes. It seems that 33" tires benefit from around 6 degrees of caster and 35" tires generally need somewhere between 5 to 5.5 degrees. If making an adjustment, you will want to fully droop the front and spin the drive shaft to make sure it doesn't bind. Also check this with the axle raised all the way up to full stuff.

But what if you want perfect pinion angle as well as proper caster? One option is to grind the welds that fuse the axle to the knuckles so they can be tilted back further and re-welded. Knuckle rotation will likely require welding on aftermarket raised sway bar link brackets so that the drag link end will clear. A second option is to install offset upper ball joints but they don't seem to get much approval by the veterans (though I've seen some positive reviews). But I do know you want to steer clear of the adjustable ball joints (which the vets may be referring to) because they can get bumped out of their setting. A third option is to replace the low pinion axle with a high pinion axle to reduce the drop distance from the transfer case, but you still may be at the mercy of the pinion on a higher lift when it comes to caster. A fourth option is to replace the stock single double cardan front shaft with a multi double cardan shaft (a double-double). Researching this fourth option, I learned these shafts are hit or miss - sometimes they can worsen/cause vibes since they are heavier and difficult to balance.

8) TOE IN: Lift and place two jack stands under each axle so the Jeep is sitting level at static ride height (springs in; fully weighted) and remove the front wheels. I took the two pieces of 3' square tubing and marked the midway point (18") on them. From this line, I marked the radius of my tire diameter on each end. Use a c-clamp on the upper caliper bracket to hold the rotor from spinning. Clamp the square tubing so they are centered and level on both rotors (you can leave the calipers on). Make sure the tubing is sitting flush with the smooth rotor surface.

Measure the distance between the outer edges of the two pieces of tubing at the front pair of tire radius marks you made. Calculate the midway point of this measurement. Using the plumbed string off the harmonic balancer from Step 3, center the tie rod by lining the string up midway the distance between the front ends of the square tubing.

In this example, the distance between the outside of the tubing is 58". This means the wheels should be turned so that the 29" mark on the tape is aligned with the plumb off the harmonic balancer.

Now measure and compare the distance between the front and back distances at the radius marks on the tubing. Your goal is to get the front measurement to be least 1/16" (but not more than 1/8") shorter than the rear measurement. That is your Toe In.

If they are off, loosen the two clamps on the tie rod (the horizontal one that connects to the driver-side knuckle). To shorten the toe (make the front of the tires point closer together), you need to twist the tie rod up. It doesn't take much rotation to do this and PB Blaster makes it much easier. Once you get between 1/16" and 1/8" of toe in, carefully tighten the clamps (no need to torque yet). Double-check the measurement once tight. Then you should put the tie rod through it's full range (static, droop, bump/stuff) to ensure that it and the clamps are not rubbing anywhere - you might want to temporarily install the steering stabilizer now for this. If it looks good, make sure your ball joints are sitting evenly/parallel on their mount points, recheck your measurement, and then torque the clamps.

This shows how toe in can be measured with the wheels on and without the square tubing.

Camber: This one is easy as there is no camber adjustment on the TJ/LJ. Moving on...

9) CENTERING THE STEERING WHEEL: Continuing from Step 8, center your front rotors by again measuring the distance between the square tubing at the front of the rotors and centering this midpoint again with the plumb line still hanging from the harmonic balancer. Now check the position of your steering wheel - it's probably not rotated to 12 o'clock if you lifted the Jeep. What I did was place some tape at the desired top-dead center of the steering wheel so I could see it from the front of the Jeep - as you make adjustments, you will see the tape rotating up through the windshield. Now loosen the two nuts that clamp the turnbuckle onto the drag link (the drag link connects the pitman arm of the steering box to the knuckle at the passenger-side wheel). Twisting the turnbuckle down rotates the tape towards the driver side and vice versa. Once the tape gets to 12 o'clock, re-check to make sure your tie rod is centered to the plumb line again. If it checks out and the ball joints aren't binding anywhere, go ahead and carefully tighten the turnbuckle clamps.

Now jack the axle as far up as it would go and run the steering through it's full range from left to right, checking for clearance (there's a limited range of circumference the clamps can sit without contacting the other bars). If nothing is binding/rubbing, you are done, though it might take a few test drives to get the steering wheel adjusted perfectly center. Make sure when turned fully left and right, nothing is making contact ...also check at full droop and bump/stuff. If so, you will want to add washers to the steering stops on the knuckles.

10) BEFORE THE TEST DRIVE: Control arms do not get their final torque until the Jeep has settled all it's weight fully onto the tires. If installed, I'd recommend removing the steering stabilizer for the tests because it could potentially mask any problems you might have that could bite you later - if you don't properly correct death wobble, it will eventually destroy your stabilizer. If you don't have adjustable track bars, you'll need to extend the factory front and rear for now (cut, lengthen with tubing, and weld) - try to make the front track bar parallel with the drag link to minimize bump steer (you only need a drop pitman arm if it helps with this alignment). If you have strong components in good shape, tires are balanced, and you didn't cut any corners in the steps above, you shouldn't be having any shimmy or wobble problems. However, use the  End All Alignment Thread  thread to help diagnose any issues. Also,  here  and  here  are in-depth looks at death wobble if that becomes a problem.

Torque Specs:
Calipers: 11 ft-lbs
FRONT SHOCKS - Upper: 17 ft-lbs; Lower: 20 ft-lbs
REAR SHOCKS - Upper: 23 ft-lbs; Lower: 74 ft-lbs
Tie Rod Ball Studs/Ends: 55 ft-lbs
Tie Rod Clamps: 20 ft-lbs
Drag Link to Pitman Arm Ball Stud: 55 ft-lbs
Drag Link Turnbuckle Clamps: 36 ft-lbs
Tie Rod to Drag Link Ball Stud: 65 ft-lbs
Front Sway/Stabilizer Bar to Upper Link Nut: 45 ft-lbs
Rear Sway/Stabilizer Bar to Lower Link: 40 ft-lbs
Front Track Bar Ball Stud: 60 ft-lbs
Front Track Bar Axle Mount: 40 ft-lbs (per the manual, not the 55 bouncing around the internet - I personally do 50 here)
Rear Track Bar: 74 ft-lbs (both ends)
Wheel Lugs: 90 ft-lbs
FRONT CONTROL ARMS - Upper: 60 ft-lbs; Lower: 130 ft-lbs
REAR CONTROL ARMS - Upper: 55 ft-lbs; Lower: 150 ft-lbs
Steering Stabilizer/Damper: 55 ft-lbs
FRONT DRIVE SHAFT U-JOINT - Axle: 14 ft-lbs; Transfer Case: 20 ft-lbs
REAR DRIVE SHAFT U-JOINT - Axle: 14 ft-lbs; Transfer Case: 20 ft-lbs
Rubicon Transfer Case Flange: 85 ft lbs

(note: when torquing bolts that are anti-seized or greased, subtract 10%)
CrankyGypsy (established 2001)