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Old 10-10-2013, 11:28 AM   #1
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Post Caster and thrust angle help, no lift.

I've read a bunch of threads about alignment and after installing my Curry HD steering kit and 1.75" front coil spacers (to compensate for new bumper and winch) I have a few questions.

I disconnected the lower control arms when installing the spacers and disregarded the adjustment cam washers on reassembly. I've read that I should align them to a 6-7 degree caster. My first question is how, suspension hanging? On the ground? Both at the same time or one at a time? Suspension hanging is a hard one... unlevel rock driveway + highlift = liveleak video...

And for the rear thrust angle, I measured front to back hub to hub and found a 1/2 inch difference from the left vs right. On visual the driver rear tire seems to be further back (uncentered) than the other one. Rear is all stock parts. I also have a rear (driver side?) clunking when I turn into my driveway. I can pull/push rear wheel in/out maybe 1/8" clunk clunk cluck, (D35). This is a DD, my user profile is current with what is new on it.

In an effort to get rid of my (minor) 40mph wobble and not so minor bump steer, I have installed new Bilstein 5100s, Monroe dampener, Curry HD steering w/new tie rod, ends, drag link. Track bar has not been checked/replaced but has minor old bushing slop at the axle (next on the list before we get new tires) Ball joints feel/look good.

For the rear, are there things I should check/replace before assuming bent frame and getting adjustable control arms to square up my wheelbase and scheduling an appointment at a frame alignment shop?

Thanks in advance...

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Old 10-10-2013, 12:31 PM   #2
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I've read that I should align them to a 6-7 degree caster. My first question is how, suspension hanging? On the ground? Both at the same time or one at a time? Suspension hanging is a hard one... unlevel rock driveway + highlift = liveleak video...
sitting on the ground at ride height...that's about where its at most of time when driving, so doing it anywhere else makes no sense. I've found no reliable way to measure caster off the housing....there's a 2° tolerance in the stock specs (7° +/- 1°). So one side could be 6.1°, while the other side could be 7.5°...from the factory!

Caster relates to pinion angle, so if you get an accurate measurement off a laser alignment rack, you can then assume pinion angle and caster change by the same amount linearly should you do mods requiring adjustment in the driveway with your own angle finder.

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And for the rear thrust angle, I measured front to back hub to hub and found a 1/2 inch difference from the left vs right.
This doesn't mean much. Do a diagonal measurement under the vehicle across symmetric points. Like a point of the left lower control arm bracket to the right side of the frame, and symmetric points on the opposite sides. Then report back.

If they are off significantly, then something may indeed be bent/damaged. Sometimes the factory brackets themselves are welded on in slightly different places along the frame.

Also, to compensate for the heavy bumper and winch, you could ditch the spacers and use V8 ZJ coils. Cheap & effective with better properties.

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Old 10-10-2013, 01:05 PM   #3
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Thanks for your reply, I've actually read a lot of your posts/replies on this subject. I will measure the rear for square (X) and post my findings...

Thanks also for the spring advice... I went with the (temporary) spacers because I needed exactly 1 3/4" in the front to level when I did my bumper/winch... and did not want to guess what lift I may or may not get from new springs, not knowing exactly what springs are currently on my Jeep...
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Old 10-10-2013, 01:19 PM   #4
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Thanks for your reply, I've actually read a lot of your posts/replies on this subject. I will measure the rear for square (X) and post my findings...
Understand that your square (X) measurements will be affected if your axles are not perfectly centered side to side.
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Old 10-10-2013, 01:57 PM   #5
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they (appear) centered and the rear is on stock non adjustable everything, but seeing how the driver rear is 1/2 further back (visible in fender flare as well as measurement to front wheels) than the passenger rear, I'm not expecting a square measurement, but I will try to get a good measurement and report back... It does not feel like its doglegging but then again, I cant see it while I'm driving it.
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Old 10-10-2013, 02:13 PM   #6
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You could set the rear axle on jackstands, remove the rear wheels, then put a straightedge on the wheel mounting surface, and measure to the frame on both sides. A little bit off side to side, will make quite a difference in an angle measurement. Once you know the exact amount of offset, you could make a mark in the middle of your transfer case skid with the same offset from center, then using the mark angle measure from the same point on each end of the axle.
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Old 10-10-2013, 04:47 PM   #7
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FWIW...this is the way I adjust my caster angle. I've got a small digital angle gauge (about $30 at Harbor Freight). Since caster angles are measured from 90 degrees of the plane that the vehicle is sitting on and my garage floor is not perfectly level, I first lay a straight edge from center of front tire to the center of the rear tire and measure the floor angle between the two (in this case .40 degrees, I then attach the magnetic base of the angle gauge to the flat spot on the steering knuckle just behind the lower ball joint and read the angle there. Since the front of the Jeep is sitting slightly higher on the floor then the back, it's simple subtraction. 5.70-.40=5.3 degrees of caster (I wanted to be around 5 for my 4" lift, TT, pinion angle). The digital gauge reads from zero on the horizontal plane, and the ball joints are at right angles from the bottom of the steering knuckle...Maybe not quite as accurate as a $50,000. alignment rack, but close enough for this guy.
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Old 10-10-2013, 05:07 PM   #8
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The digital gauge reads from zero on the horizontal plane, and the ball joints are at right angles from the bottom of the steering knuckle...Maybe not quite as accurate as a $50,000. alignment rack, but close enough for this guy.
I have the same angle finder from HF and my caster showed ~14°, just now, with your method. In the past, I've seen wildly different numbers than that too. None of which are even remotely close to the true caster of 6.5°.

I've done this trick, and many more trying to get an accurate caster measurement. Measuring off a cast surface sucks. I've tried the lower C, the socket on the ball joint, and several other "tricks". They show different results on different days of the week, and never the same twice in a row. Heck, I've read reports of some having more than a 1° difference between passenger side/drivers side.

The easiest & most accurate method I've found is to get a laser alignment, then you know what true caster is for your housing, with your control arm lengths. Now you can measure your pinion angle off a true machined surface - either the face of the pumpkin, or the u-joint cap on the pinion. Now you know caster/pinion separation. If you change pinion angle by X.X°, then you know you change caster by the same amount.

Also note when you change caster, need to check and reset toe-in.
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Old 10-10-2013, 05:19 PM   #9
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I guess that's the result of the good ole China HF amazing tools. So far on mine, it's worked reasonably well. I've checked it over several days and it remains within a few tenths, but I agree, the best method would be to have in done on a rack first.
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Old 10-11-2013, 08:16 AM   #10
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I have a possibly dumb question using logic as my only available tool.

From what I've read here...

Factory caster is 7* (ish) on a stock height TJ...
My 97 has alignment cams on the LCA
The factory removed the cams on TJs made later and replaced them with a centered washer...

Would this not add up to setting the cams centered as if using a standard washer (like later models use) to get to "factory castor 7* (ish)"

does that make sense? I Have no lift and 31s. I know "all jeeps are different" but if all the TJs made after 97 use a standard centered washer to get factory caster, then simply centering my cams "should" get me to factory specs... in theory, yes?
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Old 10-11-2013, 08:29 AM   #11
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does that make sense? I Have no lift and 31s.
no, you have 1.75" of lift in front because you put spacers on there. a winch and bumper won't make your jeep sink 1.75" unless your springs are completely trashed - at which case you need new replacement springs (which I already suggested), not spacers.
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Old 10-11-2013, 10:03 AM   #12
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no, you have 1.75" of lift in front because you put spacers on there. a winch and bumper won't make your jeep sink 1.75" unless your springs are completely trashed - at which case you need new replacement springs (which I already suggested), not spacers.

correct... I have exactly 3/4" of lift over factory or 3/4" higher than before I added the front weight to level out the rake a bit, the other 1" only put me back to where I started before adding the weight....

so you are saying that a 3/4" lift will change my goal of a factory 6* to 7* caster? If that is the case, what value should I be shooting for? I read here that a 3" lift will roughly put you at a goal of 5* to 6*, so I'm not understanding how 3/4" will take me out of the 6 to 7 range...

please excuse my questions as I'm a little confused... as to the new springs, my plan was to use OME HDs on the front and medium dutys on the rear, per advice form the ARB rep...

the only reason I have not proceeded with springs is I'm looking at a safari rack that would need the HDs on the rear too, instead of the MDs I would need without one... but after recently buying an XRC bumper and winch, Bilstein 5100s, Curry HD steering, fender flares, new stainless header, cat, muffler, o2 sensors, KC lights, etc... I wanted to sit a bit on the rack to make sure it's not part of my "mod fever" and be something we will actually use...
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Old 10-11-2013, 11:07 AM   #13
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correct... I have exactly 3/4" of lift over factory or 3/4" higher than before I added the front weight to level out the rake a bit, the other 1" only put me back to where I started before adding the weight....

so you are saying that a 3/4" lift will change my goal of a factory 6* to 7* caster? If that is the case, what value should I be shooting for? I read here that a 3" lift will roughly put you at a goal of 5* to 6*, so I'm not understanding how 3/4" will take me out of the 6 to 7 range...
it's not that a specific lift height needs a certain degree of caster. It's more based on tire size, and a compromise you have to strike between pinion angle and caster for drive-ability. As you go up in the tire size, you need less caster....but as you increase lift, you're stuck with the factory pinion angle/caster separation because that's where stuff is welded. That is of course you cut inner-C's off, rotate them, and reweld them to your desired specs. A friend of mine did that for his 7" lifted XJ on 33s...he now runs 8° of caster.

since you don't need to go to that extend for your little ~1" lift, or even a 3" lift - you instead have to find what compromise you want. More caster or less caster, and how that effects your drive-ability. There's a compromise either way you go - just figure out what works best for you. When you're reading somebody's opinion on here, you're reading what they like on their rig, for their setup. Your results may be different.

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please excuse my questions as I'm a little confused... as to the new springs, my plan was to use OME HDs on the front and medium dutys on the rear, per advice form the ARB rep...

the only reason I have not proceeded with springs is I'm looking at a safari rack that would need the HDs on the rear too, instead of the MDs I would need without one... but after recently buying an XRC bumper and winch, Bilstein 5100s, Curry HD steering, fender flares, new stainless header, cat, muffler, o2 sensors, KC lights, etc... I wanted to sit a bit on the rack to make sure it's not part of my "mod fever" and be something we will actually use...
New springs are the correct way to go about this. I wouldn't suggest a safari rack however...they really increase the pucker factor when off-road in off-camber situations. Regardless, take a look at how much weight you're carrying around, and what your final goals look like. How much weight did you add in sprung weight? Now doing some basic math, using the spring manufacturers published specs (pounds per inch) - you can identify a spring that will work for your needs, and give you the desired rack/stance.

I don't go by what the advertised "lift height" is, or even what model it's advertised for. It's a chunk of steel with some specific properties...spring rate, unloaded length and dimensions. As long as the dimensions fit, the spring rate is appropriate and the lengths work for your setup...then use that spring...doesn't matter if it's OME, BDS or whoever. OME just happens to have a wide range of selection, so it's a great place to look.
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Old 10-11-2013, 11:21 AM   #14
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If you want to make it simple........worry about your thrust angle first. Get that taken care of. After thrust angle is set, a simple test to make sure caster is good is by doing the simple test.....go down the road, take both a left turn and right turn, then let the steering wheel go. If it returns back to center, your castor is probably just fine. I think factory spec is between 5-7 degrees. If your steering returns to center from a hard turn, your most likely fine.

Curious on a side note. With such a low lift, and small tires, why did you waste money on the Currie Correctlync steering components. I don't think its recommended to use it for stock or low lifts due to some hardware clearance issues, and you could have done the ZJ tie rod upgrade for less than a 1/6th of the price with 90% of the strength with better clearance for low lift setups and run tires up to a 35" without a sweat. I would have taken that $400-450 and put it elsewhere on your build.
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Old 10-11-2013, 11:29 AM   #15
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I think factory spec is between 5-7 degrees.
factory caster spec is 7° +/- 1°.
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Old 10-11-2013, 08:31 PM   #16
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If you want to make it simple........worry about your thrust angle first. Get that taken care of. After thrust angle is set, a simple test to make sure caster is good is by doing the simple test.....go down the road, take both a left turn and right turn, then let the steering wheel go. If it returns back to center, your castor is probably just fine. I think factory spec is between 5-7 degrees. If your steering returns to center from a hard turn, your most likely fine.

Curious on a side note. With such a low lift, and small tires, why did you waste money on the Currie Correctlync steering components. I don't think its recommended to use it for stock or low lifts due to some hardware clearance issues, and you could have done the ZJ tie rod upgrade for less than a 1/6th of the price with 90% of the strength with better clearance for low lift setups and run tires up to a 35" without a sweat. I would have taken that $400-450 and put it elsewhere on your build.

My caster is not fine... it was before I took the LCA off, but I often learn AFTER my mistakes, not always before... I appreciate the input I get here on this forum...

I miss-spoke, its not curry but crown HDSTRGCR1 per advice from forum members here. Was only $150 and seemed like a no brainier upgrade to replacing my worn tie rod ends...

this weekend I'm taking the jeep to a flat spot somewhere to do some measuring on the rear and try to set my caster back to normal...
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Old 10-11-2013, 08:50 PM   #17
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factory caster spec is 7° +/- 1°.
not sure how to quote things like you do but...

by pinion angle, is that the angle of the front driveshaft where it meets the axle, and if so without getting overcomplicated, straighter is better?? Because since I put everything back on there is a knocking from the newly replaced ujoint down there. I will mess with the caster with my newfound knowledge this weekend and see what happens...

per the rack... this one has to go down as different strokes for different folks. I'm "obviously" not building our jeep into an off road monster, it is our DD that we'd like to be able to take the kids out off roading, camping, to the store... and having a full jeep of wife and kids leaves room for... well you know... nothing... hence... rack. throw the bikes on top and go to the park...

I appreciate your advice and patience with me but we love our jeep, we don't need or want 40" mudders on a gigantic lift with dana 5000 axles. We like it like we are building it. Maybe we can keep it alive for a million miles and give it to our son 13 years from now on his 16th birthday so he can take the rack off, put huge tires and a lift on it and go out and total it
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Old 10-12-2013, 01:13 PM   #18
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If this is a stock rig, or even mild lift, worrying about your front pinion angle on a PT 4wd system is a non issue. Plus add the fact that the front DS is a DC unit. In other words don't worry about it.

What I would do is to have your clunking in the rear checked and bring it to an alignment shop and have them check and potentially adjust the thrust and castor from the front lower axle cam bolts. BUT IMO, you need to pony up the 50 bucks and put it on a machine.
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Old 10-12-2013, 02:39 PM   #19
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If all said and done you are only 3/4" taller than stock you have no caster problem ,if you did nothing with the cams to change it and you were good before. You could have 8 degrees of caster on that rig and still have no pinion angle problems . As mentioned earlier in your case pinion angle is a nonissue when setting caster . I have had no problems going by this chart for measuring caster , Alignment . I have been using this for years and its been fine and never had an issue . Caster is not that critical of a setting which is why the factory posts it as plus or minus either side of 7 degrees . That's 2 degrees of tolerance . With all of the info on the Jeep forums about caster anyone should be able to get it in the zone . You can always fine tune it to your liking from there and learn what the changes actually feel like . If you are lifted above 3.5-4" just let your front drive shaft vibe be your guide if all else fails .
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Old 10-12-2013, 04:39 PM   #20
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Without a expensive alignment machine this tool is the only one that will truly measure your castor.



Static measurements are not reliable you have to swing the tire thru it's motion a set amount of degrees to calculate your castor.

There's times it's best to take your Jeep to a trusted reliable professional. With your issues of castor and thrust angle now might be a good time.

If your in the Central Florida area PM me and I'll take care of it for you.
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Old 10-14-2013, 07:24 PM   #21
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Using the link I posted front end shops have confirmed my caster settings many times . I usually use the chart as a base line to start from and adjust it slightly to my liking from their . Its to enjoyable not to experiment with yourself and feel the effects of the changes. I prefer a shop to square up the axles as I have not come up with a way I can do it confidently by my self and that's when I get my caster setting confirmation . My point is , how accurate does it have to be on our rigs when Jeep says plus or minus a degree, that's a pretty large target for any one to hit static or high tech tools.
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Old 10-14-2013, 07:39 PM   #22
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Static measurements are not reliable you have to swing the tire thru it's motion a set amount of degrees to calculate your castor.
exactly.

what is that tool? looks cool

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